552 Lucian — Distribution of the Active Deposit of 



be explained by considering the different relative distribution 

 of charged deposit particles and negative ions, the different 

 conditions of electric intensity and the consequent different 

 amount of recombination near the central electrode and in the 

 neighborhood of the boundary of the vessel. 



The curves shown in fig. 3 are plotted from those in fig. 2 by 

 taking the points in which the curves of fig. 2 intersect a verti- 

 cal line, corresponding to a given amount of emanation. 



The earlier portions of the curves show clearly the increase 

 of volume recombination with the increase of the amount of 

 emanation employed. The gradual rise of the curves after 

 200 volts shows the presence of columnar or initial recombina- 

 tion. The curves of ionization coincide at about 600 volts ; 

 the curves for the distribution of activity coincide at about 

 1000 volts (not shown in the fig.), and thenceforth, no increase 

 of voltage alters perceptibly the percentage of the cathode 

 deposit. Thus there seems to be a definite limit (94'9) to the 

 value of the cathode percentage; this limiting value for 

 actinium is considerably greater than the value (88*2) found by 

 Wellisch for the active deposit of radium. 



The dotted lines in fig. 3 show a number of curves represent- 

 ing the variation with voltage of the ionization current when 

 various amounts of the emanation were in equilibrium with 

 the deposit products. The readings of the ionization current 

 were obtained while the air current was passing and on this 

 account were not of a high order of accuracy as the amount of 

 emanation present in the vessel was subject to slight variations. 

 Hence a large number of these readings were taken for vari- 

 ous voltages and for different arbitrary amounts of emanation 

 used, and a set of average curves was plotted. All the ioni- 

 zation curves in fig. 3 were plotted by changing the scale of 

 ordinates to correspond to a saturation value of 94*9. It 

 should be noticed that the ionization current is assumed to 

 attain its saturation value at 600 volts. This is very approxi- 

 mately true ; at any rate the qualitative results that will be 

 drawn from the nature of the ionization and activity curves 

 are not invalidated by this assumption. At 1000 volts ioniza- 

 tion current readings showed no appreciable difference from 

 the values at 600 volts. 



From an inspection of the curves of fig. 3 it will be seen 

 that for any given amount of emanation the "activity" curve 

 lies continually below the ionization curve. In other words, 

 the electric field is able to bring to the central electrode a 

 larger proportion of positive ions than of positively charged 

 deposit particles. For smaller voltages this can be easily ex- 

 plained on the supposition that the deposit particles and nega- 

 tive ions contained in the volume of the vessel combine much 

 more readily than the negative and positive ions among them- 



