170 Experiments to determine 



was such as enabled him to reconcile the results of his 

 experiments with his theory ; and as later discoveries have 

 shewn his theory to be unfounded, some of his assumed 

 principles must of necessity have been erroneous. 



The most unexceptionable of the suppositions of Mr. 

 Robins relative to the subject under consideration is 

 that respecting the quantity of air, or permanently elastic 

 fluid) that is generated from gunpowder in its combus- 

 tion. It cannot, indeed, with propriety be called a sup- 

 position, for it was the result of a well-contrived ex- 

 periment. 



According to Mr. Robins, when any given quantity 

 of gunpowder is fired, the quantity of permanently 

 elastic fluid or fluids generated from it in its combus- 

 tion is such that, when cooled down to the mean tem- 

 perature of the atmosphere, it would under the mean 

 pressure of the atmosphere fill a space 250 times greater 

 than that which the unfired powder occupied. Conse- 

 quently, if this fluid were compressed into a space no 

 greater than that occupied by unfired powder, it would, 

 in its endeavours to expand itself, on being so com- 

 pressed, exert a force 250 times greater than the mean 

 pressure of the 'atmosphere ; or (to use the language, 

 employed in the foregoing paper) its force would be 

 equal to 250 atmospheres. 



This is very far indeed from 100,000 atmospheres, 

 the expansive force we have assigned to fired gunpowder, 

 but let us see how far the heat generated in the com- 

 bustion of gunpowder may be supposed to increase the 

 expansive force of the elastic fluids which are generated 

 in that process. 



From the experiments of the late General Roy, it has 

 been proved that the expansive force of common at- 



