AMMONIUM. 147 



by dissolving potassium in mercury, and adding to the potassium- 

 amalgam thus formed, a strong solution of ammonium chloride, when 

 potassium chloride and ammonium-amalgam are formed. The latter 

 is a soft, spongy, metallic-looking substance, which readily decomposes 

 into mercury, ammonia, and hydrogen : 



HgK + NH 4 C1 = KC1 + NH 4 Hg; 

 NH 4 Hg = NH 3 + H + Hg. 



The source of all ammonium compounds is ammonia NH 3 , or am- 

 monium hydroxide, NH 4 OH, both of which have been considered 

 heretofore. 



Ammonium chloride, Ammonii chloridum, NH 4 C1 = 53.4 (Sal-_ 

 ammoniac). Obtained by saturating the "ammoniacal liquor 77 of the 

 gas-works with hydrochloric acid, evaporating to dryness, and puri- 

 fying the crude article by sublimation. 



Pure ammonium chloride either is a white, crystalline powder, or 

 occurs in the form of long, fibrous crystals, which are tough and 

 flexible ; it has a cooling, saline taste ; is soluble in 3 parts of cold, 

 and in 1 part of boiling water; and like all ammonium compounds, 

 is completely volatilized by heat. 



Experiment 20. To 10 c.c. of water of ammonia add hydrochloric acid until 

 the solution is neutral to test paper. Evaporate to dryness and use the salt 

 for the analytical reactions mentioned below. How many c.c. of 32 per cent, 

 hydrochloric acid are required to saturate 10 c.c. of 10 per cent, ammonia 

 water ? 



Ammonium carbonate, Ammonii carbonas, NH 4 HCO 3 .NH 4 

 NH 2 CO 2 =157. Commercial ammonium carbonate is not the normal 

 salt, but, as shown by the above formula, a combination of acid 

 ammonium carbonate with ammonium carbamate. It is obtained by 

 sublimation of a mixture of ammonium chloride and calcium car- 

 bonate, when calcium chloride is formed, ammonia gas and water 

 escape, and ammonium carbonate condenses in the cooler part of the 

 apparatus : 



2CaCO 3 + 4NH 4 C1 = NH 4 HCO 3 NH 4 NH 2 CO 2 + 2CaCl 2 + H 2 O + NH 3 . 



Ammonium carbonate thus obtained forms white, translucent masses, losing 

 both ammonia and carbon dioxide on exposure to the air, becoming opaque, 

 and finally converted into a white powder of acid ammonium carbonate. 



NH 4 HCO 3 NH 4 NH 2 CO 2 = NH 4 HgO 3 + 2NH 3 + CO 2 . 



When commercial ammonium carbonate is dissolved in water the carbamate 

 unites with one molecule of water, forming normal ammonium carbonate. 



NH 4 NH 2 CO 2 + H 2 O = (NH 4 ) 2 CO 3 . 



