SOG 



On Chemical Tests. 



[Oct. 



43. CADMIUM. Solutions of cadmium are recognized by their 

 giving yellow precipitates with liquid sulphuretted hydrogen, or with a 

 current of hydrogen gas. This precipitate resembles orpiment, but it 

 may be distinguished by the facility with which it dissolves in muria- 

 tic acid and by its bearing a red , heat without being altered. Before 

 the blow pipe, with soda, the salts of cadmium coat the charcoal with 

 a brownish red or orange coloured powder. 



a. A considerable number of the salts of cadmium are soluble in 

 water, and the solutions are colourless, or have a slight yellow tinge. 

 The insoluble salts are white powders, and dissolve in acids. 



b. The pure oxide of cadmium gives a reddish brown powder. The 

 hydrated oxide is white. The oxide is soluble in ammonia and easily 

 dissolves in acids, and acts towards re-agents as follows. 



c. Potash, carbonate of potash, and carbonate of ammonia produce a 

 white precipitate, and hydrosulphuret of ammonia, in neutral solutions, 

 a yellow precipitate ; all of which precipitates are insoluble in an ex- 

 cess of the precipitant. Henry says, the fixed alkalies throw down a 

 white hydrated oxide soluble in ammonia. Prussiate of potash and 

 oxalate of ammonia cause a white sediment. 



d. Ammonia produces in neutral solutions a white precipitate, 

 easily soluble in an excess of ammonia; oxalic* acid does the same. 



e. Sulutions of the neutral cadmium salts redden litmus paper. 



f. A plate of zinc immersed in a solution of cadmium precipi- 

 tates it in dendritical leaves ; or according to others in grey coloured 

 spangles. 



g. Cadmium resembles tin very nearly, in colour, lustre, and the 

 sound it emits when bent. It melts below a red-heat, and volatilizes 

 at a heat not much greater than that which volatilizes mercury j 

 it condenses in drops. 



44. CALCIUM, lime is detected by oxalate of ammonia, oxalic acid, 

 or bin-oxalate of potash, all of which produce a white precipitate of oxa- 

 late of lime which is soluble in nitric acid ; — the precipitation is assisted by 

 the addition of ammonia to neutralize any free acid. See 15,35,72. Sulphu- 

 ric acid, and the carbonated alkalies, and phosphate of soda, also de- 

 tect lime, but not so satisfactorily as oxalic acid, or the oxalates. 



a. Calcareous salts are, in concentrated solutions, distinguished from 

 alkaline salts by giving a white precipitate with carbonate of potash ; or 

 dilute sulphuric acid. Lime is distinguished from barytes by its giving 

 no precipitate with hydrofluosilicic acid. See 40, 72 b ; 79 d. 



