Aluminum salts are generally colourless, soluble, and crystallise with difficulty, and are distinguished as follows:—
Tests.—1. Ammonia and the alkaline carbonates throw down a bulky white precipitate (hydrate of aluminum) from solutions of its salts, which is insoluble in excess of the precipitant.—2. Pure potassa and soda throw down white gelatinous precipitates, freely soluble in excess of the precipitant; from which the hydrate of aluminum is reprecipitated by chloride of ammonium, even in the cold:—3. Phosphate of ammonium gives a white precipitate—4. Iodide of potassium produces a white precipitate, passing into a permanent yellow:—5. Sulphuretted hydrogen gives no precipitate:—6. Sulphydrate of ammonium precipitates alumina from these solutions:—7. Bisulphate of potassium, added to concentrated solutions, gives a precipitate of octahedral crystals of alum:—8. At a red heat its salts part with some of their acid; at a white heat, most of it, if not all:—9. Aluminum compounds, ignited on charcoal before the blowpipe, and afterwards moistened with a solution of nitrate of cobalt and again strongly ignited, give an unfused mass, which, on cooling, appears blue by day, and violet by candlelight; a test, however, which is inapplicable to fusible compounds of aluminum, and such as are not free, or nearly free, from other oxides.
Aluminum, Acetate of. Syn. Acetate of Alumina. Prep. Pure hydrate of aluminum is digested, to saturation, in strong acetic acid, in the cold; and the resulting solution, after being filtered or decanted, is either evaporated by a very gentle heat to a gelatinous, semi-solid consistence (its usual form), or is preserved in the liquid state. By spontaneous evaporation it may be obtained in long, transparent crystals.
Red liquor. From alum, in powder, 4 parts; warm water, q. s. to dissolve; acetate of lead, in powder, 3 parts; the solution and mixture being effected by lengthened agitation in a tub or other wooden vessels, and the clear liquid, after repose for a sufficient time, decanted or drawn off from the sediment.
From alum, 2 parts; (dissolved in) warm water, q. s.; solution of pyrolignite of lime (20° Baumé), 3 parts; as before, but allowing a longer time for the subsidence of the precipitate, and taking more care in the decantation than when acetate of lead is employed.
By decomposing a solution of crude sulphate of alumina with neutral or monobasic acetate of lead.
Prop. Its characteristic property is the feeble affinity existing between its acid and base, which, when it is used as a mordant, is counterbalanced by that of the fibres of the cloth or yarn to which it is applied. In other respects it resembles the other simple salts of alumina.
Uses, &c. In dyeing and calico printing, as a mordant. In medicine, properly diluted, in chronic diarrhœa; and, mixed with syrup of poppies, in slight cases of hæmoptysis (spitting of blood). It has been employed by M. Gannal as an injection to preserve animal bodies, which it will do for years.—Dose, 1⁄2 to 1 dr. daily, in divided portions, taken in thin mucilage or syrup, or in barley-water; as an injection, 10 to 20 gr., to water, 4 to 6 fl. oz., in gonorrhœa, leucorrhœa, &c.
Aluminum, Chloride of. Al2Cl6. Syn. Sesquichlo′′ride of Aluminum; Alumin′ii Chlori′di, &c., L. Prep. A thick paste made of dry precipitated alumina, lampblack, and oil, is strongly heated in a covered crucible until all the organic matter is carbonised. The residuum is transferred to a porcelain tube fixed across a furnace, one end of which is connected with another tube containing dry chloride of calcium, and the other end with a small tubulated receiver. The porcelain tube is then heated to redness, whilst chlorine, dried by passing through the chloride-of-calcium tube, is transmitted through the apparatus. In one or two hours, or as soon as the tube is choked, the whole is allowed to cool, and the newly-formed SESQUICHLORIDE collected and preserved in mineral naphtha for use.
On the large scale:—Chlorine, dried as before, is passed over a mixture of pure clay, lamp-black, and coal-tar, contained in an iron retort, similar to that used in the manufacture of coal-gas (previously ignited by means of a suitable furnace), and connected with a cool chamber accurately lined with tiles of earthenware. The vapours of the SESQUICHLORIDE condense in this chamber, as a yellowish crystalline mass, which is collected and preserved as before.