LAWS AND THEORIES OF CHPIMISTRY. 



101 



weighed, it will be found that there exists a simple relation between 

 these weights and the atomic or molecular weights of the elements. 



For instance : Equal volumes of hydrogen and chlorine combine, 

 and the weights of these volumes are as 1:35.18, which numbers 

 represent also the atomic weights of the two elements. Two volumes 

 of hydrogen combine with one volume of oxygen, and the weights of 

 the volumes are as 1 : 7.94 or 2 : 15.88, the latter being the atomic 

 weight of oxygen. 



2 Vol umes 



Hydrochl j oric Acid gas. 

 W = ! 36.18 



2 Vol ; umes 



j 

 Water i -vapor 



W = j 17.88 



2 Vol j umes 

 Anna ; onia gas. 

 W = I 16.93 



2 Vol umes 

 Sulphur ic acid gas. 

 Weight !=B 97.36 



The above diagram shows the simple relation which exists between 

 combining volumes and atomic and molecular weights. It was, 

 besides other factors, the discovery of this relation that led to the 

 adoption of Avogadro's Law, which has been stated. (See Chapter 

 I., page 30.) 



Taking the law of combination by volume and Avogadro's Law as a basis of 

 argument, we can prove directly in the case of some of the elementary gases 

 that their molecules consist of more than one atom. One volume of hydrogen 

 combines with one volume of chlorine to give two volumes of hydrochloric acid 

 gas. According to Avogadro's Law the volume of hydrogen and chlorine con- 

 tain the same number of molecules, and the two volumes of product formed 

 must contain twice as many molecules as does the volume of hydrogen or chlo- 



