548 PHILOSOPHICAL TRANSACTIONS. [aNNO 1779- 



accurately to what proportion of the whole mass this part amounts in reality. 

 On this supposition we shall find, that the whole mass of gunpowder contains a 

 quantity of air in a solid state which is reduced in hulk, to near -^^, or, in other 

 words, that 1 square inch of gunpowder contains near 500 square inches of air ; 

 which being heated in the moment of inflammation will expand to 4 times its 

 diameter; so that according to this calculation gunpowder must expand in the 

 moment of explosion to near 2000 times its own bulk. 



It seems very probable, that this calculation of Mr. Bernouilli is much nearer 

 the truth than that of Mr. Robins and Count Saluce ; but yet the evaluation of 

 the 2 last-mentioned writers, though short of one half, proves in reality Mr. 

 Bernouilli's calculations to be as just as can be expected, when it is considered, 

 that this evaluation was made before the new discoveries on the nature of nitre 

 and charcoal. But this assertion will be better understood when I have explained 

 the nature of gunpowder somewhat fuller. 



If we continue to say, as we have hitherto done, that the charcoal taking fire 

 decomposes the nitre, and extricates from it that amazing quantity of elastic 

 fluid which was shut up within its substance, we only say what we see in reality 

 is the consequence of setting fire to this ingredient. But this explanation does 

 not convey a clear idea of the manner in which the extrication is carried on ; nor 

 of the reason why one single spark, of fire, thrown into an immense heap of 

 gunpowder, should almost in an instant spread the conflagration through the 

 whole mass. Neither does it explain clearly, why nitre and charcoal, which 

 separately yield no flame at all, though ever so much heated, when combined 

 and intimately mixed together, explode with as loud a report as a large ordnance 

 piece, surpassing even in loudness thunder- claps ; nor why this forcible explosion 

 is accompanied by a most brilliant flame. 



Nitre is composed of 2 different ingredients, viz. an acid, called from its pecu- 

 liar nature the nitrous acid, and the vegetable alkali. Neither of these 2 ingre- 

 dients are capable of inflammation ; nay, they even extinguish actual fire. When 

 they are both combined and constitute the neutral salt we speak of, they have 

 not, even by their coalition in one body, acquired an inflammable quality, for 

 nitre maybe made red-hot in a crucible without showing the least appearance of 

 inflammation, not even when a red-hot stone or piece of iron is thrown into it. 

 But if any common combustible substance, as wood, charcoal, or such like, is 

 thrown into the melted nitre, a flame issues with a kind of explosion, though 

 only at the very place where the two substances come into contact. The same 

 flame and explosion is observed when cold nitre is thrown upon a combustible 

 body, in a state of real ignition, on a piece of red-hot charcoal for instance. 



The true reason of this wonderful phenomenon has not been considered 

 hitherto with that degree of attention it deserves, and could not have occurred 



