and its Products of Transformation. 839 



to dryness. The activity of this was found to be 19 divs. 

 per minute. In the circumstances of such an experiment 

 this must be regarded as a very satisfactory agreement, 

 especially considering that in the second case the film is 

 always thicker than in the first, thus cutting off a little a-ray 

 activity. In another similar experiment the activities were 

 respectively 4*5 and 4*2 divs. per minute, a loss of about 

 75 per cent. 



Similar experiments showed that the /3-ray activity was 

 almost completely separated with polonium. These experi- 

 ments were repeated on a larger scale with different quantities 

 of barium salt. In some cases, when small quantities of 

 barium salt were used, the separation was incomplete (see 

 curve No. 1, fig. 2). When the quantity of barium used was 

 sufficient the /3-ray product separated in this way was found 

 to decay exponentially with a period of 5 days. The barium 

 sulphate precipitated was at first inactive, but a /3-ray product 

 was found to grow in it having the period of radium E, as 

 shown previously. The barium sulphate was always preci- 

 pitated in warm dilute solution in presence of hydrochloric 

 acid, and the precipitate was filtered immediately afterwards 

 through a special filter and washed with dilute hydrochloric 

 acid. 



Thus radium D can be separated completely from radium E 

 and polonium, and in the case of radium solution, radium 

 and radium D are precipitated and radium E and polonium 

 remain in solution. 



Summary. 



(1) Radium E has a period of 5*0 days and follows directly 

 after radium D without any intermediate product. 



(2) The absorption curve for the /3 rays from radium E is 

 exponential with a coefficient of 43 cm. -1 



(3) The time period of radium D is about 1G*5 years. 



(4) Polonium and radium E can be completely separated 

 from radium and radium D. 



In conclusion I wish to thank Professor Rutherford for 

 suo-o-estin"; this research. 



