THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE, 



[SIXTH SERIES.], 



C T B 



ER M21.^ UI r*&*A 



LVI. A Piezoelectric Method of Measuring Explosion Pres- 

 sures. By David A. Keys, .M.A , Ph.D., Sheldon Fellow 

 in Physics of Harvard University * . . 



[Plate XVI.] 

 I. Introduction. 



THE present paper contains the results of some experi- 

 ments on the measurement of the time-pressure rela- 

 tions when mixtures of electrolytic gas and air are detonated 

 at constant volume and when small charges of guncotton 

 and T.N.T. are detonated in water. In measuring- very 

 rapid changes in pressure, it is desirable to have the inertia 

 of the moving parts 'of the recording system as small as 

 possible. Especially is this true when changes of pressure 

 amounting to several hundred pounds per sq.inch take place 

 in a ten-thousandth of a second, in which case errors due to 

 the inertia of the recording system become important. To 

 overcome this source of error and to measure pressure 

 changes in very small intervals of time, Sir J, J. Thomson 

 devised the method used in the following experiments. The 

 method consisted in the application of the piezoelectric 

 properties of tourmaline crystals in conjunction with a 

 special form of cathode-ray oscillograph. Crystals of tour- 

 maline properly cut and mounted are placed in the vicinity 

 of the explosion, where the time-pressure curve is to be 



* Communicated by Prof. Sir J. J. Thomson. O.M.. F.K.S. 

 Phil Mag. S. 6. Vol." 42. No. 250. Oct. 1921. 2 K 



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