POTASH SALTS .

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of potash. Copper salts can be detected by dissolving the potash in hydro-chloric acid, supersaturating with ammonia, when, if copper be present, thesolution will become coloured blue.

The potash of the market is generally termed pearl-ash or American ash, orsalt of tartar. It is not largely employed in printing or dyeing; chiefly inTurkey-red dyeing for the emulsion of oil, and also as a solvent of annattoand safflower.

Nitrate of Poatsh.

This salt, K0,N05, occurs native as saltpetre; but it finds no applicationin dyeing or bleaching.

Bisulphate of Potash.

This salt, containing two equivalents of sulphuric acid to one of potash, issometimes employed as a substitute for tartaric acid in lower styles of work,but requires care, and is uncertain in its application.

Chromate of Potash.

There are two chromates of potash known, viz., the chromate, KO,CrC>3,and the bichromate, K0,2Cr03.

Bichromate or acid chromate of potash occurs in commerce in beautiful redcrystals, very easily soluble in water, and is employed in the preparation ofyellow, red, and green colours. When blue indigo is impregnated with bi-chromate of potash and treated with a solution of tartar, oxalic acid, or dilutedsulphuric acid, the chromic acid is set free, and the available oxygen convertsthe indigo into indigo-white. Isatine can be obtained similarly by treatingindigo-blue with permanganate of potash or with ferricyanide of potash andlime.

The impurities most generally occurring in bichromate of potash aresulphate of potash, chloride of potassium, and nitrate of potash. Sulphateof potash may be detected by treating the bichromate with hydrochloric acid,and adding chloride of barium, when, if any sulphate is present, a white pre-cipitate is formed. Chloride of potassium may be detected by the addition ofnitric acid, and precipitation with nitrate of silver. Nitrate of potash causesthe salt to detonate when thrown upon a red-hot plate.

Chromate of potash, or neutral chromate, crystallises in beautiful yellowcrystals, easily soluble in water. It can be prepared by adding carbonate ofpotash to a solution of the bichromate.

Oxalate of Potash.

Oxalate of potash occurs in three varieties, viz., as neutral oxalate, as acidoxalate or binoxalate, and as quadroxalate. The oxalate of potash of commerceis prepared by neutralising oxalic acid with carbonate of potash ; and it occursm white crystals, which may be rendered anhydrous by heat, and then willdissolve in three parts of water. Its chief application is found in printing.

The impurities are sulphate of potash, tartar, and metallic salts. Sulphateof potash may be dete&ed by dissolving a sample of the salt in warm water,and treating with hydrochloric acid and chloride of barium to obtain a whiteprecipitate. Nitrate of silver will yield a precipitate if chloride of potassium1S present, excess of nitric acid having previously been added. Tartar gives