THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



.V<CO 



Art. XXI Y. — Experiments on the Active Deposit of 

 Radium ; by E. M. Wellisch, Assistant Professor of 

 Physics, Yale University. 



Introductory. 



1. In a previous paper* the experimental result was 

 described, that when radium emanation is mixed with any gas 

 there is a definite limit to the fraction of the active deposit 

 which settles on the cathode in an electric field. This limiting 

 value is independent of the pressure of the gas, provided the 

 latter is high enough to prevent appreciable recoil on to the 

 walls of the containing vessel ; it is however, in general, 

 dependent on the nature of the gas with which the emanation is 

 mixed. The values assigned in the previous paper were 89*2 

 per cent for air and hydrogen, 80*7 per cent for carbon dioxide 

 and 10 per cent for ethyl ether. 



The physical meaning of this limiting value is that it 

 represents the fraction of the total number of deposit particles 

 which possess a positive charge at the end of the recoil path, 

 before either columnar or volume recombination have had a 

 chance to become operative. The small value of the limit in 

 the case of ethyl ether was surprising and was ascribed to the 

 large density of ionization produced by the deposit particle 

 during its motion of recoil. It had previously been shown 

 that with air or hydrogen the deposit particles are either 

 positively charged or neutral ; it became of interest to ascer- 

 tain whether negatively charged particles were present when 

 the emanation was mixed with ether. This was the immediate 

 purpose of the present investigation, but, as will be seen later, 

 the field was greatly extended as the experiment progressed. 



* Wellisch, this Journal, xxxvi, p. 315, October, 1913. 



Am. Jour. Sci.— Fourth Series, Vol. XXXVIII, No. 226.— October, 1914. 

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