PHOSPHORUS 465 rus is not luminous until the temperature is as high as 59, or unless the gas is rarefied, or diluted with nitrogen, hydrogen, or carbonic acid. Phosphorus assumes several different forms. The translucent variety, common or vitreous phosphorus, has been described. When this is exposed to light under water, it becomes white and opaque, somewhat less fusible, and of less specific gravity (1-515). This variety becomes reconverted into the common form at a temperature of 122 F. A third form, black and opaque, is obtained by suddenly cooling melted phosphorus, which by fusion and slow cooling returns again to the common form. A viscous form, analogous to viscous sulphur, is produced by suddenly cooling phosphorus heated to near its boiling point. A fifth form occurs in red scales, and is known as red or amorphous phosphorus. It has been carefully examined by Schrotter, and may be obtained by exposing phosphorus in a vacuum to the rays of the sun, or by subjecting it for 50 hours to a temperature of 446 to 464 F. in an at- mosphere of some gas with which it does not combine. This red, amorphous, opaque variety is insoluble in bisulphide of carbon or benzole, and when exposed to the air emits no odor. Its density is greater than that of common phosphorus, being from 2'089 to 2*106. It remains unchanged in the open air till heated to 500, when it melts and bursts into a flame, emitting dense clouds of phosphoric anhydride. When slightly rubbed with chlorate of potash, peroxide of manganese, or peroxide of lead, it detonates and inflames. On account of its property of remaining unchanged at ordinary temperatures, but of combining with the oxygen of oxygen compounds by means of friction, it is used advantageously in the manufacture of friction matches. For this purpose it may be mixed with the other materials, or with size and pounded glass and spread on paper, the match, tipped with chlorate of potash and sulphur, being rubbed upon it. Common or vitreous phosphorus taken into the stomach acts as a powerful irritant poison, but the amorphous variety may be swallowed with impunity. Those who work in common phosphorus are liable to be attacked with necrosis of the jaw bones. (See MATCH, and NECROSIS.) Com- pounds. With oxygen phosphorus forms two definite oxides, in which the relative quantities of oxygen are as 3 to 5. They are phosphorous anhydride, P 2 Oa, and phosphoric anhydride, P 2 O 5 . It also forms three oxidized acids : hypo- phosphorous acid (monobasic), HPH 2 O 2 ; phos- phorous acid (dibasic), H 2 PHO 3 ; and phosphoric acid (tribasic), H 3 PO 4 . The most important of the oxides, phosphoric anhydride, is that which forms phosphoric acid by uniting with water. It occurs in the native tricalcic phosphate (apa- tite) and in bone phosphate. It may be pre- pared by burning dry phosphorus in a glass vessel to which a supply of dry air is admitted. A, fig. 2, is a glass globe with a vessel, B, con- taining ignited phosphorus, suspended by a I platinum wire from the tube H, through which I phosphorus may be added, and also ignited by I means of a hot wire. is a drying tube, con- ! taining chloride of calcium, or pumice moist- i ened with oil of vitriol. A bent tube, D, leads | into the bottle E, from which proceeds another tube, F, connected with an aspirator for draw- ing air through the apparatus. Phosphoric anhydride has a powerful attraction for water. Exposed to the air for a few moments, it absorbs moisture and becomes liquid, and when thrown into water combines with it, with explosive vio- lence, being converted into phosphoric acid, and the water is so firmly bound that it cannot be separated without ultimate decomposition (P 2 6 + 3H 2 O=2H 3 PO 4 ). It is powerfully de- hydrating, abstracting water from acids, alco- hols, and other bodies, and reducing oil of vitriol to an anhydride, and is one of the most pow- erful desiccating agents known. The pure acid FIG. 2. Formation of Phosphoric Anhydride. is usually produced in a hydrated state by boil- ing one part of phosphorus in about 13 parts of nitric acid of specific gravity T2, which fur- nishes the oxygen, while nitric oxide is evolved. The nitric acid being mostly distilled off, the residue containing the phosphoric acid is trans- ferred to a platinum vessel and cautiously heat- ed to redness. This expels a portion of the water of hydration, leaving the acid in the form of a monohydrate, or the glacial phosphoric acid (metaphosphoric acid) of the pharmaco- poeia. There are three distinct forms of phos- phoric acid, a fact first shown by Graham, viz. : metaphosphoric acid, HPO 3 ; orthophosphoric acid, H 3 PO 4 ; and pyrophosphoric acid, H 4 P 2 7 . These different forms retain their characteris- tics when dissolved in water, and form salts with one, with three, and with four equivalents of metals, which are respectively called m eta- phosphates, orthophosphates, and pyrophos- phates. The study of these compounds has greatly assisted in forming the modern theory of saline compounds in general. Of these salts
