540 Lucian — Distribution of the Active Deposit of 



for the case of radium. On the other hand, some of the above 

 results are in direct contradiction to the experimental facts 

 established by Wellisch for the active deposit of radium, which 

 one would expect to hold in the case of actinium also. 



The following investigation was undertaken with a view of 

 distinguishing between the two contradictory sets of results 

 and the corresponding theories, based on them, as to the origin 

 of the charges carried by the deposit particles, their mode of 

 transfer and recombination in an electric Held, etc. The 

 main objects of the experiments contained in this paper may 

 be briefly summarized as follows : 



(1) Is it possible, under suitable conditions, to collect all the 

 active deposit of actinium on the cathode? 



(2) Is columnar as well as volume recombination present ? 



(3) Does volume recombination between the positively 

 charged actinium deposit particles and the negative ions take 

 place at the same rate as the recombination between positive 

 and negative gas ions? 



Before describing in detail the experimental procedure, it is 

 not out of place at this stage to draw attention to a funda- 

 mental difference between the method adopted by Walmsley 

 and that followed in the present investigation. In Walmsley's 

 experiments no direct measurement of the activity of the outer 

 electrode (cylindrical vessel with the air-inlet on the side) was 

 made; the total activity was assumed to be equal to the sum 

 of the activities obtained when the central rod was first made 

 the cathode and then the anode. It will be shown later that 

 this assumption is not justifiable. In the present research the 

 activities of both the case and the central electrode were 

 obtained by direct measurement. 



II. Experimental Procedure. 



The source of the actinium emanation employed was a prep- 

 aration of actinium, which Professor Boltwood kindly placed 

 at my disposal. 



The air current, which carried the emanation into the test- 

 ing vessel, was produced by means of an ordinary water-blower. 

 This gave the desired high velocities of the air current, which 

 could not be conveniently obtained by means of a Mariotte's 

 bottle or a gasometer. In order to obtain constancy of flow 

 three regulators were installed in the system ; a water-pressure 

 regulator, in series with the water-blower, and two gas-pressure 

 regulators along with several large capacities. With these 

 appliances the variations in the pressure were reduced to about 

 1 per cent. 



The air current was conducted through a concentrated solu- 

 tion of potassium hydroxide, to eliminate carbon dioxide, 



