384 



ME. J. E. PETAVEL ON THE PKESSURE OP EXPLOSIONS. 



Relation of Pressure to Gravimetric Density. 



The present work was not taken up with a view to specially investigating the above 

 subject, which has already been fully treated by NOBLE. It is, however, of interest 

 to compare the results with the much more complete set published by this 

 investigator. 



To minimise the effect of the rapid rate of cooling, which, as we have just seen, is 

 inherent to small enclosures, we must select for comparison the values obtained when 

 using cordite of relatively small diameter. The pressures obtained with cordite of 

 0'175 inch and - 035 inch diameter are shown in fig. 17, marked in on the curve 

 representing NOBLE'S results, and are, as will be seen, in close agreement with it. 



OJ5 



Gravimetric density. 

 Fig. 17. Variation of maximum pressure with the gravimetric density of the charge. 



The curve is traced out from the values given by Sir ANDREW NOBLE ; the points marked on it refer 

 to the results incidentally obtained in the course of the present work. 



Though the pressure and temperature are exceptionally high, there is no reason for 

 supposing that the products of combustion depart considerably from the law which 

 governs the pressure of gases at ordinary temperatures. 



This law may be written 



In the present case, where the temperature is very high and constant, we may put 

 RT = c, and for a first approximation neglect cohesion of the gas. 

 The formula then takes the simple form 



p (vb) = c. 



