28 PRESSURE OF GASES. 



The temperature of the system developed by the explosion 

 will then be 



4-8 



The volume of the permanent gases considered at a sufficiently 

 high temperature and at the normal pressure, being here 



t\ 



22-32 lit. (1+-) 



at 4375 will be 380 litres, this volume being yielded by 46 grins, 

 of nitrogen sulphide. 



Such a weight exploding in a capacity of 230 cms. would 

 develop by Mariotte's law a pressure equal to 1652 atm., or 

 1707 kgms. per sq. cm. 



Now, the trial made with a crusher at a density of charge 

 0*20, and calculated by the old process, gave 1703 kgms. Here 

 the calculated pressure is practically equal to the pressure given 

 by the crusher. But according to the new theory it would be 

 necessary to correct the latter figure, and to take into account 

 the uncertainty of the estimation of the heat of transformation 

 of sulphur. 



Hence it will be seen that direct experiments are necessary. 

 However, deviations of quite a different kind might have been 

 expected. 



Third Section. Density of Charge and Specific Pressure. 



1. The relation between the number of grammes expressing 

 the weight of the explosive substance and the number of cubic 

 centimetres expressing the capacity in which the explosion 

 takes place is termed density of charge. Now, if bodies sus- 

 ceptible of being completely transformed into gas at the tempera- 

 ture of the explosion be operated upon, Mariotte's law shows that 

 the pressure developed should be proportional to the density of 

 charge. The temperature, moreover, would remain the same 

 in all cases. 



2. This relation may be regarded as accurate for very low 

 densities of charge ; the ordinary laws of gases being applicable 

 between these limits. But it ceases to be so for medium den- 

 sities, starting from 01 to 0'2, as might be expected, owing to 

 the inaccuracy of Mariotte's and Gay-Lussac's laws for the 

 corresponding pressures. 



3. However, strange to say, the relation again tends to exist 

 for high densities of charge, which are the most interesting for us. 

 This approximate coincidence results, doubtless, from some com- 

 pensation between the variation of the pressures, which is more 

 rapid than Mariotte's law would show, and the variation in the 

 specific heats, which increase with the temperature and pressure 



