310 



On Chemical Tests. 



[Oct. 



50. COLUMBIUM. There is great difficulty in separating Co- 

 lumbia m from other substances. The infusion of galls produces in 

 solutions of columbium an orange precipitate, and the recently pre- 

 pared oxide of the metal is soluble in citric, tartaric, or oxalic acid. 

 The columbate of potash is crystallizable, and the oxide of the metal 

 is immediately precipitated on the addition of an acid. 



51. COFFER in solution, is detected by ammonia which in small 

 quantity turns it first green, then blue; but if iron be also in solution, 

 it ought first to be removed. Clean iron free from rust precipitates 

 metallic copper, and this distinguishes copper from nickel, for ammo- 

 nia turns nickel also blue. Metallic zinc causes a black precipitate* 

 The ammonia and iron conjointly are decisive tests. 



Potash produces a voluminous blue precipitate (hydrated oxide) 

 which when boiled with an excess of potash turns black and quickly 

 subsides. If the potash is insufficient, a light green precipitate occurs. 



Ammonia, in small quantify occasions a green precipitate which easily 

 dissolves in more ammonia and produces a blue solution. If this solu- 

 tion be boiled with caustic potash a dense black precipitate is formed. 



Carbonate of potash. A blue precipitate, rendered black by boiling. 



Carbonate of ammonia. Same as ammonia. 



Phosphate of soda. A greenish white precipitate soluble in ammonia 

 and if potash be added, a dense black precipitate takes place on boil- 

 ing. 



Oxalic acid. A greenish white precipitate. 



Prussiate of potash. A reddish brown precipitate insoluble in muri- 

 tic acid. This and clean iron are trust-worthy tests, but the solution 

 should be either neutral or slightly acid, and not alkaline. 



Red prussiate of potash, a yellow green precipitate insoluble in muria- 

 tic acid. 



Hydrosulphuret of ammonia, liquid sulphuretted hydrogen, and a 

 current of sulphuretted hydrogen gas, give black or dark brown precipi- 

 tates according to the quantity of copper in solution. 



Metallic zinc or tin precipitates copper black. 



Metallic iron, pure copper. 



a. Persalts of copper turn blue with ammonia; blue with potassa ; 

 reddish brown with prussiate of potassa, and black with hydrosulphuret 

 0 f ammonia. By these indications copper may be distinguished from 

 other metals and from nickel, as before stated, as well as also by its 

 a«tion with solution of potassa, and sulphuretted hydrogen: the first of 



