8 Petavel, High-Pressure Explosiojis. 



In spite, therefore, of the suddenness of the rise in pressure, 

 the velocity of the moving' parts remains small, and the 

 usual trouble due to inertia does not arise. Fig. 3 {Plate 10) 

 is an illustration of this fact ; at A the pressure is rising 

 at the rate of over a million pounds per square inch per 

 second, none the less the curve turns sharply at nearly a 

 right angle, without any sign of vibration. The necessary 

 data with regard to Figs. 3 and 4 {Plate 10) will be found 

 in Tables I. and II. 



It is intended to obtain similar curves covering a range 

 of pressure up to 20,000lbs. per square inch, and referring 

 to mixtures from the most explosive to the non-explosive. 

 The work will be divided into four parts, namely : I., 

 Oxygen and hydrogen; II., Coal gas and air; III., 

 Other gaseous explosive mixtures ; IV., Solid and liquid 

 explosives. 



With regard to coal gas and air, barely half the work 

 has as yet been finished ; it is, therefore, too soon to draw 

 any general conclusions. A few points, however, in the 

 records here given deserve attention. 



1. The time required to reach the maximum pressure, 

 namely, 0058 second, is not far from that which would be 

 required with the same mixture at atmospheric pressure. 



2. The ratio of explosive to initial pressure has been 

 increased. At or near atmospheric pressure the ratio for 

 this mixture would be about 7, in the present case it is 

 8"5. This fact is due to three causes which work simul- 

 taneously, namely, {a) the departure of gases from Boyle's 

 Law ; {b) the relative decrease of thermal loss during the 

 time occupied by the combustion ; {c) the increase in the 

 absolute temperature at which dissociation would take 

 place. 



3. The rate of cooling has greatly decreased. 



