346 On Chemical Tests fOc?- 



present, this test produces no effect in the cold, but if boiled till the am- 

 moniacal salt be decomposed a precipitate falls. 



Phosphate of soda in neutral solutions, a white precipitate soluble in 

 acids, potash and ammonia. 



Oxalic acid. In dilute solutions, a troubling. In stronger solutions, 

 if neutral, a white precipitate, soluble in potash, ammonia and acids. 



Prussiate potash white gelatinous precipitate, insoluble in free muri- 

 atic acid. 



Red prussiate potash yellowish red precipitate, soluble in free muria- 

 tic acid. 



Hydrosulphuret of ammonia. White precipitate of sulphuret of zinc, 

 If iron be present the precipitate may be grey, or black. 



Liquid sulphuretted hydrogen, and sulphuretted hydrogen gas, a white 

 precipitate in neutral solutions. 



a. The solutions of the neutral zinc salts redden litmus paper. 



I. A white precipitate produced by hydrosulphuret of ammonia in a 

 clear and strongly alkaline solution can consist of nothing else than sul- 

 phuret of zinc (Rose). 



c. Before the blow-pipe the salts of zinc are peculiarly easy of detec- 

 tion. If heated on charcoal with soda in the interior flame they spread 

 on the charcoal a white coat of oxide of zinc. Moistened with nitrate of 

 cobalt, and heated in the blow-pipe flame, they assume a fine green co- 

 lour. With borax, or with microcosmic salt, oxide of zinc melts into a 

 clear glass, which flaming renders milky. 



d. Metallic zinc is employed as a re-agent for separating copper? 

 lead, tin, silver, and tellurium in a metallic state from their solutions 

 in acids. The solution should be somewhat acid. 



e. To distinguish sulphate of zinc (white vitriol) from sulphate of 

 magnesia (epsom salts) a mixture which professor O'Shaughnessy 

 found to have been sold in the Calcutta bazar, add to each of the solu= 

 tions a few drops of ammonia. Place a little of the precipitate on a 

 piece of red hot charcoal, and urge the heat with a blow-pipe. The 

 zinc will appear of a splendid yellow colour; but the magnesia will re- 

 tain its whiteness. 



f. To separate zinc from copper and nickel, see 52. 



g. Zinc in solution may be distinguished from alkalies by its behavi- 

 our with carbonate of potash. And from earthy salts by its giving a 

 white precipitate with hydrosulphuret of ammonia. • 



