Wellisch — Experiments on Active Deposit of Radium. 287 



tides in the gas which are present in the steady state in the 

 volume corresponding to a height I of the condenser, is seen 

 to be 



^ (j» _ a') { V + a 2 - b l 



log* 

 a 



When a = 0,i. e. if the central rod be absent the number 

 present becomes ; this case is of special interest in con- 



nection with the determination of D (v. Section 6). 



Let us now proceed to apply equation (4) in order to esti- 

 mate the fraction of the total activity which should appear on 

 the central rod in a diffusion experiment, i. e. when the central 

 rod and the case are metallically connected. It is of interest 

 here to observe that the expression obtained in (4) for this 

 fraction is determined wholly by geometrical conditions, being 

 independent of the nature of the gas, pressure, amount of ema- 

 nation, etc. 



For the vessel employed a == '091 5 cm , h = 2*9 cm 



145 ; a ' = -001 



2log- 

 a 



fraction = *144 



This is greater than the fraction *105, which was obtained 

 for the activity distribution as a result of a series of diffusion 

 experiments under varied conditions ; however, it should be 

 remembered that expression (4) refers to an indefinitely long 

 cylinder, and there is no doubt that the corrections for the 

 diffusion to the top and bottom would bring the calculated and 

 observed values into closer agreement. 



Another diffusion experiment was performed with a central 

 rod of thin steel, the radius being *015 cm . The value obtained 

 for the fraction of the deposit on this rod was '066 ; the value 

 calculated from (4) is '095. 



To revert to the experiment when the emanation was mixed 

 with ethyl ether, we see, therefore, that the values given in 

 Table I indicate that very approximately all the deposit parti- 

 cles are uncharged and reach the electrodes as a result of diffu- 

 sion. The limiting value of 10 per cent, which was assigned 

 in the previous paper, is incorrect, on account of the erroneous 

 assumption which was there made with regard to the diffusion 

 distribution. 



It may not be out of place here to draw attention to the fact 

 that nothing has been said with regard to the charge carried 



