the Active Deposit of Radium. 435 



A very large number of experiments were performed to 

 obtain the ratios a : b : c. There was little difficulty in getting 



an accurate determination of: the value - ; this came out 7. 



c y 



for practically all the experiments. The most accurate 



determination of the ratio - is 7^. ; this was obtained about 



8 times under favourable measuring conditions. Still the 



ratio > was obtained on a few occasions ; of course there 

 15 



was always the possibility in these instances of the presence 



in the gas of charged deposit, but the amount of emanation 



was, as always, quite small. The ratio was never less than 



— . The value of p was taken as *83 ; this value represents 



the fraction of the active deposit that settles on the cathode 

 when 1G0 volts is applied to the case, the quantity of 

 emanation being supposed to be so small that volume recom- 

 bination is absent (v. Section 4). The value of / was taken 

 as '10, this value representing the fraction of the deposit that 

 settles on the central rod in the absence of an electric field 

 (v. Section 3). It was ascertained experimentally that the 

 exposure of 1 minute afforded ample time for this fraction to 

 reach the central rod. 



If we tike the ratios a : b : c as 9 : 20 : 180, then we have 

 from equations (10) and (11) D = *0445 ; £='064. 

 With a : 1> : c=12 : 20 : 180, we deduce D = '029. 



With a:b:c= 9 : 24 : 210, we deduce D = '061. 



The value D = *0445 cm. 2 sec. -1 represents the most probable 

 value for the coefficient of diffusion of uncharged atoms of 

 radium active deposit in dry air at a pressure of 1 atmosphere 

 and at room temperature. The other values for D are to be 

 regarded merely as extremes between which the true values 

 of D appear to he. 



The value obtained for D is smaller than the values which 

 have been obtained experimentally for the diffusion of radium 

 emanation in dry air. In the case of the emanation the 

 values obtained are not very different from "10. The value 

 of D for the active deposit is approximately the same as that 

 found by Townsend for the diffusion of a gaseous ion in air. 



The Experiments of Eel-man n. 

 7. In the Jahrbuch der Radioaliintat (1012), Gerhard 

 Eckmann describes the results of a series of experiments 

 bearing on the diffusion and distribution of the active deposit 



2 F 2 



