the Active Deposit of Radium. 421 



The first term, which in most cases is the more important, 

 is the same as the electrical capacity per unit length of the 

 condenser. 



By integrating equation (3) the total number of deposit 

 particles 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 



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

 present becomes — j^rrpj this case is of special interest in con- 

 nexion with the determination or 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 emanation, etc. 



For the vessel employed, a = *09l5 cm., 6 = 2*9 cm., 



= •145; «* =-001; 



2 loo- - 



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 w r e see, therefore, that the values 

 given in Table I. indicate that very approximately all the 

 deposit particles are uncharged and reach the electrodes as a 

 result of diffusion. The limiting value of 10 per cent, which 



