244 Inflammable Subjlances. [Book VI. 



fequence of the bafis of this gas becoming com- 

 bined with other bodies. All bodies, therefore, 

 which are capable of decompofing vital air, change 

 a cfuantity of latent heat into fenfible heat, and are 

 faid to be inflammable from the light and heat which 

 feem to proceed from them, but which, in fact, are 

 derived from the oxygenous gas, which is oneof die 

 component parts of the atmbfphere. 



The neceflity of the prefence of air to combuftion 

 is ftrongly maintained by M. Lavoifier, and an expe- 

 riment related by him (to the latter part of which I 

 feel fome reluctance to give an unqualified afient) 

 feems, indeed, to pFOve it to be efiejitial in all cafes. 

 Fie fucceflively placed a quantity of phofphorus, of 

 fulphur, and of gunpowder, under the receiver of an 

 air-pump, making as perfect a vacuum as the machine 

 would admit. He then threw the focus of a lens of 

 eight inches diameter on the different fubftances, which 

 were not at all ignited, only bubbled up, and at length 

 fublimed. The gunpowder was decompofed,_ the 

 fulphur of it only fubliming, and it neither took fire 

 nor exploded. 



In ordinary language, no bodies are faid to be 

 inflammable but fuch as burn eafily, or which, in other 

 words, are capable of decompofing vital air in the di- 

 luted ftate in which it exifts in the atmofphere. In a 

 more ftrict fenfe, however, the property of inflamma- 

 bility belongs to other bodies, though they poffefs it 

 in a lefs eminent degree -, as to zinc, which, when made 

 extremely hot, burns with a dazzling white light* and 

 to iron, which when heated to a proper degree, burns 

 in pure oxygenous gas. The oxygenation which all 

 metals, except the perfect, undergo from the conjoined 

 operation of heat and air, muft alfo be CQfifidered 

 3 as 



