GROUP II. (COPPER GROUP.)

Group reagent, H2S in presence of HCl.

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

The sulphides of the metals of this group are insoluble in HCl, and are therefore precipitated by H2S in an aqueous solution containing HCl. The three last metals, arsenic, antimony, and tin, form a subgroup, as their sulphides are soluble in (NH4)2S2, whilst the sulphides of the remaining metals are insoluble in that reagent.

GROUP III. (IRON GROUP.)

Group reagent, (NH4)2S, in presence of NH4Cl and (NH4)HO.

Iron, Nickel, Cobalt, Zinc, Aluminium, Manganese, and Chromium.

The sulphides and hydrated oxides of the metals of this group are insoluble in water, and are therefore precipitated on addition of the group reagent. Aluminium and chromium are precipitated as hydrated oxides, the others as sulphides.

GROUP IV. (BARIUM GROUP).

Group reagent, (NH4)2CO3, in presence of (NH1)HO and NH4Cl.

Barium, Strontium, Calcium:

The carbonates of the metals of this group are insoluble in water, and are precipitated on the addition of (NH4)2CO3; as, however, they are soluble in acids, (NH4)HO must be added when the solution is acid.

GROUP V. (POTASSIUM GROUP.)

Metals unprecipitated by the above group reagents. Magnesium, Potassium, Sodium, Ammonium.

These metals have no common precipitant, and are therefore distinguished by individual tests.

The student should at first have several metallic salts given to him, and be asked merely to determine to which of the above groups each salt belongs; he ought next to make himself familiar with the individual tests for each metal which follow, and then proceed to the separations of the different metals. It will also be well for him to attempt to frame a table of separations for each group before consulting those given in the book.

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 108.

1. HCl produces a white curdy precipitate of AgCl, insoluble in hot water and in HNO3, but readily soluble in (NH4)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 (NH,)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. 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. HCl produces a white precipitate of HgCl2 (calomel), insoluble in cold HNO3, and blackened by (NH4)HO, from formation of Hg2Cl(NH2).

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

3. NaHO produces a black precipitate of Hg,2O, insoluble in excess of NaHO or (NH1)HO.

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

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

6. 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. H2SO4 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 HNO

4. KI produces a bright yellow precipitate of PbI soluble in boiling water; the solution on cooling deposits the salt in briliant 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.

AgCl, HgCl2, PbC12.

FILTRATE.

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

Wash precipitate twice with cold water, and add washings to filtrate; then twice with hot water, and test part of this for lead with H2SO. White precipitate indicates Lead. Boil the remaining part down to obtain the needle-shaped crystals of PbCl2. If lead be found, wash the precipitate free from it with hot water, and treat the residue with warm (NH4) HO; filter.