DETONATION OF HIGH EXPLOSIVES OR BY THE IMPACT OF BULLETS. |ft| 



was estimated from experiments in which there was no piece on the end of the shaft. 

 Separate experiments were also made to determine the effect of the blast on the 

 supports of the shaft. The momentum accounted for by the blast is in each cane 

 deducted from the total recorded momentum to get the nett momentum due to the blow 

 on the end of the shaft. This correction in the case of the box amounted to about 

 8'3 units with a 15-inch shaft, and 1'2 units with a 30-inch shaft. The correction for 

 the blast on the supports of the shaft was 5 units. 



The table on p. 452 gives the results of all the trials made with the gun-cotton about 

 f inch from the end of the shaft. 



The total impulse of the blow when the air space is f inch varies from almut 35 to 

 70 units, the average being about 46 units. The percentages abHorlx.*! by the different 

 end-pieces are, however, more nearly constant, and from them a rough approximation 

 to the pressure wave transmitted by the rod in an average case may be constructed. 

 As already explained the precise form of this curve depends on the way in which the 

 pressure rises, but it may be assumed in this case that the pressure reaches its 

 maximum in a time that is short even in comparison with the duration of the blow. 

 Assuming an average total momentum of 45 units, fig. 13 has l>een constructed. The 



K> 



1 2 



Time, /o~ a secs 



area of the parallelogram marked 1 represents the momentum given to a 1-inch piece, 

 the width of this parallelogram is 10"' seconds and the height is the average pressure 

 acting during the first 1Q- 5 seconds. The parallelogram marked 2 represents the 

 excess of the momentum given to the 2-inch piece over that given to the 1-inch piece 

 and its height is the average pressure acting during the second 10'* seconds 

 dotted curve gives the same average pressures over the successive intervals of time. 

 It is obviously largely conjectural, but it gives a rough idea both of the max! 

 pressure and of the duration of the blow. 



The chief difficulty experienced hitherto in measuring by this method the pn 

 developed in the detonation of gun-cotton has been the permanent defonnation of the 

 end of the rod by the blow. No steel has yet been discovered which will stand, wn 

 flowing or cracking, the detonation of gun-cotton in contact with it, and even wh. 



