PHOSPHORUS. 229 



the hydrochloric acid combines with the sodium of the acetate, and 

 the acetic acid which is set free has no dissolving action upon the 

 ferric phosphate. 



Hydrogen phosphide, PH 3 (Phosphoretted hydrogen, phosphine). The forma- 

 tion of this compound has been mentioned in the paragraph on Hypophos- 

 phorous acid. It is a colorless, badly smelling, poisonous gas, which, when 

 generated as directed above, is .spontaneously inflammable. This last-named 

 property is due to the presence of small quantities of another compound of 

 phosphorus and hydrogen which has the composition P 2 H 4 , and is spontaneously 

 inflammable, while the compound PH 3 is not. 



Hydrogen phosphide corresponds to the analogous composition of ammonia, 

 NH 3 . While the latter is readily soluble in water and has strong basic prop- 

 erties, hydrogen phosphide is but sparingly soluble in water and its basic prop- 

 erties are very weak. However, a few salts, such as the phosphonium chloride, 

 PH 4 C1, analogous to ammonium chloride, NH 4 C1, are known. 



There is no scientific evidence whatever for the correctness of the statement, 

 found in some text-books, that hydrogen phosphide is a product of the putre- 

 faction of certain organic compounds. 



Phosphorus trichloride, PC1 3 . This is a colorless liquid, heavier than 

 water, boiling at 76 C. Its vapors are very pungent. Water decomposes it 

 very rapidly into phosphorous and hydrochloric acids, thus, PC1 3 -f- 3H 2 O = 

 HsP0 3 + 3HC1. For this reason the liquid gives white fumes in moist air. 

 It can only be obtained by direct union of the elements. This is done by 

 leading chlorine gas over phosphorus in a retort, when the elements unite with 

 combustion, and the trichloride distils over into a cold receiver. It is purified 

 by redistillation in contact with some phosphorus, which removes any penta- 

 chloride present. 



Phosphorus pentachloride, PC1 5 . This consists of pale yellow crystals, 

 and is obtained by passing chlorine into phosphorus trichloride. It decom- 

 poses at once in water into phosphoric and hydrochloric acids, PC1 5 + 4H 2 O 

 H 3 PO 4 -f 5HC1. It fumes strongly in moist air. At 300 C. it is completely 

 dissociated into trichloride and chlorine. With a small proportion of water it 

 forms phosphorus oxychloride thus, PC1 5 + H 2 O = POC1 3 + 2HC1. The oxy- 

 chloride is a colorless liquid that boils at 107.2 C. The pentachloride is often 

 used in organic chemistry to substitute chlorine for hydroxyl (OH) in compounds. 



The bromine compounds of phosphorus, PBr 3 and PBr 5 , are very similar to 

 the chlorine compounds, and are made in the same way. 



QUESTIONS. In what forms of combination is phosphorus found in na- 

 ture? Give an outline of the process for manufacturing phosphorus. What 

 are the symbol, valence, atomic, and molecular weights of phosphorus. State 

 the chemical and physical properties both of common and red phosphorus. 

 By what methods may phosphorus be detected in cases of poisoning? What 

 two oxides of phosphorus are known ; what is their composition, and what 

 four acids do they form by combining with water? State the official process 

 for making phosphoric acid, and what are its properties? By what tests may 

 the three phosphoric acids be recognized and distinguished from phosphorous 

 acid? What is a phosphide, phosphite, phosphate, and hypophosphite ? 

 What is glacial phosphoric acid, and in what respect does its action upon the 

 animal system differ from the action of common phosphoric acid? 



