1839.] 



On Chemical Tests, 



329 



b. Sulphuretted hydrogen gas precipitates the bi<sulphuret of mer- 

 cury ; if the solution is not very dilute a white or yellowish colour is 

 produced before il becomes black. Hydriodate of potash causes a beau- 

 tiful scarlet coloured precipitate of biniodide of mercury, which is so- 

 luble in an excess of the test. Protoehloride of tin produces a white 

 precipitate changing with more of the test to a greyish black ; the solu- 

 tion must be excluded from the air, otherwise bichloride of tin is form- 

 ed which does not act on the solution of corrosive sublimate. 



c. Many of the foregoing tests acts on other solutions of mercury, 

 besides the perchloride. See 82. 



86. MOLYBDENUM. No acid but the nitric or nitro-muriatic acts 

 on this metal, but several acids act on its oxide and afford blue solutions,, 

 Molybdic acid gives with nitrate of lead a white precipitate soluble in 

 nitric acid ; with the nitrates of mercury and silver a white flaky pre- 

 cipitate; with nitrate of copper a greenish precipitate, and it affords a 

 white precipitate with neutral solutions of all the following tests; sul- 

 phate of zinc ; muriates of bismuth, antimony, platinum and gold ; 

 and nitrate of nickel. Deutoxide salts of molybdenum are precipitated 

 brown by alkalies and their carbonates, see the tables of re-agents. 



a. There are two oxides of molybdenum ; the protoxide, which is 

 black, and the deutoxide, which is brown. 



87. mucus detected ; sub-acetate of lead instantly acts on animal 

 mucilage, or mucus, and produces with it a copious white and flaky pre- 

 cipitate, but subacetate of lead is not rendered turbid by a solution of 

 animal gelatine. This test acts on a variety of animal and vegetable 

 matters, and is not therefore a distinctive test for mucus, but as mucus 

 is not affected by tan the action of tan may serve to distinguish be- 

 tween mucus and gelatine, see 118. 



88. muriatic acid, AND MURIATES, detected, see 11, 83 b, 

 and 108. 



89. NICKEXi. Pure oxide of nickel is dark grey : the hydrate is 

 green., The solution is green. The following tests detect nickel. 

 There are two oxides : the protoxide and the peroxide. 



Potash, apple green precipitate. 



Ammonia, in small quantity a ' green troubling ; on adding a larger 



