426 Prof. E. M. Wellisch : Experiments on 



These aggregates diffuse very slowly 5 and therefore accumu- 

 late in the gas, so that in the steady state there is a large 

 amount of gas activity. Experiments 15, 16, and 17 in 

 conjunction show that the amount of charged activity in the 

 gas constitutes alone approximately half the total amount of 

 active deposit in radioactive equilibrium with the emanation. 

 The slow rate with which the particles diffuse is well shown 

 hy the smallness of the activity in the absence of any applied 

 potential (Sand 18). With a large positive potential applied 

 to the case the inner electrode if exposed for 1 minute 

 receives practically all the positively charged aggregates, 

 plus the positively charged deposit particles formed in 

 1 minute ; the amount formed is, however, in the circum- 

 stances to which Table II. refers comparatively small (12). 

 A large applied negative potential brings over similarly the 

 negatively charged aggregates. 



An essential condition for the presence in the gas of a 

 large amount of active deposit is that sufficient time should 

 be allowed for the particles to accumulate. Experiments 10 

 and 12 show well the difference which results from varying 

 the time allowed for accumulation. From a knowledge of 

 the activity resulting from a long exposure (cf. 11) it is 

 easy to calculate by the aid of standard transformation 

 formulae the activity which should result from an exposure 

 of 1 minute in the absence of any accumulation. The theory 

 gives that the former activity is 40 times the latter, which 

 shows that the activity in experiment 12 is due practically 

 entirely to the formation during 1 minute ; experiment 10 

 shows in consequence the preponderating influence of the 

 deposit which has been allowed to accumulate in the gas. 



There is abundant evidence that the aggregates owe their 

 charge to the ions present in the gas. Experiments 13, 14, 

 and 16 bring out this point most clearly ; in experiment 13, 

 where the duration of exposure is long, the ions are removed 

 from the gas by the applied field, and the activity measured 

 is due practically entirely to the diffusion of the neutral 

 deposit particles ; in experiment 14 there has not been 

 sufficient time for accumulation of deposit in the gas and the 

 consequent formation of aggregates ; in experiment 16 the 

 central electrode receives the negatively charged aggregates. 

 Moreover, for long exposures there is more deposit on the 

 central rod with an applied potential of —400 volts than 

 with —990 (cf 1 and 5). With the former potential it was 

 easy to show by readings of the ionization current that there 

 was considerable recombination of the ions ; this implies the 

 presence of ions in the gas, and hence an increased number 



