PYRO′LA. See Winter green.
PYROLIG′NEOUS ACID. Syn. Vinegar of wood†, Spirit of w.†, Smoking liquor†, Essence of smoke†; Acidum pyrolignosum, L. Impure acetic acid, obtained by the destructive distillation of wood in close vessels. It comes over along with tar creasote, and other liquid and gaseous matters. In this state it contains much empyreumatic matter in solution; but by separation from the tar, saturation with slaked lime or chalk, defecation, and evaporation, an impure acetate of pyrolignate of lime is obtained, which, after being gently heated, to destroy part of its empyreumatic matter, without injuring its acetic acid, is again dissolved and defecated, and then precipitated by a solution of sulphate of soda, when a solution of acetate of soda and a precipitate of sulphate of lime are formed by double decomposition. The solution is next evaporated to dryness, the dry mass (pyrolignite of soda) dissolved in water, and the new solution filtered and recrystallised. The crystals of acetate of soda, obtained by the last process, yield nearly pure acetic acid by distillation along with sulphuric acid. See Acetic acid and Vinegar.
PYROLIG′NEOUS SPIRIT. See Spirit (Pyroxilic).
PYROM′ETER. An instrument to measure high degrees of heat. Wedgwood’s pyrometer, the one best known, depends on the property which clay possesses of contracting when strongly heated. Prof Daniel’s pyrometer
consists, essentially, of a small rod or bar of platinum, which acts in a precisely opposite manner to the preceding, viz., by its expansion.
PYROPH′ORUS. Syn. Luft-Zunder, Ger. Any substance that inflames spontaneously when exposed to the air.
Prep. 1. Neutral chromate of lead, 6 parts; sulphur, 1 part; triturate them with water, q. s. to form a paste, and make this into pellets; dry these perfectly by a gentle heat, then heat them in a closed tube until the sulphur is all driven off; lastly, transfer them to a stoppered phial.
2. (Homberg’s pyrophorus.) From alum and brown sugar, equal parts; stir the mixture in an iron ladle over the fire until dry, then put it into an earthen or coated glass phial, and keep it at a red heat so long as the flame is emitted; it must then be carefully stopped up and cooled.
3. (Dr Hare.) Lampblack, 3 parts; burnt alum, 4 parts; carbonate of potassa, 8 parts; as the last.
4. (Gay Lussac.) From sulphate of potassa, 9 parts; calcined lampblack, 5 parts; as No. 2.