1839.] 



On Chemical Tests. 



327 



82. MERCURY. This metal is acted on by a great number of tests. 



It may be detected by muriatic acid, which produces a white precipi- 

 tate insoluble in simple acids; "but rendered black on the addition of 

 ammonia. 



a. The following list shews the different colours or precipitates pro- 

 duced by the same test in solutions of the protoxide and peroxide of 

 mercury. 



PROTOXIDE. 

 Potash. Black. 



Ammonia. Black. 



Carbonate of potash. Dirty yel- 

 low, which becomes black by 

 boiling. 



Carbonate of ammonia, grey : but 

 in larger quantity black. 



Prussiate of potash. White gelati- 

 nous. 



Iodide of potassium ; greenish yel- 

 Jow ; test added in larger quan- 

 tity, the colour is blackish, ex- 

 cess of test dissolves the preci- 

 pitate. 



PEROXIDE. 



Potash. Reddish brown ; added 

 in larger quantity yellow: if 

 much free acid, or if muriate of 

 ammonia be present the preci- 

 pitate is white. 



Ammonia. White. 



Carbonate of potash. Reddish 

 brown. It' muriate of ammonia 

 be present, white. 



Carbonate of ammonia. White. 



Prussiate of potash. White, chang- 

 ing after exposure to blue. 



Iodide of potassium. A cinnabar 

 red, soluble in excess of test : 

 also in muriatic acid. 



b. Silver and mercury precipitated, or held in separate solution may 

 be thus distinguished from each other. If in solution, drop a very lit- 

 tle of both solutions on different parts of a piece of clean copper : rub 

 them with a clean finger ; in each case a silvery whiteness will ap- 

 pear: but for the silver, its action will be more certain if it be rubbed 

 with a little common salt and cream of tartar mixed together. Then 

 appl) heat to the copper: the mercury will be dissipated, but tbe silver 

 will remain. If solutions of mercury and of silver be respectively pre- 

 cipitated by muriatic acid, ammonia turns black the mercurial precipi- 

 tate, but dissolves the precipitate of silver. 



c. Protosalts of mercury mixed with dry soda, placed in a glass tube 

 closed at one end, and heated to redness by the blow-pipe are reduced, 

 and the mercury sublimes in the form of a grey powder, which on being 

 rubbed produces globules of metallic mercury, 



d. Hydro-sulphurets, and sulphuretted hydrogen tarnish quicksilver; 

 and turn its solutions black. 



