418 COMPOUNDS OF HYDROGEN. 



Phosphuretted hydrogen gas, P H 3 . This gas, which is re- 

 markable for its occasional spontaneous inflammability in air, 

 was discovered by Gengembre in 1 783, and has been succes- 

 sively investigated by several chemists ; but its true nature 

 was first ascertained by Rose, who proved it to be a compound 

 analogous in constitution to ammoniacal gas, having phosphorus 

 in the place of nitrogen . The pure gas is obtained by heating 

 hydrated phosphorous acid, which is resolved into phosphuretted 

 hydrogen and hydrated phosphoric acid ; thus, 



4(3H O + P O 3 ) or 1 2 H O and 4P O 3 = P H 3 and 9H O + 3P O 5 . 



This gas does not inflame spontaneously when allowed to 

 escape into air, but kindles when a light is applied to it, and 

 burns with the white flame of phosphorus. A little air added 

 to the gas, which had no effect at first, has been observed to 

 produce occasionally an explosion after a time. The gas 

 consists of 1 volume of phosphorus vapour and 6 volumes 

 of hydrogen, condensed into 4 volumes, so that it has the same 

 combining measure as ammoniacal gas. Its density is 1185. 

 Phosphuretted hydrogen has a disagreeable alliaceous odour, is 

 but slightly soluble in water, and has no alkaline reaction. 



The same gas, in a self-inflammable state, is obtained by 

 boiling phosphorus, lime and water together. The first effect is 

 the formation of hypophosphite of lime, with the evolution of 

 phosphuretted hydrogen gas : 



4Pand3CaO and 3H O = PH 3 and 3CaO + 3PO; 



and phosphuretted hydrogen is again evolved, but mixed with 

 a considerable quantity of free hydrogen, when the hydrated 

 hypophosphite of lime is evaporated to dryness, phosphate of 

 lime being the residuary product. The self-inflammability of this 

 gas must depend upon something extraneous. Rose has shown 

 that the gas, after being passed through a long tube containing 

 chloride of calcium, to dry it thoroughly, retains this property, 

 for days, and undergoes no change in composition, whether 

 kept in obscurity or exposed to sunshine,* and, therefore, rejects 

 the theory of M. Leverrier,f that the property in question is 



* Liebig's Annalen der Pharmacie, v. 30, p 320. (1839.) 

 t An. de Ch. et dePh. t. 60, p. 174. 



