Page:The American Cyclopædia (1879) Volume XIII.djvu/482

 466 PHOSPHORUS the orthophosphates are the most common, and the most familiar example is the tricalcic phos- phate, found in bones and in the mineral apa- tite, Ca 3 2PO 4. Among other common or or- thophosphates are trisodic phosphate, Na 3 PO 4 , 12H 2 O ; sodic dihydric phosphate, NaII 2 PO 4 , H 2 O ; and triargentic phosphate, Ag 8 PO 4. Among the metaphosphates are sodic meta- phosphate, NaPO 8, and argentic metaphos- phate, AgPO 3 ; and among the pyrophosphates, sodic pyrophosphate, Na 4 P 2 O 7 ,10H 2 0, and ar- gentic pyrophosphate, Ag 4 P 2 O 7. Phosphorous anhydride, P 2 O 3, may be obtained by burning phosphorus in a limited supply of dry air, by which a white volatile, deliquescent, inflam- mable powder is produced. The acid derived from this, phosphorous acid, H 2 PHO 3, is form- ed by the union of one molecule of P 2 O 3 with three of water (P 2 O 8 + 3H 2 O=2H 2 PHO 3 ), and may be obtained by passing a stream of chlo- rine very slowly through a deep layer of phos- phorus melted under water, so that each bub- ble of gas shall be completely absorbed by the phosphorus. Chloride of phosphorus, PC1 3 is formed, and is immediately decomposed by water into hydrochloric and phosphorous acids (PC1 3 + 3H 2 6=H 2 PHO 3 + 3HC1). By concen- trating the acid liquid by heat not exceeding 390, the hydrochloric acid is expelled and the phosphorous acid obtained in deliquescent rec- tangular prisms. Phosphorous acid is dibasic, and forms two classes of salts called phosphites. The normal salts have the general formula M 2 PHO 3, and the acid salts MHPH0 8 , where M represents the metallic element. Hypophos- phorous acid, HPH 2 2, is not derived from any known phosphorus anhydride. When phos- phorus is boiled in a caustic alkaline solution, or with a hydrate of one of the alkaline earths, a hypophosphite is formed with evolution of phosphuretted hydrogen, as mentioned in de- scribing phosphuretted hydrogen. By evapo- ration the hypophosphite may be obtained, and by adding to it sulphuric acid the hypophos- phorous acid may be obtained in solution; while if lime or baryta be used, an insoluble sulphate is separated. The salts formed by the union of this acid with bases are called hy- pophosphites, and they have been shown by the researches of Dulong, Rose, and Wurtz to be monobasic, and therefore constitute but a single monobasic class, of which the hypo- phosphite of soda, NaPH 2 O2, may be regarded as the type. The hypophosphites are all solu- ble in water and generally crystallize easily, but when the evaporation takes place at a high temperature they are converted into phos- phites by absorption of oxygen. With hydro- gen phosphorus forms three compounds (phos- phides or phosphurets), PH 3, PH 2 , and P 2 H. The first is a gas, the second a liquid, and the third a solid at ordinary temperatures. The gaseous phosphide, common phosphuretted hydrogen, may be obtained pure by heating phosphorous acid in a retort, phosphoric acid and phosphuretted hydrogen being produced (4HsP0 8 = PH, + 31I,PO4). The gas has a density of 1'24, every two volumes containing three volumes of hydrogen and a half volume of phosphorus vapor. It has a disagreeable garlic odor, is slightly soluble in water, and burns with a brilliant white flame, forming water and phosphoric acid. Phosphuretted hydrogen may also be produced by boiling phosphorus in milk of lime or a solution of caustic alkali. The retort or flask should be very nearly filled, and a glass tube leading from it should dip under the surface of water to avoid explosions. The reaction is represent- ed in the following equation : 8P + 3CaII 2 O 2 + 6H 2 O=2PII 3 + 30aII 4 P 2 O 4. Calcic Water. Phosph. Calcic hypo- hydrate, hydr. phosphite. Calcic hypophosphite and phosphuretted hy- drogen are generated. Prepared by this pro- cess, the gas has the remarkable property of inflaming spontaneously in the presence of oxygen or atmospheric air. As the bubbles come to the surface they inflame and produce beautiful rings of phosphoric acid, as shown FIG. 8. Phosphuretted Hydrogen. in fig. 3, which also shows the arrangement for preparing the gas. When admitted into a jar of oxygen gas, the bursting of each bubble is attended with a brilliant flash of light and a slight concussion. The experi- ment should be made with caution, and the bubbles admitted singly. M. Th6nard has shown that this property of spontaneous com- bustibility is caused by the presence of the vapor of the liquid phosphide, PH 2, which is always formed when the gas is procured by this process. It may be separated by pass- ing the gas through a tube surrounded by a freezing mixture, when it condenses as a color- less liquid of high refractive power and great volatility. This body is removed also when phosphuretted hydrogen is kept for some time over water, whereby it loses its property of spontaneous inflammability. The vapor of the liquid phosphide in exceedingly small quanti- ties will impart the property of spontaneous inflammability to pure phosphuretted hydrogen and to other combustible gases. By the action of light it is decomposed into gaseous phos- phuretted hydrogen and the solid phosphide, P 2 H, which compound is often seen on the in- side of vessels in which the gas is kept ; it is instantly decomposed by strong acids. Pure