SECT. in. DEFINITE PROPORTIONS. 95 



Electro-chemical action, or the power of electricity to 

 combine and separate the heterogeneous atoms of mat- 

 ter, is in direct proportion to the absolute quantity 

 of electricity that passes in the current. Hence the 

 superior analytical power of voltaic over static electri- 

 city, which has enormous intensity, but is very small in 

 quantity. The electric current separates molecular 

 combinations which yield to no other means : it is the 

 most powerful instrument of analysis ; light is the most 

 delicate. 



Two simple substances are only capable of a certain 

 number of chemical combinations, which form a regular 

 series of new substances ; as for example oxygen and 

 nitrogen. Two measures of nitrogen gas will unite with 

 one measure of oxygen to form the protoxide of nitro- 

 gen ; with two measures of oxygen it unites to form the 

 binoxide of nitrogen ; with three measures of oxygen ifr 

 forms the hyponitrous_jiCid ; with four it forms nitrous 

 oxide ; and with five measures of oxygen it forms nitric^ 

 acid. Thus there are five compounds of nitrogen and 

 oxygen, no more. Affinity of kind is merely the attrac- 

 tion of one element or atom of matter for another ; affi- 

 nity of degree consists in the grades and limits of 

 combination ; the preceding series is of the fifth degree ; 

 the limit is the last term, for no further combination of 

 these two gases can take place, and these are accom- 

 plished by art. All the five substances are deleterious, 

 most of them deadly poisons, for the protoxide of 

 nitrogen, which is the laughing gas, could not be long 

 inhaled with impunity. For a long time the middle 

 term of the preceding series was wanting, but Gay- 

 Lussac formed it by attending to the laws of definite 

 proportion and sequence. 



The atoms of different kinds of matter possess an 

 affinity, or attractive force, which binds them together 

 chemically in different and very unequal degrees. Two 



