236 On the Decomposition of Salts of Ammonia. 



To avoid the interfei*ence of the atmosphere, solutions of 

 urate of ammonia and chloride of ammonium, coloured blue 

 with litmus, were evaporated in a very perfect vacuum over 

 chloride of calcium. The solution of chloride of ammonium 

 became red in less than five hours. The solution of urate of 

 ammonia formed a red edge, where the fluid evaporated, in 

 half an hour; this continued to grow broader, and after four- 

 teen hours the basin was dry, leaving a broad red deposit on 

 the side. 



Two solutions of equal quantities of chloride of ammonium 

 were made, the one in alcohol, the other in water. They 

 were both coloured with blue litmus and left to evaporate in 

 the air. The alcoholic solution became red the soonest. 



These experiments show that salts of ammonia are decom- 

 posed by evaporation at ordinary teniperatures. It was long 

 since observed by Sir H. Davy, that if the same quantity of 

 nitrate of ammonia was dissolved in much and little water, 

 the loss on evaporation by boiling was directly in proportion 

 to the quantity of water used. Part was probably carried off 

 by the steam, but tlie above experiments show that it was 

 partly decomposed, the ammonia being separated from its 

 combination with nitric acid. 



H. Rose also observed the decomposition of the sulphate 

 of ammonia when evaporated at a boiling temperature. He 

 says, " If the boiling is effected in a retort a liquid passes 

 over into the receiver, which contains free ammonia. This 

 result evidently arises from the water as base eliminating the 

 oxide of ammonium from its combination with sulphuric acid 

 and combining with the same. The quantity of the sulphate 

 of the oxide of ammonium decomposed in this way is indeed 

 small, but it must also be remembered that the oxide of am- 

 monium is one of the most powerful bases, and this result is 

 chiefly to be ascribed to its greater volatility *." 



It seems probable that the act of evaporation of the fluid, 

 in which the salt is dissolved, assists the escape of the oxide of 

 ammonium from its combinations, the alcoholic solution of 

 chloride of ammonium becoming more quickly acid than the 

 watery solution. 



The decomposition of ammoniacal salts, although so very 

 perceptible to test-paper (as may be best seen by dipping 

 blue litmus paper into an ammoniacal solution of chloride of 

 ammonium and drying in the air), is scarcely perceptible to 

 balance. 



Nitrate of ammonia loses, according to Sir H. Davy, from 

 3 to 6 grs. per cent, when the temperature of evaporation is 

 * TvHylor's Scientific Memoirs, vol. ii. p. 371. 



