PHOSPHITES. 345 



phosphuretted hydrogen gas, cannot be obtained without some 

 trouble. AVhen a few drops of water are thrown on the chlo- 

 ride of phosphorus (P C1 3 ) that compound evolves hydrochloric 

 acid gas, and gives hydrated phosphorous acid. But it is more 

 conveniently obtained by the method of Droquet. Two or 

 three ounces of phosphorus are melted in a cylindrical glass 

 receiver or sealed tube, of 8 or 10 inches in length and nearly 

 an inch in diameter, and the tube nearly filled with water. 

 This tube, which will contain a column of fluid phosphorus 

 of 5 or 6 inches in height is then properly disposed in a bason 

 or bolt-head of warm water, so as to retain the phosphorus 

 fluid. Chlorine gas is conveyed by a quill tube, from the flask 

 in which it is generated, to the bottom of the fluid phosphorus, 

 where combination takes place with ignition, and the chloride 

 of phosphorus is formed. This chloride is dissolved by the 

 water covering the phosphorus, and converted into hydrochloric 

 acid and phosphorous acid. The chlorine must be transmitted 

 very slowly through the phosphorus, as any portion of that 

 gas which reaches the water, converts the phosphorous into 

 phosphoric acid: and the absorption of the chlorine by the 

 phosphorus is most complete, when it is free from any other 

 gas. When the remaining phosphorus fixes, upon cooling, the 

 acid fluid may be poured off, and concentrated by boiling, till 

 it becomes syrupy and the volatile hydrochloric acid is entirely 

 expelled. Phosphuretted hydrogen may also be obtained from 

 the iodide of phosphorus, which is more easily prepared. 



Properties. -In its most concentrated state, the hydrate of 

 phosphorous acid contains three equivalents of water, its for- 

 mula being 3HO-j-PO 3 ; and when heated it is resolved into 

 hydrated phosphoric acid, and pure phosphuretted ^hydrogen 

 gas, which is not spontaneously inflammable. The solution of 

 phosphorous acid absorbs oxygen from the air, slowly, if con- 

 centrated, but quickly when dilute. Like sulphurous acid, it 

 takes oxygen from the salts of mercury and the less oxidable 

 metals, and precipitates the latter, particularly when aided by 

 heat. It is one of the feeblest acids known. 



Phosphites.' The class of phosphites, which has been exa- 

 mined is certainly tribasic, that is, they contain 3 atoms of base 

 to 1 of phosphorous acid. The hydrated acid is the tribasic 

 phosphite of water. All our information respecting them is 

 contained in the papers of Berzelius.* 



* An. tie Ch, etde Ph. t. 2, pp. 151, 217, 329 ; and 10, p. 278. 



