On Sal Nitrum and Nitro- Aerial Spirit 19 



agile, they seem to be much better suited for execut- 

 ing a swift and fiery movement than the crasser and 

 very soft sulphureous particles. 



But the reason for the notion that it is the sul- 

 phureous rather than the nitro-aerial particles which 

 take fire is, that the grosser sulphureous nutriment of 

 fire is always in view, while the nitro-aerial particles 

 are so fine and subtle that they quite escape observa- 

 tion, and yet it is certain that nitro-aerial particles are 

 not less necessary than sulphureous particles for the 

 production of fire. 



The following experiment confirms what has been 

 said, viz., if nitre be put into a hot crucible it will 

 soon liquefy but will not take fire, although oil will 

 immediately burn if thrown into the crucible. The 

 inference from this is that the fiery particles which 

 penetrate the glowing crucible are not of a sul- 

 phureous nature, for otherwise the nitre would be 

 kindled by the fiery particles mixed with it, for 

 sulphur particles when mixed with melted nitre 

 immediately ignite it. But the proof that the igneous 

 particles collected in the heated crucible are of a 

 nitro-saline nature is this, that any sulphureous matter 

 cast into the said crucible is ignited by those particles; 

 but sulphureous particles are not thrown into a state 

 of extremely rapid and fiery motion without the aid 

 of nitro-aerial particles. 



We remark further that sulphureous particles are of 

 so crass a nature that we can scarcely imagine, however 

 heated they may be and however minutely divided, 

 that they will become so subtle and nimble as to be 

 able to penetrate, like fiery particles, metals, glass, 

 and such like very solid things, and this seems to be 

 confirmed by the following experiment. For let a 

 polished metal plate be kept for some time in the 



