CARBONATES. 313 



salt, and thus converting the silver of the mark into 

 chloride of silver. This is soluble in ammonia, and 

 may be afterward extracted by that agent. Nitrate 

 of silver is also the basis of most dyes for the hair. 

 Describe the 790. OTHER NITRATES. Nitrate of soda 

 other nitrates. j s a wn it e salt, found native in South 

 America. It is used in the manufacture of nitric acid, 

 and, to some extent, as a fertilizer of the soil. The 

 remaining nitrates are soluble salts, of colors corres- 

 ponding to the solutions of the metals, as already de- 

 scribed. The uses of the nitrates of silver and bismuth 

 have already been mentioned. 



CARBONATES. 



Describe the 791. CARBONATES. The carbonates are, 

 carbonates. f or tne most part) wn ite or light colored 



salts, of which chalk may serve as an example. The 

 carbonate of copper is found native, both as blue and 

 green malachite. All of the carbonates, 

 excepting those of the alkalies, may be 

 decomposed by heat. The latter are sol- 

 uble, and retain their acid at the highest temperatures. 

 The figure represents a crystal of carbonate of lime or 

 calc spar. 



792. PREPARATION. The insoluble car- 



How are the ... 



insoluble car- boiiates may be produced by precipitating 

 solutions of the metals or their salts, by 

 carbonic acid or solutions of the alkaline 

 carbonates. In the latter case, a double decomposition 

 occurs, with exchange of acids and bases. 



14* 



