9 



30. But it is&quot; only when alone, or when merely mixed 

 with oxygen, as in common air, that it is so inert. In 

 combination it always plays an active part. All sub 

 stances containing it have a tendency to be decomposed. 

 Chemically, that is, intimately united with oxygen, it 

 forms one of the most violent agents known. 



31. Oxygen combines with nitrogen in five different, 

 perfectly definite proportions, by weight, viz. : 



Protoxide (first oxide) of nitrogen is 14 parts of nitrogen with 8 of oxygen. 

 Deutoxide (second oxide) &quot; 14 &quot; &quot; &quot; 16 &quot; 



Tritoxide (third oxide) &quot; 14 &quot; &quot; &quot; 24 &quot; 



Peroxide (highest oxide) &quot; 14 &quot; &quot; &quot; 32 &quot; 



Nitric acid, aquafortis, is 14 &quot; &quot; &quot; 40 &quot; 



It seems a very surprising and wonderful thing that 

 these two gases should always unite in such exact pro 

 portions ; that 14 parts by weight of nitrogen should 

 always unite with exactly 8, or twice 8, or three or four 

 times or five times 8 parts of oxygen. Yet this is always 

 the case. And not only do nitrogen and oxygen unite in 

 this exact manner, by this precise law, but all the other 

 elements unite with each other in perfectly definite, inva 

 riable proportions. How this happens no one knows. 

 All we can say is, that the Creator has made things in 

 this manner, so as to unite according to this law. And 

 this is called the Law of Definite Proportions. For when 

 things always happen exactly in one way, we say that 

 they happen according to a laiv of nature. It is incon 

 ceivable that they should always come so by accident. 



This law is universal. Oxygen always unites in the 

 proportion, by weight, of 8, or some multiple of 8. Nitro 

 gen always in the proportion of 14 ; and every other 

 element has its definite combining number. The com- 



