224 NON-METALS AND THEIR COMBINATIONS. 



metals is formed, while gaseous hydrogen phosphide, PH 3 , is lib- 

 erated and ignites spontaneously. The action may be represented 

 thus : 



3KOH + 4P + 3H 2 = 3KPH 2 O 2 + PH 3 . 

 or 



3Ca(OH) 2 + 8P + 6H 2 O = 3Ca(PH 2 O 2 ) 2 + 2PH 3 . 



From calcium hypophosphite the acid may be obtained by decom- 

 posing the salt with oxalic acid, which forms insoluble calcium 

 oxalate, while hypophosphorous acid remains in solution : 



Ca(PH 2 2 ) 2 + H 2 C 2 4 = CaC 2 4 + 2HPH 2 O 2 . 



From potassium hypophosphite the acid may be liberated by the 

 addition of tartaric acid and alcohol, when potassium acid tartrate 

 forms, which is nearly insoluble in dilute alcohol and may be sepa- 

 rated by filtration. 



Pure hypophosphorous acid is a white crystalline substance, acting 

 energetically as a deoxidizing agent. Although containing three 

 atoms of hydrogen, it is a monobasic acid, only one of the hydrogen 

 atoms being replaceable by metals. 



Hypophosphorous acid of the U. S. P. contains 30 per cent, and 

 the diluted acid 10 per cent, of the pure acid dissolved in water. 

 Both preparations are colorless acid liquids, which, upon heating, lose 

 water and are afterward decomposed into phosphoric acid and hydrogen 

 phosphide, which ignites : 



2H 3 P0 2 H 3 P0 4 + PH 3 . 



Similar to the case of sulphur, the most stable acid of phosphorus is phos- 

 phoric acid, and the others show a tendency to pass to it. These are, therefore, 

 easily oxidized and also easily reduced. Thus, hypophosphorous acid is not 

 only quickly oxidized by the usual oxidizing agents, but even precipitates many 

 metals from their salts. Hypophosphites, when brought into the presence of 

 nascent hydrogen, are reduced to phosphine gas, PH 3 (compare with sulphites). 

 All hypophosphites are soluble in water and nearly all are colorless. About 

 six are used in medicine. 



Tests for hypophosphites. 



(Use about a 5 per cent, solution of the sodium salt, NaPH 2 O 2 .) 

 1. Heat a small quantity of the dry sodium salt in a porcelain dish 

 until it ignites. The salt is decomposed into a phosphate and phos- 

 phine, which burns with a characteristic brilliant light, emitting a 

 white cloud of oxide of phosphorus. Some red phosphorus is also 

 formed. 



2NaPH 2 2 = Na 2 HPO, + PH 3 . 

 2PH 3 + 80 = P 2 5 + 3H 2 0. 2PH 3 + 30 = 2P + 3H,O. 



