ACIDIFIABLE COMBUSTIBLES. 



in a state of complete purity, and we have no 

 means of appreciating the proportion of impuri- 

 ties with which it is contaminated. It can hardly 

 be burned completely in close vessels, always 

 leaving behind an orange coloured matter, which 

 deliquesces in the air, and is gradually acidified 

 spontaneously. It would be needless to relate 

 the experiments made in succession in this way, 

 by Lavoisier, Rose, myself, Dulong and Berze- 

 lius. Sir Humphrey Davy had the sagacity to 

 obviate some of the difficulties that had proved 

 most perplexing to his predecessors, and his ex- 

 periments came by far the nearest to the truth, 

 though they did not altogether reach it. It may 

 be worth while, therefore, to mention the result 

 of his researches on this difficult subject. 



He inclosed the phosphorus in a separate tray, 

 which he introduced into the belly of a glass re- 

 tort j by this contrivance, he was enabled to 

 give a stronger and longer continued heat to 

 the phosphorus. He found that 100 parts of 

 phosphorus, when converted into phosphoric 

 acid, unite with 135 parts of oxygen. Let us 

 deduce the atomic weight of phosphoric acid 

 from this composition. 



It is obvious, that this acid is a compound of 

 one atom of phosphorus with one or more atoms 

 of oxygen. Were the quantity of oxygen only 

 one atom, the atomic weight of phosphoric acid 

 would be only 174. For 135 (the oxygen in 



