776 Dr. A. N. Lucian on the Distribution of the 



conclusion that they are o£ larger mass and size than the 

 ordinary gas ions. 



The ionization and activity curves of fig. 3, marked o, and 

 corresponding to absence of volume recombination, afford 

 further evidence as to the size of the deposit atoms. It will 

 be seen on inspection that the activity and ionization curves 

 cut the axis of ordinates at the points "36 and '66 respec- 

 tively, corresponding to 38 per cent, and 69 per cent, of the 

 total number of ions and of deposit atoms. These numbers 

 represent, according to Wellisch and Woodrow *, the per- 

 centage of the total number of ions and of deposit particles 

 which escape from the a-particle and recoil columns as a result 

 of molecular agitation and diffusion. The above numbers 

 indicate that, roughly speaking, twice as many positive ions 

 on the average escape from the a-particle column as positively 

 charged recoil atoms from the recoil column. This relative 

 slowness exhibited by the deposit particles is naturally to be 

 ascribed to their size and mass as compared with the ions. 



In all these particulars actinium active deposit seems to 

 behave, qualitatively at least, like the deposit of radium. 



A theory has already been advanced by Wellisch in ex- 

 planation of the behaviour of the radium active deposit in an 

 electric field. According to this view, after a deposit particle 

 recoils into the gas, it is subject to the chances of columnar 

 and volume recombination. But when both columnar and 

 volume recombination are avoided by the application of 

 sufficiently high potentials, the distribution of the active 

 deposit on the electrodes is determined by the relative 

 number of charged and uncharged carriers which result from 

 the process of recoil. During the motion of recoil the deposit 

 atom is unaffected by any applied electric field, so that 

 initially the relative number of charged and uncharged recoil 

 atoms is independent of the applied potential. The nature 

 of the charges carried by the deposit particles at the end of 

 their recoil path is determined by the continual process of 

 gain and loss which occurs during the recoil motion of the 

 particles. 



This theory is susceptible to modification and further de- 

 velopment, especially w T ith regard to the sign of the charges 

 acquired by the deposit particle as a result of and at the 

 end of the recoil motion, by taking into consideration the 

 mechanism of the process of ionization in the following 

 manner. To start with, the recoil atoms at their formation 

 will acquire in general an electric charge as a result of 

 the simultaneous expulsion of an a-particle and a number 



* Wellisch and Woodrow, this Journal, Sept. 1913. 



