2 - 2- 



of the explosive, then by thermodynamics 



P = (7 - 1) wS (3) 







where 8 is the density o' the explosive. 



For T.N.T. w = 3.88 X 10^ ergs per gram. 



5 = 1.2 



so that «ith y - u/3 



p = 1.56 X lo'° dynes/sq.cm. =■ 100 tons/square inch. 



Alternatively equation (2) shows that maximum pressure P^^ at distance r is related to P^ by 



P R = p r W 



max 



so that if P is determined experimentally we can estiinste ^^. Now 'or 100 lbs. T.N.T. at 

 UO feet the ptezo-electric mtthod gives P^^ = 1-02 tons/sguare inch and since R^^ = 0.7 foot 



P = 58 tons/square inch. 



Taking the latter estitmte the following Table is calculated from equations (l) and (2). 



Theoretical course of pressure-time curve 

 for 100 lbs. T.S'.T. at 40 feet. 



1.00 1.02 1.05 l.l 1.2 1.3 



10* t (seconds) = O.U5 0.73 1.06 1.60 2.10 2.58 



P/^rax 



io\ 



These values are compared with those obtained by the pieio-electric rrethod in figure 1 in which A 

 represents the theoretical curve and 8 the experimental curvG. 



It is seen that apart from the finite time required to reach the maximum pressure there 

 is very fair agreement between the theoretical and experimental curves. 



As regards other wc'ights of charge, formula (2) (with B - l) shews that the maximum pressure 

 at a given distance varies as the linear direnslon R , that is as the cube root of the weights. 

 This is in agreement with the experimental results at any rata so long as the weight exceeds 100 lbs. 

 The law of distance fur maximum pressure should theoretically by P^^ r = constant. This law is 

 found to nolo experimentally throughout the range for which the piezo-electric records have been 

 obtained but observations with Hilliar crusht^r gauges at small distances show a tendency for P^^^ 

 to be grjiter than this law would give. 



If r is so large that the second t'jrm In (2) may be neglected, the theoretical shape of 

 the Curve Is the Sciire at all distances. If we include the second term there Is a somewhat more 

 rapid fill of pressure near to the charge. The oxpcrimental evidence from the piezo-electric 

 gauges is not sufficiently precisi to test the constancy of shape. 



In 



