Qualitative analysis / by William Briggs and R.W. Stewart.

  • William Briggs
Date:
1913
Catalogue details

Licence: Public Domain Mark

Credit: Qualitative analysis / by William Briggs and R.W. Stewart. Source: Wellcome Collection.

    39/180 (page 23)
    Hg(N03)2, 2 HgS (which is white) by boiling with strong HjST03. HgS is also insoluble in ammonium sulphide and in caustic alkalies. . i 2. Stannous chloride, SnCl2, gives, with mercuric salts, a white precipitate of mercurous chloride, Hg2Cl2, which, on boiling with excess of the reagent, gives grey metallic mercury. If the solution be poured off, and the precipitate boiled with hydrochloric acid, the mercury is obtained in small globules. 2 HgCl2 + SnCl2 = Hg9Cl2 + SnCl4. Hg2Cl2 + SnCl2 = 2 Hg + SnCl4. 3. Potassium iodide, KI, gives a precipitate which is yellow at first, but rapidly changes to bright scarlet. The precipitate consists of mercuric iodide, Hgl2. 2 KI + HgCl2 = Hgl2 + 2 KOI. The two different colours correspond to two different forms of mercuric iodide. The two forms crystallize in different shapes. At ordinary temperatures the scarlet form is more stable than the yellow, but above 126° C. the reverse is the case. The precipitate of mercuric iodide is soluble in excess of either the mercuric salt or potassium iodide. 4. Potassium hydroxide, KOH, or sodium hydroxide, NaOH, gives in the cold a yelloio precipitate of mercuric oxide, HgO, insoluble in excess. 2 KOH + HgCl2 = HgO + H20 + 2 KC1. In the heat the precipitate obtained is red, but still consists of HgO. The difference in colour is due to difference in the size of the particles. 5. Ammonium hydroxide, NH4OH, gives a white pre. cipitate of mer cur ammonium chloride, NH0HgCl (infusible white precipitate)—- 2 NH4OH + HgCl2 = NH2HgCl + NH4C1 + 2 H20.