398 Mr. S. Ratner on some Properties of the 



was established between A and B, A being positively charged) 

 in order to prevent the recoil atoms of RaB from reaching 

 the disk. The experiments were carried out in air at atmo- 

 spheric pressure. 



As far as the radioactive products constituting the active 

 deposit can be separated from each other, the phenomenon 

 has been investigated for each product separately. Thus 

 sufficiently pure RaA was obtained by exposing the plate R 

 to emanation for a short time and quickly removing it to the 

 testing apparatus. RaB was obtained by recoil from RaA, 

 and RaC by dipping a nickel plate into a solution of the 

 active deposit. A great number of experiments, however, 

 have been also carried out with radium (B + C) on the 

 plate R. 



As in the course of this work activities were dealt with 

 varying in strength as 1 to 100,000, great care had to be 

 taken to protect the disks from contamination with the radio- 

 active matter from the plates. The amount of emanation 

 used varied in different experiments from 10 to more than 

 200 millicuries. The activities of the disks were usually 

 measured by a Wilson's tilted electroscope, that of the plates 

 by a ft- and 7-rays electroscope of the ordinary type. 



As shown later, it was very important in the course of 

 these experiments to be able to follow the rate of change 

 with time of the quantity of active matter acquired by the 

 disk C. This was realized by exposing to the action of 

 the active plate Rfa number of disks at definite intervals 

 one after another, and by measuring their activities. In this 

 way the period T could be easily determined during which 

 the quantity of active matter reaching the disks per unit 

 time falls to a half value. If this quantity were proportional 

 to the amount of active matter present on the plate R, 

 T would be equal to the half-value period of the corre- 

 sponding radioactive product. The experiments show, how- 

 ever, that these two periods as a rule differ from each other. 

 3. Experimental results. — In the first place it appeared 

 necessary to ascertain whether the active matter acquired by 

 the disk O belongs to the same product as that on the plate R. 

 The activity of the disks was carefully analysed and identified 

 beyond doubt with the active matter on the plate R. Thus, 

 in the case of RaA on R the active matter on the disk was 

 found to be an «-ray product with a half-value period of 

 3 min., giving up RaB by recoil. In general, the curves 

 of decay or recovery drawn for the activities on the disks 

 were found to coincide with the characteristic curves of the 

 products covering the plate R, 



