340 PHOSPHORUS. 



ware retort, previously covered with a coating of fire clay. The 

 beak of the retort is inserted into a wider copper tube of a few 

 feet in length, the free end of which is bent downwards a few 

 inches' from its extremity ; and the descending portion intro- 

 duced into a wide-mouthed bottle, containing enough of water 

 to cover the extremity of the tube to the extent of a line or two. 

 The heat of the furnace in which the retort is placed, is slowly 

 raised for three or four hours, and then urged vigorously till 

 phosphorus ceases to drop into the water from the copper tube, 

 which may continue from fifteen to thirty hours, according to 

 the size of the retort. Carbon at a high temperature takes 

 oxygen from the phosphoric acid, and becomes carbonic oxide, 

 so that the phosphorus is all along accompanied by that gas. 



Wohler recommends, instead of the preceding process, to 

 calcine ivory black, which is a mixture of phosphate of lime and 

 charcoal, with fine quartzy sand and a little more ordinary char- 

 coal, in cylinders of fire clay, at a very high temperature. Each 

 cylinder has a bent copper tube adapted to it, one branch of 

 which descends into a vessel containing water. The efficiency 

 of Wohler's process depends upon the silica acting as an acid, 

 and combining with the lime of the phosphate, at a high tem- 

 perature, while the liberated phosphoric acid is decomposed by 

 the carbon. 



Properties. At the usual temperature phosphorus is a 

 translucent soft solid of a light amber colour, which may be 

 bent or cut with a knife, and the cut surface has a waxy lustre. 

 Its density is 1.77- Phosphorus melts at 108, undergoing a re- 

 markable dilatation of 0.0314 of its volume and becoming trans- 

 parent and colourless immediately before fusion. It forms a 

 transparent liquid, possessing like most combustible bodies, a 

 high refracting power. At 217 it begins to emit a slight va- 

 pour, and boils at 550, being converted into a vapour which 

 is colourless, ofsp. gr. 4355, according to the experiment of 

 Dumas, which coincides almost with the theoretical density 

 4327. Its combining measure, like that of oxygen, is 1 volume, 

 allowing its equivalent to be 392. When fused and left un- 

 disturbed, it sometimes remains liquid for hours at the usual 

 temperature, particularly when covered by an alkaline liquid, 

 but becomes solid when touched. Thenard has observed that 

 when cooled very suddenly, as by throwing it melted into ice- 

 cold water, t becomes absolutely black. Light causes it, in 



