206 ACIDIFIABLE COMBUSTIBLES. 



acid of one volume phosphorus vapour and one 

 volume oxygen gas. But one volume of phos- 

 phorus vapour, and half a volume of oxygen gas 

 being each equivalent to an atom, it is obvious, 

 that the constitution of these two acids is the 

 following : 



Atom of 1. PHOSPHOROUS ACID, 



phospho- 

 rous acid. 1 atom phosphorus =1-5 



1 atom oxygen . = 1 



2-5 = atomic weight of acid. 



2. PHOSPHORIC ACID. 



1 atom phosphorus = 1'5 



2 atoms oxygen . = 2 



3-5 = atomic weight of acid. 



Thus an atom of phosphorous acid weighs 2%5, 

 and an atom of phosphoric acid 3*5, which is pre- 

 cisely the weight deduced in the beginning of 

 this section, from the analysis of phosphate of 

 soda. 

 Subphos. When this gas is allowed to stand for some 



phuretted 



hydrogen days over mercury or water, it undergoes no 

 sensible alteration in its volume, but deposites 

 one-fourth of its phosphorus. When thus altered, 

 it does not catch fire when mixed with common 

 air, or oxygen gas ; but combustion may be im- 

 mediately induced, by letting up into it a little 

 deutoxide of azote. When sulphur is sublimed 



16 



