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powder firft takes fire, and exerts its force on the lower part, which 

 is lafl kindled, whereby the fire and fmoke of this lall; part is driven 

 downwards : but if the perfon who gives the fire does, with a 

 light touch, fo apply the match that it may fire the lowell part of 

 the heap as foon or fooner than the upper part, it mull; follow 

 that the lower part of the powder will blow upwards what lies on 

 the upper part and fides of the heap, and this before it is fully 

 kindled, in confequence of which the paper will be little injured. 

 In a word, one man may fo fire a parcel of Gunpowder that it 

 will be deemed good powder, and another man may fire fome of 

 the fame fample in fuch a manner that it Ihall be condemned as 

 unferviceable ; that is, not fufficiently ftrong, or as being damp ; 

 for confidering that fome portion of time is required (as mull cer- 

 tainly be the cafe) for the fire of one grain of Gunpowder kindled 

 by another from beneath, to blow up the upper part of the fame 

 grain, much more time mull be required in a whole mulket charge 

 of Gunpowder for the fire of one grain to be communicated to 

 the others. 



I have alfo turned my thoughts on obferving the firing of Gun- 

 powder in a clofe glafs to the following confideration, namely, 

 whether the motion of the faltpetre particles and the fire did not 

 leave in the glafs a greater quantity of air comprelled together. 

 To make trial of this, I took feveral fmall glalles, into one of 

 which I put a large grain of Gunpowder, into another two, and 

 into another three of fuch grains, and, having perfedlly clofed all 

 the glafles, I fet fire to the Gunpowder in each of them, and left 

 the glalles at reft, until I judged that all the faltpetre particles 

 were fubfided, then opening the glalles, the air rulhed out with 

 violence. 



I afterwards repeated this experiment with feveral other glalles, 

 leaving fome of them four, others five days untouched, and, upon 

 opening them, the air rufhed out with as much violence as in the 



former experiment. 



Us 



