482 



Dr. D. A. Keys on a Piezoelectric 



no air was added, the pressure rose to its maximum in less 

 than go'oo °f a second, whereas in (he third case it rose com- 

 paratively slowly. 



Figure 7 represents two curves taken under very nearly 

 identical conditions. The initial pressure in both cases was 



Fig. 7. 



■015 -02 -02 5 



T/me , <Seooncfr. 



35 



Time-Pressure Curve for Explosion of Mixture of H 2 0, Gas, and Air. 



Volume of Mixture =765 c.c. 



Initial Pressure =76 cm. of Hg. 



One cm. displacement =220 lb./sq. inch. 

 Curve I. [- . - . -]. — Volume of Gas = 710 c.c. ; Air=55 c.c. 

 Curve II. [ ]. — „ „ =700 ., ; „ =65 „ 



one atmosphere, but in I. there were 55 c.c. of air and 710 c.c. 

 of electrolytic gas, while in II. the amount of air whs 65 -c.c, 

 the rest of the volume being filled with gas. These two 

 resulting time-pressure curves show that the apparatus gives 

 consistent results. 



The few preliminary results which have just been men- 

 tioned show how the piezoelectric method may be applied to 

 investigate such problems as arise in internal-combustion 

 engine pressures, specific heats of gases, etc. 



V. Determination of Time-Pressure Curve for Explosions of 

 Guncotton and T.N.T. in Water. 



To apply the piezoelectric method to determine the nature 

 of the explosion wave in water, the crystal detector was 

 lowered from a pontoon into the water to a depth of 11 feet. 

 The lid JK was removed and the pot filled with vaseline. 

 Small charges of dry guncotton and T.N.T. w r ere detonated 

 at different distances from the detector. The wire F 

 (figure 1) was connected to the oscillograph, which was placed 



