208 ACIDIFIABLE COMBUSTIBLES. 



0-6944, or ten times that of hydrogen ; and its 

 atomic weight is 1'25. We may distinguish this 

 altered gas by the name of sub-phosphuretted hy- 

 dro gen. 



(2.) Bihydrogmret of phosphorus was obtained 

 phosphorus, by Davy, by heating crystallized phosphorous 

 acid. When sulphur is heated in it, the volume 

 of the gas is just doubled, and it is converted in- 

 to sulphuretted hydrogen gas. Now, it will be 

 shown in the next section, that sulphuretted hy- 

 drogen gas contains just its own volume of hy- 

 drogen gas. Hence it is obvious, that bihydro- 

 guret of phosphorus contains twice its volume of 

 hydrogen gas. 



This gas has a similar smell to phosphuretted 

 hydrogen gas. It does not burn spontaneously 

 when mixed with common air, or hydrogen gas \ 

 but combustion takes place readily, if an electric 

 spark be passed through the mixture. For com- 

 plete combustion, 1 volume of it must be mixed 

 with 1-5, or with 2 volumes of oxygen gas. The 

 gases disappear ; and, with the smaller propor- 

 tion of oxygen gas, we obtain phosphorous acid, 

 with the greater phosphoric acid. From these 

 facts it is obvious that the gas is a compound of 



2 volumes hj^drogen gas 



. condensed into one volume. 

 1 volume phosphorus vapour ) 



Its specific gravity, therefore, must be the 

 sum of twice the specific gravity of hydrogen 



