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.

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    of nickel sulphide, NiS : slightly soluble in excess if yellow ammonium sulphide is used, producing a dark brown liquid. (NH4)2$ + NiS04 = NiS + (NH4)2S04. The precipitate is insoluble in acetic acid and practically so in dilute HC1. It dissolves slowly in hot concentrated HC1, rapidly in HC1 + a crystal of KC103, and in aqua regia. If acetic acid is added to the black liquid referred to above the dissolved nickel sulphide is reprecipitated. 2. Potassium hydroxide, KOH, or sodium hydroxide, NaOH, gives an apple-green precipitate of Ni(OH)2. 2 KOH + NiS04 = Ni(OH)2 + K2S04. The precipitate is insoluble in excess. 3. Ammonium hydroxide, NH4OH, produces in neutral solution the same precipitate which, however, dissolves in excess of the reagent to a blue liquid, containing the com¬ pound NiS04,4NH3. The precipitate is not formed in the presence of NH4C1 or other ammonium salts. On this account there is no precipitate when ammonium hydroxide is added to an acid solution of a nickel salt; an ammonium salt is formed and prevents the precipitation. 4. Potassium cyanide, KCN, gives a yellowish-green precipitate of nickel cyanide, Ni(CN)9: soluble in excess, giving a brownish-yellow solution, containing a double cyanide of nickel and potassium, K2Ni(CN)4. 2 KCN + NiS04 = Ni(CN)2 + K2S04. 2 KCN + Ni(CN)2 = K2Ni(CN)4. The solution undergoes no change when boiled in air. On adding caustic soda and bromine (i.e., NaOBr)* or * When bromine is added to caustic soda in the cold sodium hypobromite, NaOBr, is formed: 2 NaOH + Br2 = NaBr + NaOBr + H20.
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