554 Lucian — Distribution of the Active Deposit of 



cathode percentage of the equilibrium active deposit. This 

 behavior of the deposit atoms leads one to the conclusion that 

 they are of 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 respectively, 

 corresponding to 38 per cent and 69 per cent of the total num- 

 ber of ions and of deposit atoms. These numbers represent, 

 according to Wellisch and Woodrow,* the percentage of the 

 total number of ions and of deposit particles which escape from 

 the a-particle and recoil columns as a result of molecular agita- 

 tion 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, qualitative^ at least, like the deposit of radium. 



A theory has already been advanced by Wellisch in explan- 

 ation of the behavior 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 pro- 

 cess 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 

 development, especially with 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 mechan- 

 ism 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 expul- 

 sion of an a-particle and a number of slow-moving electrons: 

 further, the deposit atoms are at least of ionic order of magni- 

 tude and perhaps larger and move with relatively small velocities. 

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



