HISTORY OF PROPELLANTS 31 



products and of the gases. The weight of the permanent 

 gases found by them represented only 31 per cent, of the 

 weight of the powder, and occupied at C. at atmospheric 

 pressure only 193 times the volume of the unexploded 

 powder. They fixed the temperature of explosion at 

 3,340 C. and computed that the maximum pressure which 

 the gas can attain, which it may approximate to but can 

 hardly reach, is about 4,374 atmospheres, or 29 tons on the 

 square inch. 



The very high tension of 101,000 atmospheres suggested 

 by Count Rumford as the result of his latest experiments 

 does not appear ever to have been accepted, but within 

 my own time Piobert, who wrote in 1864, and who made 

 a number of important experiments, appears to have 

 accepted as tolerably correct Rumford 's first series of 

 experiments, and fixed the tension of gunpowder when 

 fired in its own space at about 23,000 atmospheres, while 

 Cavalli in 1867 arrived at nearly the same conclusion, 

 making the tension about 24,000 atmospheres. On the 

 other hand, I find that text-books in use at the Royal 

 Military Academy, Woolwich, so late as 1879 placed the 

 tension of fired gunpowder so low as 2,200 atmospheres, 

 or, say, about 14 tons per square inch. 



The authors who ascribed the enormous pressures I have 

 named much underrated the rapidity of the combustion of 

 gunpowder under pressure, and assumed that the combus- 

 tion was comparatively very slow, and that due to this 

 slow combustion the possible maximum pressure was never 

 even approximated to in the bores of guns; but it has 

 always struck me as remarkable that the authorities who 

 accepted these high tensions did not test the accuracy of 

 their assumptions by employing the simple test suggested 

 by Robins, viz., to find* what increase of energy would 

 be realized when the weight of the shot was doubled, 

 trebled, etc. 



I myself, about a century and a half after Robins, 

 repeated his experiment with means at my disposal far 



