162 CHEMISTRY. 



earth's atmosphere is limited, and consequently that 

 matter has a finite divisibility;* and that the doctrine 

 of ultimate atoms may therefore be considered as 

 established. 



Invariable Proportion. 



All chemical compounds contain the same constant 

 proportion of constituents with the most rigid accu- 

 racy, not the slightest variation ever taking place. 

 This regularity can be ascribed to nothing else than 

 the constant union of one atom of one body with one 

 atom of another; or of a determinate number of 

 atoms of one body, with a determinate number of 

 atoms of another. 



Trituration. v 



Mechanical trituration, however carefully per- 

 formed, is quite incapable of separating from each 

 other substances that are chemically united. 



The Chemico-electric Theory. 



Sir Humphrey Davy advanced the opinion, that 

 chemical affinity is identical with electric attraction ; 

 that bodies which unite chemically possess different 

 kinds of electricity ; that oxygen and acids are always 

 resinous or negative electricity; and earths and me- 

 tals always vitreous or positive electricity. Hence 

 the reason why one set is attracted by the negative 

 pole, and the other by the positive. 



It results from this theory, that bodies remain 

 united because they are in different electric states. 

 If they can be brought into a similar state by making 

 them both positive or both negative, they will repel 

 each other, and of course be decomposed. The gal- 

 vanic battery produces this effect, if it be sufficiently 

 powerful. 



* Yet of the smallest atom we can always imagine the half* 



