Grouping of the Rare Metals.

148. PRECIPITATED IN SILVER GROUP.

Tungsten (as Tungstic Acid), Thallium (as Chloride).

PRECIPITATED IN COPPER GROUP.

Palladium, Rhodium, Osmium, Ruthenium.

PRECIPITATED IN ARSENIC GROUP.

Gold, Platinum, Iridium, Molybdenum, Tellurium, Selenium.

PRECIPITATED IN IRON GROUP.

Uranium, Indium (Thallium), as sulphides; Beryllium, Zirconium, Cerium, Lanthanum, Didymium, Titanium, Tantalum, as hydrated oxides.

PRECIPITATED AS SULPHIDES ON ADDING HCl TO THE FILTRATE FROM THE IRON Group.

Vanadium (Tungsten).

FOUND IN POTASSIUM GROUP.

Lithium, Cæsium, Rubidium.

Reactions of the Rare Metals of the Silver Group.

149. TUNGSTEN. W, c.w. 184.

1. HCl produces a white precipitate of Tungstic acid H2WO, insoluble in excess, but soluble in (NH)HO. H2SO4 or HNO3 produces the same precipitate.

2. (NH4)2S does not precipitate tungstates of the alkalies, until an acid be added, when tungsten trisulphide WS, is precipitated as a light brown powder.

3. K4Fe(CN)。 in acid solutions yields a reddish brown coloration, and on standing, a precipitate of the same colour.

4. SnCl, produces a yellow precipitate. On adding HCl and heating, the precipitate becomes blue.

5. Zn in presence of phosphoric acid produces a bright blue colour.

6. With microcosmic salt in the reducing flame a blue bead is obtained, which changes to red on heating with FeSO4.

150. THALLIUM. Tl, c.w. 204.

1. HCl in strong solutions produces a white precipitate of TICI, soluble in a large quantity of water.

2. (NH4)2S produces a black precipitate of TS, insoluble in (NH4)HO, but soluble in HCl, H2SOμ and HNO3

3. KI precipitates TII (yellow) even in dilute solutions.

4. PtCl precipitates a double chloride of thallium and potassium Tl,PtCl of an orange colour.

5. Zn added to thallium solutions precipitates the metal.

6. Thallium salts colour the lamp flame intensely green.

Reactions of the Rare Metals of the Copper Group.

151. PALLADIUM. Pd, c.w. 106'6.

1. H2S precipitates PdS as a black powder, insoluble in (NH4)2S, and soluble in boiling HCl and aqua regia.

2. Hg(CN), precipitates palladium cyanide, Pd(CN)2, yellowish white and gelatinous, soluble in (NH)HO and in HCI.

3. KI produces a black precipitate of PdI.

4. KCl in strong solutions precipitates K,PdCl in yellow needles, insoluble in absolute alcohol, but soluble in water, forming a dark-red fluid.

152. RHODIUM. Rh, c.w. 104'4.

1. H,S precipitates Rh2S, (brown), especially in warm solutions ; it is insoluble in (NH4)2S, but soluble in hot HNO3.

2. KHO produces a yellowish precipitate of Rh(HO), H2O, soluble in excess of the reagent; on boiling the solution, brown Rh(HO), is precipitated.

3. Zn produces a precipitate of metallic rhodium.

4. Dry compounds when ignited in a current of hydrogen are reduced to metal, insoluble in aqua regia, but soluble on fusing with HKSO.

153. OSMIUM. Os, c.w. 199°2.

1. H2S in presence of acid precipitates OSS (brownish black), insoluble in (NH4)2S.

2. OsO4 (osmic acid) decolorizes indigo solution. 3. KI is decomposed with liberation of iodine. 4. Na2SO, yields a violet coloration, and after a time OSSO, (deep blue) separates out.

5. FeSO4 precipitates black OsOg

6. Zn in presence of acids precipitates the metal. 7. Dry compounds when ignited in a current of hydrogen are reduced to metal.

8. The metal and the mono- and di-oxides, when heated in air, yield OsO4, which is recognized by its peculiar irritating smell (resembling chlorine). This is an exceedingly characteristic reaction.

154. RUTHENIUM. Ru, c.w. 104'4.

1. H2S produces no immediate precipitate, but on standing, the solution turns blue, and brown Ru,S, is precipitated.

2. (NH4)2S precipitates Ru,S,, difficultly soluble in

excess.

3. KHO precipitates black sesquioxide Ru(HO), insoluble in excess, but soluble in acids.

4. KCNS in pure solutions produces on standing, a red coloration, which becomes first purple, and then on heating violet.

5. Zn produces a blue coloration, and ultimately the metal separates out.

Reactions of the Rare Metals of the Arsenic Group.

155. GOLD. Au, c.w. 197.

1. H&S produces in cold solutions black Au2S, in hot solutions brown Au2S. Both precipitates are insoluble in HNO, and in HCl, but dissolve in aqua regia. They dissolve in yellow, but not in colourless ammonium sulphide.

2. (NH4)2S produces a black precipitate of Au,S3. 3. (NH4)HO in strong solutions precipitates ammonium aurate (fulminating gold).

4. FeSO4 produces a precipitate of the metal, as a brown powder, which, when rubbed, assumes a yellow colour and metallic lustre.

5. KNO, also produces a precipitate of the metal.

6. SnCl,+SnCl produce a purplish precipitate (purple of Cassius) even in highly dilute solutions; the precipitate is insoluble in HCI.

7. Heated on charcoal with Na,CO, before the blowpipe, malleable yellow beads of the metal are obtained. (See also flame reaction, 59.)

156. PLATINUM. Pt, c.w. 197 ̊5.

1. H&S produces in cold solutions on standing, brown PtS2; on heating, the precipitate forms at once. It is soluble in a large excess of yellow ammonium sulphide ; it is insoluble in HCl and in HNO3, but soluble in aqua regia.

2. (NH4)2S produces the same precipitate as H,S.