80 ON THE STRUCTURE OF ATOMS. 



A cubic foot of oxygen will weigh just sixteen times as mucli as 

 a cubic foot of hydrogen, because the atom of oxygen is sixteen 

 times heavier than the atom of hydrogen. It is immaterial then 

 whether we say two atoms or two measures of hydrogen unite 

 with one of oxygen to form water. In this case the three vol- 

 umes of the original gases are condensed in the combination into 

 two volumes of water-vapor or steam. If we were to suppose 

 that these measures were cubic inches, and that each one con- 

 tained 1,000 atoms, then the case would stand in this wise : 2,000 

 atoms of hydrogen have combined with 1,000 atoms of oxygen, 

 and these 3,000 have formed 2,000 molecules of water-gas. 

 Each molecule of the water therefore contains one atom of 

 hydrogen and one-half an atom of oxygen. The oxygen atom 

 has divided itself into two, and the hydrogen has not divided. 



Let us take another instance. Three atoms of hydrogen unite 

 with one of nitrogen to form two molecules of ammonia. The 

 compression in this case is four volumes into two. Of course 

 each molecule of ammonia contains one and a half atoms of hy- 

 drogen and one-half atom of nitrogen. Both hydrogen and 

 nitrogen have in this case divided their atoms into two. Again, 

 one atom of hydrogen unites with one atom of chlorine to make 

 two molecules of hydrochloric acid, each molecule of the latter 

 containing one-half atom each of hydrogen and chlorine. Now 

 one molecule of ammonia will unite with one molecule, of hydro- 

 chloric acid to form two molecules of sal-ammoniac or muriate of 

 ammonia. Evidently a molecule of the latter is composed in 

 the following manner : (|H. + JN) + (JH + JC1) ; and here is the 

 proof of it. Reducing the above to their atomic weights: 4- 

 3 + J-f 8-J = 13f = atomic weight of sal-ammoniac. Now, any 

 given measure of air being called 1, the same measure of H. 

 will weigh .069, which is called its specific gravity. The atomic 

 weight of any gas multiplied into that decimal will give the 

 specific gravity of that gas. Therefore 13f multiplied into .069, 

 which is .92, is the calculated specific gravity of muriate of am- 

 monia gas. This gas has been carefully weighed, and the ob- 

 served specific gravity found to be .89. The two are considered 

 to correspond within the limits of error. 



