SOME DESIRABLE CHARACTERISTICS INCHEMISTRY DEMONSTRATION

EXPERIMENTS

BY RALPH E. DUNBARDakota Wesleyan University, Mitchell, South Dakota

At the May, 1928 meeting of the Eastern Association ofPhysics Teachers, Duff1 enumerated certain desirable charac-teristics for demonstration experiments in physics. These cri-teria seemed equally applicable to the field of chemistry andhave been made the nucleus of the following suggestions forchemistry as well. The list has been extended, modified andexamples given from this additional field.

1. APPARATUS SHOULD BE ON A LARGE SCALEUse small beakers or similar containers instead of test-tubes

for the usual precipitation experiments. Use empty one and fivepound salt bottles instead of the customary four ounce gasbottles for tests involving harmless gases. Use equipment largeenough to be seen from the farthest corner of the room.

2. APPARATUS SHOULD BE AS SIMPLE AS POSSIBLE

Demonstrate the variations in the vapor pressure of differentliquids by introducing a small amount of each liquid into thespace above the mercury in several simple barometers. Theoxidation of ammonia gas can be shown by suspending a heatedcoil of platinum wire in the mouth of a small flask containingslightly heated ammonium hydroxide.

3. THE PREPARATIONS AND EXPERIMENTS SHOULDBE CAREFULLY ARRANGED

The equipment should be placed in order on the lecturetable so that the demonstrator can proceed logically from onedemonstration to the next. The apparatus should be placedwell forward on the desk, facing outward toward the studentswho are to observe the procedure and results.

4. EXPERIMENTS SHOULD STIMULATE FURTHER THOUGHTMagnesium ribbon burns in an atmosphere of carbon dioxide

while a candle does not. Why? Colloidal graphite in water,

* Duff, A. W., "Desirable Qualities in Demonstration Experiments," SCHOOL SCIENCE & MATHE-MATICS, 28, 857 (Nov., 1928).

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treated with a solution of sodium chloride, may be separatedby filtration while a like dispersion, without the salt treatment,can not be similarly separated. Why?

5. POSITIVE EFFECTS ARE MORE EFFECTIVETHAN NEGATIVE

An ammonia fountain will emphasize the great solubility ofthis gas in water as contrasted to many other gases. Gaseouscarbon dioxide, poured into a large beaker counterpoised on agood trip scale, will demonstrate the relatively high density ofthis gas.

6. A SLIGHT DRAMATIC ELEMENT Is SOMETIMES USEFUL

Spontaneous combustion can be demonstrated by the useof pyrophoric lead or iron.2 Hydrogen soap bubbles will empha-size the low density of this gas.

7. An ELEMENT OF THE UNEXPECTED IsSOMETIMES EFFECTIVE

Glowing charcoal will continue to burn under the surface offreshly prepared, concentrated nitric acid. The iodine clockexperiment3 shows the principle of reaction velocity.

8. EXPERIMENTS SHOULD ILLUSTRATE PRINCIPLESOF SOME IMPORTANCE

The preparation of volatile acids by the action of sulfuricacid on sodium chloride is preferable to the use of sodium iodide.Concentrated and dilute acetic acid may be used in conductivityexperiments.

9. The SPEED OF ACTION SHOULD BE SUITABLE

Quantitative experiments must be carefully planned and usedsparingly. Necessary weighings, in so far as possible, should becompleted in advance. Metallic sodium, magnesium and alumi-num may be used to demonstrate equivalent weights.

10. EXPERIMENTS SHOULD BE AS NEARLYINFALLIBLE AS POSSIBLE

Difficult or doubtful experiments should be rehearsed inadvance and all variables carefully controlled to guarantee

2 Walton, James H., "Lecture demonstrations in general chemistry,"Journal of Chemical Education,8,303-6 (Feb., 1931).

3 Deming, Horace G., General Chemistry, 3rd Ed., John Wiley & Sons, Inc.. New York City. 1930,p. 284.

NATURE QUESTS 637

success. It is practically impossible to obtain a sample of ferroussulfide by the direct combination of iron and sulfur that is notmagnetic, due to excess or uncombined iron. Iron wire willburn readily in oxygen if a small amount of sulfur is attached tothe end of the wire before the initial heating, to start the reac-tion.

11. THE DEMONSTRATION SHOULD BE A MODEL FOR

THE PUPILS IN CLEARNESS, VIVIDNESS, AND

GOOD FORM IN PRESENTATION

Good technic on the part of the demonstrator will stimulatebetter laboratory work for the pupils. The outline for discussionshould be carefully planned and well in mind. Conclusionsshould be logically deduced and accurately and clearly stated.

SATURDAY MORNING NATURE QUESTS INDOWNTOWN INDIANAPOLIS*

BY WILLIAM G. VINALNational Recreation Association

You are about to be sent on a nature quest. If in a groupelect a leader. When you have agreed on the answer to eachquery which follows write it down. At the end of the quest studythe items occurring at the end of page 5.

In case you wish to compete, the numbers in parenthesesindicate the score for a correct answer.

I. A TREE TRAILGo west on New York Avenue and cross Capitol.On this expedition look for an advertisement that hasa. Mouse (1)b. A Christmas Tree (1)c. A White Horse (5)d. A Shell (1)e. Snow (1)f. Star (1)1. What is the kind of rock used for paving Capitol? (1)2. The trees in front of 221 are Ailanthus. They have fruit

and leaf stems. What part of a motor boat does one seed re-semble? Try it in the air and see if it works. (1)

* This exercise is typical of what can be done in any downtown district. Tlie following was preparedfor "Leaders" in Nature Recreation at the Indianapolis Institute.