290 OXIDES. 



OXIDE OF AMMONIUM. 

 725. FORMATION. When hydrated 



WJiatissaid . . 



of oxide of sulphuric acid combines with ammonia, 

 ammonium? tne wa ter which it contains is regarded 

 as converting the ammonia into oxide of ammonium, 

 with which the acid then combines. The action of 

 other hydrated acids is the same. In naming the cor- 

 responding salts, the oxide of ammonium is called 

 ammonia. Thus, the compound with sulphuric acid, 

 is called sulphate of ammonia. It is to be borne in 

 mind, that oxide of ammonium of such salts, contains 

 an atom of water, in addition to the constituents of 

 ammoniacal gas. 



OXIDE OF CALCIUM. 



How is lime 726. LIME. Lime or oxide of calcium 



obtained? is best obtained by heating chalk, marble 

 or limestone. These are all carbonates of lime. Under 

 the influence of a high temperature, the tendency of 

 the carbonic acid to assume the gaseous form is so 

 increased, that the chemical affinities of the base are 

 overcome. The carbonic acid escapes, leaving the caus- 

 tic lime behind. This is the process of the ordinary lime 

 kiln. The superior strength of potassa and soda, as 

 bases, is illustrated by the fact that the carbonic acid 

 cannot be removed from them through the agency of 

 heat. 



TO* , , ^27. HYDRATE OF LIME. SLAKED LIME. 

 What is hy- 

 drate of * When water is added to lime, one equiva- 

 ^^me? j ent j mme( ji ate ]y combines with it, and 



