QD
41 53
EXCHANGE
BULLETIN
or
THE UNIVERSITY OFTEXAS
NO. 210
FOUR TIMES A MONTH
OFFICIAL SERIES No.
Chemistry in High Schools
BY
E, P. SCHOCH, PH. D.,
Professor of Physical Chemistry The University of Texas
PUBLISHED BY
THE UNIVERSITY OF TEXAS
AUSTIN, TEXAS
Entered as iccond-class mail matter at the postoffice at Austin, Texas
BULLETIN
OF
THE UNIVERSITY OF TEXAS
NO. 210
FOUR TIMES A MONTH OFFICIAL SERIES No. 64 DECEMBER 8,
Chemistry in High Schools
BY
E. P. ^CHOCH, PH. D.,
Professor of Physical Chemistry
The University of Texas
PUBLISHED BY
THE UNIVERSITY OP TEXAS
AUSTIN, TEXAS
Entered as second-class mail matter at the postoffice at Austin, Texas
EXCHANGE
Acknowledgment.
Many teachers of science in Texas schools have kindly fa- vored the writer with expressions of their experience on several topics considered in this paper, and their collective advice has been carefully incorporated. Indebtedness is hereby grate- fully acknowledged.
WHAT SOME OF OUR SMALLER TOWNS HAVE DONE FOR CHEMISTRY.
Chemical Laboratory, Winnsboro (Texas) High School.
Chemical Laboratory, Corpus Christi (Texas) High School.
WHAT SOME OF OUR SMALLER TOWNS HAVE DONE FOR CHEMISTRY.
Chemical Laboratory, San Marcos (Texas) High School.
Chemical Laboratory (on left), Eagle Lake (Texas) High School.
TABLE OF CONTENTS.
PART I. EQUIPMENT.
Page.
The Teacher — Qualifications . , 9
When and Where to Order Laboratory Supplies 9
Selection of a Room for the Laboratory. .' 10
Draft Hoods 11
Arrangement of Desks, Shelves, etc., in the Laboratory. ... 13
Details of Desks 14
Plumbing 17
Cost of Desks and Plumbing 18
Other Furniture 18
Other Desk Designs and Ready-Made Desks 18
Laboratory Burners and Fuel Supply 19
A Home-Made Gasoline Gas Machine 21
Source of Current for Electrolytic Work 23
A Modern Current Rectifier 24
A Small Cheap Current Rectifier 25
Supplies 25
Individual Outfit 26
Notes on Student's Outfit 27
General Laboratory Supplies for a Class of Twelve Students 28
Special Apparatus for Quantitative Experiments 32
Apparatus for the Section of Electrolysis, lonisation, Bat- tery Cells, etc 32
Apparatus for the Demonstration of Combining Volumes of
Gases 33
Chemicals 33
Cost of Supplies 36
First Cost of Laboratory 37
Cost of Maintenance 37
PART II. PLAN AND CONDUCT OF THE COURSE.
Main Object of the Course. 38
Which First — Chemistry or Physics 38
Time Allowance for the Course 38
Time Allowance for Preparation of Laboratory and Lecture
Table Experiments 39
Manner of Conducting Laboratory Work 40
Note on Quantitative Experiments 41
The Note Book 42
How to Begin the Course 44
TABLE OF CONTENTS. vii
The Introduction of Symbols and of the Notions of Atoms
and Molecules 44
The Introduction of Valence 46
The Fundamental Facts of Electrolysis and Its Introduction
in the Course 46
General Discussion of an Outline for the First Part of an
Introductory Course 47
Other Subjects That May Be Studied 51
Experiments Which Should Accompany, the Study of Avo-
gadro 's Hypothesis 53
Chemical Information of Direct Economic Value in Texas . . 56 The University of Texas Requirements for One Unit
Entrance Credit 60
Some Suitable Text-Books in Chemistry 60
PART III. OUTLINE OF AN INTRODUCTION TO THE FIRST PRINCIPLES.
Oxygen 62
Hydrogen 63
Chlorine 64
Hydrogen Chloride 65
Acids. Bases and Salts 65
Hydration of Oxides 67
Solubility of Salts 68
Table of Solubilities of Salts 68
Acid Salts 69
Carbon 71
Sulphur 72.
Ammonia 73
Other Optional Topics 73
lonisation, and the General Relation Between Dissolved
Substances which Results in Metathetical Reactions 73
Exercise 81
Electrolysis 81
The Electro-Motive Force of Galvanic Cells 87
Action of General Reagents Upon Solutions of Salts 91
Sodium (or Potassium) Hydroxide as a Reagent 91
Ammonia as a Reagent 93
Soluble Sulphides as Reagents 95
Reactivities of Sulphides 96
Colors of Sulphides 97
List of Useful Special Properties and Reactions of Metals . . 98
Chemical Problems 99
Text-Book Reading 100
Chemical Changes Involving Oxidation and Reduction. . 101
viii TABLE OF CONTENTS.
Exercise . 102
Exercise 104
Nitric Acid and Its Reduction Products 105
Note on the Oxidizing Action of Sulphuric Acid 108
Table of Electromotive Forces of Battery Poles 109
APPENDIX: THE DETAILS OF CONSTRUCTION AND ACTION OF ALTER- NATING CURRENT RECTIFIERS.
The Action of the Electrolytic Cell 113
Construction of Large Electrolytic Jars for Rectifier Set
No. 1 114
Design and Action of Special Transformer 115
Preparation of Solution for Electrolytic Jars 117
Manipulation of the Rectifier Set No. 1 117
A Small Cheap Rectifier 118
How to Rectify Both Alternations Without a Transformer. . 119
CHEMISTRY IN HIGH SCHOOLS.
PART I :— EQUIPMENT.
The Teacher
First and most important is the teacher. He should be above all a science man, both by inclination and training, — a person whose inclinations and desires naturally make him fond of the subject. He should have had some sound training in chemistry and he should have received this training at a place where that subject is taught extensively rather than at a place where only introductory work is given, since much necessary information is absorbed from the proper "atmosphere." The extent of the person 's training in chemistry should not be less than two thor- ough courses in a first-class college or university, and in addi- tion some college training (at least one course) in either physics or in a biological subject (botany or zoology). This minimum requirement is not excessive, and frequently persons may be obtained who have had much more training than this.
When and Where to Order Laboratory Supplies.
The teacher who is to use the laboratory should design its equipment and order the materials.
The supplies should be ordered early in June. It is quite profitable to submit large orders to several of the large import- ing houses for quotations for duty free importation and deliv- ered at your railway station. If the ordering is delayed beyond July 1st it will scarcely be possible to secure a duty free im- portation by the time the session opens in the fall. All of the large chemical dealers mentioned in the list below will import apparatus duty free if requested to do so. C. H. Stoelting Co., successors to Chicago Laboratory
Supply & Scale Co., 31-45 W. Randolph St Chicago, 111.
1C ' B •/«*«*„« University of Texas Bulletin
Central Scientific Co., 20-28 Michigan St Chicago, 111.
Edward P. Martin Co., 144-146 E. Erie St Chicago, 111.
L. E. Knott Apparatus Co Boston, Mass.
Bausch & Lomb Optical Co Rochester, N Y.
Woldenberg & Schaar, 1025 S. State St Chicago, Til.
Eimer & Amend, 205-211 3rd Ave New York.
The Kny-Scheerer Co., 404 West 27th St New York.
E. H. Sargent & Co Chicago, 111.
Selection of a Room for the Laboratory.
In the selection of a room for the chemical laboratory the fol- lowing requirements must be met:
The room must have such means of ventilation that all fumes may be removed rapidly and not blown into other parts of the building.
Communicating with the laboratory there must be a small room where the supplies may be kept under lock, and in which the teacher may prepare experiments and solutions.
The store and preparation room in turn must communicate with the class room so that the setting up and removal of lec- ture apparatus may be facilitated.
If the teacher also teaches physics, then the store and prepa- ration room, as well as the class room, may be used for both subjects; but in that case the physical laboratory should be located conveniently near so that apparatus may be transferred to and from the store room without unnecessary trouble.
The simplest way to meet the requirement of an adequate draft is to select a room with outer walls and windows on at least two sides. If an inner room with only one exposure (south!) must be used, then there must be provided at the far- ther end of the room from the windows one or more ventilating shafts so located that all parts of the room may be swept by the air current coming in at the windows and passing out through the shafts. Such a shaft should be one to two feet in diam- eter, and it should extend straight to the top of the building. The cover or cap on the roof over the top of this shaft should be placed very high (say twelve inches) above the top of the shaft, so that it will not impede the draft. Cornice men frequently
Chemistry in High Schools 11
place this cap entirely too low. It is desirable to aid the draft by putting a gas flame or an electric fan at the bottom inlet.
The form of ventilators frequently employed for ventilating ordinary buildings (that is, narrow shafts extending up in the wall, and opening into the rooms by means of a series of holes near the ceiling of the room) provides insufficient ventilation for a chemical laboratory.
Draft Hoods.
Obnoxious gases should not be allowed to escape freely into the atmosphere of the laboratory, but should be confined to special draft hoods. Such draft hoods must be carefully designed, other- wise they are worse than useless. The following rules should be observed in their design :
1. The hood should be as small as practicable. More and smaller hoods should be the rule.
2. The stack should be vertical throughout its entire length.
3. The hood proper, which is the part below the stack in which the apparatus is placed, should be as small as possible, so that the velocity with which the air moves through it may not be less than one-third of that with which it moves in the stack. The velocity of the draft should be great enough to lift the heaviest vapors, as, for instance, those of sulphuric acid. The inlet for the draft should be placed so that the current of air from that point to the chimney may sweep through all parts of the hood. For this purpose some stops are usually placed so as to prevent closing entirely the front door of the hood. This carefully adjusted .air inlet is essential to the successful opera- tion of the hood. The hood proper should be made as low as convenience will permit in order that the length of the slowly moving air column in the hood may be as short as possible.
4. The stack or chimney should be proportionate to the size of the hood and its cross sections should not be essentially less than one-third of the cross section of the hood proper.
5. A large gas burner should be placed at the base of the stack at a point at which it is possible to light the gas by reach- ing up into the hood with a burning candle on a stick. This gas flame need not always be lit when the hood is used, but in
12
University of Texas Bulletin
la.
Fiq 1 b,
Examples of Faulty Hood Design.
.2 a.
front
Examples of Proper Hood Design. From the Chemical Engineer.
Chemistry in High Schools 13
quiet weather it must be lit in order to establish a sharp draft in the chimney.
6. A cap covering the stack for the purpose of keeping out rain is frequently not necessary and naturally the hood will operate best without the cap. Should a cap be found necessary, then care must be taken to place it very high above the top edge of the stack in order that the draft may not be impeded by it.
Hoods are frequently constructed without any consideration of the fundamental principles to be observed in order to get a good draft. Fig. 1-a shows a hood in which the stack is en- tirely too small. In Fig. 1-b, the stack suffers from the fur- ther impediment of not being straight. These mistakes in de- sign are frequently found in actual hood construction. Fig. 2-a shows the ideal hood construction. In this hood the stack runs straight up from the closet and is large enough to provide for a sharp draft. Fig. 2-b shows a mode of construction in which the closet is built to connect with a large flue in the wall. If the diameter of this flue is large enough and a flame is placed as shown, then the hood will operate properly. All these fig- ures show the form in which the hood proper, or closet, is gen- erally built. The bottom of the closet is usually at the height of the ordinary laboratory desk and the height of the closet above the table to the contracting portion is 30 to 36 inches. The sliding front door, as well as the two sides, should be mnde of glass.
Arrangement of Desks, Shelves, etc., in the Laboratory.
In the placing of the laboratory desks and the supply shelves care must be taken to leave enough room for the students and instructor to pass each other and secure their supplies readily. The distance between the desks should be 4 ft. 6 in., certainly not less than 4 ft. Desks should not be placed adjacent to the wall anywhere, and a space at least 6 ft. wide should be left between the wall and the desks all around the room. However, this space is large enough to place shelves along the wall wherever desired, as well as shelves for blast lamps, balances, and other special apparatus. It is advisable to place a platform with a suitable table and a black-board in the room so situated that
14 University of Texas Bulletin
the instructor may make special demonstrations before the class or give special explanations while laboratory work is in progress.
In placing the desks, the manner of running the gas, water and sewer mains should be considered: It is most desirable to run these underneath the ceiling of the room below the labora- tory— hence open to view and accessible for repairs at any time ; this permits the placing of the desks in any way desired. If, however, the pipe mains must be placed in the floor, then they should run so as not to cross the floor joists, and the desks must be placed accordingly. The floors over the pipe mains should not be nailed down again, but made "trap-door" fashion.
There should be no high shelves or other super-structure on top of the laboratory desks which would prevent the instructor from looking across the room and seeing what is on top of any desk. The sets of reagent bottles are to be placed on small, low, movable shelves, 36 to 40 inches in length, designed to hold one row of bottles on each side, with a partition at the centre not over six inches high. The bottoms of the shelves should be six inches "clear" above the table top, but the total height of the shelf and bottles should not exceed 12 to 14 inches.
Details of Desks.
In most schools the laboratory is to be used by two sets of students on different days. This is easily arranged, because the amount of desk top space required by a student while working is large enough to construct two independent lockers under- neath it. In some cases instructors have even arranged for three independent lockers under this space so that the laboratory may be used by three distinct groups of students at different periods. They place four deep drawers in the space of the two lockers used in the former arrangement : — three of these are locked sep- arately and in them are placed the perishable apparatus dealt out to the students individually. The fourth is not locked and in it are placed the iron ring stand, the wooden funnel stand, the burners and other large and usually non-breakable appa- ratus to be used by three students in common. This arrange- ment is not as convenient as the two student arrangement.
The table top space allowed per student, while at work,
Chemistry in Hi<jh Schools 15
should be 42 inches in width, and 24 inches in depth The desks should be 36 inches high. Each student should have for his use two gas cocks and between each of the two students working together there should be a water faucet and a sink. These should be placed in the center of the desks so as to be accessible from both sides, and hence be used by four students in common. The pipes run from one end of the desk under- neath the top along the center of the desk.
Each locker should be closed by a large door hinged so that when open it may be folded back upon the unused locker. The lower part of the cupboard should be left open to a height of 26 inches, and in it should be placed a shelf 12 inches wide placed 8 inches above the floor in the back of the cupboard. In the upper part of the cupboard there should be a drawer the size of which, however, need not occupy the whole free space, which is eight inches; instead, the drawer need be only 3l/z inches. high. The partition between the two sets of cupboards facing each other may be made of the cheapest sort of lumber- boxing. It should be placed 2 to 3 inches "off-centre," so that the pipes may be placed along the centre. The side partitions, that is, those at the ends of the desks and between the indi- vidual lockers, may be made of ceiling, the strips running vertically. The door also may be made of ceiling and the hinges should be placed so that screws cannot be drawn when the door is closed. Stout hasps should be supplied with which to lock each door. For further details of construction see Fig. 3. The tops may be made of flooring; though it is advis- able to make them of 114 inch white pine, or cypress. The surface should be covered twice with a half-saturated solution of par- affin in gasoline, and it should be covered once at intervals of a year or so. This is a better surface treatment for these desks than most other "so-called acid proof" treatments. The solu- tion is prepared by saturating some gasoline with finely sliced paraffin, and then adding an equal volume of gasoline to the solution.
The desks should not be too long: 14 ft. is the maximum length desirable; such a desk contains 16 lockers, and top
16
University of Texas Bulletin
o|
c=J
Chemical Laboratory Desk.
Chemistry in High Schools 17
space for eight students working simultaneously four on each side. It is advisable to make the desks only half as long, that is, with only 4 lockers to the side, and then to place sinks at the ends of the desks.
Plumbing.
It is unnecessary to "trap" each one of the sinks separately; the main pipe only needs to be trapped at some convenient point; or better still, it may empty into a "hopper/ The lat- ter acts also as a sieve to catch solids, etc., and thus prevents the choking up of the sewer beyond the hopper.
The desks should be so arranged that the main pipes pass up the center or one side of the laboratory so as to touch the end' of each desk. Of course, the size of these mains depends on the number of desks. In the laboratory to which the accom- panying figures refer, built to accommodate 236 individual Icekers, the sewer main is a cast iron pipe 4 inches in diameter, the water main is a 2 inch pipe and the gas main is a 2 inch pipe. The laterals for a 16 locker desk unit as used in this laboratory are of the following dimensions : drain pipe, 2 inches (cast iron) ; water and gas, one inch each. Where the drain pipe comes out of the desks and turns downward, a "1 '" should be placed instead of an elbow. By this means an ob- struction in the pipe may be readily dislodged. Here the pipes should be joined by a union in order that a desk may be easily 'lisconnected.
The sinks may be of porcelain : a 14 inch hemispherical bowl such as may be obtained for about one dollar, or a little above, will serve the purpose very well. It should not be fastened to the drain pipe, but the spout should merely extend into a short piece of lead pipfe connecting with the drain pipe. Sinks placed at the ends of desks should be of rectangular form, lead lined, 16 by 20, and 10 in. deep inside. A water faucet of the ordinary bar-fixture type, will be found suitable. When in use a short piece of rubber tubing should be attached to the faucet to prevent any splashing of water.
The gas cocks should be chosen carefully so as to fit the* size of rubber tubing used on the Bunsen burners. The gas cocks commonly used by plumbers for dwellings are entirely Uo large for this purpose.
18 University of Texas Bulletin
Cost of Desks and Plumbing.
At present the cost of desks made according to this design is, in Austin, approximately four dollars per locker. The plumbing, including mains, etc., is about $1.50 per locker ad- ditional.
Oilier Furniture.
One or several hoods will be required. It is difficult to give an estimate of these because the cost depends entirely upon the design. However, the hood proper without the stack need not cost more than $15 to $18.
The store-room and the teacher's work room should be sup- plied with large, commodious, plain shelves, for the stock of supplies, etc. Placed in a separate, well-closed small room, as they should be, they need no doors to keep out the dust, and su(-h open cupboards are much more practical than closed cup- boards. The teacher's room should also have a commodious table supplied with gas, and a large sink.
Other Desk Designs and Ready-Made Desk*.
Tn many schools individual desks are now used, ani they are arranged so that all the students face in the same direction. Furthermore, a space is left beneath them so that a student can sit conveniently upon a stool while doing his work. Such a desk can be readily designed by taking the space occupied by two cupboards in the former design, adding to it about 20 inches for the open space beneath where the student puts his feet in •sitting, thus making a unit of 62 inches width, about 30 inches depth and 36 inches height. The two cupboards are placed on the two sides with the central open space between them. The -water, gas and sink may be placed anywhere on the back part •of the desk, though they are usually placed in the space between the two lockers and as near the back edge of the top as is pos- sible. The cost of this construction is necessarily greater than that mentioned above. Inclusive of plumbing, it cannot be less than $20.00 per desk with two lockers, even if it is constructed as cheaply as possible.
Chemistry in High Schools 19
Frequently school authorities not wishing the trouble of con- structing desks, desire to secure them ready made from some reliable business firm. Desks built by manufacturers, who make a specialty of such work, present many points of advan- tage ; they are generally well designed and well made. Naturally their cost will be much greater than the cost of the simple desks mentioned above. The following parties make a specialty of man- ufacturing laboratory furniture, and it is advisable to obtain the catalogues of several houses while studying this matter:
The Kewaunee Manufacturing Co., (Catalogue No. 4), Ke- waunee, Wis.
Leonard, Peterson & Co., 1240 Fullerton Ave., Chicago, 111.
L. E. Knott Apparatus Co., Boston, Mass.
The best design of an individual desk found on the market is that of the Altaffer Individual Desk, which is designed and manufactured by L. B. Altaffer, 1445 Wyandot Ave., Cleveland, Ohio.
Laboratory Burners and Fuel Supply.
The alcohol lamp is so feeble that nearly all teachers agree in reporting it as absolutely unsatisfactory.
The small gasoline torch sold by all dealers (e. g. Central Scientific Co., Cat. No. 4449), is reported as quite satisfactory by some teachers and as unsatisfactory by others. The dif- ference in opinion is probably due to the fact that the valves of the pump do not last longer than one session and then, give much trouble; again, the gasoline must be filtered through a chamois bag, si-nee otherwise the small gasoline vent in the burner is choked up frequently. Usually repairs have to be made by the teacher, hence with heavy laboratory work, and more than a few students, the loss of time caused by these burners becomes prohibitive.
The valve-less gasoline burner (e. g. Central Scientific Co., Cat. No. 4455) is rather feeble and exceedingly troublesome, hence it is not to be recommended.
Acetylene gas may be burned in a Bunsen burner of special construction (Central Scientific Co., Cat. No. 4632). It is a very convenient and satisfactory sourse of heat, but its cost appears to be prohibitive.
20 University of Texas Bulletin
Gasoline Gas Machines. There are at least three distinct machines of this sort on the market: the F-P Gas Machine, sold in this state by the Texas Lighting Co., Box 687, Dallas; the Standard Vacuum Gas Machine, manufactured by the Standard-Gillett Light Co., 9-11 West Michigan St., Chicago; and the Tirrill Gas Machine, manufactured by the Tirrill Gas Machine Ltg. Co., 509 Fifth Aye., New York. See also the Home-Made Machine farther on.
The smallest unit of the F-P Gas Machine is for five burners, and the prices up to the fifteen burner size are much smaller that the price of the smallest unit (twenty-five burners) of the cheaper one of the other machines ; but for a larger number of burners the others are at least as cheap, when all is considered, and they are certainly to be preferred. The writer has not seen the F-P machine in operation, but he really doubts that it is suitable for chemical laboratories because the burners are perma- nently attached to the supply pipes, and the number of burners can be increased only by having the makers put in the additional equipment.
The two other gas machines, the Tirrill and the Standard Vacuum, are practically of the same type, and of quite a dif- ferent type from the F-P machine. Of the Tirrell machines there are several now in successful operation within the state. Both machines are furnished in several sizes, the smallest of which furnishes gas for 25 lights. As quoted to the writer, the price, of the Standard- Vacuum Machine is considerably less than the price of the Tirrill. Attention must be called to the fact that the prices for these machines are f. o. b. factories, and that the cost of their installation is considerable.
Although the purchase of one of these machines may appear to be an unduly large expenditure for this one need, namely, that of fuel, yet it must not be forgotten that these machines furnish the best fuel for laboratory purposes and save on other expenses, first of all on the cost of the burners, and second in saving the time which is otherwise lost by both the teacher and the pupil in keeping the other kinds of lamps in operation. Hence for a class of 20 or more a machine of this sort is much more economical than a number of gasoline blast lamps plus the cost of time for their operation. But even for smaller classes,
Chemistry in High Schools
21
A Home-Made Gasoline Gas Machine.
for instance, of 10 students, the extra expense involved in the purchase of such a machine will be balanced by the saving in several years.
.1 Ilo*n< -Made, Inexpensive, G-asoline-Gas Machine.
A home-made, inexpensive gasoline-gas machine was installed in the Mexia High School last summer and it has been in suc- cessful operation during the fall. Mr. A. G. Koenig, who de- signed and installed it, has kindly furnished the following de- scription of it:
The gasoline gas machine now in use in the Mexia High School consists of four parts: 1. The pump. 2. The air tank. 3. The carburater and gasoline tank. 4. The source of power. These are assembled as shown in Fig. 4. The pump used is one having an internal diameter of 1.12 inches, the stroke is about 4
22
University of Texas Bulletin
inches, and running at the rate of 150 strokes per minute it fur- nishes about 1-4 cu. ft. of air per minute, which is enough to supply 12-15 Bunsen burners with the gasoline gas. This pump was obtained from the Columbia School Supply Co., Indianap- olis, Indiana, at $4.90. The air tank is. a No. 1827 pressure tank sold by Columbia School Supply Co. for $3.75.
Mechanical Power for Gas Machine.
The carburater consists of a five gallon oil can which can be bought for $0.60, and about 3 ft. of 1-4 inch lead tube closed at one end and coiled up in the bottom of the can as shown in the diagram. A large number of very fine holes were made in this lead coil by means of a sewing needle or a fine awl. The air passing through these numerous holes in the coil at the bottom of the gasoline becomes saturated with gasoline vapor. It is advisable to place two rolls of wire gauze in the iron pipes con-
Chemistry in High Schools 2S
veying the gas from this carbureter to the laboratory; this pre- vents the flashing back of the flame through the pipes. Instead of the ordinary Bunsen burner it is advisable to use one in which the air and the gas supplies may be independently and accu- rately regulated. The expense for gasoline during the past three months has been about one cent per hour for ten burners.
The air pump is driven by a six-inch water motor manufac- tured by the Divine Water Motor Co. of Utica, N. Y., price $5.00. The pulleys and mechanism for applying the power to the pump were obtained by adapting the foot-power mechanism of an old sewing machine at a cost of $2.00.
There would be no difficulty in substituting a small electric motor (say a strong fan motor) for the water motor above.
Where neither electric nor water power is available the fol- lowing device may be used as a source of power: A derrick consisting of four 2x4 scantlings, well braced, and about 20 ft. high is used to raise a strong box filled with sand or other heavy objects. In order to have enough rope or wire cable to wind on the drum, a system of pulleys, consisting of 3 or 4 fixed at the top and 2 or 3 at the bottom, is used. This will give 100 or 140 ft. of rope to be wound on the drum. The mechanism of the whole device is shown in Fig. 5.
The large cog-wheel a and the drum & run on the same axle. The rachet c allows the drum to be turned from right to left in winding up the weight.
Source of Current for Electrolytic Work.
As a rule, electrolytic work requires a direct current of low voltage. At present this is obtained either from battery cells (dry cells), or from high voltage (110 volts) direct-current light- ing systems by wasting nine-tenths of the energy. Both of these sources are inefficient, uneconomical, or troublesome, and it is desirable to secure a better source. This is obtained by trans- forming and rectifying the alternating lighting current which is found even in the smallest towns. Since no really first-class, modern apparatus for this purpose appears to be in the market, the following detailed description for securing such is here given.
Two distinct rectifying sets are described below. The first
24
University of Texas Bulletin
is the best design for this purpose that can be made at present. It naturally costs more than the second, but even its cost is much less than the cost of anything offered in the market that could take its place. In both sets the electrolytic jars or rectif yet- proper can be easily assembled at home, as well as, and perhaps better than, it is done by the manufacturers; and at much less
fia.6. AC
Mam
A Modern Current Rectifier.
cost. The second represents the design followed by many manu- facturers; a combination of a lamp-bank rheostat with the rectifier proper. The particular form here described costs only a trifle, and is very easily constructed.
(1) A current rectifier for 10 amperes direct current and any pressure up to 45 volts. This apparatus consists of the following :
Chemistry in High Schools 25
(a) A specially designed transformer (price, $13.00, f. o. b., St. Louis, Mo., Moloney Electric Co.). For details see p. 116.
(b) Two electrolytic jars (or one double-jar) ; approximate cost of material .$2.50 ; for details of construction, see p. 114.
(c) Three double-pole, double-throw switches (smallest Bry- ant Baby Knife switches on porcelain bases) ; secure locally or from Western Electric Co., approximate price, $1.50.
(d) Two binding posts, 30 cts.
(e) One rheostat with approximately 10 ohms resistance and a current capacity of 10 amperes on at least a part of the rheo- stat. A Ward-Leonard Co. (Bronxville, N. Y.) Field Rheostat, FF 810, price $5.80, or FF 820, price $7.30, will be found to be very serviceable, and probably cheaper than other equivalent rheostats. The whole is to be assembled as shown in Fig. 6.
This apparatus operates extremely economically and admits of convenient regulation to any desired current or voltage. Both alterations of the alterating current are "rectified," mak- ing the direct current obtained practically continuous. It is just as serviceable, and cheaper than a storage battery. The nearest approach to it in the market is a four- jar rectifier (see page 119 combined with a lamb-bank rheostat, the cost of which is as much, if not more, than this, while it is not nearly as serviceable.
(2) A cheap small current rectifier. This apparatus is de- signed for a maximum of about 3 amperes, at 4 to 8 volts ; the total cost of material for the apparatus is about $3.50, and it can be made, i. e. assembled, in one or two hours. It will be found much cheaper, more convenient, and more serviceable tlian pri- mary batteries or dry cells. The details for construction are given on page 118. Only one alternation of the alternating current is rectified, giving a pulsating current. However it is just as serviceable for electrolytic work as a continuous current.
The details for construction, action, and operation of rectify- ing sets are given at length on page 113.
SUPPLIES.
These lists of apparatus and chemicals include all that is needed for the work given in most .text-books, and also for the work outlined in this paper, with the possible omission
26 University of Texas Bulletin
of a few things which are easily obtained locally. Naturally, special experiments Driven in particular laboratory manuals are not provided for here, but since nearly all modern lab- oratory manuals give lists of the apparatus and chemicals needed, the extra material may be easily added. This list calls for some- what larger quantities than those given in the manuals, but these larger quantities will be found very desirable.
In ordering supplies, an individual set should be secured for the teacher. Of the perishable material, half as much again as is necessary for the individual sets should be secured.
Individual Outfit.
1 Burner, either a Bunsen burner with 2 ft. of rubber tubing of best white rubber wrapped in cloth, diam. 11x6 . $ .50 or a gasoline torch ($2.75.)
1 Wing top (for Bunsen burner only) 10
1 Iron stand (24 inches) with three rings 65
1 Iron burette-clamp and clamp-holder 35
1 Burette 50 cc. with glass stop-cock (See Note 1) 70
1 Deflagrating spoon 03
1 Piece of wire gauze, iron, heavily tinned, 5 "x5 " 07
1 Piece of asbestos board 5"x5" ys" thick (See Note 2) . . .02
2 Porcelain evaporating dishes : 1-3 ' ' ; 1-5 " 25
1 Small mortar and pestle of wedgewood, 3% to 4" in
diameter 40
1 Wash bottle (1000 cc.) with rubber stopper and glass
tube fittings (See Note 3) 30
1 Nest of 4 beakers— 50 cc., 150 cc., 250 cc., 400 cc 40
1 Crucible Tongs 50
1 Porcelain Crucible with lid, 18cc 20
1 Clay-covered Iron Triangle 03
2 or 3 Wide Mouth (or salt mouth) Bottles, 500 cc. (See Note 7) 20
.2 or 3 Pieces of Window Glass, 4x4. . .10
Chemistry in High Schools 27
12 Test-tubes, 16-160 mm. .01 each 12
1 Test-tube rack with pins 28
1 Dropping Funnel with cylindrical, open top, 50 cc. capac- ity ; stem length, 12 cm., diam. 6 mm 40
1 Test-tube Holder (wire) 08
2 Glass Funnels : 2% ' ' and 3% ' ' respectively 25
1 Test-tube Brush 03
1 Wooden Funnel Stand for 2 funnels 60
1 Triangular File (See Note 4) 05
1 Pneumatic Trough (See Note 5) 35
1/2 Pack (50) Filter papers 12 % cm. (5") 10
1 Thistle Top'Funnel tube, length 12 in., diam. of stem, 6mm .03
1 Graduate, or one open top, graduated, cylinder, 100 cc. . .15
2 Erlenmeyer Flasks with two hole rubber stoppers to fit. . .40 1 flask-250 cc. with No. 3 or No. 4 rubber stopper : 1 flask-
400 cc. with No. 4 or No. 5 rubber stopper (See note 6).
2 Watch Glasses: 3" and 5" 20
3 ft. Glass Rodding, diameter 3mm., per Ib 50
10 ft. Glass Tubing, diameters 6x4 mm. or 5x3 mm., per Ib. .12 2 Hard Glass Test-Tubes of best hard glass, 18x160 mm. . . .20 1 Porcelain spoon and spatula, length 10 cm., width of
spoon, 14mm 10
1 Piece of platinum wire, No. 28 B. & S. gage, length 5 cm.
fused into the end of a piece of glass rodding 16
1 Piece of black rubber tubing, length 12 inches, diameters
7x4 mm !20
Notes on Student's Outfit.
(1) All ground glass stop-cocks should be taken out and tied on the apparatus when not in actual use.
(2) This piece of asbestos board is to be used in place of a water bath, and for elementary work is much more serviceable. Should a water bath be absolutely required, then a large size beaker will probably serve the purpose. No water bath is in- cluded in the list.
(3) Buy flat bottom, 1 liter, Bohemian flasks, cover the necks with cord, secure two hole rubber stoppers to fit mouth of .flask (probably No. 6 rubber stopper), and during one of the earliest
28 University of Texas Bulletin
laboratory periods teach the student how to make the glass-tube fittings.
(4) Purchase the triangular files by the dozen from a local hardware dealer.
(5) Buy small dish pans and paint these inside and out with asphalt paint ; they will serve the purpose just as well as the more expensive regular pneumatic troughs.
(6) These flasks with the rubber stoppers serve as generating flasks, as gas wash bottles, etc.
(7) Almost any sort of a wide-mouth bottle (pickle bottle, fruit-jars, etc.) may serve for these bottles. The pieces of glass to be used as covers may be supplied by a local dealer.
(8) All rubber ware, i. e. stoppers and tubing, when not in actual use, should be disconnected, or tubes drawn out of stop- pers, etc., and should be laid away in the dark, since light de- composes rubber rapidly.
General Laboratory Supplies for a Class of Twelve Students.
One blast lamp and foot bellows for gas (or a large gasoline torch.) There is no foot blower listed by American dealers that is as satisfactory and as lasting as the one listed by Dr. Bender and Dr. Hobein, Munich, Germany, Cat. No. 2201. The blower, No. 2 diameter 30 cm. is listed at 40 mark ($10.00) and is quite satisfactory. No. 2245 in the same catalogue gives an extremely useful blast lamp (list price $3.00) to be used with the blower. A blast lamp outfit is not absolutely necessary but is extremely desirable. By its means a teacher can make many pieces of sim- ple glass apparatus, which otherwise is impossible. Simple glass- blowing can and should be mastered by every teacher of chemis- try Helpful hints on glass-blowing are found in the booklet: Shenstone, "The Methods of Glassblowing. " (Longmans, Green & Co.)
Six sets of eight desk reagent bottles, with labels blown in the glass, capacity 500 cc. ; with ground glass stoppers (except where marked). , (One set for every two students working simulta- neously and one extra set for the teacher).
Chemistry in High Schools 29
Concentrated Sulphuric Acid .................. ,
Dilute Sulphuric Acid ......................
Concentrated Hydrochloric Acid ..............
<fc-| Q
Dilute Hydrochloric Acid .......................
- for Concentrated Nitric Acid
Dilute Nitric Acid ............... . ...........
Ammomium Hydroxide .......................
Sodium Hydroxide (rubber stopper) ...........
50 to 75 solution bottles for the general side shelf in the lab- oratory ; capacity, 500 cc., ground glass stoppers. To be labeled as desired, with paper labels.
For this purpose secure one or two label books (.70). The labels should be pasted carefully so that the paper will not "pucker up", the "gum" allowed to dry thoroughly, and then a layer of melted paraffin spread with a brush over the label, beyond the edges.
The salt mouth bottles for the general supply shelf probably need not be purchased separately, as the bottles in which salts are shipped serve well for this purpose.
Balances for ordinary weighing, capacity 1000 grams. A very desirable balance is the Laboratory Balance, Cat. No. L 6010 (list price, $12.00), manufactured by Wm. Gaertner & Co., 5345 Lake Ave., Chicago. One such balance will suffice for 10 students.
1 set of weights, third class, 10 grams up to 2 Kg. (This bal- ance has a sliding weight for .the smaller weight down to 0.1 gram).
Water Still. If running water is at hand, a small automatic still (for instance, a J&well] should be installed (one of capac- ity % gallon per hour will be ample for 10 to 20 students). If the laboratory is not supplied with gas, a small (1 hole) blue- flame kerosene stove should be bought, and placed in position to heat the still. If running water is not available in the laboratory, a (5 gallon) copper retort (tin lined) and a block tin worm con- denser may be used. It can be heated with a Fletcher radial gas burner or with a kerosene blue-flame stove. Either distilling apparatus will cost slightly above $20.00. Two 5 gallon stout
30 University of Texas Bulletin
glass bottles for collecting and storing distilled water should be secured ($3.00), and one of them should be fitted with a glass syphon and pinch cock for drawing the water.
Two Acid Pots, stone ware, 3 gallons capacity, for dilut- ing acids $2.00
3 Sets of 3 smallest sizes of cork borers 1.50
1 Set of 6 smallest sizes of cork borers 80
3 Kipps automatic gas generators, capacity 1 pt., with a broad base having a " tubular" in it for emptying the spent acid. For convenience in ' ' filling, ' ' the tubu- lar in the middle "globe" should be of 3^2 cm. inner
diameter 9.00
100 ft. Tubing of soft glass, for bending, etc., diam. 9%x
121/2 mm 85
30 ft. Tubing of soft glass, for bending, etc., diam. 14x18 .50 100 ft. Tubing of soft glass, for bending, etc., 5mm. outer
diam 42
100 ft. Tubing of soft glass, for bending, etc., diam. 6x4. .. .50 100 ft. Tubing of soft glass, for bending, etc., diam. 7x5. . . .45
30 ft. soft glass rodding, 3 mm. diameter 15
10 ft. soft glass rodding, 6 mm. diameter 10
6 Thermometers, solid stem, graduated up to 360° C 7.50
12 Calcium Chloride U-tubes, 6 in. with side tubes at- tached 72
12 Mohr 's pinchcock clamps 98
12 Screw clamps for compressing rubber tubing 3.00
6 Lead dishes, 3 inches in diameter .75
12 Distilling flasks, 350 to 400 cc. with effluent tube half- way up the neck. They are to be used in place of re- torts. For a condenser, use a piece of soft glass tubing diameters 10x13 mm. Fit this over the side tube of the distilling flask by wrapping a strip of asbestos around the latter. When necessary place a wet towel around the condensing tube, or let this extend into a receiving flask submerged in water. To apply heat, place the dis- tilling flask over a hole (1% to 2 inches diameter) in a piece of asbestos board which is 5x5 inches in size. This prevents the flame from striking portions of the flask above the level of the liquid in it 1.50
Chemistry in High Schools 31
2 Large porcelain spoons 50
1 Measuring cylinder, 1000 cc. open top 50
4 Volumetric flasks without glass stoppers:
1_1000 cc 35
1— 500 cc 25
1— 250 cc 20
1— 100 cc 16
1 Measuring cylinder, 1000 cc. glass stoppered 63
2 10 cc. Pipettes 10
2 25 cc. Pipettes 14
2 Glass funnels, 6 inches diameter • . . . .40
4 Porcelain evaporating dishes, ordinary form :
1 — 5 inch diam 20
1—6 inch diam 23
1 — 7 inch diam 30
1—8 inch diam 38
2 Large porous cups and 1 rubber stopper to fit these — to be used for the demonstration of gaseous diffusion. A bell jar can probably be borrowed from the physical laboratory for this purpose. Beakers of best Bohemian glass :
3 nests each, about 600 cc., 800 cc. and 1000 cc 1.80
1 Package of 100 circular filter papers, 12 inch diam 16
1 Glass tube cutter (inside cutter) with extra cutting
wheels. (E. &' A. Cat. 3684) 1.25
1 filter Pump (Aspirator), of brass, medium size 1.50
"Picein" rubber cement, very convenient and useful for tightening joints and stoppers in apparatus. It is applied like sealing wax, but is preferable to the latter. Dealers can secure same from Fritz Koehler, Leipzig, Germany, 4
pieces at 15 cents apiece, approximately 60
Cork stoppers, best quality — regular size. Diam. Small End.
100 14 38
" 16 50
" 18 60
" 20 1.00
50... 22 55
..24.. .60
32 University of Texas Bulletin
".., 26 65
" 28 75
" 30 1.00
il 32 1.10
Rubber Tubing. Besides that necessary for the Bunsen burn- ers and the black rubber tubing in the individual outfits, "for connections, ' ' secure the following :
Rubber tubing, white, best quality, wrapped in cloth, Amount Diam.
20 ft. 13x 7 mm $3.60
10 ft. 15x11 mm 3.00
Special Apparatus for Quantitative Experiments.
Balance for quantitative work. This should be a balance in a glass case sensitive to a milligram. The capacity of the balance should be 300 grams, and a set of second (not third) class weights should be provided for it, and a supply of extra fractional weights should be on hand to replace any that may be lost. The balance shown in Eimer end Amend 's catalogue No. 2122, and the set of weights No. 2198 (200 grams) are suitable for this purpose. In general, one such balance will.be enough for seven or eight students only, hence if much of this work is to be done, two such balances should be provided for a class of twelve stu- dents. The price of such a balance and weights is about $20.00 to $25.00.
12 Porcelain combustion boats, 7x70 mm. or 10x60 mm.
Apparatus for the Section on Electrolysis, lonisation, etc.
See special section on electrolysis and battery action. The following will be needed :
12 Porous cups, height 3 inches, diameter, 1%. They should be well protected against dust.
12 Rubber stoppers to fit these. Holes can be cut in them as needed. This is easily done by means of the ordinary cork borer if it is moistened with sodium hydroxide solution or with alcohol .
1 Drying Tower (E. & A. Cat. N. 3055), 18 inches high. .$ .50 12 small carbon rods — i. e. arc light electrodes — can be secured
locally.
Chemistry in High Schools 33
4 Plantinum electrodes each consisting of a thin piece of platinum foil 2x5 cm. to one end of which is welded a short piece of No. 22 platinum wire. The latter is fused into a four-inch piece of strong glass tubing (extending to the inside), having 7 mm. outer diameter, and for elec- trical connection, a little mercury is poured into the tube $5.00
2 Porcelain jars, with diameter 6" to 8," height 4" to 6"
can be secured at a local dealer 40
Ammeter, voltmeter, rheostat, etc., may probably be bor- rowed temporarily from the physical laboratory. If not, then at least one ammeter with two ranges (1 amp. and 10 amp.) and one voltmeter with two ranges (3 volts and 30 volts) should be bought. These instruments should be of fairly good grade, hence they should cost at least $15.00 a piece.
1 Piece fairly stiff sheet copper (about the thickness used in lining bath tubs) 16x16 inches 50
1 Wooden "Conductivity" vessel made to order (see page 77 2.50
y2 lb. Picric acid 75
1/2 lb Naphthalene c. p 25
1 Liter absolute alcohol 35
Apparatus for the Demonstration of Combining Volumes of Gases
1 Hoffman Electrolysis apparatus ; for details see page 53 . $6.00 1 Eudiometer Tube of special design (see page 53) for the
explosion of hydrogen and oxygen 5.00
1 Hoffman apparatus tube to demonstrate the volume re- lations for. ammonia — this tube to be modified as stated on page 55 3.00
Chemicals for a Cla\ss of Twelve Students.
5 Ibs. Acetic Acid glacial $1.02
18 Ibs. Hydrochloric Acid c. p. in 6 lb. sealed bottles 2.16
7 Ibs. Nitric Acid, c. p. in 7 lb. sealed bottles 1.00
2 Ibs. Fuming Nitric Acid , 1.10
34 . University of Texas Bulletin
1 Ib. Oxalic Acid, commercial 12
27 Ibs. Sulphuric Acid, c. p. in 9 Ib. sealed bottles 2.85
1 Ib. Tartaric Acid 64
2 qt. 95% Alcohol 50
1 Ib. Ammonium Carbonate 25
^4 Ib. Ammonium Oxalate 12
1 Ib. Potassic Alum 08
% Ib. Aluminium, filings or shavings 35
5 Ibs. Ammonium Chloride, pure 90
1A Ib. Ammonium Sulphate 10
16 Ibs. Ammonium Hydroxide in 4 Ib bottles 2.80
3 Ibs. Ammonium Nitrate 70
8 ozs. Antimony, powdered 25
4 ozs. Arsenic Trioxide 13
Y2 Ib. Asbestos wool 20
1 sq. yd. Thin Asbestos paper 10
2 Ibs. Barium Chloride, crystals .25
*4 Ib. Barium Nitrate *. 10
% Ib- Barium Peroxide 35
1 oz. Bismuth 30
1 Ib. Borax 18
% Ib. Bromine in 2 oz. bottles 50
1 Ib. Calcium Chloride, crystals 35
2 Ib. Calcium Chloride, anhydrous, fused 80
1 Ib. Cadmium Chloride 1.3-6
1 Ib. Calcium Fluoride 10
Calcium oxide, buy locally
*4 Ib. Cadmium Nitrate 40
1 Ib. Calcium Nitrate 80
% Ib. Chrome Alum, c. p 25
1 Ib. Chloroform, Squibb's 90
5 Ibs. Calcium Sulphate, Plaster of Paris 15
1 Ib. Carbon Bisulphide '. 16
10 Ibs. Calcium Carbonate, marble chips 50
2 Ibs. Bone Black 15
1 oz. Cobalt Nitrate 15
1 doz. sticks Willow Charco:al 36
1 Ib. Thin Copper Foil 50
2 Ibs. Copper Turnings, fine 40
Chemistry in High Schools 35
2 Ibs. Copper Nitrate 65
1 Ib. Copper Oxide, black powdered 75
5 Ibs. Copper Sulphate 50
2 oz. Iodine, pure, crystals 75
2 Ibs. Ferrous Sulphate in 2 oz. bottles 40
1 Ib. Ferric Chloride 12
2 Ibs. Iron Filings 10
5 Ibs. Iron Sulphide - 35
2 Ibs. Sheet Lead .-. . . .20
1 Ib. Lead Nitrate 18
1 Ib. Litharge 12
1 Ib. Lead Peroxide 36
1 oz. Litmus 10
1 Quire Litmus paper, red 50
1 Quire Litmus paper, blue 50
2 ozs. Magnesium ribbon 1.20
1 Ib. Magnesium Chloride 12
1 Ib. Manganese Chloride 50
2 Ibs. Manganese Dioxide, powdered 85
3 Ibs. Manganese Dioxide, in lumps 1.00
5 Ibs. Mercury 4.00
4 Ib. Mercuric Chloride 40
8 ozs. Red Oxide of Mercury 80
± Ib. Mercurous Nitrate 40
1 Ib. Nickel Chloride 70
1 oz. Phenolphthalein 10
5 Ibs. Paraffin 75
1 oz. Red Phosphorus 15
± Ib. Yellow Phosphorus 25
± oz. Potassium 45
1 Ib. Potassium Bromide 20
2 Ibs. Potassium Hydroxide, sticks 60
1 Ib. Potassium Carbonate 16
5 Ibs. Potassium Chlorate, crystals 70
1 Ib. Antimony :and Potassium Tartrate 60
2 Ibs. Potassium Bichromate 32
Ib. Potassium Ferrocyanide 30
36 University of Texas Bulletin
1/2 lb. Potassium Ferricyanide 30
V2 lb. Potassium Iodide 2.40
1 lb. Potassium Nitrate 15
% lb. Potassium Sulphocyanate 15
3 Ibs. Potassium Chloride 25
1/2 lb. Potassium Permanganate 10
1 oz. Platinized Asbestos 5.00
y2 oz. Silver foil 60
1/2 lb. Silver nitrate 4.00
8 oz. Sodium '. 70
2 Ibs. Sodium carbonate crystals 25
3 Ibs. Caustic soda, sticks 75
2 Ibs. Sodium chloride, c. p 50
% lb. Sodium chlorate 10
3 Ibs. Sodium nitrate 42
2 Ibs. Sodium sulphate, crystals 25
1 lb. Sodium, sulphide, crystals 10
2 Ibs. Sodium hyposulphite 15
1 lb. Sodium phosphate 4 ;10
2 Ibs. Sodium bisulphite 60
1/2 lb. Sodium acetate •. 25
1 lb. Sodium peroxide, commercial 70
1/2 lb. Stannous chloride 25
1 oz. Strontium chloride 10
5 Ibs. Boll sulphur 25
1 lb. Flowers of Sulphur 08
3 Ibs. Granulated zinc 45
3 lb. Zinc in sticks, at least 6 in. in length 25
5 Ibs. Zinc in lumps or short, thick rods, 1 in. long, "for
Kipps" 1.25
1 lb. Zinc sulphate 25
y2 lb. Zinc nitrate 50
1 lb. Granulated tin .55
2 ozs. Glass wool, fine 1.00
Cost of Supplies.
The prices given in the list of "Individual Supplies" are those that would be charged at Austin, hence they include freight.
Chemistry in High Schools 37
The prices for the other supplies are to serve as indications merely; they have not been obtained by special quotation from a firm; and they do not include freight. For the latter about 10 to 15% must be added to the price.
The total cost of the supplies in this list, figured for a teacher and twelve students, and including freight is :
Individual Sets $182.96
General Supplies 53.75
Freight and Drayage, l2l/2% on the latter 6.50
Total $243.21
First Cost of Laboratory.
If all furniture is constructed as cheaply as possible, its cost will be approximately as follows :
12 lockers, for students, including plumbing $ 75.00
Reagent side shelves, shelves in store room, work table for
teacher, and large sink 50.00
One draft hood '. 25.00
Chemical supplies 250.00
Total $400.00
Cost of Maintenance.
The least annual cost of maintenance is about $8.00 to $12.00 per student. Of this amount from $2.50 to $5.00 may be borne by the student, and the remainder by the Board. In many Texas High Schools, the Board's appropriation is as much as $10.00 per student annually.
38 University of Texas Bulletin
PART II: PLAN AND CONDUCT OF THE COURSE.
Main Object of Course.
The question to be considered here is : for which set of students shall the course be designed — those who end their school days with the high school, or those who go to college? The writer believes that the course should be designed primarily for the student who will not continue his studies beyond the high school ; and the following plan and suggestions have been made with that in view. Furthermore, the writer believes that such a course will also be the best introduction to the subject for the student who continues the study of chemistry in college.
For this purpose the course should consist mainly of a presen- tation of experimental facts connected by the least amount of theory necessary to aid in their study. Emphasis should con- stantly be given to the recognition and retention of the experi- mental facts themselves. Furthermore an essential part of the course should deal with facts with which the student will be con- cerned later in life.
Which first, Chemistry or Physics?
The question whether chemistry or physics shall precede in the high school course is a matter that should be left entirely to the high school people. Read in this connection, The Teaching of Chemistry and Physics, pages 29 to 37. Attention should be called to the fact that the progress of the class will naturally be slower if chemistry is given earlier in the course than if it is given during the last year. Furthermore, one topic must be given special consideration, that is the topic of battery cells and electrolysis. This subject should be given in the chemistry course rather than in the physics course because it is essentially a chemical subject. It cannot be presented without involving chemical considerations, and -elementary chemistry cannot be presented properly without it (see page 81 et. seq.).
Time Allowance for the Course.
The time given to chemistry in the high school should be three recitation periods of 45 minutes and two laboratory periods of at
Chemistry in High Schools 39
least double that time a week. Each double period for laboratory- work should be uninterrupted, that is, there should be two con- secutive periods. There should be no difficulty in arranging the schedule for this, because a study period may be placed just be- fore or after the recitation period, and on days on which labora- tory work is taken, the recitation period together with the study period then form the laboratory period. This arrangement is desirable for another reason : it frequently happens that the ra- tio between laboratory and recitation work temporarily should be changed in either way possible, because at times the recita- tion work requires more attention and at others the laboratory work. The arrangement of the schedule here suggested permits of such a change, and hence is highly desirable.
Time Allowance for Preparation of Laboratory and Lecture Table Experiments.
\
Considerable time must be spent by the teacher in the prepara- tion of special apparatus, in the preparations of solutions for the laboratory, and in the preparation of lecture table experiments. In addition to this there is the unavoidable labor of putting away the apparatus properly after use, and arranging the side shelf reagents, etc., after periods of laboratory work. As a rule su- perintendents and principals either do not realize how time con- suming this work is or they are disposed to minimize its impor- tance. Some will consider that this is essentially janitorial work, for which some cheap help might either be hired, or which if done by the teacher does not deserve any consideration as a part of his teaching work. This is utterly wrong. The teacher of chemistry should be allowed time enough to do such work properly, and such time should be a part of his teaching time, and not of hours after school work. If the suggestion made above for the scheduling of the laboratory and of the recitation work is followed, then in addition to the double period each day, kept open throughout the week for chemistry, there should be set aside another period each day for the teacher to look after the equip- ment. In this way he will have two periods three times a week and one period twice a week, a total of eight periods to prepare his experimental work. This is not excessive and will be very profitable to the school. If classes are large, the teacher must be
40. University of Texas Bulletin
given, in addition, assistants to aid him in cleaning up the lab- oratory, etc. Such service can be secured very reasonably from some member of the chemistry class. The cleaning up should not be done without the direction of the teacher, because he should know where everything is placed.
However, such time allowance, etc., puts a responsibility upon the teacher which he must not shirk. A chemistry teacher must be "up and about" doing experimental work with his own hands. All "sitting back" and letting the students only do experimental work or ordering around some assistant to prepare experiments and reagents is indictative of a person unfit to be a teacher of science. He must be the chief experimenter; he must be pos- sessed of a desire to do experimental work, and with his own hands attend to matters in the laboratory.
Manner of Conducting laboratory Work.
Beginners in chemistry are frequently inclined to do their laboratory work in a mechanical manner merely, and the new- ness of the subject inclines them also to take too much time in the performance of experiments. Hence the teacher must use a method of conducting laboratory work which will keep the mental aspect of the subject constantly before them and force them to do their work expeditiously. This may be done by con- ducting the laboratory work in a manner similar to that of con- ducting class work. Thus at suitable times during the periods of laboratory work, the teacher should discuss with the whole class the chemical changes dealt with, and drill his pupils on all re- lated matter. He should strive by all means possible to enliven the activity of laboratory practice, realizing that it is in the lab- oratory rather than in the lecture room that chemistry may be taught and learned.
In the treatment of the experimental material the aim should be to teach the common properties of substances in the broadest manner. Thus in connection with the preparation of oxygen, the student should not be taught that "the laboratory method for the preparation of oxygen consists of heating a mixture of potassium chlorate and manganese dioxide," but he should be taught that "there are some compounds of oxygen that decom- pose when exposed to a sufficiently high temperature and yield
Chemistry in High Schools 41
•
oxygen as one of the products of decomposition. Of course not all substances break up in the temperatures at our command, yet quite a number do so, among which may be mentioned lead peroxide, mercuric oxide, potassium chlorate, potassium nitrate, etc. These should be remembered as substances not only rich in oxygen but that yield it up when exposed to a moderately high temperature obtainable in the laboratory." By this means the student has not only learned how oxygen may be prepared, but he has learned to some extent the behavior of oxygen compounds exposed to different temperatures. The information thus con- veyed is farther reaching and more general than the mere prep- aration of oxygen. This effort to teach something of general bearing in connection with the specific information conveyed should be made wherever it is possible. In the Outline for a Course which is given farther on in this paper, this principle is applied rather carefully, as may be noticed by looking at the first few topics given.
In the teaching of experimental work it should be empha- sized that an experiment is valuable only if it is clearly remem- bered by the student. There exists a mistaken notion that ex- perimental work is intended primarily to train the student in the performance of such work somewhat for the same reason that training is necessary in carpenter work, metal work, etc. Such training is only an incidental object which is attained without particular effort if the work is done properly. The main object is to learn something about the substances, and the whole value of the work is lost if the experiment is forgotten. It is practically true that the value of the course is propor- tional to the accuracy with which everything, including details of a set of well selected experiments, is remembered.
Note on Quantitative Experiments.
Although quantitative experiments are usually introduced early in the course, yet it appears to the writer that it is in- advisable to do so. It is only when the student has a fairly extensive knowledge of chemical phenomena that he can appre- ciate quantitative relations. However, later in the course quan- titative experiments are extremely valuable. In this connec- tion see page 52.
42 University of Texas Bulletin
• The Note Book.
The first thing to insist upon in the note books is correct spelling and correct composition.
Next, all attempts to use blanks, to be filled in, or detailed "patterns," to be followed for the writing up of experiments, are to be discouraged. A few general directions are naturally necessary, but any approach to a "formula" to be used in writ- ing up experiments should be decidedly discouraged.
The first general direction given to students for writing up their notes is to call attention to the fact that the name of the book should be indicative of its use; it should be a note book, and not a re-written text book or a book of essays. If in per- forming the experiments, printed directions have been fol- lowed, then these directions should not be copied into the note book. Of course such directions should be definitely referred to in some such manner as this: "Experiment (number) - page — - in Smith's Laboratory Manual was
performed in full (or "with the following exceptions"). If additional experiments in which printed directions were not followed have been performed by the student, then these may be written out in full.
In the note book the experiments may be numbered merely for the sake of indicating the order. However, the most im- portant thing is to devise for each experiment a heading which states clearly the nature and object of the experiment. Con- siderable time may be spent in thought in order to devise head- ings that may be properly significant. A suitable heading is just :as important in itself as all the notes that follow, and the devising of proper headings is one of the best means to force the student to realize what he is doing and what he is doing it for. The heading should not be merely a general term, • and not more than one definite subject should be put under it. Thus it is absurd to give the heading "oxygen" to all the ex- periments given in connection with the study of that subject. Some of the experiments in connection with oxygen have been made with the view of demonstrating with what chemicals and with what operations it may be prepared. Other experiments may have been made with the view of preparing certain bottles
Chemistry in High Schools 43
f ul of the gas and showing some of its common properties. Hence it would be logical to head one experiment as follows: "To demonstrate with what substances and what operation oxygen may be prepared." The other experiment should be headed somewhat as follows: "The preparation and collection of oxygen gas and the demonstration of some of its properties. ' '
The assignment of separate headings to distinct parts of ex- perimental work should not be carried to the extreme. It is unnecessary to divide the last experiment discussed above into the following: first, the preparation and collection of the gas; second, the combustion of sulphur in oxygen, etc. The collec- tion of several operations under one heading naturally requires thought, and during the first part of the course the student will have much difficulty with it, but the benefit gained both as far as grasping the subject is concerned and as far as training in composition is concerned will amply repay the time spent upon this work.
In the body of the "write up" the first thing to be given is a direct reference to the directions followed, e. g. : Smith, Exp. - — , page - — , was performed in full" (or
with the following exceptions"), etc.
Then should follow a brief definite statement of what was actually noted or observed, which has not been given in the printed directions referred to above. For example, under the last heading mentioned would appear: sulphur, carbon, phos- phorus and sodium after they were heated to their kindling temperatures burned vigorously in the oxygen gas. The prod- uct of combustion of carbon (carbon dioxide) is an invisible, inodorous gas; that of sulphur is an invisible gas with suffocat- ing odor; that of phosphorus is a white solid and that of so- dium is a white solid. Treated with water, these substances give solutions the first three of which turned blue litmus red and the last turned red litmus blue. The equations for the chemical actions which take place during combustion and after- wards on treatment of water are as follows: "
The notes should always show the equations of the reactions in the experiment. Care must be taken by the teacher to see that they are written correctly.
44 University of Texas Bulletin
How to Begin the Course.
Avoid beginning by giving definitions, for instance of ele- ments, compounds, chemistry, atoms, molecules, etc. Starting with definitions reverses the attitude of the student towards the subject matter, and is really contrary to the natural method of learning a new subject. We teach a child a certain thing by mentioning its name and showing the thing, and perhaps speak- ing about it. This should be the mode of procedure in the in- troduction of this subject, which presents entirely new things to the student. Without attempting an explanation, the teacher should bring before the student the preparation and properties of several elements, oxygen, hydrogen, chlorine, etc., and tell him that these are elements. The formation of compounds, the various indications that chemical changes take place, are all shown incidentally in connection with these examples, and after a little while the student will be in position to form a definite notion as to what the terms, elements, compounds, chemical ac- tions, etc., mean. The attempt to introduce the fundamental terms abstractly at the very beginning of the subject consumes a great deal of time and is rather unprofitable.
Introductory chapters concerning experimental examples of chemical change, the influence of heat, what is meant by a solu- tion, exercises in weighing, measuring, etc., are also of ques- tionable value. . At best they are rather unfruitful and cer- tainly uninteresting to the student. At the University of Texas they are omitted altogeher, and the first exercise given is the study of the preparation of oxygen.
The Introduction of Symbols and of the Notions of Atoms and
Molecules.
It is a mistake to speak constantly about atoms and molec- ules and treat them as something absolutely essential to chemistry. Students are naturally inclined to consider that atoms and molecules are the main things with which chemistry deals, hence a particular effort must be made against this in- clination. Emphasize, at the beginning, that chemistry deals with facts, with things in this world as they are, and that the
Chemistry in High Schools 45
notion of atoms and molecules is introduced merely for the purpose of forming a simple mental picture.
It is highly desirable to use chemical symbols and formulae as early and as extensively as possible. However, these are not necessarily dependent upon any notion of the existence of atoms and molecules. They are mere short-hand expressions for the relations of the weights of substances which undergo chemical changes (which relations are merely the results of quantitative experiments). When it has been determined that 108 parts by weight of mercuric oxide give 100 parts by weight of mercury, and 8 parts by weight of oxygen, then instead of stating this fact in the way that it was just stated, chemists state it by writing
HgO=Hg+0
and the student need only be told that this is a special short- hand system devised to represent or express the proportions of these substances, the symbols standing for certain numbers selected partly with an eye to simplicity or convenience. The symbols need not mean anything else, and this is their funda- mental meaning and main use. Used in this simple sense, and for this definite purpose, symbols and equations should be in- troduced from the very beginning, and the fundamental (quan- titative) significance should be constantly referred to by the teacher.
After some seven or eight chapters dealing with different kinds of chemical substances have been studied, then the teacher may point out briefly (1) that we imagine any one ele- ment made up of distinct little pieces all of the same weight (atoms), which weights show the same relation as the num- bers represented by their symbols, and (2) that compounds are merely collections of clusters of the atoms of elements in such bunches as are indicated by the formulae of compounds. With this the student has been told all that he need be told for the present about the atomic and molecular structure of matter. All attempts to show how the atomic weight table was derived, all attempts to show that the atomic hypothesis rests upon the laws of definite and of multiple proportion will necessarily be philosophical, and it is questionable whether such attempts can be made profitably at this time. (In this connection see page 52.)
46 University of Texas Bulletin
Nearly all text books consider fairly early the relations by volume of combining gases, which naturally leads to the presentation of Avogadro's Hypothesis and the determina- tion of molecular weights. These topics as constituents of the first two-thirds of the high school chemistry course are wholly undesirable. They should not be given till later. If given earJy they tend to incline the student too much toward the theoretical aspects of the subject, an inclination which is alto- gether too great in most young students.
However, toward the end of the course such topics may be introduced, provided some of the experimental facts which show the relations by volume in which gases combine are ac- tually presented. The emphasis is to be placed on the presen- tation of the experiments. If the experiments are not per- formed, then the whole topic should be omitted. In order that the teacher may not lose time in selecting simple, easily per- formed experiments for this purpose, a list of suitable experi- ments and apparatus is given in this paper (see page 53). However, in any case, the consideration given to these topics should not be too great;
The Introduction of Valence.
Say nothing about valence until several substances have been studied. In studying the first, few substances give the stu- dents the formulae and equations and ask them to memorize these blindly. State merely that they are "short-hand" ex- pressions for the relations of the weights of the substances in- volved. Note where and how valence is introduced in the "Outline of the Course," page 66.
The Fundamental Facts of Electrolysis and Its Introduction
in the Course.
Do not give the electrolysis of dilute sulphuric acid, nor the electrolysis of any other substance as examples of the decom- position of these substances, and do not attempt to show by means of the relation of volumes of the gases obtained by elec- trolysis that water is composed of two volumes of hydrogen to
Chemistry in High Schools 47
one volume of oxygen. The first fundamental and most impor- tant fact concerning electrolysis and the action of batteries is that the chemical actions at the two poles are chemically in no wise related. The actions at the two poles are also very complex and it is only under special conditions that the relation of the volumes of the gases produced by electrolysis is just the same as that in which they combine to form water. The latter fact can be demonstrated by showing that the two gases, mixed in the proper proportion and exploded, combine completely to form water, but it does not follow as a conclusion from the re- sults obtained by electrolysis.
Electrolysis is a complex subject, and should not be treated in the early part of the course, but should be left to be pre- sented in connection with other electrolytic phenomena so that the whole subject may be clearly and connectedly shown by ex- periment. An example of a modern treatment of this subject is presented at length in Part III, page 81.
General Discussion of an Outline for the First Part of an Intro- ductory Course.
In the foregoing there has been presented (page 38) the first fundamental principle for the selection of topics in this course, which principle may be restated thus: make the course primarily a presentation of experimental facts and introduce theory to as slight an extent as possible.
The second fundamental principle governs the arrangement of the material. This should be arranged with the view of presenting at first only simple types of reactions, particularly reactions of hydration and metathesis, and deferring the pres- entation of the more complex types until the simpler types have received thorough consideration.
In the arrangement of subjects found in most text books neither the general types of reactions nor any classification ac- according to the most prominent chemical properties of the substances have been considered. Thus, nitrogen and its com- pounds are invariably presented very early in the course, al- though the reactions between nitric acid and metals are always complex. They involve not only the simple reactions of hydra-
48 University of Texas Bulletin
tion and double decomposition, but they also involve oxida- tion and reduction, and hence they should really be placed at a point farther on in the course. Again, many simple reactions which are presented by the interaction of salts of metals with common reagents, such as silver nitrate with hydrochloric acid, ferric chloride with sodium hydroxide, etc., are usually given at the end of the course, and yet they are the simplest kinds of chemical changes. As a result of the constant mixing up of all kinds of changes from the very beginning of the course, the student generally fails to grasp the fundamental principles in any, and instead of learning the properties of elements and com- pounds in their proper relation, that is, each as an, example of a general fact, he tries to learn them all as isolated specific prop- erties.
During the last thirty years our knowledge of reactions in aqueous solutions has increased so much that we may now be certain of the fundamental facts concerning them: it is defi- nitely known that metathetical reactions depend upon the de- gree of ionic dissociation, while reactions involving oxidation and reduction depend upon additional facts, namely, those learned in the study of the galvanic batteries. The study of chemistry is immensely simplified by the application of this knowledge and a course arranged to set forth clearly these two fundamental types of chemical changes will enable the student to get a grasp of the chemically important properties of sub- stances which is otherwise not so easily obtained. For this reason it is advised here to arrange the material according to our second fundamental principle; more particularly, it is ad- vised to present at first only substances which undergo reac- tions of hydration and metathesis, and then to present later on reactions involving changes of valence.
Although the arrangement of the subject matter according to this principle is quite different from that found in text- books, it will not be found difficult to follow this principle while using any good text. In order to make it convenient for teach- ers to do this, a detailed outline of the course prepared for this purpose is presented on pages 62 to 111. This outline is also issued separately so that it may be put into the bands of every student. The special experiments and directions which are
Chemistry in High Schools 49
not found in text books have been written out fully. It is in- tended that this outline may be used together with any one of the text-books and laboratory manuals listed on page 60. The separate prints of the outline may be obtained from the author.
An examination of this. Outline of the Course (see page 62) will show that in its first part it differs only slightly from the presentation usually given; but farther on in the presentation of the fundamental facts involved in metathetical reactions it differs radically from what is ordinarily found in texts. For details, see pages 73 to 80.
Since the reactions of the compounds of the metals involve nothing but metathetical reactions, these reactions are taken up next in order after the general discussion of the metathet- ical reaction.
How much of the reactions of the compounds of the metals should be taught in such a course as this? This has been, and possibly is still a great question. On one point, however, there is unaniminity of opinion, and that is : systematic qualitative, analysis must not be attempted in a high school course.
But this leaves us with the question: which of the reactions of the metals should be taught and how should they be taught T An examination of the laboratory manuals now on the market reveals great differences of opinion. Some manuals, such as Alexander Smith's and B. W. Feet's present the reactions found in the ordinary outline for qualitative analysis, the only differ- ence between this arrangement and that used in qualitative analysis being that in this case the reactions are presented dis- connectedly, and outlines for the systematic analytical procedure are deliberately omitted.
Other manuals such as the Laboratory Exercises by Brownlee and Others make no particular attempt to teach the reactions of the metals; but the latter book in Exercises 47 to 51 indicates that it is desirable to present certain features of this work. These features, which all authors are trying to present by their various methods, may be summed up as follows:
1. To change or transpose a metal from one of its com- pounds to another by means of the common reagents.
2. To separate the compound of a metal out of its mixture with compounds of other metals.
50 University of Texas Bulletin
3. To recognize or identify a certain metal in its compounds.
The first object is illustrative of the methods of manufacture of many commercially important salts and compounds from the commercial sources of the metal. The second is particularly illustrative of the chemical purifying of substances. The object of the third is self-evident. There can be no question as to the desirability of including some of this work in the course and the only thing we need to consider is its extent and the method of treatment. With reference to its extent, that presented by Brownlee and Others is inadequate, while that presented by Smith and by Peet requires too much time. Newell uses the same method as Smith and as Peet, but he attempts to save time by lessening the number of exercises. This makes the work weak, if not utterly valueless. As a way out of these various difficulties, the following experimental procedure is suggested : take solutions of water soluble salts of the common metals an.d study their reactions with several general reagents. Then add special properties of some of the compounds of the metals such as the solubility of lead chloride in hot water, the hydrolysis of bismuth salts, the flame colorations, etc. Finally, add a list of exercises designed to make the student use these facts in the solution of special problems. The list of exercises given in the Outline is drawn up with this in view. These reactions of the metals give the student enough experience with the meta- thetical reaction to become well grounded in its fundamental facts.:
Reactions involving oxidation and reduction — i. e., involving changes in valence — may be taken up next. These should be considered separately from hydration and metathetical changes because they involve entirely different fundamental facts. They 'should not be considered until after changes of hydration and metathetical reactions have been fully mastered, because they in- volve the latter.
The terms oxidation and reduction are rather misleading; many changes to be considered under this heading do not involve oxygen in any apparent manner. As the terms are now used, their direct significance is as follows : oxidation is an increase of positive electric charges on an element or radical (or the ab-
Chemistry in High Schools 51
straction of negative electric charges) ; and reduction is the re- verse electric change. The conception involved here can not be considered without a study of the action of battery cells, because the battery cell is, in a sense, an experimental analysis of oxida- tion and reduction reactions which presents the essential parts in their true relation. Any mixture in which oxidation and re- duction take place represents merely the case in which the electric charges, instead of being transferred by means of conducting poles and their connecting wires, are transferred by direct contact between the two parts undergoing the changes in valence. Hence battery cells should be studied in this connection (see pages 87 to 91).
Following this presentation of the battery cell, oxidation and reduction may be introduced as given on pages 101 to 111.
The question now arises : How much of this last subject should be taught in a high school course? The greatest danger is to attempt too much of it. The work presented in the accompany- ing outline, extending through the oxidizing actions of nitric acid (to page 108) is as much as should ~be given. However after this, whenever in the presentation of descriptive matter connected with any topic there occur equations for oxidation and reduction actions, then the valences of the ''valence-changing elements ' ' or radicals should be plainly marked in the equations, as shown in the accompanying introduction to this subject (see page 106). By this means the equations will be made vastly more significant than without it.
Other Subjects That May Be Studied.
Beyond this point other subjects may be taken up in almost any order that may appear desirable.
The following subjects are worthy of consideration here: (a) elements not yet studied and their important compounds, fb) theoretical topics, such :as the atomic and molecular the- ories,
(c) topics of practical interest.
Under (a) the following subjects may be considered: first of all, the halogens (bromine, iodine, fluorine), if they have not
52 University of Texas Bulletin
been previously studied; then any of the following in whatever order desired : phosphorus, arsenic, boron, manganese, chromium, and the oxy-halogen compounds. Only a few of the most com- mon experimental facts should be considered. The classification of the elements according to the periodic system should be pointed out briefly.
Under (b) in connection with the atomic theory, the law of definite proportion and the law of simple multiple proportion may be considered. The law of combining weights (see Smith's College Chemistry, page 34) is probably too difficult and may just as well be omitted. At this period of the student 's develop- ment, it would not be out of place to present the philosophical considerations, which, based upon these general facts, have built up the conception of the atomic structure of matter. However, do not mix with this topic any consideration of the molecular theory based on Avogodro's Hypothesis. This mistake is found in many texts, and must be guarded against It is very de- sirable to give some quantitative experiments in connection with this topic, such as the determination of the hydrogen equiv- alents of metals, or the ratio in which metals combine with oxygen or with chlorine. In the choice of these experiments the teacher must exercise great care to select those only that arc most easily and accurately carried out. The law of definite pro- portion may also be illustrated by the repeated titration of a base with an acid, using different quantities each time. Other suitable quantitative experiments are determinations of the sol- ubilities of salts, the determination of water of crystalliza- tion in salts, etc. Good workable quantitative experiments are found in Smith, Chap. 7.
If the molecular theory, and Avogodro's Hypothesis are in- troduced, several fundamental demonstrations should be made. If such demonstrations cannot be made, then it is questionable whether the topic should be taken up at all. The following three experiments are probably the simplest and most work- able that can be used in this connection, and those wishing to present this topic are strongly advised to perform these, at
Chemistry in High Schools 53
Experiments Which Should Accompany the Study of Avogat- dro's Hypothesis.
(1) . To DETERMINE THE KATIO BY VOLUME IN WHICH HYDRO- GEN AND OXYGEN COMBINE TO FORM WATER.
For this purpose it is advisable to secure a specially made eudiometer tube constructed as follows: a very heavy glass tube of 50-60 cm. length and about 100 cc. capacity terminates in both ends in stout tubes with a small, almost capillary, bore, in which are fitted specially well ground stop-cocks. One of these terminal tubes should be bent twice at a right angle, its stop- cock should be placed about 1 inch from the open end of the cap- illary tube, and the tube should be calibrated, beginning at the stop-cock and marking every half cc. The tube should also be sup- plied with platinum wire electrodes placed in the wide tube near the end to which the bent capillary terminal is attached. It should be specified that the connecting loops of the platinum wire elec- trodes outside of the tube should be constructed so as not to be easily breakable. In addition to this tube there should be se- cured a Hoffmann electrolytic apparatus such as is shown in Eimer & Amend 's catalog No. 3902. It should be specified, however, that the terminal tubes in which the stop-cocks are placed and through which the gases may be discharged, should have a small, almost capillary bore, and it should also be specified that the outer terminals of the electrodes should be specially well constructed so as to be practically unbreakable. To fill the eudiometer with hydrogen and oxygen it is first filled with water by suction, care being taken to fill the connecting tubes with liquid. The eudiometer is then placed beside the elec- trolytic apparatus, the bent end of the eudiometer tube is connected by means of a piece of rubber tubing with one of the gas-discharging tubes of the electrolytic apparatus, care being taken to bring the two ends of the glass tubes in direct contact. About 20 cc. of hydrogen and exactly half as much oxygen are thus transferred to the eudiometer. In measuring the gases in the eudiometer the differences in pressure due to the differences in the heights of the column of water in the eudiometer tubes may be neglected. The total vol-
54 University of Texas Bulletin
ume of explosive mixture used should not exceed 25 cc. or at most 30 cc., since otherwise the explosion may shatter the tube. Before exploding the mixture the lower stop-cock is also closed. The lower end of the tube should extend into some water in a beaker, and after the explosion the lower stop-cock should be opened rather cautiously, so that the inrush of the water may not shatter the tube.
This apparatus is simple, and easy to handle, and by its means it is easy to demonstrate exactly that two volumes of hydrogen combine with one volume of oxygen. Even at the risk of being tedious the author cannot refrain from pointing out again that this fact cannot be demonstrated by means of the simple elec- trolysis of dilute sulphuric acid, — which is erroneously desig- nated as the electrolysis of water. In this case, the production of the two gases is due to two entirely separate reactions, as has been pointed out elsewhere. Frequently the ratio of the volume of the hydrogen to the volume of the oxygen obtained by electrolysis is even greater than "two," on account of the fact that not all of the reaction at the anode produces simple oxygen gas.
Since, for the same reason the electrolysis of hydrochloric acid cannot be considered to be a demonstration of the fact that one volume of hydrogen combines with one volume of chlorine to form hydrochloric acid, it appears to be desirable to demon- 'strate the direct union of hydrogen and chlorine. However, this reaction is so violent and so troublesome that it is not ad- visable to attempt it for classroom demonstration. Mere men- tion of the experimental result should be made in this connec- tion.
(2) To DEMONSTRATE THE RATIO BY VOLUME BETWEEN Aw-
MONIA GAS AND THE NlTROGEN OBTAINED FROM IT.
The next important point to demonstrate is to show the volume relation between original and resulting gases. For theoretical reasons it would be most advisable to use the example just re- ferred to, by means of which it would be found that half a tube of hydrogen plus half a tube of chlorine would give a tube
Chemistry in High Schools 55
full of hydrochloric acid gas. On account of the difficulty of performing this experiment it is inadvisable to use it as a dem- onstration. To demonstrate such a relation the following ex- periment should be performed. A tube full of dry ammonia gas should be treated with bromine (more specifically sodium hypo- bromite) by means of which all the hydrogen in the ammonia is abstracted and the nitrogen left free. This nitrogen, it will be found, occupies just one-half the volume occupied by the ammonia from which it was obtained. The Hoffman lecture apparatus tube for the demonstration of the volume relations in ammonia, which tube is shown in Eimer & Amend 's catalog No 3904, — this tube should be obtained with an additional stop- cock attached to the closed end. The bore of the tube of this stop-cock should not be less than 2 or 3 mm. and the tube should be cleaned and dried by rinsing it first with water and after- wards with alcohol, and finally drawing air through it with the aid of the suction pump or by means of the foot pump, and at the same time warming the tube gently with the flame. It is clamped in a vertical position and filled with ammonia gas gen- erated by boiling a concentrated solution of ammonia, and passing it through a drying tower filled with quicklime. The gas should be passed in at the top of the tube at a fairly good rate. After the tube has been filled with ammonia and closed, it can be laid aside until the time for the lecture. For the decomposi- tion of the ammonia about 50 to 100 cc. of 20 per cent sodium hydroxide solution is treated with bromine until tfce solution has a straw yellow color. The mixture must be stirred vigor- ously while adding the bromine. This solution is added cau- tiously through the " funnel end," care being taken not to admit air. Finally the upper stop-cock is closed, and the lower stop-cock is opened while this end of the tube is dipped under water so that the latter may rise in the tube until the pressure inside the tube is equal to the atmospheric pressure.
This experiment is very easily performed, and gives the facts for the following argument. If the "tubeful" of gas contains "a" molecules, then the half "tubeful" contains ''a/2" molecules and since each one of the "a" molecules of ammonia contains ai least one atoms of nitrogen, then there
56 University of Texas Bulletin
must be at least "a" atoms of nitrogen in "a/2" molecules of nitrogen, or at least two atoms in each molecule of nitrogen. The corresponding facts concerning hydrogen and chlorine pro- ducing hydrochloric acid gas and also hydrogen and oxygen producing steam, with the same argument, lead to the conclu- sion that the molecules of hydrogen, of chlorine, and of oxygen, each contain at least two atoms.
(3) To DEMONSTRATE THE RATIO BY VOLUME BETWEEN OXY- GEN AND THE SULPHUR DIOXIDE FORMED FROM IT.
For this purpose secure a piece of hard glass tubing about 24 inches long, closed at one end, and bent almost at right angle at a point about 5 inches from the closed end. Place a little sulphur in the closed end of the tube and fasten it there by melting the sulphur slightly. Then fill the tube partly with oxygen over mercury and place it with the short arm in a hori- zontal position. The action is started by gently heating the sulphur. Usually no gas will escape, and after the tube has been allowed to cool, the mercury will rise to the original posi- tion, which shows that the volume of the sulphur dioxide is equal to the volume of the original oxygen.
Chemical Information of Direct Economic Value in Texas.
Perhaps the most important additional topic to be added to the course is the presentation of subjects of practical interest. While the two preceding topics may be omitted entirely with- out any loss to the student, this last topic should not be omitted, because the major part of the direct value of the course to the high school student is obtained through the proper conveyance of accurate information on practical subjects with which he will have to deal more or less during the rest of his life. The value of such work and the desirability of presenting it in this course have never been doubted, but the results, obtained by many of the attempts made to present it, have frequently been worth very little, and occasionally they even serve to discredit both subject and teacher in the eyes of the general public. This back set, in general, is due to two causes : the first is the ignorance
Chemistry in High Schools 57
of many teachers in the practical application of chemistry, and the second is a mistaken method of presenting it due to the zeal of the teacher to give this subject prominence. The subject is so important that proper methods of presentation and errors to be avoided should be given here.
Teachers just beginning to teach chemistry, whether college graduates or trained in other ways, are as a rule, not only ignorant of the practical applications of the subject, but their interest in the pure science, inclines them to stress the pure, scientific subjects to the exclusion of the practical ones. If they continue to teach the subject, sooner or later they are impressed with the importance of the practical applications and in their effort to give this prominence, they may go to the other extreme. The writer has at hand some outlines prepared by prominent teachers of chemistry in various parts of the United States, in which an attempt is made to introduce prac- tical subjects from the very beginning of the course. Long before the student has any knowledge of the simple chemical facts involved, these outlines present problems of water soften- ing, the testing of coal gas for impurities, the solvent action of water on lead, the tests for organic matter in potable water, etc. Such information, though valuable in itself, becomes valueless when presented so early in the course that the stu- dent's lack of knowledge of pure chemical phenomena pre- vents a recognition of the simple fundamental phenomena in- volved. The mere mechanical testing of certain constituents of a potable water before the student has even learned or seen reactions between pure salt solutions, such as the reaction be- tween sodium carbonate and calcium chloride, cannot be of much value either as an informational or as a training exer- cise.
Another mistake is the selection of applications which are nothing but empiric operations. Thus we find various at- tempts made to present the chemistry of cooking, the chemistry of cleaning, etc., under which headings many useful topics are offered. When, however, such subjects are presented by them- selves, and particularly when the presentation crowds out fun- damental chemical phenomena, they degrade the course into the mere "trying out" of a number of shop recipes.
58 University of T&xas Bulletin
A course filled with such material cannot give a well devel- oped exposition, of the subject. However, the entire neglect of these (applications is probably just as great a mistake. The problem to be solved is to present enough of the fundamentals to give the student some sound training and then to add suffi- cient applications to give the subject "life." The first thing necessary to accomplish this end is for the teacher to read and study in order to inform himself on practical subjects. As a rule he will not get this information in college: he must se- cure it by informing himself in a general way, — as for in- stance, by reading books affording information on practical topics, by noting the operations and practices of practical men and artisans around him, etc. To be more definite, he should attempt to inform himself on such subjects as the following: soils, fertilizers, and irrigation waters; feed and food-stuffs; the technology of petroleum oils, tar oils, cotton seed oil, lin- seed oil, the manufacture of soap, paints, paper, etc. The fol- lowing books will furnish him with a great deal of information on these subjects:
Soils and Fertilizers, by Harry Snyder (The Macmillan Co.).
Alkali Soils and Irrigation Waters, by G. S. Fraps, Bull. 130 of the Texas Agricultural Exp. Station.
Nature and Use of Commercial Fertilizers, G-. S. Fraps, Bull. 112, Texas Agricultural Exp. Station.
Outlines of Industrial Chemistry, by F. H. Thorp (The MacMillan Co.).
Chemistry of Plant and Animal Life, Harry Snyder (The MacMillan Co.).
In the study of these subjects it will be found advisable to direct the attention to the following points :
The chemical analysis of a soil at present does not enable one to judge what ails an infertile soil; the value of fertil- izers is determined by "pot" or "basket" experiments; the essential constitutents of fertilizers are the nitrogen, potas- sium /and phosphorus compounds in it; why rotation of crops is necessary; the Texas feed analysis law requires the deter- mination of carbohydrates, fats, proteins, indigestible matter or crude fiber, water and mineral solids ; what is meant by these divisions of food stuffs and how they are experimentally deter-
Chemistry in High Schools 59
mined; the relative proportions of these constituents, in food or feedstuffs; the essential properties of the three classes of foodstuffs, that is, of carbohydrates, of fats, and of proteins; starch can be converted to dextrine and to glucose, and the latter can be fermented to alcohol; fats of vegetable or animal origin can be used to make soap; how cotton seed oil is made and refined; the essential difference between cotton seed oil and linseed oil, which makes the latter valuable to be used in paints; white lead is the most valuable pigment for paints and the best paints contain this together with just enough of some coloring matter to give the desired tints; the essential constitu- ents of coal and their determination; how hard waters may be softened cheaply for boiler purposes ; how potable waters may be purified in case they are unsanitary ; how kerosene, gasoline, par- affin, etc., are obtained from crude petroleum and how they may be refined; what is meant by the flash point of kerosene; oils obtained by the distillation of tar are chemically more active than petroleum oils and hence form the starting point of the many synthetic dyes iand drugs ; oils obtained from tar, in con- tradistinction to the oils obtained from petroleum, are germi- cidal, and hence the cheapest portions of the tar distillates are used for wood preservation; how cement is made; the chemis- try of photography and of blue-printing, etc.
If the teacher has no knowledge of organic chemistry, he should study certain parts of Remsen's Organic Chemistry. This book, though small, will give him the necessary scientific foundation for the parts in the foregoing list which deal with organic chemistry.
The introduction of this information into the course is rather difficult at present on account of the absence of a suitable text- book. The best text-books on the market today present a good introduction to the science, but do not present in any adequate manner such "practical" information as above indicated.
It is difficult to say how much of this can be done in a high school course, but it is certain that none will be done unless the teacher is actively engaged in increasing his own knowledge in this line. Young teachers in chemistry frequently continue their collegiate course by attending summer schools, and in this way they increase their knowledge of pure chemistry. Such
60 University of Texas Bulletin
a practice is extremely commendable <and valuable for both the teacher and his school, but unless he makes a special effort outside of the college course to increase his knowledge of chem- ical applications, his knowledge of the subject and hence his teaching will continue to be one-sided and much less fruitful than if he also increases his knowledge of practical affairs.
The University of Texas Requirements for One Unit Entrance
Credit.
The suggestions and directions in this paper need not be followed to secure affiliation in chemistry at the University of Texas. They are offered to teachers as aids in shaping their courses in chemistry, and whether or not these suggestions are followed has nothing to do with securing (affiliation. The Uni- versity aims to be exceedingly liberal and broad-minded in its requirements for affiliation as shown by the following list of requirements.
1. A properly prepared teacher : — see page 9.
2. A proper class-time allowance. The time spent in the course must not be less than three recitation periods of 45 minutes and two 90 minute laboratory periods a week for one year.
3. A fairly well equipped laboratory in which the students do individual work.
4. Some evidence that the (competent) teacher occupies the time with a well planned and well conducted course. This evidence is obtained by a personal visit of an official, and an inspection of the note books and examination papers of the students in the course.
Some Suitable Text Books in Chemistry.
Brownlee & Others, First Principles of Chemistry, Allyn & Bacon.
Hollis Godfrey, Elementary Chemistry, Longmans, Green & Co.
Hessler and Smith, Essentials of Chemistry, Benjamin San- born Co.
Chemistry in High Schools 61
McPherson and Henderson, Elementary Chemistry, Ginn & Co.
Morgan & Lyman, Elementary Text on Chemistry, MacMil- lan Co.
Newell, Inorganic Chemistry, D. C. vHeath & Co.
B. W. Peet, Laboratory Manual in Chemistry, published by the author at Ypsilanti, Mich.
Remsen, Introduction to Chemistry (Briefer Course)1., H. Holt & Co.
Smith, Laboratory Outline of General Chemistry (4th Edi- tion) Century Co. This is the book referred to in Part III where Smith appears. It is primarily a college text, but is likely to be in the hands of every teacher, and the author preferred to refer to it alone rather than to all the high school texts.
Smith & Hall, The Teaching of Chemistry and Physics in Secondary Schools, Longmans, Green & Co.
Alexander Smith, Inorganic Chemistry, Century Co.
Julius Stieglitz, Qualitative Analysis, Century Co.
Prescott & Johnson, Qualitative Analysis, Van Nostrand Co.
Roscoe & Schorlemmer, Inorganic Chemistry, 2 volumes, MacMillan Co.
PART III.*
OUTLINE OF AN INTRODUCTION TO THE FIRST PRIN- CIPLES OF CHEMISTRY, t
Oxygen.
1. Demonstration of its preparation by the decomposition of oxygen compounds at high temperatures (Smith, Art. 10). The weight relations of the substances which decompose giving oxygen are as follows:
Ba02=BaO+0
Pb02=--PbO+0
3Mn02=Mn304+20 KC103=HC1+30
The names of these substances and the above information con- cerning the quantities involved in the reactions should be com- mitted to memory by the students. "These are particular sub- stances which show the general behavior of giving up oxygen readily at high temperatures." Note the significance of co- efficients and subscripts in chemical formulae and equations. Fundamentally the symbols represent a certain number of parts by weight of a particular substance, which number is given in an accompanying table commonly referred to as a table of atomic weights. The student should not stumble at the word "atomic weights," — he should simply accept this for the pres- ent as merely a name for the table. The quantitative signifi- cance of the symbols and equations should be emphasized by problems based on them.
2. Catalytic Effect of Manganese Dioxide in the Decomposi- tion of Potassium Chlorate (Smith, Art. 11).
Avoid presenting Mn02 in the equation for the decomposi- tion of potassium chlorate; equations are expressions of quan- titative relations only, and the manganese dioxide undergoes no
*This part has been issued separately by the author. •{•Copyrighted, 1912, by E. P. Schoch.
Chemistry in High Schools 63
change and is not necessarily present in any particular propor- tion, hence its quantity is not involved and should not appear in the equation.
3. Preparation and Collection of Several Bottles Full of the Gas, and the Combustion of Sulphur, Phosphorus, Carbon, So- dium and Iron In It. Perform this in the usual manner. This shows experimentally that oxygen is very slightly soluble in water, that it is a colorless inodorous gas, that it is as heavy as — if not heavier than — air, etc. Students should learn these proper- ties from experiments rather than from the printed page.
The products of combustion should be treated with water and the resulting solutions tested with litmus. These substances react with water in the following proportions: C02+H20=H2CO, S02+H20=H2S03 P205+3H20=2H3P04 Na20+H20=2NaOH Fe203 does not react with water.
These equations are to be memorized and their quantitative significance to be emphasized with numerical problems. Such reactions with water are called hydration and this is a very common chemical phenomenon. Note the general fact here illus- trated, that non-metals form acid oxides and metals form basic oxides. This is a fundamental fact and should be remembered.
Hydrogen.
1. General facts concerning its preparation: the interaction of metals and acids:
(a) Many non-oxidizing acids (hydrochloric, dilute sulphu- ric, acetic, phosphoric) react with any metal above hydrogen in the electromotive force table (e. g. iron, zinc, aluminium, mag- nesium— see page 110) to form hydrogen and one other prod- uct (salt) ; while there is no action with the metals below hydro- gen in the table.
(b) Oxidizing acids (nitric acid, concentrated sulphuric acid) act on almost all metals except the lowest in the table (gold, platinum) ; but hydrogen does not appear as one of the products, and the action is altogether more complex than any action with non-oxidizing acids.
64 University of Texas Bulletin
The above general facts (a and b) should be learned and re- tained by the student. He should realize that by this means he learns a great number of important facts easily.
In connection with (a) the following quantitative data is given:
Fe-f2HCl=FeCl2+2H Zn+2HCl= ZnCl2+2H A1+3HC1=A1C13+3H Fe+H2SO4=FeS04+2H Zn+H2SO4= ZnS04+2H 2A1+3H2S04=A12 ( S04) 3+6H.
These equations should be committed to memory and drilled on by means of numerical problems.
2. Preparation and collection of the gas to show some of its common properties. Perform as given in any text. The experi- ment shows that the gas is not very soluble in water, that it is lighter than air, that it forms water on burning and that when mixed with air in certain proportions it forms explosive mix- tures.
3. Qualitative reduction of some metal oxide (lead oxide or copper oxide), Smith, Art. 20. Point out how this experimental procedure may be used (as it was used, by Dumas) to get the proportion by weight in which hydrogen and oxygen combine to form water.
Incidentally the relative rate of diffusion of gases may be demonstrated, as usual, by means of hydrogen and air.
The change of gas volumes through change of temperature and pressure may also be considered here.
Chlorine.
1. The reactions involved in the preparation of chlorine are all complex reactions of oxidation and reduction, hence the prep- aration of chlorine does not fit into our general plan at this point. However, it is desirable to demonstrate here the proper- ties of the element. For the reason just given, the details of the reactions involved in the preparation of chlorine are not consid- ered and the general fact alone is given, namely, that it is pre- pared by the action of oxidizing agents upon hydrochloric acid.
Chemistry in High Schools 65
The oxidizing agents serve in a sense as suppliers of oxygen merely, and the oxygen that they supply combines with the hydro- gen of the hydrochloric acid to form water. The following equa- tion represents this change and is the only one that should be given and learned in this connection :
0+2HC1=H20+2C1.
Use several oxidizing agents to illustrate this general method of producing chlorine (Smith, Art. 29a).
2. Prepare and collect several bottles full of the gas to dem- onstrate some of its properties. Proceed as given in any text.
Hydrogen Chloride.
1. A general method for producing this substance is the re- action between a metal chloride and a relatively non-volatile and non-oxidizing (toward HC1) acid. The mixture must not con- tain water since otherwise the gas dissolves in it. See Smith, Art. 31 (a) and (b). Call attention to the fact that concentrated sulphuric acid is not an oxidizing agent toward HC1 while it is towards metals.
The study of water as a solvent, as water of crytallization, etc.. and of air, .its composition, etc., may be introduced any- where here at the option of the instructor.
Acides, Bases and Salts.
A thorough treatment of this topic is advisable at this point. The fundamental relation is "an acid with a base gives a salt and water." This is the only real criterion for the definition of the terms acid, base and salt. Such properties as the effect upon litmus paper, taste, etc., characterize only those par- ticular acids or bases which are soluble and they are not general or defining characteristics. In order that the above relation, that an acid with base gives a salt and water, may really serve to identify a particular substance, we must admit that there are some substances such as sodium hydroxide, calcium hydroxide, etc., which everybody agrees to call bases, and when one of these reacts with ian unknown substance in a manner similar to its re- action with a well recognized acid, then the unknown substance
66 University of Texas Bulletin
is thus recognized to be an acid; and the corresponding argu- ment is applied when an unknown substance reacts with a sub- stance which everybody agrees to call an acid, such as hydro- chloric or sulphuric acid. All other descriptive properties con- cerning these substances are not essential to define or characterize them as acids, bases or salts respectively.
In the experimental demonstration give first the neutraliza- tion of a soluble base by a soluble acid with the aid of an in- dicator; and second the neutralization of a soluble acid by an insoluble base. For instance, add copper oxide to warm dilute sulphuric acid until some of the insoluble oxide remains un- acted upon, then concentrate the solution. The salt will crys- tallize out on cooling.
All acids, bases and salts are binary compounds. This should be accepted as a plain fact, without any discussion. The two kinds of constituent parts are called ions, for reasons given later on.
At this point it is advisable to enlarge very much upon the usual treatment of Acids, Bases and Salts in text books. For this purpose students should memorize the formulae of about eight to ten basic oxides (e. g. Na20, K20, CaO, CuO, MgO, ZnO, A1203, Fe2O3), as well as the formulae for a num- ber of acids in addition to those already met with before (e. g. HN03, H3P04, H2C03, H2S04, H2S03, H (C2H303).
Next in order, the student should learn to r&cognize the valence of the metal ions or of the acid ions from the formulae of the bases or acids just given. Without any reference to the atomic theory, define valence as follows: "The valence of an ion (that is, one of the two kinds of parts into which any acid, base, or salt primarily divides) is the number of H's it appears to take the place of, or to combine with, as shown by the for- mulae of different compounds on comparison."
Note that this definition presents valence as a numerical re- lation shown by the formula® and does not mention the word atom. Reference to the atomic theory is thus seen not to be necessary; though there is no objection to considering valence as a property of atoms or groups of atoms if the connection between the formulae and the atomic theory of matter has been pointed out before this.
Chemistry in High Schools 67
Next in order, the student should learn how the metal iona and acid ions from the above memorized formulae must be put together in accordance with the demands of valence in order to obtain the formulae of the normal salts. This should be drilled upon, and the fundamentals of nomenclature should be given.
Finally drill the student in writing equations between all the acids and all the bases which have been memorized. They are &11 metathetical reactions.
Definition of the metathetical raction : It is one in which two binary compounds exchange their negative parts (or their posi- tive parts) producing only two new compounds, the valences of all ions remaining constant during this change. Whenever two substances are said to react metathetically, this one word tells fully what takes place: with this knowledge, anyone is able to write the equation of a change if he knows the formulae of the substances involved.
Hydration of Oxides.
1. To be illustrated with the slaking of quick lime; then follows the general information:
(a) Basic oxides when hydrated usually appear as hydrated to the maximum extent, that is, two hydroxyls are formed from every 0 in the formula of the oxide, e. g., CaO+H,0=Ca(OH)2 (drill in writing such equations with other basic oxides).
(b) When placed in contact with water, only those oxides the hydroxides of which are soluble actually take up water to form hydroxides. Of the common hydroxides only those of the alkali and alkaline earth metals are soluble. Drill!
2. The hydroxides of metals also are bases, just as well as the oxides. Drill on writing all the equations of the reactions between the hydroxides of the eight metals (in the list of bases memorized above) with the acids given above.
3. Recall the fact that metals form basic oxides and non- metals form acid oxides. The latter hydrate just as well as the basic oxides; however, the extent of hydration follows no rule, and is usually less than the maximum. Common acid oxides are-: S02, S03, C02, P2O5, N2O5 N208, P203. Drill on writing
68 University of Texas Bulletin
the relation between these plus water, giving the ordinary acids, (H2S03, H2S04, H2C03, H3P04, HN03, HN02, H3PO,). 4. The actual hydration of acid oxides on contact takes place readily with nearly all acid oxides because the resulting acid is soluble in nearly all cases (exceptions: silicic acid H2Si03. from Si02; arsenious acid, HAs02, from As203).
Solubility of Salts.
By solubility is meant the solubility of these substances in water, not their solubility in a solution which acts on them chemically. None of these substances are absolutely insoluble; they are all slightly soluble and they present enormous relative differences in their actual solubilities.
A short table, of the solubilities of the ordinary salts such as is given below, should be committed to memory by the stu- dent.
Table of Solubilities of Salts.
Nitrates and Acetates. All soluble.
Sulphates. All soluble except PbS04, BaS04, SrS04, and CaS04. The last is perceptibly soluble.
Chlorides. All soluble except AgCl, HgCl, PbCl2. The last is slightly soluble in cold water, and quite soluble in hot water.
Normal Carbonates and Phosphates. All insoluble except those of the alkali metals, Na, K and "NH4."
The solubilities of the substances is one of the largest factors which determine whether or not metathetical reaction will take place. Thus even in the reaction between a base and an acid, for which there is always a decided tendency, insolubility will retard the action somewhat in proportion to the insolubility of the salt formed, and may prevent it practically entirely. The following experimental procedure serves to show this. The ex- periment is an excellent one to develop chemical notions :
Put into each of three test-tubes a pinch of zinc oxide, and add to one just enough dilute HC1 so that when the mixture is stirred and warmed the zinc oxide dissolves. Treat the second
Chemistry in High Schools 69
portion of zinc oxide with HN03, and the third with dilute H,S04. In the same way try calcium oxide (or hydroxide), and lead oxide. Do you observe any relation between the sol- ubilities of the salts that are, or should be, formed, and the rate at which reaction takes place?
When insoluble salts are, or would be, thus formed, is there absolutely no action or is the action merely retarded? To find the answer to this question examine particularly the mixtures of lead oxide with HC1 and H2S04, respectively. The change from yellow oxide to white salt in these cases will reveal whether or not any action takes place. If you conclude that the action is merely retarded, and you wish to find an explanation of this, drop a small lump of marble into some dilute H2S04 and observe that a copious evolution of C02 takes place for just a moment, fol- lowed by a very slow action. Take out the piece of marble, scrape off the outer layer and drop the lump into dilute H2SO4 again. Rapid action which lasts only for a short while is again observed. It is evident that the layer of insoluble calcium sul- phate formed covers the lump and retards the diffusion of the acid to the calcium carbonate. In the experiments above, the particles are much smaller, yet the actions are retarded in the same way.
Acid Salts.
With due consideration of what the ionisation theory teaches concerning the ionisation of polybasic acids, acid salts should be treated somewhat as follows: when an acid such as. phos- phoric, H3P04, separates into its main constituent parts (ions), at first only one H separates, leaving the remainder intact as a monovalent ion ( H2P04 ) ' ; and when the first portions of a base are added to a solution of such an acid, the reaction of neutralization takes place as though this were a monovalent acid, the composition of the acid radical of which is (H2P04) '. Hence the aluminium salt would have the formula A1(H2P04)3.
Note: — the valence of metals and all positive ions is desig- nated with an asterisk — e. g. H* ; that of acid radicals and other negative ions by an apostrophe, as N03', S04", etc.
After enough base has been added to neutralize all of the first
70 University of Texas Bulletin
set of H-ions, then the second H ionizes extensively and leaves the bivalent ion (HPO4) "; hence salts formed under these con- ditions appear to have a formula similar to those formed with bivaJentacid ions, e. g., A12(HPO4)3.
After the second hydrogen has been neutralized, then the tendency to ionize the third hydrogen may become effectve, leaving the trivalent ion, (P04)'".
Of course if enough base is added all at once to neutralize more than one or two H's the reaction immediately proceeds to the corresponding extent. Thus if a drop of sulphuric acid is added to more than enough of sodium hydroxide solution to neutralize the acid completely, then the salt Na2S04 is formed immediately; but when the procedure is reversed, that is, when a drop of sodium hydroxide solution is added to a great deal of sulphuric acid, then it will form only the acid salt Na(HS04).
That the (experimental) formation of acid salts, with poly- basic acids, depends only on the relative proportions of acid and bases mixed should be strongly emphasized and drilled upon. In the following lessons the reactions between carbon dioxide and lime water ; and the passing of S02 into sodium hydroxide solution until no more is absorbed — these and others furnish excellent examples to bring out this same point; and this reaction also furnishes a good opportunity to develop chem- ical notions as distinct from the mere arithmetic notions in- volved in equation writing.
The following experiment is here given in full to demonstrate the actual formation of acid salts :
"Secure a fresh solution of tartaric acid, H2(C4H406), con- taining about 200 grams per liter, and a solution of potassium hydroxide containing about 150 grams to the liter and fill two burettes with these solutions respectively. Measure out 20 cc. of potassium hydroxide solution into a small flask, add 30 cc. of the tartaric acid solution measured from the other burette, then heat the mixture to the boiling point, add a drop or two of phenolphthalein solution and finish neutralizing it by adding more tartaric acid from its burette. Cool the mixture under a jet of tap water and add to it as much tartaric acid again as was necessary to neutralize the potassium hydroxide. Crystals of potassium acid-tartrate will be formed. Next heat the mixture
Chemistry in High Schools 71
to boiling and add KOH slowly, with constant stirring until an amount approximately equal to the original amount has been added. Note that the crystals dissolve as KOH is added. Ex- plain what happens in each step and write the equations of the three reactions ; they are all metathetical changes. Note that the second portion of potassium hydroxide used is equal to the first portion used. The composition of the crystals that separated from the solution is KH(C4H4O6), potassium acid-tartrate, or potassium bitartrate. Give reasons for both names.
Carbon.
Present some of the properties of the element, the discussion of the flame, some descriptive matter concerning the importance of carbon monoxide on account of its presence in water gas and its use in the reduction of ores (e. g. of iron ores).
2. Show that the preparation of carbon dioxide from prac- tically any carbonate is in general similar to the preparation of HC1 (noting however the difference in the solubilities of the two gases and that carbon dioxide is not oxidizible; hence almost any ordinary acid may be used to liberate it from its salts). Show some of its common properties and emphasize that the portion dissolved in water is largely hydrated; when- ever it acts, in solution, as an acid on a base, then it is H2C03 which is the actually acting substance, and not CO2. A sep- arate equation should always be written to express the hydra- tion and dehydration that may precede or follow a metathet- ical reaction. Thus when carbon dioxide is absorbed by lime water the following reactions take place in the order here given:
(a) C02+H20=H2C03.
(b) H2C03+Ca(OH)2=CaCO3+2H20.
These reactions should not be combined into the following ex- pressions :
C02+Ca(OH)2:=CaC03+H20. (avoid this!)
Be certain to make the experiment of passing carbon dioxide into lime water until the solution clears up again; and then boi! the solution. The student should know this experiment and action thoroughly, and also know its application in nature and in the production of boiler scale (temporary hardness of potable water).
72 University of Texas Bulletin
Sulphur.
Deal briefly wtih the properties of the element (the phenom- ena presented by melted and cooled sulphur, etc., need not be considered). Emphasize the source and extraction of commer- cial spulphur.
Deal with hydrogen sulphide very briefly here. Make some iron sulphide and liberate hydrogen sulphide from it. Note that the gas is poisonous. The reactions involved in these examples are mainly simple or metathetical, and the complex oxidation reactions of hydrogen sulphide must be omitted here. The use of hydrogen sulphide as a laboratory reagent will be sufficiently illustrated later.
Prepare sulphur dioxide by means of the reaction between sulphites and acids. Point out that the method in general is the same as that employed for the production of carbon dioxide and of HCL The student should learn this and also remember the particular substances that he actually handled in this con- nection in the laboratory. In the equations involved, the ex- pression for hydration and dehydration should be separated from the metathetical reactions — as was advised for carbon dioxide. The main chemical property of S02 (or of sulphurous acid) is its tendency to be oxidized to sulphuric acid. This may be illustrated as follows:
Prepare a saturated aqueous solution of S02. Put a little of it in a test tube, add a few drops of hydrochloric acid and a drop or two of barium chloride solution. Only a slight or negligible precipitate will be formed. Now add to the main portion of the solution one or two cc. of concentrated nitric acid and heat gently to boiling. Some brown fumes of oxides of nitrogen will be formed to a slight extent, which show that the nitric acid has acted as an oxidizing agent. Now test the solution again with barium chloride previously acidified with a few drops of HC1. A copious precipitate of barium sulphate will be ob- tained. This test depends upon the fact that barium sulphite is soluble in this mixture while barium sulphate is not; hence not until the sulphurous acid is changed to sulphuric will a precipitate be formed.
The commercial production of sulphuric acid by the contact
Chemistry in High Schools 73
method may be given here. If the old English method is given, no reference need be made to the formation of nitrosyl sul- phuric acid. It is perfectly correct to state that NO takes up oxygen to form N02 and this change takes place more readily and hence faster than the direct reaction between S02 and the oxygen of the air. The oxides of nitrogen are merely catalytic agents, and the impelling tendency of the action is always the tendency of S02 to take up oxygen.
Ammonia.
Stress the commercial source of ammonia; its liberation from the salts by a general method which corresponds to the general method for the liberation of carbon dioxide, HC1, and SO2, Any ammonium salt and any base may serve for this purpose although the reaction takes place readily only with a strong (soluble) base. Stress the fact that ammonia hydrates readily — otherwise the usual treatment found in texts may be given.
Other Optional Topics.
The following topics may be treated here at the option of the teacher :
1. The liberation of nitric acid from its salt, — but do not consider at this point the production of oxides of nitrogen, or the reaction of nitric acid with metals, etc.
2. The other halogens: fluorine, bromine and iodine.
For fluorine the etching effect of hydrofluoric acid upon glass is the only experiment to be given. For bromine and iodine, show, with test tube trials, the liberation of HBr and HI from their salts by means of phosphoric acid (do not use sulphuric), and then show the liberation of the elements from these acids by means of an oxidizing agent (add powdered Mn02 to the mix- tures in the test tubes) : The displacement, by chlorine, of bro- mine from bromides and of iodine from iodides, should also be presented here.
lonisation and the General Relation Between Dissolved Sub- stances Which Results in Metathetical Reaction* This topic should be begun by showing experimentally some fundamental facts concerning electrical conductivity of so!u-
*Read pages 47-49 in this connection.
74 University of Texas Bulletin
tions. This may be shown most conveniently by means of an alternating electric light current and an incandescent lamp. Cut one of the two wires of an "extension cord" and, to the two ends thus obtained, attach platinum wires for electrodes. Dip the latter into a beaker filled with distilled water, attach the plug to the light circuit, and insert the lamp into the socket of the cord. It will be found that distilled water does not conduct the current sufficiently well to light up the lamp. Next pour a little hydrochloric acid into the water: the lamp will burn brightly, which shows that this solution conducts well. Repeat with fresh water and acetic acid: the lamp will burn dimly, which shows that the solution conducts poorly. In the same way try sodium hydroxide solution, ammonium hydroxide solution, alcohol in water, and various salt solutions. These experiments suffice to dispose the student favorably to receive the following general facts.
Acids, bases, and salts, when dissolved in water dissociate into parts, called ions, each of which carries a definite number of positive or negative unit charges, the number of which cor- responds to the valence. Metals and hydrogen carry positive charges, while the non-metals, acid radicals, and the hydroxyl radical carry negative charges.
Not all of an acid, base, or salt in a solution is present in the form of ions. A part is present in the undissociated or com- bined form. This is due to the tendency of ions to recombine. These two opposing tendencies, of ionisation and of recombina- tion, hold each other in equilibrium when a certain fraction of the dissolved substance is in the form of ions and undissociated part, respectively. These fractions have different values with different substances, and the "ion" fractions increase with dilu- tion, while the undissociated decrease.
The following general statement covers the degrees of disso- ciation of all common substances. It should be committed to memory :
All normal salts, all strong acids (hydrochloric, nitric, sul- phuric), all strong bases (that is, all soluble bases except am- monia) ionize extensively in aqueous solutions.
All weak acids (acetic, carbonic, sulphurous, phosphoric), all weak bases (ammonia) and water itself, are very slightly dissociated (about 1% and much less) in aqueous solutions.
Chemistry in High Schools 75
Insoluble or very slightly soluble substances can not form many ions in solution and hence should be included here as slightly dissociated substances.
The chemical activity of acids, bases, and salts depends upon the concentration of their ions; in other words, it is primarily the ions, rather than the undissociated portions, which take part in chemical reactions. This is suitably illustrated by means of the rates of action of hydrochloric acid upon zinc, and of acetic acid upon zinc, or the rates of action of these acids upon marble, all of which is readily shown by means of test-tube trials.
The fact that a dissolved acid, base, or salt is present in solu- tion in two forms, either one of which tends to change to the other one until they hold each other in equilibrium, — this fact appears strange to the beginner, and yet it is similar to the familiar phenomenon of a salt dissolving in water until the solution is saturated, and hence it is in equilibrium with the solid salt; it is also similar to the evaporation of a liquid until its saturated vapor is in equilibrium with it. However, there is one essen- tial difference between these equilibria and the equilibrium be- tween a salt and its ions, namely, there are always two kinds of ions, and neither one kind alone can hold the equilibrium with the undissociated salt. Both must be present, but their amounts or numbers per cc. necessary for any one state of equilibrium need not be equal, — only the product of these numbers per cc. must remain the same. Thus, if 10 H ions and 10 acetate ions (per cc.) are present in a certain solution (and hence holding in equilibrium the undissociated acetic acid present) then this equilibrium would also be held by 1 H ion with 100 acetate ions (99 of them from another acetate), or by 1 acetate ion with 100 H ions (99 from another acid), because in all three in- stances the product would amount to 100. In other words, the effect of the ions in the equilibrium relation with their compound is measured by the ion-product*
The following experiment, which involves exactly the same re- lation, demonstrates its operation in the simplest manner.
Prepare one-half test tube full of a cold saturated solution
*This relation does not hold exactly with greatly dissociated acids, bases, or salts; but even with these, the fundamental relation is prob- ably the same, and hence the illustration serves for all.
76 University of Texas Bulletin
of naphthalene in absolute alcohol and one-half test tube full of a cold saturated solution of picric acid. Pour into a small (clean and dry) flask one-half of the clear saturated solution of picric acid and two-thirds as much of the naphthalene solution, the two quantities being gauged as accurately as possible with the eye. They unite to form naphthalene picrate, designated by NP. This solution and all others in this experiment must be kept cool, — they should not be warmer than 18 degrees C. Allow the mother liquid to drain from these crystals, and pre- pare a saturated solution of NP by adding a small portion of absolute alcohol, shaking the mixture vigorously, and repeating this treatment until most of the crystals (not all !) have dissolved. To o/ne-half of this solution add one-eighth as much (by volume) of the remaining clear picric acid solution. Some of the com- pound NP should separate from the solution. To the other half of the saturated NP solution add one-eighth as much of the clear naphthalene solution. Again some of the compound NP should separate from the solution.
Since in one test-tube full of solution of N P, the addition pf N resulted in the formation of more of the compound, there must have been some (free) picric acid in this solution; and since in the other test-tube full of this solution the addition of P resulted also in the formation of more of the compound, it follows that the solution also contained some (free) naphtha- lene. Hence the solution contains both free N and free P be- sides the compound NP. The effect of the free N and free P upon the equilibrium with their compound NP is measured t>y the product of their numbers per cc., say aXb (if a is the num- ber of N per cc. and b is the number of P). When a is increased by adding a little of the saturated solution of naphthalene, then aXb is increased and the equilibrium disturbed. In order to regain equilibrium, some of the free N and free P combine, thus reducing a and b until aXb reaches its former value again; and this newly formed NP separates from the solution because the latter is saturated with NP. The corresponding change takes place when picric acid is added.
Chemistry in High Schools
77
Inches — Inside-
D.C Main.
Rheostat
Conductivity Trough and Connections
78 University of Texas Bulletin
In order to demonstrate the determination of the per cent of dissociation in electrolytes it is better to use the conductivity method rather than others such as a freezing point method, be- cause the connection between the experiment and the notion to be demonstrated is more direct. The following experimental arrangement makes the procedure extremely simple. This ex- periment also serves to demonstrate that the degree of ionisation of a dissolved substance increases with dilution.
Have a carpenter make a wooden vessel of the shape and di- mensions given in Fig. 8. Stout cypress or soft pine boards, at least ly^ inch thick and perfectly smooth on both sides, are to be used. The vessel should be as nearly water tight as the car- penter can make it. It should then be thoroughly covered on the inside wilth melted paraffin to make it absolutely water tight, and in order that the boards may not take up any of the solutions poured in it. Now secure from a plumber or cornice maker a piece of fairly stiff sheet copper, at least 16 inches square. Cut it from one corner diagonally across to the oppo- site corner into two triangular pieces. Trim each piece if nec- essary, so that each sheet of copper may cover exactly one of the triangular ends of the trough. Bend over the excess of each plate at the top, arid clamp or place each copper plate so that it may stick closely to the wooden end of the trough it covers. Provide any suitable means for connecting the copper sheets to the wires of an electric circuit. Shake up about 200 grams of crystals of copper nitrate with about 200 cc. of water until a saturated solution is obtained. Take about 100 cc. of this solution and pour it into the trough. (1) Secure an am- meter with a total capacity of 1 or only a few amperes,
(2) a volt-meter with a capacity of 3 volts or only a little more,
(3) a source of direct electric current with a voltage of 2 to 10 volts, and (4) a rheostat of such capacity and construction that the current used in this experiment may be controlled to within 0.01 ampere. Connect up all this apparatus and the trough as shown in Fig. 9. Turn on the current and adjust it with a rheostat until it is 1-5 or 1-6 of the total that the ammeter can carry, but not exceeding % ampere. Note both ammeter and voltmeter readings that are then shown. In the following op- erations adjust the current so that the first voltage between the
Chemistry in High Schools 79
poles (which the voltmeter indicated) is kept constant, and record in parallel columns the amount of current that flows after each dilution of the solution. Dilute the solution by add- ing measured amounts of distilled water: at first in portions of 100 cc. at a time, subsequently in larger portions of sev- eral 100 cc. At the beginning, the increase in current will be relatively large with each addition of water; then it will be- come less until finally no further increase in current is obtained.
Divide the final (maximum) value into the first value (ob- tained with the original solution) : this gives the fraction of the salt present as ions in the original solution.
The larger current obtained after dilution shows that the num- ber of ions arriving at the poles each second is larger after dilu- tion than before. Since the attractive force (voltage) is kept con- stant and hence the ions move at the same speed, and since on dilution they are moved parallel to the poles but remain, as a whole, at the same perpendicular distances from them, there remains no other way to account for the greater number of ions arriving at the poles after dilution except the conclusion that the number of ions is increased with dilution until all the ions pos- sible have been formed.
Point out next the general conditions under which metathet- ical reactions take place, and apply this to the neutralization of an acid with a base and to the experiments given below. The following outline may be helpful here.
(a) Whenever two solutions (or a solution and a slightly sol- uble solid) are mixed, the (accidental) meeting of the ca- tions from one solution with the anions from the other solution will produce at least small amounts of all the new compounds possible.
(b) Note the amount (in a general way, that is, whether large or small) of each free ion in the mixture at the beginning.
(c) Note the amount (i. e. large or small) of free ions that can be produced by each of the resulting substances. This is the amount of its ions with which each one would be in equilib- rium,— this is very small in the case of slightly soluble and slightly dissociated substances.*
*To be exact, we should consider here the product aXb, of the con- centrations of each pair of ions in place of their amounts (see page 75).
80 University of Texas Bulletin
(d) If an insoluble or slightly dissociated substance is among the resulting ones, and the amount of its ions in the original mixture is much larger than the small amount with which it would be in equilibrium,* then this pair of free ions will com- bine and thus they will reduce their amounts until these are small enough for equilibrium. As thus the free ions disappear, any undissociated portions of their original compounds will ionize and be used up in turn.
If one of the original substances is only slightly soluble (as in d below), then at first it will dissolve only in the small amount which saturates the solution. Then as the amount in solution is changed by reaction, more solid will dissolve, and so on.
All metathetical reactions are due to such extensive reduc- tion of the original number of a certain pair of ions. A slight formation of a new compound, by ions combining to a slight extent, is not considered to be a reaction.
The student should make test-tube trials with the following mixtures, and point out in each case the particular pair of ions which by combining extensively serve in a sense as the primary cause of the reaction:
(a) Mix any one of several barium salt solutions with any one of several sulphates, producing in this way barium sul- phate from at least nine different mixtures.
(b) Produce silver chloride from several different mixtures.
(c) Produce ferric hydroxide from several different mix- tures.
(d) Dissolve calcium phosphate in dilute hydrochloric acid. Here the least ionized combination is a combination of H ions with P04 ions, for instance, (H2P04) ', the calcium salt of which acid radical is soluble.
(e) To the mixture obtained in (d), add ammonia to neu- tralize the acid. The ammonium phosphate thus produced will introduce many P04 ions, and calcium phosphate will be ob- tained as a precipitate.
(f) Add solution of sodium carbonate to an aqueous solu-
*Or, to be exact, the original amounts of its ions form a larger ion-product than that with which the insoluble or slightly-dissociated substance can be in equilibrium.
Chemistry in High Schools 81
tion of the salt of any metal that forms insoluble carbonates. Filter and dissolve the precipitate by means of the addition of any acid that forms a soluble salt. Repeat with the salts of five other such metals.
These experiments enable the student to see that whenever he knows the general relations between the ionized substances in a given mixture, then he may predict whether or not reaction will take place.
Exercise.
Which of the substances given below when mixed will react? give a reason for your answer.
1. Lead oxide and water.
2. Barium oxide and water.
3. Calcium carbonate and hydrochloric acid.
4. Sodium acetate solution and hydrochloric acid.
5. Copper sulphate and sodium phosphate solution.
6. Since dry sodium chloride and concentrated phosphoric acid react to form HC1 by metathesis, what are likely to be the ionisation relations in this liquid medium (concentrated phos- phoric acid) to bring about this change?
7. If the liquid medium in (6) is changed by the addition of much water, will any reaction take place extensively? What are the ionisation relations in this latter case.
Other questions of similar character may ~be added.
Electrolysis.
The first experiment to be given is the electrolysis of hydro- chloric acid, and this should be carried out with the following apparatus: Secure two small porous cups, 3 to 4 inches high and V/2 to 2 inches in diameter. Dip the upper edges to a depth of one inch into melted paraffin in order to close up the pores in that portion of the cup. Fit rubber stoppers to the
82 University of Texas Bulletin
cups. Through each stopper cut two holes, — one to fit a piece of retort carbon, the other to fit the glass tubing with which the apparatus is to be connected.* Secure also a porcelain jar 4 or 5 inches in depth and 5 or 6 inches in diameter in which the porous cups are to be placed: This jar is to be filled with a saturated salt solution. Secure a tall, slender bottle, of at least one quart capacity, fit it with a rubber stop- per and two glass tubes one of which extends to the bottom of the bottle while the other terminates just below the stopper. In place of this bottle, the cylinder shown in Fig. 10 may be used. This bottle or cylinder serves to retain the chlorine, and allows an equal volume of air to be discharged in place of the chlorine. Air may be collected over water without ap- preciable loss, while chlorine cannot be collected over water because it is too soluble. Glass tubes for connections should now be bent as shown in Fig. 10. The tube fitted to the cup on the left should have no rubber joints in it, because hydrogen is to be evolved at this pole, and this gas would dif- fuse through the rubber tubing joints, and thus vitiate the ex- periment. The ends of the delivery tubes which are to be placed under the burettes should be drawn out to a small open- ing. Secure two burettes and two dishes or beakers full of water. Place the burettes in position with the lower ends ex- tending into the water, and fill them by drawing up water by means of a piece of rubber tubing. By this means they may be quickly refilled when the experiment is to be repeated. For electric connection, twist some bare copper wire around two arc light carbon rods, insert these through the rubber stoppers into the porous cups, and connect the copper wire with the ter- minals of an electric circuit which supplies direct current at a voltage of 10 to 25 volts. The electrode on the right should be connected to the positive terminal. Insert a switch in the circuit with which the current may be conveniently turned on or off.
Fill the porous cups three-fourths full of a mixture of equal
*For cutting holes in rubber stoppers, sharpen the edge of a cork borer by means of a file, thus producing a rough saw-like edge which is very effective, dip the end of the borer into caustic soda solution or into alcohol and proceed as with cork stoppers.
Chemistry in High Schools
83
|
\ |
|||
|
, |
! |
||
|
\ |
+ |
! |
|
|
v |
o |
£ |
|
|
1 |
4-1 O |
||
|
2 |
|||
|
s |
|||
|
i |
|||
|
*\ |
|||
|
tf %l |
- |
84 University of Texas Bulletin
parts of concentrated hydrochloric acid and .water. To the cup on the right add a few crystals of potassium permangan- ate. By this means the liquid is immediately saturated with chlorine. Now join up the apparatus, and turn on the cur- rent, but allow the gases discharged by the delivery tubes to escape into the air and not collect in the burettes. After elec- trolysis has been in progress for a minute or two interrupt the current, place the burettes over the openings of the de- livery tubes and turn the current on again. It will be found that the two gases are evolved at equal rates by volume.
Replace the hydrochloric acid in the cathode (negative pole) cup by dilute sulphuric acid, and turn the curent on again, i.e., repeat the experiment with the two cups thus filed with different solutions.
Take the apparatus apart and place the porous cups in dis- tilled water to leach out the solution contained in the pores. Salts crystallizing in the pores would crack the jars.
The last experiment indicates that the fact that hydrogen and chlorine are obtained in equal volumes cannot be due to any ' ' de- composing" of hydrochloric acid because this substance is present at the chlorine pole only, and the hydrogen liberated is certainly not obtained from the hydrochloric acid because practically no hydrogen passes through the intervening salt solution — a fact that could be easily demonstrated.
Before taking up the theory of the changes in this electro- lytic cell, it is necessary to present the views held at present concerning the nature of electricity. "Electrical matter'* is considered to be made up of definite unit charges, or particles of definite size. Electrically neutral substances contain an equal number of positive and negative unit charges, while ions contain an excess of positive or negative charges corre- sponding to their valence.
Only negative charges are mobile, and may move from one material particle to another, or from one kind of matter to another. These mobile negative charges are called electrons. The positive charges are fixed upon each particular particle of mater, and are never transferred from one particle to an- other.
Chemistry in High Schools 85
In accordance with this theory, the change at the cathode takes place as follows: the electromotive force of the battery forces electrons to pass from the cathode to those hydrogen ions which are next to the surface of the cathode (negative pole) thus changing these ions to neutral hydrogen, — i. e. or- dinary, gaseous hydrogen. During the same period of time, an equal number of chlorine ions which are next to the sur- face of the anode (positive pole) give up their negative charges or electrons to the pole, thus changing to neutral chlorine or ordinary gaseous chlorine.
Since a drop of any solution is electrically neutral to the out- side it follows that it must contain as many ions with postive charges as it contains ions with negative charges. When ions are discharged at the cathode, the drops of liquid which have lost the cations are momentarily left with an excess of negative charge while the opposite state of affairs exists simultaneously at the anode. These drops at the extreme end act upon their neighbors so as to obtain from them the kinds of ions that are necessary to re-establish their electric neutrality. This action communicates itself from drop to drop, from one pole to the other, and results in a slight shift of all the positive ions to- ward the cathode and all the negative ions toward the anode, as a result of which all the drops of solution regain .their elec- tric neutrality. With the discharge of the next ions at the poles, this action again takes place and so on.
These are the essentials that have to be brought out in con- nection with electrolysis. The writer realizes that this treat- ment is very dogmatic, and that there has been no attempt made to show why scientists have arrived at the fundamental notions which are involved her, but he believes that the young mind is scarcely ready to follow the experimental evidence.
However, it must be emphasized that the fundamental no- tions presented above are very important, and should be taught in the manner in which they are presented here.
The following further experimental demonstrations of elec- trolysis should now be brought before the students.
Make a 10 or 15 per cent solution of zinc chloride, and fill two porous cups with this solution. As before) place the two cups in a jar filled with salt water, and into one place
86 University of Texas Bulletin
a carbon rod for an anode, and into the other a strip of sheet copper for a cathode, but leave the cups open — i. e. unstop- pered. Make the necesary electrical connections and pass a current through this cell. Zinc will be deposited at the cathode, and will show itself by its gray color; while chlorine will be evolved at the anode and will reveal itself by its odor.
Replace the zinc chloride in the cathode (negative pole) cup by- a copper sulphate solution, insert a clean sheet copper pole and turn on the current again. Copper will be deposited upon the cathode, while the reaction at the anode is the same as before.
Show next the electrolysis of dilute sulphuric acid, using either the apparatus used above for the electrolysis of hydro- chloric acid, or a Hoffmann apparatus (see page 53 with ref- erence to the purchase of the latter.)
Next fill the same apparatus with a solution of sodium sul- phate in place of sulphuric acid and show that when this solu- tion is electrolyzed, hydrogen and oxygen are liberated in the same proportion by volume as with sulphuric acid. Do not at- tempt to force a large current through this solution because it is a poor conductor, and the heat effect of the current is liable to crack the apparatus at the electrodes.
Then secure two clean porous cups, the pores of which contain neither an acid nor an alkali. Fill them with a solution of sodium sulphate, insert platinum electrodes, and pfece the cups in a salt water jar as before. Before the current is turned on, show with the aid of litmus paper that the solution in the cups con- tains neither an acid nor an alkali. Then turn on the current, and show that the solution in the cathode cup becomes alkaline and the solution in the anode cup becomes acid as the result of the passing of the current.
Replace the liquid in the cathode cup by a dilute solution of copper sulphate, and show that copper is deposited when the current is passed through this apparatus.
These experiments show that the nature of a chemical change at a pole during electrolysis is determined by the nature of the substances present right at the pole, and that it is not depend- ent upon the nature of the substances present at the other pole or anywhere else.
The electrolytic discharge of the ions zinc, copper, hydrogen,
Chemistry in High Schools 87
and chlorine, requires no further explanation ; but the discharge of hydrogen out of the solution of a sodium salt and of oxygen out of a solution of a sulphate require further consideration. For an understanding of these phenomena, the following funda- mental or general facts must be recognized:
1. Water and all aqueous solutions contain the ions of water (i. e. hydrogen and oxygen ions practically), and although the amounts of these ions present are small, yet if they are ever used up, more will be formed as fast as the others are used up.
2. If two or more different ions which may be discharged are present at a pole, that particular one will be discharged which will set up the least opposing electromotive force after its discharge. In this connection see page 91, and also page 112. In other words, the ion discharged is the one requiring the least voltage for its discharge.
With these two fundamental facts the discharge of hydrogen from a solution of a sodium salt is readily understood. Since the voltage required for the discharge of the sodium ions is much greater than that required to discharge the hydrogen ions which are also present, the latter are discharged; and the hydroxyl ions which are formed from the water as the hydrogen ions are discharged impart the alkalinity to the solution, or in other words, they together with the sodium ions form sodium hydroxide.
Since oxygen is obtained during electrolysis at a platinum anode surrounded by a solution of a sulphate, it follows that the oxygen ions of the water are more easily discharged than the sulphate ions themselves; and the hydrogen ions which are formed from the water as the oxygen ions are discharged impart the acidity to the solution, or in other words, they together wtih the sulphate ions form sulphuric acid.
The Electro-Motive Force of Battery Cells.
The subject of electrolysis has not been presented fully unless the electro-motive force of the product formed at the poles has been pointed out, and since this electro-motive force when con- sidered by itself presents the cell as a galvanic battery, it is ad- visable to consider the latter subject in this connection.
In the treatment of this topic as in the treatment of elee-
88 University of Texas Bulletin
trolysis, it must be realized that the fundamental fact is the utter independence of the chemical actions which take place or tend to take place at the two poles. Without this a logical presenta- tion of the facts involved becomes practically impossible and it is on this account that the methods of presentation now ordi- narily employed are comparatively valueless, if not actually harmful.
For the following experimental demonstration, secure four small porous cups, a jar with strong sodium chloride solution, and a sensitive voltmeter with a total range of three volts or very little more. Fit the cups with cork or rubber stoppers, which are to be perforated to fit the electrode rods mentioned below. With one porous cup make a chlorine pole by using a carbon electrode rod, filling the cup with a mixture of equal parts of concentrated hydrochloric acid and water, and then saturating the solution with chlorine (preferably by electrolysis, otherwise by adding a little potassium permanganate). For the second pole, fill the cup with zinc sulphate solution, and use a rod of zinc for the electrode rod. For the third pole, use a plat- inum pole (see page 33) — or, less suitably, a carbon rod, and fill the cup with ferric chloride solution to which has been added a little of a ferrous salt (FeSOJ. For the fourth pole use a copper rod and copper sulphate solution.
Put the copper sulphate pole into the salt solution jar and then put with it in turn each one of the other three poles and measure the voltage between each' of them and the copper sulphate pole. Now plot the results on a line as follows: mark a point on the line to denote the voltage of the copper- copper sulphate pole and refer to it arbitraily as a "zero voltage." Since the zinc sulphate pole is the negative pole when combined into a cell with this copper-copper sulphate pole,, and since the combination has a voltage of (about) 1.1 volts, then if we consider the force of the copper pole to be zero (arbitrarily), it follows that the voltage of the zinc pole is — 1.1 volts. To represent this on our plot we measure from the copper pole point eleven spaces of any arbitrary length to the left arid mark this point (see Fig. 11). Then lay off the voltage of the chlorine pole (which is about +1.0 volt) and the voltage of the ferrous- ferric salt pole (the lat-
Chemistry in High Schools 89
ter will be about +.4 to +.5 volts.) Measure next the voltage of all other combinations of any two of these poles and com- pare the values obtained with the number of unit lengths be- tween them shown in the plot. It will be found that, allow- ing for slight inaccuracies due to this rough procedure, the numbers will agree. This shows that the voltage of a cell is the sum of the two independent voltages of the poles.
The primary cause of the action of a pole is the natural tendency to give up or take up electrons which some sub- stance present at the pole possesses; e. g., metals and hydrogen have a tendency to give up electrons and become positively charged ions; while non-metal (oxygen, chlorine, bromine, iodine) possess a tendency to take up electrons and become negatively charged ions.
Such tendencies to give up or take up electrons depend also on the particular resulting substances formed: many resulting substances may be changed back simply by reversing the direc- tion of the electric change (i. e., reversing the direction of the current), and such substances actually exert tendencies which oppose the tendencies of the original substances.
Hence the force of a pole depends on the nature of the orig- inal substance and on the particular kind of resulting substance formed during its action. Furthermore, the force- depends on the concentrations of the original and of the resulting substances : both the forward and the reverse tendencies to change increase somewhat with the amounts, per cc., of the original and of the re- sulting substances respectively. Hence, in recording measure- ments of the electromotive forces of poles, we must state the ex- act concentrations of the original and of the resulting substances in the poles when the measurements are made. Note how this is done in the table on page 110.
These pole-changes may be expressed by equations. Thus for copper and zinc, which are used in the demonstrations above, the equations are :
Cu°— 2(— )=Cu** Zn°— 2— =Zn**.
The Cu and Zn on the left side of the equation are marked with a zero to denote the fact that they are elements, i. e. they have
90 University of Texas Bulletin
no ionic charges. An electron by itself is represented by ( — ), and the expression —2 ( — ) denotes that two electrons are given up by one atom of copper or of zinc.
For the other two substances, the expressions of the pole changes are —
Fe***+l(— )=Fe**
by which is meant that these substances take up one electron per atom and become chlorine ion and ferrous ion respectively.
But although a particular "pole" may have a tendency to give up electrons, it cannot actually do so unless it is connected with another pole which will take up electrons. When the "copper- copper sulphate" cup is placed in the connecting salt trough, together with the chlorine cup, and the poles are connected by a wire, then the copper actually changes to Cu** ions because the electrons given up by the copper are "transferred" in a sense through the wire connection to the chlorine pole and are there taken up by neutral chlorine, which becomes Cl' ions.
In this particular combination both elements change to ions when the current flows. But when a "copper-copper sulphate" and a "zinc-zinc sulphate" pole are combined into a cell, then only one of these can change from metal to ions, i. e., only one metal can give up electrons, and the other takes up electrons and changes in the reverse manner, as represented by this ex- pression —
Cu**+2(— )=Cu°
The direction in which a pole actually changes when it is com- bined with another pole to form a cell depends upon the relation of the tendencies of the two poles. This relation has been ascer- tained for all poles by ascertaining the relations of all other poles to a common * ' reference " or " zero ' ' pole : since the tendency of a single pole is independent of the other pole with which it is combined, the relation between this reference pole and all other poles gives also the mutual relations between these other poles. This procedure was illustrated in the demonstration above. All the data and further information needed in this connection is
Note. — An asterisk designates positive electric charges; an apos- trophe, negative charges.
Chemistry in High Schools 91
given in the "Table of Electromotive Forces of Battery Poles," pag'e 109, which see.
Further general consideration of the galvanic cell need not be given here, but will be given in connection with the subject of oxidation and reduction (which see). It remains only to point out the connection between battery cells and electrolytic cells.
The substances produced by electrolysis (hydrogen from acids or water, copper from copper salts, chlorine from chlo- rides, etc.) naturally exert a tendency to regain the ionic state, thus each pole acts as the pole of a battery with an electromo- tive force opposite to the applied force. This is the electromo- tive force of polarization. It is absent before electrolysis be- gins and hence at the beginning any applied force, however small, will produce a current; but as soon as products of the electrode discharges are present, their electromotive force is exerted, and in order that electrolysis may continue, the ap- plied force must be larger than this opposing force.
The Action of General Reagents Upon Solutions of Salts*
The action of reagants, the results of which depend only on our general knowledge of solubility and ionic dissociation, has already been illustrated above. Many other reagents, however, present special conditions of ionic dissociation which require separate consideration. Of the reagents which present special conditions, only those commonly used will be considered. It will be found that the special properties of the latter are also essential parts of chemical information.
1. Sodium (or Potassium) Hydroxide as a Reagent.
Experiment. Secure solutions of water soluble salts of the following cations: Cu, Ag, Zn, Cd, Hg (ous), Hg (ic), Pb, Fe (ous), Fe (ic), Ni, Al, Mg, Ca.
To a few cubic centimeters of each of these solutions in a test-tube add a few drops of sodium hydroxide solution, shake in order to mix thoroughly, observe the effect, add a few drops more of the reagent, and so continue until the reagent has been
*Read pages 49 and 50 in this connection.
92 University of Texas Bulletin
added in a relatively large amount, say about twice as much reagent by volume as of salt solution, if the two solutions are of approximately equivalent concentrations. Compare the re- sults with the statements in the table below.
General Facts. By strict metathetical reaction the hydrox- ides should be obtained in the mixtures below. However, in many cases the substances finally obtained are not the hydrox- ides of the metals but substances derived from them through one or both of the two following changes:
(a) Dehydration, — complete (Hg(OH)2 to HgO) or partial (Cn(OH)2toCu802 (OH)2).
(b) Dissolution of the precipitated hydroxide by excess of the reagent, thus showing that the precipitated hydroxide func- tionates as an acid, e. g. Zn(OH)2 dissolves in excess of NaOH solution as per equation:
H2Zn02+NaOH= Na2ZnO,+2H20.
The formula for zinc hydroxide is thus written to suggest its functionating as an acid.
Table showing Results of Action of NaOH (or KOH) Solu- tions upon ' * Water Soluble ' ' Salts of the Following Metals : Ba — Ba(OH)2 is precipitated only from concentrated solu- tions because it is soluble in 20 parts of water — white. Sr— Ppt. Sr(OH)2 sol. in 60 parts of H20— white— not pre- cipitated from dilute solutions.
Ca— Ppt. Ca(OH)2 sol. in 700 parts H20— white— not pre- cipitated from very dilute solutions. Mg— Ppt. Mg(OH)2 sol. in 6000 parts H20— white.
Al — Ppt. A1(OH)3 white, sol. in excess of reagent, giving
NaA102.
Zn— Ppt. Zn(OH)2 white, sol. in excess— Na2Zn02. Pb— Ppt. Pb(OH)2 white, sol. in excess— Na2Pb02. Ferrous — Fe(OH)2 white ppt., darkens on exposure to air
(oxidizes).
Ferric — Fe(OII)3 reddish brown, flocculent ppt. Mn — Ppt. Mn ( OH )2— "flesh" colored, darkens on exposure to
air. Ni— Ppt. Ni(OH)2— pale green.
Chemistry in High Schools 93
Cu — in cold solution, Cu(OH)2 — bluish white ppt., soluble in large excess of reagent; in hot solution, CuO — black ppt.
Cd— Cd(OH)2, white ppt. Bi— Bi(OH)3, white ppt. Ag — Ppt. Ag20 — greyish brown. Hg(— ous)— Ppt. Hg20— black.
Hg (ic) — Ppt. HgO — yellow — in order to avoid the forma- tion of different colored basic salts, the Hg salt solu- tion must be poured into the reagent.
Exercise (a). In what way can it be readily ascertained whether or not a substance has been completely precipitated, say Fe(OH)3 by NaOH? Hence would sodium hydroxide be employed as a precipitant for aluminium if it be required that precipitation be complete? From the metals given in the table above select those for which sodium hydroxide may thus be used as a precipitant.
(b) Since it is easy to convert a hydroxide completely to any salt by treatment with the necessary acid, and there is no troublesome ( ?) by-product formed, it is plain why the pre- cipitation of metals in the form of hydroxides is very desirable. By means of such an intermediate step many metals may be readily changed from one salt to another — a change that may not be possible in one step otherwise. Give directions for changing the magnesium in magnesium sulphate to magnesium chloride; also for changing copper in copper nitrate to copper chloride.
(c) Given a solution containing aluminium and ferric salts. State how these metals may be obtained separately in the form of any compound. Similarly, how may zinc and cadmium be separated ?
2. Ammonia as a Reagent.
Preliminary Considerations. Since a solution of ammonia contains OH ions we expect to find that it reacts just as sodium hydroxide does in the preceding exercise; that is, as a reagent to precipitate metal hydroxides. However, it differs from so- dium hydroxide in being a weak base, and hence it has no effect
94 University of Texas Bulletin
on solutions of salts of the strong bases (which are these?). With reference to the other bases, the following holds. Am- monia precipitates the hydroxides of the trivalent metals com- pletely under all conditions, but it does not precipitate these of the other weak-basic cations if enough of an ammonium salt (i. e.} many NH* ions) is present (exceptions — lead and mer- cury, which with ammonia always form insoluble, complex am- monium compounds). This influence of the NH* ion is ex- erted as follows: since ammonia is very slightly ionized, the product (NH4*)X(OH'), which holds an equilibrium with the undissociated NH4OH, must remain practically constant; hence when (NH4*) is increased by the addition of an ammonium salt (e. g. HN4C1) which is largely dissociated, (OH') must de- crease, or in other words, ammonia is less dissociated in the presence of an ammonium salt than in the, absence of the latter. The concentration of the OH ion in such a mixture is so small that the product obtained by multiplying this OH ' concentration with the concentration of any bivalent metal ion that may be added ( [M*] X [OH] ') will be less than the "ion-product" that a resulting precipitate itself could produce. The formation of a precipitate does not take place because thereby the ion-product would be increased, and reactions take place only when an ion- product is decreased. But the ion-products of the tri-valent- metal-hydroxides are smaller than those of the bivalent-metal- hydroxides, and whenever a tri-valent-metal-ion is introduced into a solution containing any OH' ions, the product [M] X [OH] is always greater than the ion-product of the precipitate, — hence the precipitate is formed because thereby the product of these ions in this solution is reduced.
To demonstrate this effect, add some ammonia to one portion of magnesium chloride solution, and to another portion add some ammonium chloride solution and then ammonia.
Exercise. By the use of ammonia, separate bismuth from a solution containing bismuth and copper salts; Al from a solu- tion containing Al and Ni salts; Fe (ic) from a solution con- taining ferric and Mg Salts.
Give directions for changing the aluminium in potash alum completely to aluminium chloride.
Chemistry in High Schools 95
3. Soluble Sulphides as Reagents.
Note. Hydrogen sulphide is poisonous, hence the generators of this gas should be used either outside of the building or in well drawing hoods.
Preliminary Considerations. Since all sulphides except those of the alkali and alkaline earth metals (Na, K, "NH4," Ca, Sr, Ba, Mg) are insoluble, it is to be expected that a precipi- tate of the corresponding sulphide will be obtained whenever a soluble sulphide is added to a solution of a salt of any of the other metals. And such is the case except when hydrogen sulphide is used. Judging from its properties, this substance appears to be an exceedingly weak acid — very slightly disso- ciated— and its ion product (H*)X(S") is very small. A great increase of H* ions, through the addition of a strong acid, lessens its S" concentration greatly for the same reason that an increase of NH4 ion concentration decreases the OH' con- centration in ammonia. Hence the following general fact con- cerning the effect of hydrogen sulphide as a regeant:-
Even in the presence of a moderate concentration of hydro- gen ions (a strong acid), hydrogen sulphide precipitates com- pletely the sulphides of some metals, among them Ag, Hg, Pb, Bi. and Cd, which for convenience may be called the hydrogen sulphide group; and only in the absence of hydrogen ions (ab- sence of acid) does it precipitate completely the sulphides of other metals, among which may be mentioned Fe, Zn, Ni, Mn, the ammonium sulphide group.
Demonstration. Put 10 to 20 cc. of dilute copper sulphate solution and an equal amount of zinc sulphate solu- tion in a small flask, add 10 to 20 drops of dilute HC1, heat to boiling, treat with H2S in excess and filter. What is the sub- stance on the filter paper? The reaction that has taken place is metathetical — write the equation. What is the by-product? Evidently the concentration of the hydrogen ion has been in- creased during the progress of the reaction. Since with exces- sive concentration of hydrogen ion, hydrogen sulphide is un- able to precipitate sulphides of this group even (?), and since it is possible that in this experiment the concentration of the acid has become excessive, the last portion of copper may not
96 University of Texas Bulletin
be precipitable under the conditions. Hence a small part of the solution must be diluted largely by adding an equal volume or more of water, or the acid may be partially neutralized by the cautious addition of a base. Then it should be heated again and treated with hydrogen sulphide. If necessary, treat the main portion of the solution in this way and repeat this pro- cedure until precipitation is complete.
Before proceeding to precipitate the zinc sulphide, it is de- sirable to remove the remnant of hydrogen sulphide which re- mains dissolved in the liquid, since otherwise it starts precip- itation :as soon as the acid is neutralized by ammonia or any other base. To remove this gas, boil the liquid well for two or three minutes.
Then add ammonia to the clear (and odorless) solution until it is plainly alkaline. If enough ammonium salt is present (from what source?), then no precipitate will be formed. Next, treat the solution with hydrogen sulphide again. A white pre- cipitate (ZnS) will be formed (a trace of iron compounds in- troduced by the hydrogen sulphide may impart a "dirty" color to the precipitate). Filter and wash the precipitate.
The ammonia added above performs two functions: first, it neutralizes the free acid present, and second, it forms ammo- nium sulphide with the hydrogen sulphide. Write the meta- thetical reaction of the action of ammonium sulphide with the zinc salt.
Transfer the CuS to a dish, add a little dilute HN03, and warm the mixture. A solution of Cu (N03)2 will be obtained by complex reaction. Note the free sulphur formed.
Drip dilute HC1 slowly upon the ZnS on its filter paper until all has been dissolved and collected in a beaker placed below. The reaction is metathetical ( ? ) . Note the evolution of H2S.
What is the object of this whole experiment?
Reactivities of Sulphides.
The reagents under (b) and (c) below will also react upon the sulphides in the groups above their own; but the reagents of (a) and (b) do not react upon the sulphides in the groups
Chemistry in High Schools 97
below them. In all cases the metals dissolve because they are changed to water soluble salts.
(a) Sulphides which react metathetically with dilute HC1 or dilute H2S04 :—
ZnS, FeS, MnS, CdS. CdS requires a stronger "dilute" HC1 than the others.
(b) Sulphides which react with dilute HN03— action com- plex, resulting in free sulphur and nitrates of metals:—
Ag2S, PbS, CuS, Bi2S3.
(c) Sulphides which react with aqua regia only (aqua regia is essentially a concentrated solution of free chlorine which acts to produce free sulphur and chlorides of the metals) : —
NiS, CoS, HgS.
Colors of Sulphides.
The colors of sulphides are a valuable means of identifying the metals. By proper means (?) prepare small portions of the colored sulphides. They have the following colors: —
FeS, NiS, Ag2S, HgS, PbS, Bi2S3— dull black. CuS — brownish black. ZnS— White (when pure!). CdS— yellow.
MnS — pink or flesh color.
Note: — during precipitation HgS frequently exhibits several other colors — black, yellow, red — but with excess of H2S it finally becomes black.
Exercise. For how many metals may soluble sulphides be used as precipitation reagents? Into how many classes may metals be separated by means of soluble sulphides? The an- swers to these two questions will indicate why soluble sulphides are the most valuble general reagents known.
Precipitate separately as sulphides the metals from a solution containing any one of the following pairs of metals — copper and zinc, cadmium and nickel, bismuth and manganese. Continue the treatment for the precipitation of the first metal until the second sulphide can be obtained pure — as shown by its color. Wash the copper, cadmium, or bismuth sulphide with distilled water while it is on the filter paper (to remove remnants of the salt of
98 University of Texas Bulletin
the second metal), and convert it to the nitrate. Convert the zinc, nickel, or manganese to the chloride.
List of Useful Special Properties and Reactions of Metals.
These properties and reactions are only briefly indicated here. Consult a text book for further information. These properties and reactions need not be definitely remembered, since they may be looked up when needed. The student should make simple trials to acquaint himself experimentally with these facts.
1. AgCl is soluble in ammonia, from which solution AgCl may be reobtained by neutralizing the ammonia with an acid (HNO,-).
2. PbCl2 is very soluble in hot water, though not in cold water.
3. HgCl forms a black compound with ammonia, for which the formula and reaction need not be learned.
4. HgCl2 is reduced to HgCl or Hg by SnC'l2 solution, the latter becoming SnCl4.
5. Bi salt solutions hydrolyze when the concentration of free acid (H* ion!) in the solution falls below :a certain limit. "Hy- drolysis "is a metathetical reaction between water and a salt which produces the free acid and the free base (or a basic salt), e. g. BiCl3+H20=BiOCl+2HCl.
A1,S3+6H20=2A1(OH)3+3H2S.
All salts of weak acids or of weak bases are hydrolyzod, though some only so slightly that the effect can not be noticed except by some delicate means such as the effect upon litmus. For demonstration, test solutions of the following normal salts with litmus :
Sodium carbonate.
Sodium acetate.
Copper sulphate.
Zinc chloride.
Chemistry in High Schools 99
6. Note that the following salts and their solutions are col- ored : —
Copper salts — blue or green. Nickel salts — blue or green. Ferrous salts — pale green. Ferric salts — reddish yellow. Manganous salts — pale amethyst.
7. Compounds of the following metals will color the Bunsen flame. To try this use a clean platinum wire, dip it into solu- tions of these metals and hold the drop of the solution in the flame : —
Bright red— Sr. Brick red — Ca. Yellow— Na. Yellowish green — Ba. Green to blue— Cu. Blue, pale— Pb. ' Violet— K.
8. Ammonia in compounds is revealed by treating them with a strong base (e. g. NaOH solution), warming the mixture, and noting the odor.
9. Sodium hydroxide cannot be used as a precipitating rea- gent in the presence of ammonium salts because it reacts with the latter. Ammonium salts may be removed by evaporating the solution to dryness and then heating the dish and contents to low redness until fumes cease to be given oft*.
Chemical Problems.
The following problems are to be solved by means of the fore- going facts:
1. Students should be given solutions of water soluble salts, each solution should contain only one metal, and the student should ascertain what the metal is. Salts of the following inetals may be given — copper, silver, bismuth, lead, mercury (both valences), cadmium, iron (ferric only) manganese, nickel, zinc, calcium, strontium, barium, magnesium, sodium, potassium, am- monium. Twelve to fifteen solutions should thus be worked out by every student.
100 University of Texas Bulletin
In trying to find the metal, the student should note the color of the solution; he should ascertain if it would color the flame of the Bunsen burner; and on very small portions of the solu- tion he should try the effect of reagents in the order given be- low.
(a) Add dilute hydrochloric acid. If a precipitate is ob- tained, then special tests 1 to 3 should be tried on the ppt. after it has been filtered off and washed.
(b) Add dilute sulphuric acid.
(c) Acidify moderately with either HOI or H2S04 (which- ever produces no precipitate), and then treat wtih hydrogen sulphide (see "g" below).
(d) Add ammonium chloride and ammonia. Ammonium chloride will produce a ppt. if HC1 did, but such a ppt. should be removed by filtration before ammonia is added.
(e) Irrespective of the presence or absence of any ppt. pro- duced by ammonia, treat the resulting mixture from (d) with hydrogen sulphide (see "g" below).
(f ) Add sodium hydroxide.
(g) If a black sulphide has been obtained, then to decide which metal sulphide it is, try special tests 4 and 5 above, and also ascertain the reactivity of the sulphide with acids after it has been filtered off and washed.
2. Prepare KNO3 by the commercial method, from NaN03 and KC1. (See Smith, Art. 127.)
3. Prepare NaOH by the commercial method, from Na2C03 and Ca(OH)2. (See Smith, Art. 126.)
4. Prepare pure sodium chloride by precipitation with HC1. (See Smith, Art. 132.)
Text-Book Reading.
Parallel with this laboratory work on the metals some of the usual text-book reading found under the various metals should be given. However, it should be more or less confined to the commerically imporant facts and compounds, such as the com- mercial sources, and the methods of preparation, from these sources, of the commercially important products.
The choice of what is commercially important varies some-
Chemistry in High Schools 101
what with the locality. In an agricultural state such as Texas the source of potassium salts and the composition of fertilizers is of vastly greater importance than the source of copper, and the methods of its extraction from its ores; while in a mining state such as Arizona just the reverse holds good. The empha- sis in the informational reading should be laid accordingly.
Chemical Changes Involving Oxidation and Reduction.
lonisation and Valence. In contradistinction to the changes studied thus far (metathetical changes and hydration) in which the valence of all ions (or constituent parts of compounds) re- mained constant, the changes now to be studied specially . are those involving changes of valences. As has been shown, valence means the number of electric charges on an ion (or that would be on any particular part of an acid, base, or salt after it had been changed to an ion). Thus the valence of the N03 ion is 1 because in the ionization of any one of its com- pounds— e. g. NaN03 or HNO3, the Na or H gives one negative ionic charge (electron) to the N03.
So far the attention has not been directed to the complete ionisation of such complex compounds as HN03, NH4C1, CuS04, etc., which would yield each element of a compound in the form of a separate ion, and this must now be taken up. Thus the pri- mary ionisation of NH4C1 yields NH4* and Cl', but complete ionisation into the elemental parts requires the further ionisa- tion of NH4*. Since 4H* result from this ionization, and thus 3 new (-]-) charges appear, it follows that 3 ( — ) have been given up by the H's and left upon the N ion (written N3' or N'"). The whole compound in the form of ions may be ex- pressed thus (4H*, N3', Cl'). In the same way the complete ionisation of H.,SO4 requires, after the primary ionisation into 2H* and S04", the further ionisation of S04". Since 40" would result from this secondary ionisation, and hence 6 new ( — ) charges appear, then the 6 ( + ) produced simultaneously
Note. — An asterisk designates positive electric charges; an apos- trophe, negative charges.
102 University of Texas Bulletin
must reside on the S ion (written S6* or S******).' The whole may be written 2H*, S6*, 40".
It is a general fact that in aqueous solutions hydrogen and metals become cations while 0 (or OH), the halogens (F, Cl, Br, I) and the cyanogen radical (ON) all become anions.
It has been shown above that in electrolytic and battery cells, during action, the substances at one pole undergo one kind of a valence change while the substances present at the other pole undergo the opposite kind of a valence change.
The proportion of the substances changing valences simul- taneously at the two poles depends merely upon the fact that the number of electrons simultaneously transferred "at" the two. poles are equal (but they are transferred in opposite senses at the two poles). Thus if the two "pole changes" are
then the proportion in' which the two substances change simul- taneously is Zn :2C1.
When the results produced upon a substance by these changes in valence are compared with the results produced upon it by oxidizing (or reducing) agents, it is found that an increase of positive ionic charges (or decrease of negative) produces the same result as oxidation, and the reverse electric change pro- duces the same result as reduction. This has been found to be always true. For illustration, consider the production of chlo- rine from HC1. Hence the following simple and perfectly gen- eral definition: — oxidation is the increase of positive charges or valences of an element or radical (or the decrease of negative charges). Reduction is the reverse change.
Exercise.
Ascertain whether the elements italicized when changed from the first to the second form undergo oxidation or reduction. Express the amount of change in numbers of ionic charges per atom of the changed element.
Chemistry in High Schools 103
First Form. Second Form.
(a) KCl HC7
(b) Chlorine HCl (e) ZnS04 ZnCl2 (d). Zinc ZnC\2
(e) K2S04 KCl
(f) UNO, #H4OH
(g) KMnO, MnS04
(h) \FeS04 FeCl3
(i) K2CrO4 CrCl,
In the light of this definition of oxidation and reduction, it is seen that in every electrolytic cell and every battery cell, oxida- tion takes place at one pole, and reduction at the other.
Study next the "Table of Electromotive Forces of Battery Poles," page 109.
If the "valence-changing" substances of the two poles of a battery cell are put in direct contact, (i e. mixed together) they will undergo the same changes without the use of the metallic poles and their connecting wires. Here evidently the transfer of the electrons is direct from one valence-changing substance to the other. This is easily shown by the following test-tube trials with some of the same substances used in the battery cells shown before : —
(a) Put granulated zinc into some copper sulphate solution, and shake the mixture at intervals until the solution is colorless. Then test solution .with H2S for zinc ion. Con- clusion ?
(b) In place of chlorine in a chloride solution it is better to use iodine dissolved in KI solution (or bromine water). Treat this with zinc until the free iodine (or bromine) has disappeared. Then test the solution for zinc ion. Conclusion ?
(c) Treat a ferric chloride solution with zinc until the red- dish brown color of the ferric ion has disappeared. Test with NH4C1 and NH4OH to ascertain if the change is complete.
104 University of Texas Bulletin
k The three equations for these reactions are: —
(a) Zn° +Cu2'S04:=ZnS04-f Cu
to 2» to 0
(b) Zn° +21° =ZnI2.
to 2* to 1'
(c) Zn° -f-2Fe3*Cl3=ZnCl2+2FeCl2.
to 2* to 2*
The numbers of electric charges on the valence changing sub- stances are written as shown in order to show at a glance which substances are oxidized and which are reduced. Point out which are oxidized, — which reduced.
The proportion between the valence-changing substances in a reaction is determined by making the number of electrons given up by one substance equal to the number of electrons taken up by the other substance. Thus in (b) above, one Zn gives up 2( — ) while one I takes up only 1( — ) ; hence their ratio in the reaction is IZn to 21. Another way of stating the fact is to say that the amount of oxidation in a reaction is equal to the amount of reduction.
Exercise :
Make test tube trials of the following substances : —
1. Treat ferric chloride solution with excess of hydrogen sul- phide, and test with ammonium hydroxide.
2. Add a slight excess of bromine water to a ferrous salt solu- tion and test with NH4OH. .
3. Treat dilute bromine water with hydrogen sulphide.
4 Put a rod of zinc into a concentrated solution of stannous chloride.
5. Put a piece of copper into some mercuric chloride or nitrate solution.
Write the equations for these reactions as in the illustration above.
The foregoing reactions are evidently quite simple, yet they present all the principles involved, and other reactions which appear to be more complex really involve no new facts. As a
Chemistry in High Schools 105
rule they differ only by involving some additional metathetical actions. This is well illustrated by the oxidizing actions of HNO, which will now be discussed.
Nitric acid and its Reduction Products. The following should be among the experiments shown : —
1. The preparation of HN03 by distillation from NaN03 and concentrated H2S04.
2. The ease with which HN03 gives up oxygen is strikingly illustrated by dropping a glowing piece of charcoal into some hot fuming nitric acid in a test tube.
3. The preparation of NO by the reduction of dilute HN03 with copper. To be performed as usual. Show that NO combines with oxygen to form N02 and that this dis- solves in cold water forming HN03+HN02.
4. The extreme reduction of the nitrogen in the nitrate ion by means of a metal very high in the electromotive force table (see page 110), — e. g. zinc or aluminium: take concentrated sodium hydroxide solution, add a little of a nitrate, then add either one of these metals in the form of shavings or powder. Warm the mixture. After violent reaction has set in, the odor of ammonia can be easily noticed.
5. Treat some cold, freshly prepared, ferrous sulphate solu-
tion with dilute HN03. A black compound (of FeS04, NO) will be formed. Heat the mixture to boiling. The NO escapes, and the reddish brown color of the solution shows the presence of ferric iron.
6. Pass H2S through warm dilute HN03. Sulphur and NO
will appear.
In order to consider properly the oxidizing actions of HN03 the following facts must be noted:—
The nitrogen in nitric acid and in nitrates is in the highest state of oxidation in which it ever occurs; and the nitrogen in ammonia or ammonium compounds is in the lowest state of oxidation, — it cannot be reduced further. Between these two limits there are a number of oxidation stages, the order and re- lation of which is shown in the following table. Note that the free element occupies an intermediate position.
106 University of Texas Bulletin
Nitrogen Name. Ion.
Nitric acid, HN03 and nitrates N5*
Nitric peroxide or nitrogen textroxide, N02 or N204 .... N4*
Nitrous acid, HN02 and nitrites N3*
Nitric acid or nitrogen dioxide, NO N2*
Hyponitrous acid, NHO, and nitrous oxide N20 N*
Nitrogen, N2 N°
Ammonia, and its salts, (NHJ * N3 '
The equations for the experiments above may now be de- rived.
Experiment (3). When completely ionized, HN03 is H*, N5*, 30")- Since the nitrogen finally appears as NO,— i. e. (N2*, O") — it has received 3( — ), three electrons. Since these electrons are obtained from Cu° becoming Cu2*, it follows that these two substances must change in the ratio 3Cu to 2HN03 in order that the number of electrons given up by the Cu shall be completely taken up by the changing HN03. But when 2HN03 change (to 2NO), then 2H* and 40" will become free ions, and since 0" ions cannot remain free in the presence of H* ions, they will form 4H20. This requires 8H*, for which the 2HN03 just considered supply only 2H*, and 6 extra HN03 must give up their H* ions. The 6NO3' from these 6HN03 balance up with the 3Cu** formed in this action. Considering all this we write — 3Cu° +2HN5*03+6HNO3=3Cu(NO3)2+2NO+4H2O
to 2* to 2*
Which substance is oxidized? which reduced? Is the amount of oxidation equal to the amount of reduction?
Experiment (4). In the change from nitrate ion to ammonia, each "N" receives 8 electrons, while each "Al" gives up 3 elec- trons ; hence the ratio between the number of Al and the number of N03' which change simultaneously is
8A1:3NO8'
In the presence of sodium hydroxide, the Al*** ion combines with INa* and 20" to form NaA102. The N3' ion forms NH3,
Note. — All aqueous solutions contain H* and O" ions, and when these free ions are used up more will be formed by further ionisation.
Chemistry in High Schools 107
hence it combines with 3H*. Considering all this, we arrive at the following equation:—
8A1° -f 3NaN5*O3+5NaOH+2H2O==8NaAlO2+ 3NH3.
to 3» to 3'
Which element or substance is oxidized? which reduced? Is the amount of oxidation equal to the amount of reduction? These questions should be asked in connection with all equa- tions of oxidation and reduction.
Exp. (5). One Fe** gives up one electron to become Fe***, and since the nitrogen is reduced from HN03 to NO (i. e., 3 elec- trons are taken up by 1 N), then the ratio between the valence- changing substances is 3 FeS04 :HN03. The other considerations are the same as in (3) above. The equation arrived at is:— 3Fe**S04+HN5*03+3HN03=
to 3» to 2*
Fe2 (SOJ 3+Fe (N08) 8+NO+2H20.
Exp. (6). S" ions change to S°. Since NO is formed from NO3', the ratio between the valence-changing substances is
3H2S :2HNO3. Hence the equation is: —
3H2S2' +2HN5*03==2NO+3S-f4H2O.
to 0 to 2*
One more equation should be added here: the reaction of ''aqua regia. " Considering that NO is the reduction product and free chlorine is the oxidation product, the ratio between the valence changing substances must be
3HC1:1HN08 and the equation is
3HC1 '-fHN5*03=2H20+3Cl+NO.
to 0 to 2*
The foregoing arithmetic considerations are second in impor- tance to the real chemical knowledge to be gained from the ex- •periments above. The latter consists of knowing what particular products of oxidation or reduction are obtained under particular circumstances. This must be remembered. The "chemical" as- pect of the experiments with nitric acid involves the following general facts (see also the Table of Electromotive Forces of Battery Poles) :—
The extent of reduction of nitrogen in compounds depends
108 University of Texas Bulletin
upon the strength of the reducing agent and upon the dilu- tion of the nitrogen compound. For example, with dilute nitric acid, copper produces NO, while zinc produces nitrogen. Again, with concentrated nitric acid, copper produces N02; and with very dilute nitric acid, zinc reduces the nitrogen from nitric acid to ammonia.
These general relations should be impressed by drill with spe- cial examples as illustrated in the following exercise.
Exercise.
1. Figure out the equation of the reaction that takes place when copper sulphide is dissolved in dilute nitric acid if at the end the sulphur is present as free sulphur and the nitrogen as nitric oxide.
2. Do the same with bismuth sulphide, and again with silver sulphide.
3. If aqua regia, after its preparation by mixing the acids, is essentially a solution of chlorine (see equation above), what will be the equation for its action upon mercuric sulphide which re- sults in a solution of mercuric chloride?
4. Note the position of silver, relative to copper, in the Elec- tromotive Force Table, page 110, and hence infer what will be the probable reduction product of nitric acid if the concentrated acid reacts with silver. Write the equation for this action.
5. Do the same for lead and dilute nitric acid ; and again for cadmium and very dilute nitric acid.
Note on the Oxidizing Action of Sulphuric Acid. Sulphuric acid is occasionally used as an oxidizing agent. The student may have occasion to meet it in connection with the dissolution of metals in it, or in its action upon potassium bromide and potas- sium iodide. Since the reduction products of sulphuric acid are all known to the student, it is advisable to add here the few re- marks necessary to inform him fully concerning these particular reactions.
The order of the reduction products of sulphuric acid and of their ions is as follows:
Chemistry in High Schools 109
Order Substance Ion.
1 Highest state of oxidation H2S04 S€*
2. Next lower H2S03 or S02 S4»
3. Next lower S S°
4. Lowest H2S S" With weak reducing agents such as metallic silver and metallic
copper concentrated sulphuric acid will be reduced to S02 only. Of course the sulphate of the metal is produced in the reaction.
With the strong reducing agents such as zinc, the reduction product is H2S.
Concentrated sulphuric acid does not oxidize chlorine from HC1; but it oxidizes bromine from bromides forming free bro- mine, and the sulphuric acid itself is reduced the least amount only, namely to S02. Iodine from iodides is so easily oxidized that the sulphuric acid is reduced to H2S even.
For a numerical exercise, the first five equations for the five reactions just mentioned may be figured out.
Table of Electromotive Forces of Battery Poles.
In the table below, of electromotive forces of some battery poles, the voltages given are those of the cells formed by combin- ing each of these poles with a hydrogen pole, which latter serves as a zero or reference pole.
The prefixed algebric signs indicate the polarity of the " meas- ured" pole in this combination.
The accompanying scale of these forces shows their mutual relation.
When a pole-component changes so as to be deprived of or give up electrons, then it is oxidized, or acts as the negative pole of a battery cell.
Any pole in the table combined with any other pole will form a battery cell the force of which is shown in the ' ' Scale showing the relation of EMF's": it is represented by the distance be- tween the poles. The pole uppermost in the table acts as the negative pole in this combination, — here oxidation takes place.
When the substance that would be used up at one pole during the action of a cell is mixed or placed in direct contact with the substance that would be used up at the other pole, then
110
University of Texas Bulletin
p
5-9
0 c a -2
1=
.? .
. 1
.
^ .D.S « 2 g
o
3
-- PM ft»Z5
o o c o o o o o o o 2 2 .2 .2 .2 .2 .2 .2 .2 5 .2 o
§ B
wquCJjoJVVwww 5}3!)J)3$2>Q)q;q2qj?Qjq;'t^ "t* $ Q? $ t^ $ £$
Tj'''''''''
oooo
Xl£iXlX5
-»-> o
~ X2
a
"
^
t»5 I
|*6
a*
III
S80*** * O « ° * 03 * m * * •" - • O ^^
AS*J* "**no'*OQ** a* *** ^tr! 'oaix-soQ*'a'c
* «8 os MJL rt 3 a>nb,aO.«;a a* o S -*a> &0&J.S «.S ^ S«(^
M^OS^N^^O^»^(^t»W'-gO g^<HW g J S go «^~-a
-Jpg SSSS ^ «
i- rn o o p p c> p p o o o r- r- IH i-! i-I i-< i-J i-4 IH ,-i
i i TTT TT IT T +++++++++ ++ ++++ + +
Scale showlnr relation of EMFs.
-K —3.0-
— Na
— Oa
—2.0—
-JAf
— Al
-1.0-
— Zn
— S
— Cd
— PblO -Ni
— Pbl8. 8n 0.0-H
-Aa. Sb. Bl
— Ou
—I
— Fel8
+1.0-
— Br
— HNOs
— Or23
— Ol
— Mn27.
— O — F +2.0-
Chemistry in High Schools 111
these two substances react in the same way as in the battery cell. Direct contact makes the connecting wires, etc., for the transfer of the electrons unnecessary. All mixtures undergoing oxidation and reduction reactions may be considered to be made up in this way.
The substances in the higher states of oxidation (in the wide column on the left) are all oxidizing agents : they appear in the ascending order of strength as oxidizers.
The reducing agents are in the column on the right: they ap- pear in the descending order of strength as reducers.
Any reducing agent in the table will react with any oxidizer below it in the table. The following two common examples of this fact should be noticed :
(a) Any metal in the table will displace (reduce) any metal below it from a solution of its simple salts. Thus, zinc or iron will displace copper from copper sulphate, silver from silver nitrate,' or hydrogen from hydrochloric acid.
(b) Anyone of the non-metals (Cl, Br, I, S), will be displaced (oxidized) from its simple-ion compounds (chlorides, bromides, iodides, sulphides), by any one of the non-metals below it in the table. Thus, chlorine liberates bromine from bromides, sulphur from sulphides, etc.
The metals above zinc in- the table below, and fluorine, cannot be used as poles for practical batteries, or as reducing (respect- ively, oxidizing) agents in ordinary chemical (aqueous) mix- tures because these elements react with water.
Note on the potential of chlorine: its potential is less noble ("noble" means the direction in the table from hydrogen to- wards gold) if the concentration of the free chlorine is less or if the concentration of the chloride compound is greater than as given in the table. Hence the formation of the first portions of free chlodine in a concentrated solution of hydrochloric acid will take place with a potential between +1.35 and +1.0 volts. This explains why nitric acid oxidizes hydrochloric acid.
Note on the "Back" Electromotive Force of the Poles During Electrolysis.
The products formed at the poles during electrolysis exert an "opposing" electromotive force, i. e. "opposed" to the ap-
112 University of Texas Bulletin
plied force. They exert about the same force as the battery poles composed of the same materials.
Of different chemical changes possible at the cathode of any particular cell that one will take place which will exert the least "zincic" potential (zincic means the direction in the table from hydrogen toward zinc).
At the anode that particular change will take place which re- quires the least " noble " potential.
For the liberation of hydrogen on metals other than platinum, a more zinzic voltage is required than for platinum. This addi- tional voltage amounts to as much as 0.5 — 0.7 volts for the metals lead, zinc, and mercury.
Chemistry in High Schools 113
APPENDIX.
The Details of Construction, Action and Operation of Alter- nating Current Rectifyers.
The Action of the Electrolytic Cell.
The electrolytic cell used to "rectify" the alternating cur- rent, as ordinarily constructed, has one pole of aluminium, the other of lead, and between them a solution of sodium phos- phate. When prepared for operation, the cell allows only that alternation of the current to pass which makes the aluminium pole the cathode, or negative pole, and it prevents the passage of the reverse alternation, which would make the aluminium the anode or positive pole. This property of the cell is due to the fact that the aluminium is covered with a non-conduct- ing film of aluminium hydroxide or basic salt with a gas (oxygen) held in its "meshes" or pores. Such a film over a metal does not prevent the passage of the current when this metal serves as the cathode; but it hinders the passage of the current when this metal serves as an anode. It is as though the cations need not actually touch the metal of the pole in order to be discharged, while the anions cannot be discharged unless they come in direct contact with the metal surface. Hence a cell in which one pole is covered with such an insulating film and the other not covered, or with a "conduct- ing" surface, is " uni-directional " in its action.
The materials used for this purpose, aluminium and lead, are particularly well suited for this purpose on account of the fol- lowing advantageous properties possessed by them :
(a) when a bare surface of aluminium is exposed to anodic discharge (in solutions of phosphates, sulphates, borates, etc.) a film (of aluminium hydroxide) is almost immediately formed; and this film is not disturbed by any cathodic dis- charge such as takes place in sodium salt solutions. Hence when a bare aluminium pole is connected with an alternating current, that alternation which makes it the anode will quickly cover it with such an insulating film, and the formation of this
114 University of Texas Bulletin
film will not be hindered by the reverse alternation of the cur- rent.
(b) a lead pole, which in the rectifier acts mostly as the anode, has its surface converted to lead peroxide by the anodic discharge, and this material, in contradistinction to the alumin- ium film is a good conductor. If the lead acts as a cathode, this , peroxide is reduced to metallic lead. Thus neither anodic nor cathodic action covers the lead with an insulating layer.
With high voltages, or hot solutions, the aluminium film breaks down frequently in its weaker spots, and considerable leakage of current occurs. Free acid in the electrolyte also increases the leakage current. But with cold, neutral solutions and a voltage below 70 volts, the leakage current is not exces- sive.
Construction of Large Electrolytic Jars for Rectifier Set No. 1.
Secure 2 jars of 2 to 4 quarts capacity, with a depth of from 7 to 11 inches. Have a carpenter cut 4 discs of one-inch pine lumber, two discs of