836 Mr. G. N. Antonoff on Radium D 



respective fractions of the total volume for the rings. If m 

 be the number of u particles per sq. cm. per second falling 

 on the screen, the total number of a particles emitted is 

 4:7rd 2 m. A typical experiment is described below. A conical 

 tube of the shape shown in fig. 4 was filled on December 7th, 



1908, with an amount of emanation corresponding to the 

 equilibrium quantity from 10*5 mgrm. of radium. This 

 was opened and the scintillations counted on October 23rd, 



1909, an interval of 320 days. The distance of the zinc 

 sulphide screen from the end of the tube was 12'4 cm. The 

 number of scintillations observed, with the 10 per cent, cor- 

 rection added, was 31*2 per minute, or 0*54 per second, for 

 an area of screen of *00866 sq. cm. The corresponding 

 number m per second for 1 sq. cm. of the screen is 60*0. 

 The tube used was 10*3 cm. long, and for the purpose of 

 calculation was divided into five parts of equal length. If 

 v u r 2? v 3: v i-> v 5 represent the volumes of the parts, we have 



^ = •474 v ^=13*3 cm. 



v 2 = *293i' ^2 = 15*3 cm. 



t? 3 = '156 v c/ 3 = 17*3cm. 



d 4 ='066 v ^4=19*3 cm. 



r 6 = -009w ^ 5 =21-3 cm. 



where v is the total volume, and where d^ d 2 , d %) d^ d~ 0) are 

 the mean distances of the rings. 



^=•0462 



d 2 = 216-0. 



The total number of a particles emitted per second, 

 S = 47rd 2 ??i=r63x 10 5 . This is the number of a particles 

 from the polonium, at a time 320 days alter the tube was 

 filled. 



By means of the approximate theory already considered 

 the constant of change A2 of radium D is given by 



i(i-«- A *0 



Now S = l'63xl0 5 , the toial number of a, particles 

 emitted from the polonium per second ; \ x for the emanation 

 = 2'08xl0- 6 (sec." 1 ) ; (l-<r A ^) = '79.83, taking the half 



