306 Danysz and Duane — Electric Charges of a- and $-Rays. 



Assuming that each atom of emanation that disintegrates 

 produces one atom of helium, it appears that the volume of 

 helium produced per second by the emanation alone (i. e. \v) 

 must equal the volume of emanation that disappears per 

 second, and this from the definition of X is XV. Hence 



iv — XV = 1-24X10- 9 

 and Y = -594 mm at 15° 



mm* •& 



3 



The average of the best measurements of this volume is 60 mmS , 

 the measurements themselves varying between -52 mm3 and -6Q mm 



The constant of radium itself can be calculated from the vol- 

 ume of helium (Jv) produced per second from one gram, 

 and from the atomic weight of radium 226 : for, assuming that 

 one atom of radium on disintegrating produces one atom of 

 helium, \v represents the volume that would be occupied by 

 the fraction of a gram of radium disintegrating per second, 

 if it were a gas. The mass of this fraction equals \v multi- 

 plied by 226 and by one-half the mass of a cubic centimeter of 

 hydrogen, and also equals by definition the constant X of 

 radium. Hence 



X' = 1-26X10- U (sec"'). 



This corresponds to the disintegration of half a given mass of 

 radium in 1800 years. 



In making the above calculations we have followed the gen- 

 erally accepted theory of radio-active transformations, assum- 

 ing that each atom that disintegrates, except those of radium 

 B, emits a single atom of helium carrying a double charge. 

 The only data used in addition to the charge carried by the 

 a-rays from a given quantity of emanation are such well known 

 constants as the mass of a cm 3 of hydrogen, the volume of 

 hydrogen liberated per second by one ampere of current, the 

 constant of the emanation and the atomic weight of radium. 

 The actual number N of molecules per cm 3 of gas and the 

 magnitude of the elementary charge do not enter separately 

 into the calculations. We may obtain a value of the elemen- 

 tary charge, however, by taking the number of a-particles 

 expelled per second by the quantity of radium C in equilibrium 

 with one gram of radium determined by Rutherford and 

 (xeiger.f This number is n — 3'4XlO~ 10 , from which we have 



e = 4-46xl0- 10 e. s. u. 



This is several per cent smaller than some of the best values 

 recently published, and if we take 4*7 XlO -10 as a good aver- 

 age of these values of 0, we get for n 



n— 3'22xiO to 



* Rutherford, Phil. Mag., 1908; Debierne, Comptes rendus, May, 1909; 

 Ramsay and Gray, Chem. Soc, 1909. 



fRoy. Soc. Proc, A, lxxxi, Aug. 27, 1908 ; Phys. Zeitschr., 1909. 



