PHOSPHORUS. 



43 



acid left in solution. This is evaporated, mixed with charcoal and 

 exposed to a high heat ; the phosphorus distils over into water. 



Prop.— When pure it much resembles wax, being soft and flexible, 

 and of a flesh colour; sp. gr. 1-77; — fuses at 108°; — boils at 550°; 

 — insoluble in water, but dissolves in naphtha and oils; — very inflam- 

 mable ; — burns with a bright flame generating phosphoric acid. It 

 undergoes a slow combustion in the open air, giving a luminous 

 appearance in the dark ; this combustion may, however, be entirely 

 prevented by the presence of defiant gas, vapour of ether, or an 

 essential oil. Eq.=15-7, or (according to some) 31*4. Symb. P. 



Phosphorus forms four compounds with oxygen. 



Oxide of phosphorus, Ffi, or Ffi, formed by melting phosphorus 

 under hot water, and bringing a stream of oxygen gas in contact 

 with it : — it has a red colour; — is insoluble in water, alcohol, or ether. 



Hypophosphorous acid, P^O, or PO ; — is formed when phos- 

 phuret of barium is put into water; — it is a powerful deoxidizing 

 agent. 



Phosphorous acid, PgOg, or POg; formed by burning phosphorus in 

 a limited supply of oxygen or air ; in this state it is anhydrous, and 

 is in the form of a white powder, very deliquescent. It forms phos- 

 phites, which are of little importance. 



Phosphoric acid, Fjd^, or PO^; — prepared by burning phosphorus 

 in the open air or in oxygen, by which it is procured in the anhy- 

 drous form ; also by heating phosphorus in nitric acid ; also from 

 bones, by acting in the phosphate of lime (which is formed as already 

 described) by carbonate of ammonia, then evaporating the phosphate 

 of ammonia, and heating in a platina crucible. 



Prop. — Very deliquescent ; is a powerful acid ; very sour, but 

 does not corrode like nitric and sulphuric acids. It is capable of 

 existing in three different states or modifications, forming three 

 separate classes of salts, which differ completely in properties and 

 constitution. They are distinguished by the names tribasic, hibasic, 

 and monobasic acids, according to the number of equivalents of base 

 required to form neutral salts. 



The tribasic phosphoric acid is the acid of the well-known phos- 

 phates ; it is characterized by yielding with a soluble salt of silver, 

 a yellow insoluble phosphate. It contains 3 eq. water. 



The bibasic phosphoric acid, also called ihe pyrophosphoric acid, 

 is procured by heating the former acid at a temperature of 415°; — 

 it is distinguished from the tribasic acid by yielding a white instead 

 of a yellow precipitate with the salts of silver. It contains 2 eq. of 

 water. 



The monobasic phosphoric acid, also named par aphosphoric acid, 

 is procured when phosphorus is heated in the open air, and also 

 when a concentrated solution of the tribasic or bibasic acids is heated 

 to redness. By the former method, it is anhydrous ; by the latter, 



