2 Petavel, High-Pressure Explosions. 



The relative strength of solid explosives was in those 

 early days also estimated by the two following methods : — 



I. Firing them in a closed chamber in the centre 



of a block of lead, the permanent increase of 

 volume of the chamber being taken as a 

 measure of the explosive force. 



II. Measuring the angle through which a heavy 



pendulum was moved when acted upon by the 

 explosion. 



The next important advance was due to Rodman, 

 who, in 1859, invented the crusher gauge. This instrument 

 has been almost exclusively used during the last fifty 

 years. A piston works in a steel cylinder screwed into 

 the explosion chamber. One end of the piston is flush 

 with the inner surface of the explosion chamber, the other 

 rests on a short copper cylinder. The explosion crushes 

 the copper by an amount which bears a known relation to 

 the maximum pressure attained. 



In 1875 Noble and Abel measured the explosive 

 pressure of gunpowder by determining the rate of accele- 

 ration of a projectile. 



In recent years many new instruments have been 

 devised. Le Chatelier and Mallard have used a modifica- 

 tion of the Bourdon gauge ; Vieille has used a piston con- 

 trolled by a stiff spring ; Noble and others have obtained 

 records from an instrument not unlike an ordinary steam- 

 engine indicator, the initial compression of the spring 

 being, however, regulated to nearly correspond with the 

 maximum explosive pressure. 



Many useful results have been obtained by causing 

 the piston of the ordinary crusher gauge to inscribe its 

 rate of motion on a revolving cylinder. 



Finally, the chemical phenomena which occur during 

 the firing of the charge, and the rate of the explosion of 



