PHOSPHOBUS. 1 89 



taneously, emitting a bright yellow light ; and the smoke 

 rises in rings, which enlarge as they go up, exhibiting at 

 the same time a singular rotary movement. The reaction 

 is complicated : 



,,, . Potassium Phosphoretted Potassium 



Phosphorus. Water. hydrate> hydrogen, hypophosphite. 



P 4 + 3H 2 + 3KHO = H 3 P + 3KPH 3 O 3 



It is this gas, forming with hydrogen and nitrogen in the 

 decomposition in the mud of marshes, which causes the light 

 called " will-o'-the-wisp." 



256. Another "Way of Making Phosphoretted Hydrogen, 

 Phosphide of calcium thrown into water acidulated with 

 hydrochloric acid gives off phosphoretted hydrogen, which 

 ignites spontaneously. This experiment can be made in a 

 wine-glass without danger. 



257. Compounds of Phosphorus -with Oxygen. These are 

 two in number. First we have phosphorous anhydride, 

 formed by slow combustion, as exemplified in the first ex- 

 periment in 250. Then we have phosphoric anhydride, 

 the result of perfect combustion, as in the second experi- 

 ment, and in the burning of phosphorus in oxygen gas, no- 

 ticed in 58. Both of these anhydrides dissolve in water, 

 forming corresponding acids. Phosphoric acid is made in 

 another way, however, as this is inconvenient. Phosphorus 

 is heated with moderately strong nitric acid, the phosphor- 

 us is oxidized by the acid, and on concentrating the solu- 

 tion the excess of nitric acid is expelled and a sirupy liquid 

 remains. Phosphoric acid, H 3 PO 4 , containing three atoms 

 of hydrogen, is a tri-basic acid, and forms a great variety 

 of salts. 



A third acid is known, hypophosphorous acid, the compounds of which 

 are used in medicine. Its anhydride has not as yet been prepared. 



