I 



Active Deposit of Radium. 403 



assumption must be rejected, since the volatilization of the 

 active deposit at lower, and its condensation at higher, tem- 

 peratures would contradict the fundamental principles oE 

 Thermodynamics. 



The suggestion made by Russ and Makower (loc. cit.), 

 namely, that groups of radioactive atoms may be set free by 

 recoil when an a-particle is ejected by one of the atoms in 

 the group, was tested in the following way. A number of 

 disks were exposed in the apparatus, 3 inin. one after 

 another, to a plate covered with RaB. It is evident that 

 with the increase of RaC on the plate the chances for the 

 groups to be set free also increase, and therefore the 

 quantity of active matter expanding from the plate should 

 be expected to increase with time, if the assumption were 

 true. The experiments show, however, that this quantity 

 decreases with a certain period T varying within the limits 

 given above. 



The striking regularity of the phenomenon in the case of 

 RaA led to the assumption that the spreading of the active 

 matter is not a secondary mechanical effect on the surface of 

 the plate, but is due in some way to interatomic forces in the 

 active deposit. With the knowledge now available one could 

 easily imagine that a number of branch products are present 

 in small quantities in the active deposit of radium, giving up 

 by recoil the active matter found on the collecting disks. 

 The period T=l*4 min. for RaA, for instance, would be 

 nothing else but the half- value period of the unknown branch 

 product giving up RaA by recoil. This assumption seemed 

 to be a very promising one, since it could serve as a guide 

 for the investigation not only of the phenomenon itself, but 

 also of the supposed branch products of radium. The results 

 of numerous experiments carried out in this direction failed, 

 however, to be in favour of this theory; and some of them, 

 on the contrary, furnished sufficient evidence ngainst it. 

 Thus, as mentioned above, the amount of active matter given 

 off by RaA does not depend on the time of exposure of the 

 plate to emanation, though one can hardly imagine a radio- 

 active product accumulating from the emanation to its full 

 value during a small fraction of a second and decaying with 

 a half-value period of 1*4 min. Further, the collecting disk, 

 after being exposed to a plate coated with RaA, was put in 

 place of the plate, and was found to give off RaA in its turn, 

 though it is evident that this disk could not contain the 

 branch product giving up RaA by recoil. 



It could also be suggested that some of the radioactive 

 atoms (or particles) are but slightly attached to the active 



