372 



MR. J. E. PETAVEL ON THE PRESSURE OF EXPLOSIONS. 



to 0'02 and the maximum pressures recorded below one half ton per square inch. It 

 is necessary to point out that such a method may not infrequently lead to most serious 

 errors. 



Finally, it is generally understood that, in connection with this subject, numerous 

 experiments have been carried out at Woolwich under the direction of Major HOLDEN, 

 but no results have as yet been published. 



Experimental Work. 



A preliminary question to be decided, before starting the series of experiments, 

 referred to the method of ignition. The usual practice is to fire the charge of cordite 

 by means of a small quantity of fine powder, which is ignited either by a percussion 

 cap, or by a metallic wire which is brought to incandescence by an electric current. 

 Some records were taken in this way, but it was soon found that alterations in the 

 amount and disposition of this firing charge, though leaving the actual maximum 

 pressure almost unaffected, caused some variation in the shape of pressure curve (see 

 fig. 9). When a relatively small quantity of the igniting charge is used in an 



o.oi 



0.0? 



0.03 



0.01 0.02 0.03 



Time in seconds. 



Fig. 9. Comparison of the effect of ignition by oxyhydrogen and gunpowder. 



Cordite of 0-175 inch diameter in a cylindrical enclosure; charge uniformly distributed; gravimetric 

 density 1 ; A, fired with oxyhydrogen gas ; B, fired with fine-grained powder. 



enclosure of considerable length, only the part of the cordite in immediate proximity 

 seems at first to take fire, and the flame is then propagated from layer to layer of the 

 explosive. When the firing charge is larger, or the dimensions of the enclosure 



