On Sal Nitriim and Nitro- Aerial Spirit 8i 



the air contains and by their coUision drive them 

 forcibly out, and that at last from these, violently 

 ejected and in vehement commotion, fire is produced, 

 as will be shown more fully below. 



Further, it is a reasonable supposition that the aerial 

 particles, deprived in the manner aforesaid of nitro- 

 aerial particles, become not only unfit for sustain- 

 ing fire but also change from rigid to flexible and in 

 consequence are deprived of their elasticity, for that 

 the rigidity of aerial particles is due to nitro-aerial 

 particles fixed in them, while their elasticity results 

 from their rigidity, I have already endeavoured to show. 

 Indeed aerial particles when passing out from flame 

 appear to be in a condition very similar to that of a 

 steel plate which is slowly cooled after it has been 

 heated, for this also loses its elasticity as the fiery 

 particles extricate themselves from its structure, and 

 becomes moreover incapable of having, as before, 

 sparks struck out of it by flint. And in fact fire seems 

 to be nothing else than a collection of very minute 

 sparks very densely struck out from aerial particles by 

 the collision of sulphureous particles. For the case is 

 very much as if we were to suppose that innumerable 

 little particles of flint and steel collide at the same 

 instant with each other. For as aerial particles are 

 solid bodies and are rigid like steel plates, they seem 

 to be fit enough for having fire struck out of them. 

 Hence if the sulphureous particles are too volatile and 

 fine the flame produced by them is very sluggish, such 

 as is the flame of burning spirit of wine or the very 

 feeble and almost harmless fires which are produced by 

 the sulphureous effluviae of animals, for since these 

 extremely fine and volatile sulphureous particles only 

 collide in a feeble and gentle manner with the aerial 

 particles, they are scarcely able to strike effectively 



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