ix SULPHUR AND PHOSPHORUS 185 



These substances liberate their additional sulphur when acids 

 are added, giving an increased yield of milk of sulphur. 



C. PHOSPHORUS 



Phosphorus, first prepared by distilling urine with sand, burns 

 very readily to a white, snowy oxide, increasing greatly in weight 

 (Lavoisier, 1777) : 



P 4 + 50 2 -> P 4 10 . 



The white oxide, phosphoric anhydride, P 4 O 10 , dissolves in water 

 to phosphoric acid, 



P 4 10 + 6H 2 -> 4H 3 P0 4 , 

 from which series of phosphates 'may be prepared, thus : 



Sodium phosphates, NaH 2 PO 4 , Na 2 HPO 4 , Na 3 PO 4 

 Potassium phosphates, KH 2 PO 4 , K 2 HPO 4 , K 3 PO 4 

 Calcium phosphates, CaH 4 (PO 4 ) 2 , Ca 2 H 2 (PO 4 ) 2 , Ca 3 (PO 4 ) 2 . 



The smouldering of phosphorus gives rise to phosphorous 

 acid, 



P.J + 3O 2 + 6H 2 O -> 4H 3 PO 3 , 



from which phosphites may be prepared, e.g. : 



Sodium phosphite, Na 3 PO 3 

 Potassium phosphite, K 3 PO 3 . 



In attempting to prepare a liver of phosphorus, Gengembre, 

 in 1783, obtained an inflammable gaseous phosphoretted hydrogen 

 Q\: phosphine, PH 3 : 



P 4 + 3 KOH + 3H 2 -> 3KH 2 P0 2 + PH 3 . 



Potassium Phosphine 

 hypophosphite 



The same gas is obtained by heating phosphorous acid : 

 4 H 3 P0 3 -> H 3 P + 3 H 3 P0 4 . 



Phosphorous Phosphine Phosphoric 

 acid acid 



The gas prepared by Gengembre, by the action of hot alkali on 

 phosphorus, was spontaneously inflammable on account of the 

 presence of the vapour of a liquid phosphoretted hydrogen, P 2 H 4 . 



