VOL. LXIX.] PHILOSOPHICAL TfiANSACTIONS. 54Q 



to any body before our modern philosophers had discovered the nature of various 

 kinds of air, and the manner of extracting them from bodies. Inflammable air, 

 the gas fiammeum of Van Hehnont, was considered as an aerial fluid, susceptible 

 of inflammation by itself. But we now know, that inflammable gas concen- 

 trated will not burn at all ; but on the contrary extinguishes flame. Mr. 

 Cavendish was the first who set this matter in a proper light. He discovered, by 

 experiments, that a mixture of a small quantity of common air with a great 

 proportion of inflammable air, as, for instance, 2 parts of common air with 8 

 parts of inflammable air, caught fire without noise, and consumed gradually ; 

 but that 3 parts of inflammable air and 7 parts of respirable air exploded with a 

 very loud sound. 



It was Dr. Priestley's important discovery which suggested to me the theory I 

 intend to lay before the r. s. This acute philosopher found that, if instead of 

 common air, dephlogisticated air is mixed with a due proportion of inflammable 

 air, the explosion is considerably louder. The principal ingredients of gun- 

 powder, and those to which it owes its force, are nitre and charcoal ; for these 2 

 ingredients, well mixed together, constitute gunpowder at least equal if not 

 superior in strength to common gunpowder, as I found by experience, and may 

 be seen in the Memoire of Count Saluce, inserted in the Melanges de Philoso- 

 phie et de Mathematiques de I'Acad. Royale de Turin. The sulphur seems to 

 serve only for the purpose of setting fire to the mass with a less degree of heat. 



Nitre yields by heat a surprizing quantity of pure dephlogisticated air. Char- 

 coal yields by heat a considerable quantity of inflammable air. The fire employed 

 to inflame the gunpowder extricates these 2 airs, and sets fire to them at the same 

 instant of their extrication. Thus the difference between the inflammation of 

 gunpowder and that of a mixture of inflammable air with dephlogisticated air in 

 an ordinary air pistol, as these last are now contrived for a philosophical amuse- 

 ment, seems to be, that the compound of the 2 airs in the air pistol takes fire, 

 when already extricated and existing in a space without compression or condensa- 

 tion ; that is to say, when they are in no condition of exerting a much greater 

 elasticity than what they acquired by the heat generated in the moment of their 

 explosion ; which heat can only expand them to 4 times their former bulk, ac- 

 cording to Mr. Robins : whereas in gunpowder the 2 airs, existing in a solid 

 state before their extrication, and occupying, according to Mr. Robins, about 

 .j-i-j- of the space they take up after they are set loose, but most probably even 

 less than -j-i-^^, as will be seen by and by, are extricated all at once, when con- 

 fined, as in fire arms, in a space 250 or rather 500 times less than they can 

 occupy when reduced to the temperature of the common atmosphere, and of 

 consequence 2000 less than they can occupy when heated in the moment of in- 



