\M11TE PRECIPITATE. 657 



crystalline form of this compound, therefore, belongs to the 

 regular system, like that of sal ammoniac. 



The compound known as white precipitate, is formed when 

 ammonia is added to a solution of chloride of mercury. When 

 first produced, it is bulky and milk white ; it is decomposed by 

 hot water or by much washing with cold water, and acquires a 

 yellow tinge. Dr. Kane has demonstrated that white precipi- 

 tate is free from oxygen, and contains nothing but the elements 

 of a double chloride and amide of mercury, and represents it 

 by the formula, HgCl + Hg, NH 2 . White precipitate is dis- 

 tinguished from calomel by solution of ammonia, which does 

 not alter the former, but blackens the latter ; it is readily dis- 

 solved by acids. Mitscherlich has observed that when white 

 precipitate is gradually heated by a metal bath, and the heat con- 

 tinued for a long time, three atoms of it lose two atoms of am- 

 monia and one atom of chloride of mercury, while a red matter 

 remains in crystalline scales, having much the appearance of 

 red oxide of mercury produced by the oxidation of the metal 

 in air, which contains two atoms of chloride of mercury united 

 with a compound of one atom of nitrogen and three atoms of 

 mercury, 2Hg Cl-j-NHg 3 . He concludes, that the atom of 

 white precipitate should be multiplied by three, its decomposi- 

 tion by the heat of the metal bath would then be represented 

 thus : 



3HgCl + 3(Hg,NH 2 ) = 2HgCl+NHg 3 and 2NH 3 and HgCl. 



The red compound is itself decomposed by a temperature 

 above 680, and resolved into chloride of mercury, mercury and 

 nitrogen. It is insoluble in water, and is not altered in boiling 

 solutions of the alkalies. It may be boiled without change in 

 diluted or concentrated nitric acid, and in pretty concentrated 

 sulphuric acid, but it is decomposed and dissolved when 

 boiled in the most concentrated sulphuric acid or in hy- 

 drochloric acid; no gas is evolved, but chloride of mer- 

 cury and ammonia are found in the acid solution. The 

 compound NHg 3 is not isolated, by passing ammonia 

 over the heated red compound. Mercury conducts itself 

 in these compounds in the same way as potassium with 

 ammonia ; the olive coloured substance produced by the action 

 of dry ammonia upon potassium being the amide of potassium, 

 3(K, NH 2 ), and the plumbago looking substance left on heating 



u u 2 



