302

THEOfcY AND PRACTICE

TRACT 3?.

177. On this principle it was that Mr. Robins made allhis experiments, and performed all his calculations in’ gun-nery. But it is manifest that this method of guessing at thedegree of heat of the dame must be very uncertain and un-satisfactory, as much below the truth, since all our notionsand experience of the heat of inflamed powder convince us,that it is higher than that of red-hot iron ; and indeed it hasclearly appeared from our experiments, that its heat is atleast double of that of red-hot iron, and that it increases theelasticity of the elastic fluid more than 8 times. Mr. Robins,as before mentioned, stated that he computed the clastic fluidproduced by the fired powder, when cooled, to be 244 timesdenser and stronger than common air: this however is a ra-dical error, the effect of which runs through all his after cal-culations; and it happened in increasing the number 520,by its -r 1 ,. part, erroneously stating it thereby to become 575,instead of only 555 ; in consequence it happened that hebrought out the number 244, instead of 236, which is thetrue measure of the elasticity of the cool elastic fluid, whenoccupying the same space as its producing powder. But ithas been found, from our experiments, that by the heat ofthe flame, the elasticity is increased to 2000 times that of theatmosphere, which is an increase of almost 9 times the force,by means of the heat of the inflamed powder, instead of 4times only.

178. We may hence also deduce the amazing degree ofcondensation of the elastic air in the nitre and gunpowder,and the astonishing force experienced by its explosion. Itlias been found by Mr. Robins and other philosophers, that

of the mass of the powder consists of the pure condensedair, or that the weight of the condensed air is equal to ofthe whole composition. But the whole composition of thepowder consists of 8 parts by weight, of which 6 parts arenitre, 1 sulphur, and 1 charcoal ; of which the nitre, or | ofthe composition, furnishes the whole of the condensed air,while the sulphur and charcoal only give the fire that pro-