Page:Collier's New Encyclopedia v. 07.djvu/466

PYBOGALLIC ACID 390 PYBRHIC PYROGALLIC ACID, in chemistry, C6H603=CaH3(OH)3, pyrogallol, an acid, discovered by Scheele. Extensively used in photography as a reducing agent. PYRO GRAPH, an apparatus for en- graving on w^ood or leather by means of a red-hot metallic point. PYROLIGNEOUS ACID, impure acet- ic acid, obtained by the destructive dis- tillation of wood. PYROLITH, or LIQUID MARBLE, a composite, plastic material that so close- ly resembles marble that no one can detect any difference. It fulfils the re- quirements of the sculptor as to durabil- ity and hardness and forms an imperish- able material, easy to work and capable of receiving every delicate line and curve of the clay model. It was discovered by George Julian Zolnay, an American sculptor, the result of years of hard work. PYROLUSITE, one of the most im- portant of the ores of manganese. Used in preparing oxygen gas, with which it parts at a red heat; and also in glass making. PYROMETER, a term originally ap- plied to an instrument in the form of a single metallic bar, employed by Mus- chenbroek about 1730, to indicate tem- peratures above the boiling point of mer- cury, 660° F. It is now applied to any instrument used for such purpose, Tremeschini's pyrometer is founded on the expansion of a thin plate of plati- num, heated by a mass of metal previ- ously raised to the temperature of the medium. The Trampler pyrometer is based on the difference in the coeffi- cients of dilatation for iron and graph- ite; the Gauntlet pyrometer on the dif- ference of those of iron and fire-clay. The Ducomet pyrometer consists of a series of rings made of alloys which have slightly different melting points. In pyrometers on the Watertype principle, the temperature is determined by notmg the amount of heat communicated to a current of water of known temperature which is kept circulating in the medium to be observed. PYROPE, in mineralogy, one of the garnet group. Color, a deep-red; trans- parent. Found associated with serpen- tines, and in streams in Bohemia. Much used in jewelry. PYROPHYLLITE, a hydrated silicate of alumina, occurring in foliated masses, which split into layers on heating. Crystallizes in the monoclinic system. The color may be either yellow or green, some specimens being almost pure white. It somewhat resembles talc, possessing a soapy feeling, and Is used in the manufacture of tailors' chalk and slate pencils. In China and Japan harder varieties are used for making small im- ages. It is found in North Carolina, (Georgia, Arkansas, Brazil, Sweden and the Urals. PYROSCOPE, an instrument, invented by Leslie, to measure the intensity of heat radiating from a hot body or the frigorific influence of a cold body. The instrument is like a differential ther- mometer, one ball being covered with thick silver-leaf; the other ball is naked and forms the pyroscope. PYROSOMA, the sole genus of Pyro- somidse, a family of Tunicata, with three species. They are brilliantly phosphor- escent, and Peron compared them to small incandescent cylinders of iron. PYROTECHNY, in the proper sense, the science which teaches the manage- ment and application of fires. In the more popular sense, however, the word chiefly refers to the art of making fire- works. The principal ingredients used are purified saltpeter, sulphur, and char- coal. PYROXENE, a name used for a group of minerals of very variable composition and origin, but all of which are refer- able (like the analogous group of am- phiboles) to the same chemical type, under the general formula ROSiOs, where R may represent lime, magnesia, the protoxides of iron and manganese, and sometimes soda, potash, and oxide of zinc. Two or more of these bases are always present, the most frequent being lime, magnesia, and protoxide of iron, lime being always present and in a large percentage. PYROXYLIC SPIRIT, WOOD SPIRIT, or WOOD NAPHTHA, a mix- ture of acetone, methyl-alcohol, acetate of methyl, etc., obtained by the destruc- tive distillation of wood in the manufac- ture of PYROLIGNEOUS ACID {q. V.) . It is of nearly equal value to alcohol in making varnishes, as it dissolves the resins, oils, and other similar substances. It is used in making Methylated Spirit {q. v.). PYROXYLIN, a form of nitrocellulose, produced by the action of a mixture of sulphuric and nitric acids, slightly dilut- ed with water, on cotton. Soluble in a mixture of alcohol and ether. This so- lution, on evaporating, leaves a film of collodion. Pyroxylin is largely used in photography. (See Nitrocellulose). PYRRHIC, a species of warlike dance, which is said to have been invented by Pyrrhus to grace the funeral of his