342 PHOSPHORUS. 



and there is reason to believe are themselves undergoing a slow 

 oxidation at the same time. Now when two oxidable bodies 

 are in contact, one of them often takes precedence in combining 

 with oxygen, to the entire exclusion of the other. Potassium 

 is defended from oxidation in air, by the same vapours, al- 

 though to a less degree.* It is curious that in pure oxygen, 

 phosphorus may remain without oxidating at all, at tempera- 

 tures below 60, but an inconsiderable rarefaction of the gas, 

 from diminution of the pressure upon it, will cause the phos- 

 phorus to burst into the luminous condition. The dilution of 

 the oxygen with nitrogen, hydrogen or carbonic acid produces 

 the same effect. When gradually heated in air, phosphorus 

 generally catches fire, and begins to undergo the high combus- 

 tion, before its temperature has risen to 1 40; of this high com- 

 bustion, the sole product is phosphoric acid. 



Phosphorus is susceptible of four different degrees of oxida- 

 tion, the highest of which is a powerful acid, while the acid 

 character is not absent even in the lowest. These compounds 

 are: 



Oxide of phosphorus. . . 2P + O 



Hypophosphorous acid. . . P + O 



Phosphorous acid . . . P + 3O 



Phosphoric acid. . . . P-f 5O. 



OXIDE OF PHOSPHORUS. 



Eg. 884.56 or 70.88 ; P 2 O. 



When burned in air or oxygen, phosphorus generally leaves 

 behind it a small quantity of a red matter, which is an oxide of 

 phosphorus. The same compound is obtained, in larger quan- 

 tity, by directing a stream of oxygen gas, upon melted phos- 

 phorus, under hot water, and was found by Pelouze to contain 

 3 equivalents of phosphorus to 2 of oxygen. f 



But this oxide is impure, and the definite oxide appears to 

 have been first obtained by Leverrier, who has carefully exa- 

 mined it.l His process is to expose to the air small fragments 



* Quarterly Journal of Science, N.S. vol vi. p. 83. 

 t An. de Ch. et de Ph. t. 50, p. 83. 

 J An. de Ch. et de Ph t. 65, p. 257. 



