COMBINING PROPORTIONS. 109 



and is on that account taken here as unity. But the other 

 series which is the most convenient, being adopted, it may then 

 be stated in general terms that the combining proportion of a 

 simple substance represents the quantity of that substance which 

 combines with \ 00 parts of oxygen to form a protoxide. 



The first law of combination is, that bodies unite with each 

 other in their combining proportions only, or in multiples of 

 them, and in no intermediate proportions. This law may be 

 illustrated by the compounds of nitrogen and oxygen, which 

 are five in number, and are composed as follows : 



Protoxide of nitrogen . . Nitrogen 177? oxygen 100 



Deutoxide of nitrogen . . Nitrogen 177? oxygen 200 



Nitrous acid .... Nitrogen 177? oxygen 300 



Peroxide of nitrogen . . . Nitrogen 177, oxygen 400 



Nitric acid .... Nitrogen J 77? oxygen 500 



The. first compound consists of a single combining pro- 

 portion of each of its constituents. Bat in the other com- 

 pounds a single proportion of nitrogen is united with quantities 

 of oxygen which correspond exactly with two, three, four and 

 five combining proportions of that element. In the greater 

 number of binary compounds, one of the constituents at least is 

 present in the proportion of a single equivalent, like the nitrogen 

 in this series, while the other constituent, generally the oxygen 

 in oxides, and the electro-negative element in other compounds, 

 is present in a multiple of its combining proportion. But the 

 number of combining proportions which may enter into a com- 

 pound, is subject to considerable variation as will appear from 

 the following examples. 



One proportion oxygen + One proportion hydrogen, forms water. 



Two proportions oxygen + One hydrogen, form peroxide of hydrogen. 



One proportion oxygen + Two proportions copper, forms suboxide of copper. 



e > sulphur + Three oxygen, sulphuric acid. 



Two proportions sulphur + Two oxygen, form hyposulphurous acid. 



Two " iron + Three oxygen, peroxide of iron. 



Tvvo " sulphur + Five oxygen, ,, hyposulphuric acid. 



Two manganese + Seven oxygen, hypermanganic acid. 



Representing the constituents of a binary compound by A 

 and B, the last being the oxygen or electro-negative constituent, 

 the most frequent combination is A + B, then A-J-2B, A + 3B, 

 and A + 5B. The combination of 2A + 3B, is not unfrequent, 

 but 2A + B, A-J-4B, A + 7B, 2 A + 2B, or 2A + 5B are of com- 



