126 METALS AND THEIR COMBINATIONS. 



The source of all ammonium compounds is ammonia, 

 or ammonium hydrate, NH 4 HO, which have both been con- 

 sidered heretofore. 



Ammonium chloride, Ammonii chloridum, NH 4 C1 = 53.4 ( Chloride 

 of ammonium, Sal-ammoniac}. Obtained by saturating the " am- 

 moniacal liquor" of the gas-works with hydrochloric acid, 

 evaporating to dry ness, and subliming the impure article for 

 purification. 



The pure ammonium chloride is either a white, crystalline 

 powder, or presents itself 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 1.5 part of boiling water; and, 

 like all ammonium compounds, is completely volatilized by heat. 



Ammonium carbonate, Ammonii carbonas, NH 4 HC0 3 .NH 4 NH 2 C0 2 



= 157 (Carbonate of ammonium}. The commercial ammonium 

 carbonate is not the pure salt, but, as shown by the above 

 formula, a combination of acid carbonate of ammonium with 

 carbamate of ammonium. It is obtained by sublimation of a 

 mixture of ammonium chloride and calcium carbonate, when 

 calcium chloride is formed, ammonia gas and water escape, 

 and ammonium carbonate condenses in the cooler part of the 

 apparatus : 



2CaC0 3 + 4NH 4 C1 = NH 4 HCO 3 .]SrH 4 ]SrH 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 carbonate of ammonium : 



NH 4 HC0 3 .NH 4 NH 2 C0 2 = NH 4 HCO 3 + 2NH 3 + CO 2 . 



When ammonium carbonate is dissolved in water, the car- 

 bamate unites with one molecule of water, forming neutral car- 

 bonate of ammonium : 



NH 4 NH 2 C0 2 + H 2 O = (NH 4 ) 2 C0 3 . 



A solution of the common ammonium carbonate in water, is, 

 consequently, a liquid containing both acid and neutral carbon- 

 ate of ammonium ; by the addition of some ammonia water the 



