dissolve it in as little HCl as possible, and evaporate it almost to dryness. On adding water to this solution, a precipitate of BiOCl at once forms, which is insoluble in tartaric acid (compare corresponding reaction with antimony, 74, 4). Solutions of bismuth salts containing much free acid do not give this reaction with H2O until the excess of acid has been expelled by evaporation. 4. K2CrO4 produces a yellow precipitate of Big(CrO4)39 soluble in HNO3, and insoluble in NaHO. (Compare reaction for lead, 65, 3.) 5. Heated on charcoal with NaHCO in the reducing flame of the blow-pipe, yields brittle metallic globules; also a slight yellow incrustation of oxide on the charcoal. 70. COPPER. Cu, c.w. 63'5. 1. HS produces a black precipitate of CuS, soluble in HNO3, but insoluble in KHS, and only slightly soluble in (NH4)2S2. CuS is also dissolved by KCN, but is insoluble in hot dilute H2SO4 2. KHO produces a pale blue precipitate of Cu(HO)2, insoluble in excess of the precipitant. If the KHO be added in excess and the mixture boiled, the precipitate becomes black and loses water. 3. (NH4)HO produces, when added in small quantities, a greenish blue precipitate of a basic salt, soluble in excess to a dark blue solution, which consists of a double basic salt of copper and ammonium. 4. K4Fe(CN), produces a brown precipitate of Cu,Fe(CN)6, insoluble in dilute acids, but decomposed by KHO. 5. Fe precipitates copper in the metallic state, from its solutions, especially in presence of a little free acid. The iron ought to be bright and clean. 6. Zn also precipitates copper solutions. If a solution of copper containing a few drops of HCl be placed in a platinum capsule, and a fragment of zinc added, the copper will be precipitated on the platinum as a red coating. 7. Compounds of copper, when heated in the Bunsen lamp flame, impart a green colour to it, especially after addition of AgCl. 8. Mixed with NaHCO3 + KCN and heated on charcoal before the reducing blow-pipe flame, yields bright red metallic particles, soluble in HNO„ and giving a deep blue solution on adding (NH)HO. 71. CADMIUM. Cd, c.w. 112. 1. H2S produces a yellow precipitate of CdS, soluble in HNO3, but insoluble in KHS, in (NH4)2S, and in KCN. CdS is dissolved by hot dilute H2SO4. (Compare reaction for copper, 70, 1.) 2. KHO produces a white precipitate of Cd(HO)2, insoluble in an excess of the precipitant. 3. (NH1)HO also precipitates Cd(HO)2, but the precipitate is soluble in excess. 4. Heated on charcoal with NaHCO3 in the reducing blow-pipe flame, yields no metallic bead, but a brown incrustation of CdO. 72.-COPPER GROUP (II.). TABLE D. Separation of Mercury, Lead, Bismuth, Copper, and Cadmium (Sub-Group A). To the filtrate from the Silver Group add an equal bulk of HCl, boil down nearly to dryness, dilute with H2O, and pass H2S through the hot solution. Filter. KESIDUE. FILTRATE. HgS, PbS, Bi2S3, CuS, CdS, SnS, SnS2, Sb2S3, and As2S3. Groups III., IV., and V. Wash with hot H2O containing H2S, until free from Cl; digest residue with (NH4)2S2 for about fifteen RESIDUE. HgS, PbS, Bi2S3, CuS and CdS. Wash with hot H2O till no longer alkaline; add a small quantity of boiling HNO3, pouring it on several times. Filter. RESIDUE. Hgs. Dissolve in aqua regia, boil down to expel acid, and test with SnCl2. White precipitate changing to grey indicates Mercury. Confirm by reduction test, or Bunsen's test for mercury (59). FILTRATE. Pb, Bi, Cu, Cd. Add H2SO4, and boil down. White precipitate indicates Lead. Filter from PbSO4, and add (NH4)HO to filtrate. Filter. METHOD I. Add to the blue solution KCN till colourless; pass a few bubbles of H2S through the solution. Yellow precipitate indicates Cadmium. (Excess of H2S must be avoided, because traces of mercury may be present.) METHOD II. Add HCl till acid; pass H2S through; filter; wash rapidly and thoroughly, and treat with hot dilute H2SO4. Black residue indicates Copper. To filtrate, add H2S. Yellow precipitate indicates Cadmium. 73. SUB-GROUP B.-Sulphides soluble in (NH4)2S viz., those of Tin, Antimony, and Arsenic. TIN, Sn, c.w. 118. Stannous Salts. 1. HS produces a dark brown precipitate of SnS, soluble in (NH4)2S1⁄2 (yellow), but nearly insoluble in (NH4)2S (colourless). From its solution in (NH4)2S2 it is re-precipitated as SnS, (yellow) on adding HCl. SnS is also soluble in KHO, and, on the addition of acids, is re-precipitated as SnS (brown). 2. KHO produces a white precipitate of Sn (HO), soluble in excess of the reagent. 3. (NH)HO also produces a precipitate of Sn(HO), but not soluble in excess. 4. HgCl2 produces at first a white precipitate of HgCl2, and on boiling with excess of the reagent, a grey precipitate of Hg. 5. AuCl, produces a purple precipitate (purple of Cassius) on addition of a little HNO3. 6. Zn produces a precipitate of metallic tin, in shining laminæ or as a spongy mass. 7. Mixed with NaHCO3 + KCN and heated on charcoal in the reducing blow-pipe flame, yields small globules of Sn and a white incrustation of SnO2 Stannic Salts.—1. H2S produces a yellow precipitate of SnS2, soluble in (NH4)2S, in KHO, and in boiling concentrated HCl. It is with difficulty soluble in (NH1)HO, and insoluble in (NH4)2CO3. 2. KHO or (NH4)HO produces a white precipitate of SnO(HO)2, soluble in an excess of the precipitant. |