Reactions of the Metals of the Silver Group.†

63. Metals whose chlorides are insoluble in water, and which are precipitated on addition of the group reagent, HC1:

Silver, Mercury, Lead.

SILVER. Ag, combining weight 103.

1. HCl produces a white curdy precipitate of AgCl, insoluble in hot water and in HNO3, but readily soluble in (NH1)HO.

2. H2S, or (NH4)2S, produces a black precipitate of Ag2S, soluble in boiling HNO3, with separation of sulphur.

3. NaHO produces a light brown precipitate of Ag2O, insoluble in excess of NaHO, but soluble in (NH4)HO.

*4. K2CrO4 produces a dark red precipitate of Ag2CrO4, soluble in hot HNO3; this solution deposits on cooling an acid chromate in needle-shaped crystals.

5. KI produces a pale yellow precipitate of Agl insoluble in HNO3.

6. Heated on charcoal with Na2CO3, in the reducing flame of the blow-pipe, yields bright, malleable metallic beads, soluble in HNO3 (56, a).

64. MERCURY. Hg, c.w. 200. Mercurous Salts. 1. HC produces a white precipitate of Hg,Cl2 (calomel), insoluble in cold HNO3, and blackened by (NH4)HO, from formation of Hg2Cl(NH2).

The best confirmatory tests are indicated in the following pages by an asterisk.

2. H2S, or (NH4)2S, produces a black precipitate of Hg2S, not dissolved by boiling HNO3.

3. NaHO produces a black precipitate of Hg2O, insoluble in excess of NaHO or (NH4)HO.

*4. SnCl2 produces a grey precipitate of Hg. If the fluid be poured off and the residue boiled with HCl, distinct globules are obtained.

5. KI

Hg2l2.

produces a dark green precipitate of

6. K2CrO4 produces an orange precipitate of mercurous chromate.

7. If a drop of neutral or only slightly acid solution of a mercurous salt be placed on a bright piece of copper, metallic mercury is deposited and the stair. becomes bright on rubbing: it disappears on heating, owing to the volatility of the mercury.

8. Heated in a small tube with NaHCO3, yields grey deposit of Hg, which on rubbing appears in distinct globules (59).

65. LEAD. Pb, c.w. 207.

1. HCl produces a white precipitate of PbCl, which is converted into a basic salt on adding ammonia, but without change of appearance. PbCl is soluble in a small quantity of hot water, or in a large quantity of cold water.

2. H2SO produces a heavy white precipitate of PbSO4, soluble in NaHO. In dilute solutions this precipitate appears only on standing; if therefore there is no immediate precipitation, the solution should be concentrated by evaporation. PbSO4 is soluble in boiling HCl, and the solution on cooling deposits needle-shaped crystals of PbCl

3. K2CrO4 produces a bright yellow precipitate of PbCrO4, readily soluble in NaHO, but with difficulty in HNO3.

*4. KI produces a bright yellow precipitate of PbI, soluble in boiling water; the solution on cooling deposits the salt in brilliant golden hexagonal scales.

5. Heated on charcoal with NaHCO3, yields malleable beads, and at the same time a yellow incrustation of PbO on the charcoal (56, a).

TABLE C.

SILVER GROUP (I.).

66. Separation of Silver, Mercury, and Lead.

Add HCl and filter from the precipitated chlorides.

PRECIPITATE.

FILTRATE.

Groups II., III., IV. & V.

AgCl, Hg2Cl2, PbCl

Wash precipitate twice with cold water, and add washings to filtrate, then twice with hot water, and test part of this for lead with dilute H2SO4. White precipitate indicates Lead. Boil the remaining part down to obtain the needle-shaped crystals of PbCl. If lead be found, wash the precipitate free from it with hot water, and treat the residue repeatedly with warm (NH4)HO; filter.

Reactions of the Metals of the Copper Group.

67. Metals whose sulphides are insoluble in HCl and are precipitated in presence of that acid by the group reagent H2S.

Mercury, Lead, Bismuth, Copper, Cadmium, Arsenic, Antimony, and Tin.

SUB-GROUP A.-Sulphides of the above metals insoluble in (NH4)2S2, viz., Mercury, Lead, Copper, Bismuth, and Cadmium.

MERCURY. Hg, c.w. 200. Mercuric Salts.

1. H2S produces, when added by degrees, first a white precipitate, which changes to orange, then to brownish red, and finally to a black precipitate of HgS. These successive changes of colour on the addition of H&S are exceedingly characteristic. This precipitate is insoluble in HCl and in HNO3, even on boiling; it is soluble, however, in KHS and in aqua regia.

2. KHO produces a yellow precipitate of HgO, which is insoluble in excess of the precipitant, except when added to very acid solutions.

3. (NH)HO produces in solutions of HgCl, a white precipitate of HgCl(NH2) ("white precipi tate").

*

4. SnCl, produces, when added in small quantities, a white precipitate of HgCl2, but on adding an excess of the reagent, metallic mercury precipitates as a grey powder, and may be united into a coherent globule by boiling with HCl.

5. KI produces a bright red precipitate of Hgl, soluble in excess either of KI or of HgCl2.

6. Reactions 6 and 7 for mercurous salts (64) are also produced with mercuric salts.

68. LEAD. Pb, c.w. 207.

1. H2S produces a black precipitate of PbS, even in solutions of PbCl2, so that a weak solution of a lead salt which has not been precipitated with HCl will be precipitated with HS. Hence lead occurs both in

the silver and copper groups.

2. Reactions 2, 3, 4, and 5, for lead, in Group I. (65), are also applicable in this group.

69. BISMUTH. Bi, c.w. 210.

1. H2S produces a black precipitate of Bi2S„, insoluble in KHS and KHO, but soluble in HNO3.

2. KHO or (NH4)HO produces a white precipitate, which on boiling becomes yellow (Bi2O3); the precipitate is insoluble in excess of either reagent.

* 3. H2O, when added in considerable quantity to normal salts of bismuth, produces an immediate white precipitate of a basic salt of bismuth.

Bismuth trichloride is most easily precipitated by H2O. If another salt of this metal is being examined, it is best to precipitate the oxide first by ammonia;