CHEMISTRY. 31 



It will be seen that while the nitrogen remains the same, the 

 oxygen increases by multiples of 8, which is its equivalent 

 number. The nitrogen, although willing to unite with several 

 whole proportions of oxygen, would reject a quarter or half 

 of an equivalent, and not unite with it : so, in the preparation 

 of any compound, if an excess of either element be used, it is 

 not combined, but left alone in its original state. 



The equivalent or combining number of a body is that which 

 represents the smallest in which it is known to combine with 

 other bodies. The representative number of a compound, is 

 the sum of the combining equivalents of its components. Com- 

 bining proportions are reckoned by weight and by volume ; in 

 these two estimations of course different equivalent numbers 

 are used. 



