270 METALS AND THEIR COMBINATIONS. 



Ammonium sulphate, (NH 4 ) 2 SO 4 , Ammonium nitrate, NH 4 NO 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 S0 4 + 2NH 4 OH = (NH 4 ) 2 S0 4 -f 2H 2 O. 

 HNO 3 + NH 4 OH = NH 4 NO 3 -f H 2 O. 

 H 3 P0 4 + 2NH 4 OH = (NH 4 ) 2 HP0 4 + 2H 2 O. 

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



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 -f K 2 SO 4 ; 

 2KBr + (NH 4 ) 2 S0 4 = 2NH 4 Br 



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, Ammonium sulphydrate). Obtained by passing hydrogen 

 sulphide through ammonia water 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. This behavior 

 is characteristic of the soluble hydrosulphides in general, and is due 

 to the liberation of sulphur by oxidation, thus : 



NH 4 SH + O = NH 4 OH + S. 



The sulphur combines with undecomposed hydrosulphide, forming 

 polysulphides, which are yellow. The normal sulphide, (NH 4 ) 2 S, can 

 be obtained in the solid state, but it quickly loses half of its ammonia 

 and forms hydrosulphide. In solution it is almost completely hydro- 

 lyzed, thus : 



(NH 4 ) 2 S + H 2 ^ NH 4 OH + NH 4 SH. 

 A mixture corresponding to the normal sulphide is obtained by add- 



