44 



PRINCIPLES OF CHEMISTRY. 



f The law of chemical combination by volume, or the Law of 

 I Gay-Lussac, may be stated as follows : When two or more gaseous 

 I constituents combine chemically to form a gaseous compound, the volumes 

 \of the individual constituents bear a simple relation to the volume of the 

 product. The law may be divided into two laws, thus : 1. Gases 

 combine by volume in a simple ratio. 2. The resulting volume of 

 the compound, when in the form of a gas, bears a simple ratio to the 

 volumes of the constituents. For instance : 1 volume of hydrogen 

 combines with 1 volume of chlorine, forming 2 volumes of hydro- 

 chloric acid gas ; 2 volumes of hydrogen combine with 1 volume of 

 oxygen, forming 2 volumes of water- vapor ; 3 volumes of hydrogen 

 combine with 1 volume of nitrogen, forming 2 volumes of ammonia. 

 If the different combining volumes of the gases mentioned are 

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

 these volumes 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 : 35.4, 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 : 8 or 2 : 16, the latter being the atomic weight 

 of oxygen. 



