Page:The American Cyclopædia (1879) Volume XIII.djvu/480

 464: PHOSPHORUS phosphorus. In 1680 it was noticed in the " Philosophical Transactions " of the royal so- ciety of London, and it was soon prepared in considerable quantities by Godfrey Hank- witz under the direction of Robert Boyle. In 1737 the French government purchased and published a method of preparing phosphorus from urine ; but the unpleasant and expensive process was abandoned after Gahn in 1769 discovered it as a constituent of bones, and Scheele six years later devised a process for its extraction, by which burnt bones were di- gested with dilute nitric acid, the lime pre- cipitated by sulphuric acid, and the nitrate evaporated to a sirup, which was then mixed with charcoal powder and subjected to distil- lation, phosphorus being set free and coming over as a vapor, which was condensed in water. It was afterward found to be a con- stituent of certain primitive rocks, especially of the mineral apatite. (See LIME, vol. x., p. 478.) The decomposition of these rocks fur- nishes phosphorus in the form of phosphate of calcium to the soil, from which it is appro- priated by plants, these in turn supplying the animals which feed upon them, for the build- ing of whose structures, particularly the bones and the nervous system, it is indispensable. Phosphorus is now prepared from bones and also from the native calcic phosphate. (For the chemical composition of bones, see BONE, and BONE DUST.) In the preparation of phos- phorus the bones were formerly calcined in an open fire, but now the gelatine is first ex- tracted by water with the aid of heat and pres- sure, or they are first made into bone black, which after being employed for refining sugar is burned. Three parts of powdered bone ash are mixed with two of concentrated sulphuric acid, or three parts of the crude acid of specific gravity 1'55 arid 18 or 20 parts of water. After standing two or three days, the mixture is placed in a strong linen bag, and the liquid containing the phosphoric acid is separated from the sulphate of lime (calcic sulphate) by pressure. Water is added to the residue, and the washings are added to the filtrate. The sulphuric acid should be just sufficient to re- move two thirds of the calcium, leaving the remainder as a soluble acid salt combined with all the phosphoric acid, which is often called superphosphate of lime. The reaction is shown in the following equation : Ca 3 2PO 4 + 2H 2 SO 4 = H 4 Ca2PO 4 + 20aSO 4 Tricalcic phos- Sulph. acid. Acid calcic phos- Calcic sul- phate, phate. phate. The acid solution, after being evaporated to a sirupy form, is mixed with one third or one half its weight of charcoal and raised to a nearly red heat in an iron pot, and then trans- ferred while hot to an earthen retort, &, fig. 1. It is then gradually heated to full redness, by which means the carbon combines with the calcium base and with oxygen to produce water, tricalcic phosphate, and phosphorus. This reaction is divided into two stages. The superphosphate is first decomposed into wa- ter and calcic metaphosphate (H 4 Oa2PO 4 =Ca 2PO 3 + 2H 2 O), and the metaphosphate, by the FIG. 1. Manufacture of Phosphorus. action of carbon, is reconverted into tricalcic phosphate (bone phosphate), carbonic oxide, and phosphorus, the two latter passing over in a gaseous form (3Ca2PO 3 + 10C=4P + Ca 8 2PO 4 + 10CO). The phosphorus may be purified by fusing it under water containing some bleach- ing powder, and squeezing through wash leath- er. It is moulded in the form of sticks by raising it in glass tubes by atmospheric pres- sure. Properties. Phosphorus is a soft, trans- lucent, colorless solid, of a waxy consistency, becoming brittle at low temperatures. Its sym- bol is P, its atomic weight 31, and its specific gravity when solid 1-83, when liquid below its melting point 1'76 (Gladstone and Dale) ; its observed vapor density is 4'42 ; its melting point 111 -5 F. If melted under an alkaline liquid and cooled slowly, it will remain for some time fluid at ordinary temperatures, but when touched with a rod will suddenly so- lidify. Its boiling point is 550, an atom of its vapor occupying once and a half as much space as an atom of hydrogen. According to Deville, this relation of volumes is not affect- ed by a temperature of 1904. When melted phosphorus is slowly cooled, well formed do- decahedrons may be obtained. It is insoluble in water, for which reason it is usually pre- served in that liquid ; is soluble in oil, in petroleum naphtha, and in bisulphide of car- bon. It is exceedingly inflammable, taking fire by the heat of the hand, and a blow will often kindle it. In the open air it burns with a bright flame, forming with oxygen phos- phoric acid. At ordinary temperatures a stick of phosphorus emits a white smoke, which is luminous in the dark, in consequence of slow combustion, and upon this action depends one of the methods of analyzing the air. (See NI- TROGEN.) This slow combustion (oxidation) may be prevented by a small quantity of ole- fiant gas, vapor of ether, or some essential oil. It is remarkable that in pure oxygen phospho-