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LEFT PHOSPHATE 231 PHOTOCHEMISTRY Cla. A colorless liquid, occurring as a gas at ordinary temperatures. Boiling point 8-2 C, specific gravity 1-432 at 0° C. Soluble in acetic acid and benzine. In contact with moisture it decomposes, forming carbon dioxide and hydrochloric acid. CO CI. + H2O = CO2 + 2 HCl Combines with ammonia to form urea and ammonium chloride. Prepared by passing carbon monoxide and chlorine through charcoal with or without a cat- alyst. It is a very poisonous, asphyxiat- ing gas at temperatures above its boiling point, and this property was made use of in the World War, phosgene being used as a filling for shells, usually in combination with other gases. It is also used for bleaching sand employed in glass manufacture, and in the prepara- tion of dye stuffs. PHOSPHATE, in chemistry, the gen- eric term for the salts formed by the union of phosphoric anhydride with bases or water or both. They play a leading part in the chemistry of animal and plant life, the most important in this connection being the phosphate of soda, phosphate of lime, and the basic phos- phate of magnesia. In agriculture the adequate supply of phosphates to plants in the form of manures becomes a matter of necessity in all deplenished soils. These phosphatic manures consist for the most part of bones, ground bones, min- eral phosphates, bone ash and phosphatic guano. PHOSPHORESCENCE, the property which many substances and organic be- ings possess of emitting light under cer- tain conditions; also a phosphoric light. Among animals, some of Cuvier's sub- kingdom Radiata have the power of emit- ting light in the dark, and the phos- phorescence of the sea in tropical, and even at times in temperate climates, is attributed to a small infusorial animal- cule. On land, of insects, some milli- pedes, the female glow-worm, and the fireflies, emit light. In the glow-worm the light is from the under side of the final segments of the abdomen. PHOSPHORIC ACID, in chemistry, H^POi, ortho-phosphoric acid, a tribasic acid formed by the action of nitric acid upon phosphorus, or by the hydration of phosphoric anhydride. It is given in a very dilute state in diabetes and scrofula. PHOSPHORITE, a species of calca- reous earth; a sub-species of apatite. It is an amorphous phosphate of lime, and is valuable as a fertilizer. PHOSPHOROUS ACID, in chemistry, ■ HijPOs. Prepared by adding water to the trichloride of phosphorus, PCL+H;0= HsPOa+SHCl. Heated in a close vessel, it forms phosphoreted hydrogen and phosphoric acid. PHOSPHORUS, in Greek mythology, the morning-star; Phosphor. In chem- istry, symbol P; at. wt.= 31, a non- metallic pentad element; found in a state of combination in the unstratified rocks, the soil, the organism of plants, and the bodies of animals. Discovered by Brandt in 1669. It is prepared from powdered calcined bones by treating them with two-thirds of their weight of sul- phuric acid diluted with water, evaporat- ing the liquid portion, and, after mixing with charcoal, desiccating by heating in an iron vessel. The dry mass is then introduced into a stone retort, heated, and the phosphorus evolved^ collected un- der water. It is insoluble in water, and is kept in that liquid, but dissolves in native naphtha and bisulphide of carbon; is very inflammable, and sometimes takes fire from the heat of the hand. A re- markable modification exists under the name of amorphous phosphorus, prepared by exposing common phosphorus to 250° for 50 hours. It is not luminous in the dark. Used on a very large scale in the preparation of safety matches. It has been given in small doses in intercostal and trigeminal neuralgia, psoriasis, eczema, and goiter; but even in minute doses it is dangerous. In larger ones it produces jaundice, vomiting, hemorrhage, and death. PHOTOCHEMISTRY, that branch of science which deals with the chemical changes brought about by the agency of light. The fact that changes in the composition or structure of matter can be brought about by light has been known, probably, since the early part of the eighteenth century, Schultze ob- serving in 1727, that silver chloride, when exposed to sunlight, changed from a creamy white to purplish brown. Gen- erally speaking, the rate of chemical ac- tion is proportional to the intensity of the light, but the exact determination of the activity of light was first suggested by John W. Draper, of New York Uni- versity, who measured the rate of com- bination brought about by light in a mixture of hydrogen and chlorine. Later, Bunsen and Roscoe made use of a photographic film, measuring the time required to darken the film to a standard tint. The action of light is not confined to any particular wave length, but the most active are the violet and ultra- violet, or so-called actinic, rays. Red light is, for most practical purposes, in- active, and this fact is made use of in