344 PHOSPHORUS. 



hypophosphorous acid undergoes decomposition, being con- 

 verted into phosphoric acid, with the evolution of phosphuretted 

 hydrogen and a deposition of phosphorus (Dulong). 



The hypophosphites are all soluble in water, and like the salts 

 of the magnesian family, such as those of magnesia and cobalt, 

 easily crystallized. The dry salts are permanent in the air, but 

 their solutions evaporated by heat, absorb oxygen. They con- 

 tain 1| equivalents of water, which are essential to their cons- 

 titution (Rose). 



Considering the disposition of the acids of phosphorus to 

 be bibasic and tribasic, it is not impossible that the real 

 equivalent of this acid may be either 2P + 2O, like hyposulphu- 

 rous acid, or 3P+3O, instead of PO. The subject requires 

 farther investigation. 



PHOSPHOROUS ACID. 

 Eq. 692.28, or 55.44; PO 3 . 



Preparation. This acid is the principal product of the slow 

 combustion of phosphorus, but changes after its formation into 

 phosphoric acid, from the absorption of oxygen. It may be 

 obtained in the anhydrous condition by burning phosphorus 

 with imperfect access of air. Berzelius recommends for this 

 operation a tube of glass, about 10 inches in length and i inch 

 in diameter, which is nearly closed at one end, an opening no 

 greater than a large pin hole being left there, and at a distance 

 of an inch from this extremity the tube is bent at an obtuse 

 angle. A small fragment of phosphorus is introduced into 

 the angle of the tube, and heated till it takes fire. It burns 

 with a pale greenish flame, and the phosphorous acid produced 

 is carried along by the feeble current of air, and condenses in 

 the ascending part of the tube, as a white powder, not in the 

 slightest degree crystalline. The phosphorus must not be so 

 much heated as to cause it to sublime unchanged. In contact 

 with air, phosphorous acid is apt to inflame, from the heat oc- 

 casioned by the condensation of moisture, and is converted into 

 phosphoric acid. The phosphorous acid itself is immediately 

 soluble in water, while the phosphoric acid, which it sometimes 

 contains, remains for a short time undissolved, in the form 

 of white translucent flocks. 



Hydrated phosphorous acid, which is the source of pure 



