VOL.7, NO.3
CORRESPONDENCE
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AVOGADRO AND EUCLID Recent elementary chemistry textbooks tend to minimize theory and to introduce an enormous amount of descriptive matter. The rapid development and enlargement of chemistry demand that recent progress be described and that less attention be paid to older or more remote processes. The tendency has been to enlarge upon subjects such as alloy steels, electric furnace products, rayon, and organic chemistry, and to omit or merely mention the LeBlanc process, Nordhausen acid, gas mantles, and other old-time favorites. New topics +re forcing their way into texts via newspaper headlines in ever-increasing numbers. In this msh to be up to the minute there may be a tendency to pay too little attention to the methods of scientific thought. Avogadro's principle furnishes an excellent example of this neglect. Some authors merely state the principle; others tantalize the student by stating that this is one of the most important principles in chemistry, but do not follow it through; and none of ten elementary texts selected a t random carry this topic to a thorough conclusion. In fact, some students seem to gain the impression that Avogadro's principle was the administrator of his school. I. The story of Avogadro's hypothesis can well be emphasized in the elementary course as an example of the development from a theory to a hypothesis and finally to a law. Avogadro had a perfectly definite set of phenomena to explain the regularity of behavior of gases, and he assumed the familiar explanation. Since this accorded with the work of Boyle, Charles, and Gay-Lussac, the theory was sufficiently valid to be a working hypothesis. We are told that later investigators used this hypothesis successfully and developed it. It is interesting to note that this hypothesis has now become dignified by the term "law." 1 1 The consequences of this theory are worth developing in the mind
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JOURNAL OF CHEMICAL EDUCATION
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of the elementary student. If we assume with Avogadro that equal volumes of gases under the same conditions of temperature and pressure contain the same number of molecules, several conclusions emanate. 1. Boyle's law, Charles' law, and Gay-Lussac's law of combining volumes are all satisfactorily explained-as Avogadro intended. 2. Equal volumes of two different gases (under the same conditions of measurement) have the same weight ratio as the weight ratio of the individual molecules of these gases. 3. If the formula of a gasis known, its density can be calculated by comparison with molecular weight hydrogen. (Vapor density method: x 0.09). 2 4. A gram molecular weight of any gas wcupies 22.4 liters. 5. Four common gases (O*, N,, H2. Cl1) have two atoms per molecule, and the number of atoms per molecule can he found for any other elementary gas which undergoes chemical change.
I11 A new form for presenting the proof of two atoms per molecule is offered. This seems t o "take" better than a page from the textbook,
Given: Avogadro's Hypothesis. To Prove: The oxygen molecule has two atoms.
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1. 2 volumes hydrogen 1 volume oxygen +2 volumes steam. 2. Let one volume oxygen contain 1000 molecules, then 2000 mol. H 1000 mol. 0 -+2000 mol. steam.
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3. Water (steam) is composed of a t least two sorts of atoms. 4. Since each molecule of steam has a t least 2 atoms, in 2000 molecules of steam there are a t least 4000 a t o m s a t least 2000 atoms of 0, and 2000 atoms of H. 5. 1000 mol. 0 contain a t least 2@00 atoms. 6. One molecule of oxygen has a t least 2 atoms. Q.E. D.
1 . Erfierimental measurements. 2. Avogadro's hypothesis-Equal uolumes? of gases under sane conditions of temperature and pressure have the same number of molecules. 3. Electrolysis of water experiment yields hydrogen and oxygen. 4. Law of Conservation of MatterMatter cannot be created nor destroyed.
5.
From 2 and 4 eboue.
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No claim for originality of this material is made. It is offered for whatever value i t may be to teachers having difficulty carrying Avogadro's hypothesis to a conclusion with their students. ELBERT C. WEAVER BVLKELEY HIGHSCHOOL HARTFORD. Co~mm'rcur
