PHOSPHORUS. 223 



It should be mentioned that the luminosity of phosphorus vapors is dimin- 

 ished, or even prevented, by vapors of essential oils (oil of turpentine, for 

 instance), ether, olefiant gas, and a few other substances. 



Oxides of phosphorus. Four oxides of phosphorus are known. 

 They are phosphorus monoxide, P 4 O, phosphorus trioxidc, P 2 O 3 , phos- 

 phorus tetroxide, P 2 O 4 , and phosphorus pentoxide, P 2 O 5 . The three 

 lower oxides are obtained by slow oxidation, or by the burning of 

 phosphorus in a limited supply of air ; while the pentoxide is formed 



FIG. 43. 



Apparatus for detection of phosphorus in cases of poisoning. 



whenever phosphorus burns under ordinary conditions. The pent- 

 oxide is a white powder possessing an intense affinity for water, 

 with which it combines to form phosphoric acid, while the trioxide 

 with water produces phosphorous acid. 



Hypophosphorous acid, Acidum hypophosphorosum, H 3 PO 2 , 

 PO.H 2 .OH = 65.53. When phosphorus is heated with solution of 

 potassium, sodium,, or calcium hydroxide, the hypophosphite of these 



