Lucian — Distribution of Deposit in an Electric Field. 539 



Art. L. — The Distribution of the Active Deposit of 

 Actinium in an Electric Field ; by A. .N. Lucian, Ph.D. 

 (Yale). 



I. Introduction. 



The observation first made by Rutherford, that the active 

 deposit of radium is to a large extent concentrated on the 

 cathode in an electric field, led naturally to the supposition that 

 the deposit consisted of positively charged particles and that 

 under suitable conditions the concentration could be made 

 complete. The results obtained by Welliseh and JBronson* 

 and by Wellischf separately showed that this supposition is 

 not justifiable. In the second paper cited, it has been shown 

 that the radium deposit atoms consist of neutral and positively 

 charged particles ; that even under the most favorable condi- 

 tions only a definite proportion (about 90 per cent) of the 

 particles is deposited on the cathode ; that there is distinct 

 evidence of columnar or initial as well as volume recombina- 

 tion and that in general both effects are much more pro- 

 nounced for the case of deposit particles and gas ions than for 

 the gas ions among themselves. 



The work on the actinium active deposit had been quite 

 inconsistent from the beginning and had given rise to various 

 views in regard to the origin and the sign of the charges car- 

 ried by the deposit atoms and the mechanism of the transfer in 

 an electric field. Recently, Walmsley^; published the results 

 of a series of experiments in which he eliminated the disturb- 

 ing causes existing in the work of previous investigators, 

 such as presence of dust, moisture, etc. and arrived at the fol- 

 lowing conclusions : (1) The distribution of the active deposit 

 of actinium between the electrodes is independent of the 

 amount of the emanation, (2) with suitable fields all of the 

 deposit can be collected on the cathode, (3) actinium A and B 

 acquire their positive charge in the process of their creation, 

 (4) in an electric field actinium A and B behave exactly like 

 the positive gas ions produced by their radiations ; they recom- 

 bine in exactly the same way (initial recombination being 

 absent) ; and the activity on the anode is due entirely to the 

 diffusion of uncharged deposit atoms formed by recombination 

 in the volume of the gas. 



The observation that the distribution of activity over a wide 

 range is independent of the amount of emanation and that the 

 activity on the anode is due to the diffusion of neutral par- 

 ticles are in agreement with the results obtained by Welliseh 



* Welliseh and Bronson, Phil. Mag., vol. xxiii, May, 1912. 

 f Welliseh, this Journal, vol. xxxvi, Oct. 1913. 

 iH. P. Walmsley, Phil. Mag., vol. xxvi, Sept. 1913. 



Am. Jour. Sci.— Fourth Series, Vol. XXXVIII, No. 228. —December, 1914. 

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