148 METALS AND THEIR COMBINATIONS. 



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

 liquid containing both acid and normal carbonate of ammonium ; by the addi- 

 tion of some ammonia water the acid carbonate is converted into the normal 

 salt. The solution thus obtained is used frequently as a reagent. 



The Aromatic spirit of ammonia (sal volatile) is a solution of normal ammo- 

 nium carbonate in diluted alcohol to which some essential oils have been added. 



Ammonium sulphate, (NH 4 ) 2 SO 4 , Ammonium nitrate, NH 4 N0 3 , 

 and Ammonium phosphate, (NH 4 ) 2 HPO 4 , may be obtained by the 

 addition of the respective acids to ammonia water or ammonium 

 carbonate : 



H 2 SO 4 + 2NH 4 OH = (NHJ 2 S0 4 + 2H 2 O. 

 HNO 8 + NH 4 OH = NH 4 N0 3 -f H 2 O. 

 H 3 PO 4 + 2NH 4 OH = (NH 4 ) 2 HPO 4 4- 2H 2 O. 

 H 2 S0 4 -f- (NH 4 ) 2 C0 3 = (NH 4 ) 2 S0 4 + H 2 O + CO 2 . 



Ammonium iodide, Ammonii iodidum, NH 4 I, and Ammonium 

 bromide, Ammonii bromidum, NH 4 Br, may be obtained by mixing 

 together strong solutions of potassium iodide (or bromide) and am- 

 monium sulphate, and adding alcohol, which precipitates the potas- 

 sium sulphate formed ; by evaporation of the solution the ammonium 

 iodide (or bromide) is obtained : 



2KI + (NH 4 ) 2 SO 4 = 2NH 4 I + K 2 SO 4 ; 

 2KBr + (NH 4 ) 2 S0 4 = 2NH,Br + K 2 SO 4 . 



Another mode of preparing these compounds is by the decomposi- 

 tion of ferrous bromide (or iodide) by ammonium hydroxide : 

 FeBr 2 + 2NH 4 OH = 2NH 4 Br + Fe(OH) 2 . 



Ammonium iodide is the principal constituent of the Decolorized 

 tincture of iodine. 



Ammonium hydrogen sulphide, NH 4 SH (Ammonium hydro- 

 sulphide j Ammonium sulphydrate). Obtained by passing hydrogen 

 sulphide through water of ammonia until this is saturated : 

 H 2 S + NH 4 OH == NH 4 SH 4- H 2 O. 



The solution thus obtained is, when recently prepared, a colorless 

 liquid, having the odor of both ammonia and of hydrogen sulphide ; 

 when exposed to the air it soon assumes a yellow color. By the 

 addition of ammonia water it is converted into ammonium sulphide, 



(NH 4 ) 2 S: 



NH.SH + NH 4 OH = (NH 4 ) 2 S + H 2 O. 



Both substances, the ammonium hydrogen sulphide and ammonium sulphide, 

 are valuable reagents, frequently used for precipitation of certain heavy metals, 

 or for dissolving certain metallic sulphides. 



