_Properties._--Usually met with in the form of solid lumps, or in cylindrical sticks, which are formed by melting the potash and running it into a mould. It always contain some atoms of water, which cannot be driven off by the application of heat. Potash is soluble almost to any extent in water, much heat being evolved. The solution is powerfully alkaline and acts rapidly upon the skin; it dissolves fatty and resinous bodies, converting them into soaps; Solution of potash absorbs carbonic acid quickly from the air, and should therefore be preserved in stoppered bottles; the glass stoppers must be wiped occasionally, in order to prevent them from becoming immovably fixed by the solvent action of the potash upon the silica of the glass. The liquor potassæ of the London Pharmacopoeia has a sp. gr. of 1·063, and contains about 5 per cent; of real potash. It is usually contaminated with _carbonate_ of potash, which causes it to effervesce on the addition of acids; also, to a less extent, with sulphate of potash, chloride of potassium, silica, etc. Potash, Carbonate of. Symbol, KO CO{2}. Atomic weight, 70. The impure carbonate of potash, termed _pearlash_, is obtained from the ashes of wood and vegetable matter, in the same manner as carbonate of soda is prepared from the ashes of seaweeds. Salts of potash and of soda appear essential to vegetation, and are absorbed and approximated by the living tissues of the plant. They exist in the vegetable structure combined with organic acids in the form of salts, like the oxalate, tartrate, etc., which when burned are converted into carbonates. _Properties._--The pearlash of commerce contains large and variable quantities of chloride of potassium, sulphate of potash, etc. A purer carbonate is sold, which is free from sulphates, and with only a trace of chlorides. Carbonate of potash is a strongly alkaline salt, deliquescent, and soluble in twice its weight of cold water; insoluble in alcohol, and employed to deprive it of water. Pyrogallic Acid. Symbol, C{8}H{4}O{4} (Stenhouse). Atomic weight. 84. The term _pyro_ prefixed to gallic acid implies that the new substance is obtained by the _action of heat_ upon that body. At a temperature of about 410° Fahr., gallic acid is decomposed, and a white sublimate forms, which condenses in lamellar Crystals; this is pyrogallic acid. Pyrogallic acid is very soluble in cold water, and in alcohol and ether; the solution decomposes and becomes brown by exposure to the air. It gives an indigo blue color with protosulphate of iron, which changes to dark green if any persulphate be present.