PRESSURE DEVELOPED. 25 



With powdered gun-cotton (density of charge 0'20), r is also 

 inappreciable, and the maximum pressure equal to 1985 kgms., 

 the weight of the piston having varied from 727 grms. to 

 42*7 grms. Dynamite (density of charge 0'30) is decomposed 

 slower than gun-cotton, but quicker than black powder; the 

 detonation being of course produced by the aid of fulminate. 

 It therefore supplies an intermediate case, in which the dis- 

 cussion of the measurements is more delicate. By employing 

 pistons of medium weight, and even light pistons, it is very 

 difficult to attain the lower limit (1), at least with a certainty 

 comparable to that of the experiments relative to the preceding 

 substances. On the other hand, towards the opposite limit 



(2), the ratio - may be neglected by giving the piston a mass 



^0 



of 4 kgms. ; the crushing was then nearly double that obtained 

 with pistons weighing 3 '8 grms. and 6*9 grms. Hence, it can 

 be seen that the two limiting cases have been realized with 

 dynamite, as also the intermediate cases, by modifying the mass 

 of the piston. 



The maximum pressure for a piston of 4 kgms. has been 

 found equal to 2413 kgms. per sq. cm. for the density of 

 charge 0'30. With a piston of mean weight, that is weighing 

 only 5 9 '7 grms., the density of charge still being 0'30, dynamite 

 and picrate give the same crushing; however, the maximum 

 pressures are very different. 



What characterises the experiments made with dynamite is, 

 that the calculation made for very light pistons from formula (1), 

 and for very heavy pistons from formula (2), should give, and in 

 fact does give, the same figure for the value of the pressure 

 exerted. 



It is clear from the above with what precaution the 

 crushers must be employed to measure the maximum pressures 

 of explosives. The study of these pressures should be made by 

 the new method of Sarrau and Vieille. 



9. It should here be remarked that the measurements thus 

 obtained correspond only to a certain mean of pressures, a mean 

 which is capable of being considerably exceeded at certain 

 points. In reality, the gases suddenly developed by the 

 chemical reaction represent real whirlwinds in which there 

 exist jets of matter under very different states of compression, 

 and an interior fluctuation. This is shown by the mechanical 

 effects produced by these gases on solid substances, and 

 especially on metals, which are hollowed and furrowed in places 

 as if they had received the impress of an extremely hard solid 

 body. 



The measurement of initial pressures in cannons likewise 

 manifests local irregularities and differences, sometimes enor- 

 mous, between the pressures observed at the same instant at 



