Prepared in an impure condition as a white, very infusible, hard metal, by igniting the oxide with charcoal, at a white heat, in a lime crucible.
Chromous Chloride. CrCl2. Syn. Protochloride. Prep. Ignite the chromic chloride in a current of dry hydrogen. A white, foliated mass, soluble in water (evolving much heat), and yielding a blue solution, which absorbs atmospheric oxygen with astonishing rapidity, acquiring a deep-green colour, and passing into the state of oxychloride of chromium. It is the most powerful reducing or deoxidising agent known.
Chromic Chloride. Cr2Cl6. Syn. Sesquichloride. Prep. Pass dry chlorine over a mixture of sesquioxide of chromium and charcoal, heated to redness, in a porcelain tube. The chloride collects as a sublimate, of a peach or violet colour, in the cool part of the tube.
Dissolve chromic oxide in hydrochloric acid and evaporate to dryness; the residue is chromic chloride. It forms a dark green mass, containing water, which is evolved by igniting at a temperature of 400°, turning a purplish red.
Chromium Oxides:—
Chromous Oxide. CrO. Syn. Protoxide of chromium. This oxide has not yet been obtained in a satisfactory manner, but the hydrate is prepared by the addition of potassium
hydrate solution to a solution of chromous chloride or sulphate. A brownish-red powder, speedily passing to a deep foxy-red, with disengagement of hydrogen, and forming pale blue-coloured salts with the acids, which absorb oxygen with avidity, whilst the metal passes into a higher state of oxidation.
Chromic Oxide. CrO3. Syn. Sesquioxide. Prepared by igniting potassium bichromate at a red heat and well washing the residue, and as hydrate by cautiously adding equal parts of hydrochloric acid and alcohol or sugar to a boiling solution of chromate of potassa in water, in small portions at a time, until the red tint disappears, and the liquid assumes a green colour; pure ammonia, in excess, is next added, and the precipitate which subsides is collected and washed with water.
Prop., &c. The anhydrous oxide is a rich crystalline, green powder, insoluble in both water and acids; fused with borax and glass, it imparts a beautiful green colour.
The hydrate is soluble in the acids and in alkaline lyes; with the first it forms salts which have a green or purple colour. These compounds may be made by direct solution of the hydrate in the dilute acids. Chromic sulphate combines with the sulphates of potassium and ammonium, giving rise to salts (CHROME ALUMS) which crystallise in magnificent octahedrons of a deep claret colour. The finest crystals are obtained by spontaneous evaporation.