_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 contains one atom 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 (p. 308), 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 Pharmacopœia 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 (see page 196). PYROGALLIC ACID. Symbol, C{8}H{4}O{4} (Stenhouse). Atomic weight, 84. The chemistry of Pyrogallic Acid has been described at page 28. SEL D'OR. _See_ Gold, Hyposulphite of. SILVER. Symbol, Ag. Atomic weight, 108. This metal, the _Luna_ or _Diana_ of the alchemists, is found native in Peru and Mexico; it occurs also in the form of Sulphuret of Silver. When pure it has a sp. gr. of 10·5, and is very malleable and ductile; melts at a bright red heat. Silver does not oxidize in the air, but when exposed to an impure atmosphere containing traces of Sulphuretted Hydrogen, it is slowly tarnished from formation of Sulphuret of Silver. It dissolves in Sulphuric Acid, but the best solvent is Nitric Acid. The standard coin of the realm is an alloy of Silver and Copper, containing about one-eleventh of the latter metal.