Chap. 37] Acids formed by Combuftion. 245 



as a flow combuftion. In fhorr, all fubftances may 

 be faid to be inflammable which are capable, in any 

 circumftances, of decomposing vital air, or which have 

 a ftronger attraction for the bafis of that air than that 

 bafis has for caloric or fire. 



In all inftances of inflammation a certain degree of 

 heat is necefTary to begin the procefs. Different in- 

 flammable fubftances require different degrees of heat 

 for this purpofe. Phofphorus is fully inflamed at the 

 heat of 86 degrees of Fahrenheit, but undergoes a more 

 gradual combuftion at a much lower temperature. 

 Sulphur requires much more heat than phofphorus, 

 and charcoal ftill more than fulphur. There are fame 

 fubftances in nature which are fo combuftible, or have 

 fo ftrong an attraction for oxygen, as never to have 

 been found uncombined with that principle ; of this 

 kind are the unknown bafes of the boracic, fluoric, and 

 muriatic acids. 



Though an acid is always formed by the combuf- 

 tion of every inflammable fubftance, this fact was 

 never attended to, or at leaft never properly appre- 

 hended, till within thefe few years. In ordinary cafes, 

 indeed, this circumftance was likely to pafs unob- 

 ferved ; for the acid produced by the inflammation of 

 charcoal, which is the principal ingredient in all kinds 

 of fuel, is the carbonic acid gas, or fixed air, which 

 Hcapes without leaving any traces. In the combuf- 

 tion of fulphur alfo, the acid flies off in fumes, unlefs 

 collected by a particular procefs, which was defcribed 

 in treating of the fulphuric or vitriolic acid. The 

 phofphoric acid, however, is a concrete body, and 

 therefore cannot eafily be overlooked. When inflam- 

 mable bodies are united with oxygen they become 

 acids, and having no longer fufficient attratftion for 

 R 3 oxygen 



