_Potass_ in its caustic state, as usually met with in the shops, forms little gray-coloured cylinders or cakes which have a radiated, crystalline fracture, and an excessively acrid caustic taste, and feel soapy if touched with the wet finger. It deliquesces rapidly in moist air, and then attracts carbonic acid from the atmosphere. It is easily fused by heat, and is exceedingly soluble in water. The solution has a strong alkaline reaction on vegetable colours, restoring reddened litmus to blue, turning syrup of violets or infusion or red cabbage to green, and rendering infusion of turmeric brown. It is distinguished from the alkaline earths when in solution, by not precipitating with carbonic or sulphuric acid, and from soda by the tests to be presently mentioned for its carbonate. _Carbonate of potash_ [subcarbonate, salt of tartar], is usually sold, when pure, in small white grains, formed by melting the salt and stirring it rapidly as it cools. In its impure state it is called in this country potashes, and when somewhat purified, pearl ash. It has then a mixed grayish, yellowish, or bluish colour, and is sold in crumbly lumps of various sizes. In every state it is deliquescent and very caustic. It cannot be crystallized. It gives out carbonic acid gas with the addition of any stronger acid, such as sulphuric, muriatic, or acetic acid. Its solution precipitates yellow with the chloride of platinum, gives a crystalline precipitate with perchloric acid, when the salt forms not less than a fortieth or fiftieth part,—is similarly acted on by a considerable excess of tartaric acid, if the salt constitute about a thirtieth of the fluid,—and yields with the soluble salts of baryta a white precipitate soluble in nitric acid.