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



(P, p}, the smaller end of which (^>) is exposed to the force of the explosion, while 

 the larger end (P) closes' a cylinder filled with gas at a known pressure. The piston, 



Fig. 1. Explosion gauge. (Maximum pressure indicator.) 



The gauge consists of a double-headed piston, P, p. The smaller head p is exposed to the pressure of the 

 explosion, which is counterbalanced by a fixed gaseous pressure acting on the larger head P. The ratio 

 of the two areas (and therefore of the two pressures when in balance) is fifty to one in the case of the 

 gauge illustrated in this drawing. The lift of the piston is limited to about one hundredth of an inch, 

 the distance of the stop B being adjusted by means of a fine screw. The piston on lifting closes an 

 electric circuit and works an indicator. S is the stuffing box through which the stop B passes, C the 

 cover of the cylinder in which the piston P works ; it is held clown by the nut N. G is the gas inlet 

 by means of which the space E is connected to a source of supply of gas under pressure and to a 

 gauge. K is the plug through which the electric connection to the insulated contact-piece H is made. 

 To prevent back pressure, which might arise through leakage past either of the leathers, the space X 

 is connected with the atmosphere by means of the vent V. 



on lifting, closes an electric circuit and works an indicator. To ensure rapid action, 

 the travel of the piston is limited to about a hundredth of an inch. 



Two such instruments were constructed. The first, for pressures up to 100 

 atmospheres, had a ratio of 4 to 1 ; in the second (shown in fig. 1), intended for use 

 up to 1000 atmospheres, the ratio of the areas of the two sides of the piston was 

 50 to 1. Fairly satisfactory measurements of the maximum pressure were obtained 

 by means of this apparatus. 



