CH. XXXVI. LAW OF DEFINITE PROPORTIONS. 373 



And this never varies. Again, if you take some ammonia 

 and decompose 1 7 ounces of it you will collect 



3 volumes of hydrogen weighing i oz. each . . 3 ozs. 

 I volume of nitrogen weighing 14 oz. . . . 14 ozs. 



17 ozs. 



And this again never varies. Wherever you get ammonia it 

 will always be made up of these proportionate weights of 

 hydrogen and nitrogen. 



This combination of the different elements in fixed 

 quantities is called the law of definite proportions. It was 

 hinted at by four chemists before Dalton ; namely Proust, 

 Wenzel, Higgins, and Richter, but it was very little under- 

 stood, and some eminent chemists, such as Berthelot, even 

 doubted whether it was true. Dalton, however, made a re- 

 markable discovery which both proved the truth of the law 

 itself and showed that it meant a great deal more than had 

 been imagined. 



He found that not only are the elements in any one 

 substance always in a fixed proportion, but that each ele- 

 ment, such as oxygen, has a weight of its own, and will 

 only combine with other elements in proportions of this 

 fixed weight. For example, oxygen will join itself to 

 nitrogen in five different proportions, making five different 

 substances, and in each case the same fixed weight of oxy- 

 gen is added. Thus, if you decompose 22*4 litres of 



Volumes of Weighing 



Nitrogen Oxygen Nitrogen Oxygen 



. 28 grammes 16 grammes 



. 28 „ 32 



. 28 „ 48 



. 28 „ 64 



. 28 „ 80 



So that each substance contains one more volume of oxygen 



