116 NON-METALS AND THEIR COMBINATIONS. 



From calcium hype-phosphite 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 a 2 ) 2 + H 2 C 2 3 = CaC 2 3 + 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. 



The diluted hypophosphorous acid, Acidum hypophosphorosum dilu- 

 tum of the U.S. P., contains 10 per cent, of absolute acid. It is a 

 colorless acid liquid, which, upon heating, loses water and is afterward 

 decomposed into phosphoric acid and hydrogen phosphide, which 



ignites : 



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



Tests for hypophosphites. 

 (Sodium hypophosphite, NaPH 2 O 2 , may be used.) 



1. Heated over a flame they burn with a phosphorescent light, in 

 consequence of their decomposition into inflammable hydrogen phos- 

 phide and a phosphate. 



2. From solutions of mercuric chloride and silver nitrate they 

 precipitate the metals in consequence of the deoxidizing action of 

 hypophosphorous acid. 



3. With zinc and diluted sulphuric acid they evolve hydrogen and 

 phosphoretted hydrogen . 



4. An acid solution of potassium permanganate is readily decolor- 

 ized. 



5. Ammonium molybdate solution produces a blue precipitate ; a 

 green color would indicate the presence of a phosphate, which alone 

 gives a yellow precipitate with the reagent. 



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

 tion of this compound has been mentioned in the previous paragraph. 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. 



