Page:EB1911 - Volume 22.djvu/709

Rh Ohio a quantity of pyrites is obtained as a by-product in coal mining. Newfoundland yields cupreous pyrites, worked at Pilley's Island, whilst the nickeliferous pyrites of Sudbury in Ontario is partly magnetic (see ). Magnetic pyrites of commercial importance occurs also in Virginia and Tennessee. The United Kingdom yields but little pyrites, the annual output being not more than about 10,000 tons. Large quantities of “ sulphur ore ” were, however, formerly worked in the Vale of Avoca, Co. Wicklow, Ireland. Finely crystallized specimens of pyrite are obtained from many other localities, especially from Cornwall, Elba and Traversella, near Ivrea, in Piedmont.

See, for the early history of pyrites, J. F. Henkel's Pyritologia, oder Kieshistorie (Leipzig, 1725); of which an English translation appeared in 1757, entitled Pyritologia; or a History of the Pyrites, the Principal Body in the Mineral Kingdom. For a modern description of the deposit of pyrites of economic importance reference may be made to A Treatise on Ore Deposits, by J. A. Phillips (2nd ed. by H. Louis, 1896). For chemical means of distinguishing pyrite from marcasite consult H. N. Stokes, “ On Pyrite and Marcasite," Bull. U. S. Geol. Surv. No. 186 (1901).

PYRITZ, a town of Germany, in the Prussian province of Pomerania, 16 m. S.W. of Stargard by the railway to Ciistrin. Pop. (1905), 8600. It is still surrounded by walls with towers, and has two Evangelical churches. There are small manufactures of machinery, bricks and sugar. Excellent wheat is grown in the vicinity, while another industry is the breeding of cattle. Near the town is a fountain, erected to mark the spring in which Otto, bishop of Bamberg, baptized the first Pomeranian converts to Christianity in 1124. Pyritz became a town in 1150.

PYROCATECHIN, or, ortho-dioxybenzene, C6H4(OH)2, first prepared in 1839 by H. Reinsch on distilling catechin (the juice of Mimosa catechu); occurs free in kino and in beechwood tar; its sulphonic acid is present in the urine of the horse and man. It results in the alkaline fusion of many resins, and may be prepared by fusing ortho-phenolsulphonic acid, o-chlorphenol, o-bromphenol, and o-phenoldisulphonic acid with potash, or, better, by heating its methyl ether, guaiacol, C6H4(OH)(OCH3), a constituent of beechwood tar, with hydriodic acid.

Pyrocatechin crystallizes in white rhombic prisms, which melt at 104° and boil at 245°; it is readily soluble in water, alcohol and ether. Ferric chloride gives a green coloration with the aqueous solution, whilst the alkaline solution rapidly changes to a green and finally to a black colour on exposure to the air. It reduces silver solutions in the cold and alkaline copper on heating.

Guaiacol may be obtained directly from beechwood tar, from pyrocatechin by methylation with potash and potassium methyl sulphate at 180°, or from anisol by nitration, reduction of the ortho-nitroanisol to amino-anisol, which is then diazotized and boiled with water. It melts at 28° and boils at 250°. It is employed in medicine as an expectorant. The dimethyl ether or veratrol is also used in medicine. Many other pyrocatechin derivatives have been suggested for therapeutic application. Guaiacol carbonate is known as duotal, the phosphate as phosphatol, the phosphate as guaiaco-phosphal; phosphotal is a mixture of the phosphates of crcosote phenols. The valerianic ester of guaiacol is known as geosote, the benzoic as benzosol, the salicylic as guaiacolsalol, while the glycerin ether appears as guaiamar.

Pyrocatechin readily condenses to form heterocyclic compounds; cyclic esters are formed by phosphorus trichloride and oxychloride, carbonyl chloride, sulphuryl chloride, &c.; whilst ortho-phenylenediamine, o-aminophenol, and o-aminothiophenol give phenazine, phenoxazine and thiodiphenylamine.

 PYROGALLOL, or, a trioxybenzene, C6H3(OH)3 (1: 2: 3), prepared by Scheele in 1786 by heating gallic acid, C6H3(OH)3CO2H. It is also obtained by heating para-chlorphenoldisulphonic acid with potassium hydroxide. It forms white plates, melting at 132°, readily soluble in water, and subliming without decomposition. It is an energetic reducing agent, a property utilized in its application in gas analysis to absorb oxygen, and in (q.v.) as a developer. The aqueous solution is turned bluish black by ferrous sulphate containing a ferric salt. It does not combine with hydroxylamine, as does the isomeric phloroglucin which yields a trioxide (see ). Pyrogallol dimethyl ether is found in beechwood tar. Pyrogallol has antiseptic properties and is employed medicinally in the treatment of psoriasis. Eugallol, or monacetyl pyrogallol and lenigallel, or triacetyl pyrogallol, are also used.

 PYROLUSITE, a mineral consisting essentially of manganese dioxide (MnO2), of importance as an ore of manganese. It is a soft, black, amorphous mineral, often with a granular, fibrous or columnar structure, and sometimes forming reniform crusts. It has a metallic lustre, and a black or bluish-black streak, and readily soils the fingers. The specific gravity is about 4.8. Supposed crystals of pyrolusite have been proved to be pseudomorphs after manganite; in fact the mineral often results by the dehydration and oxidation of manganite (Mn2O3⋅H2O), and for this reason it frequently contains a little water. True crystals of manganese dioxide are referred to the rare species polianite: they are tetragonal and isomorphous with cassiterite. Pyrolusite is an alteration product of other manganese minerals—manganite, rhodochrosite, rhodonite, &c. It occurs as irregular masses and nodules in the residual clayey materials resulting from the decomposition of various rocks, for example, limestone. That it is readily deposited from solution is shown by the frequent occurrence of black dendritic markings in the crevices of rocks, excellent examples of which are seen in mocha stone (q.v.) and in the lithographic stone of Solenhofen in Bavaria. It is deposited from the waters of some springs, and manganiferous nodules are dredged from the Hoor of the deep sea.

As an ore it is extensively mined at Ilmenau and several other places in Thuringia, at Vorderehrensdorf near Prossnitz in Moravia, Platten in Bohemia, in North Wales, at several places in the United States (Vermont, Virginia, Arkansas, &c.), Nova Scotia and Brazil. Pyrolusite, together with the rather less important ore, psilomelane, has various economic applications. It is extensively used for the manufacture of spiegeleisen and ferromanganese, and of various alloys, such as manganese-bronze. As an oxidizing agent it is used in the preparation of chlorine and disinfectants (permanganates), and for decolorizing glass: when mixed with molten glass it oxidizes the ferrous iron to ferric iron, and so discharges the green and brown tints, hence the name pyrolusite, from Gr. πῦρ (fire) and λύειν (to wash). As a colouring material, it is used in calico printing and dyeing; for imparting violet, amber and black colours to glass, pottery and bricks; and in the manufacture of green and violet paints. (L. J. S.)

 PYROMETER (Gr. πῦρ, fire, μέτρον, a measure), an instrument for measuring high temperatures. The term was first used by Musschenbroek to denote an instrument wherein the expansion of a metal rod measured the temperature. Discontinuous thermoscopes, depending on the fusion of a metal or salt, are also employed. Prinsep prepared a series of alloys of silver and gold, and of gold and platinum, whose melting points, as determined by accurate instruments, covered a range of temperature from 954° to 1775°, at intervals of from 25° to 30°. By placing ingots in a furnace and observing which one melted a fair idea of the temperature was obtained. Carnelley and Williams employed certain salts of known melting point; whilst the Seger's cones, employed in porcelain manufacture, depend on the fusion of small cones made of clay. (See for scientific forms.)

 PYROMORPHITE, a mineral species composed of lead chlorophosphate (PbCl)Pb4(PO4)3, sometimes occurring in sufficient abundance to be mined as an ore of lead.

Crystals are common, and have the form of a hexagonal prism terminated by the basal planes, sometimes combined with narrow faces of a hexagonal pyramid. Crystals with a barrel-like curvature are not uncommon. Globular and reniform masses are also found. As proved by the etched figures on the faces, crystals possess the same parallel-faced hemihedrism as apatite, with which mineral pyromorphite and also mimetite are isomorphous. Between pyromorphite and the corresponding chloro-arsenate (mimetite, (q.v.) the resemblance in external characters is so close that, as a rule, it is only possible to distinguish between them by chemical tests: and they were formerly confused under the names “ green lead ore ” and “ brown lead ore ” (German, Grünbleierz and Braunbleierz). The phosphate was first distinguished chemically by M. H. Klaproth, in 1784, and it was named pyromorphite by J. F. L. Hausmann in 1813, being so named from the Gr. πῦρ (fire) and μορφή (form), because when a fragment of the mineral is fused the globule assumes a faceted form on solidifying. The colour of the mineral is usually some bright shade of green, yellow or brown, and the lustre is resinous. The hardness is 3½ and the specific gravity 6.5–7.1. Owing to isomorphous replacement of the phosphorus by arsenic there may be a gradual passage from pyromorphite to mimetite. Varieties containing calcium isomorphously replacing lead are lower in density (specific gravity 5.9–6.5) and usually lighter in colour; they bear the names "polysphaerite" (because of the globular form), "' miesite ” from Mies in Bohemia, “ nussierite ” from Nussière near Beaujeu, Rhône, France, and "c heroine" from Cherokee county in Georgia.