The charges on ions produced by radium

Abstract

In a paper on “The Charges on Positive and Negative Ions in Gases,” Prof. Townsend has described a method for the direct determination of the quantity N e , where N is the number of molecules in a cubic centimetre of a gas at standard pressure and temperature and e the charge on an ion. His experiments were carried out on ions produced by the action of secondary Rontgen rays, and he showed that for negative ions the method led with great accuracy to the value 1.23 x 10 10 for N e , the same as that for NE, where E is the charge on a monovalent ion in a liquid electrolyte. For positive ions the value obtained in the first set of experiments was 2.4 x 10 10 , but subsequently with less penetrating secondary rays it was found to be as low as 1.26 x 10 10 . It would therefore appear that the positive ions have in some cases a single and in others a double atomic charge, whereas the charge on the negative ions is always the same. With a view of testing the theory for ions produced by radium, experiments have been made with an apparatus precisely similar to that used by Prof. Townsend, and the results obtained confirm the reliability of the method. After making due allowance for experimental and other known sources of error the positive ion appears to behave at all pressures and under all forces in accordance with the theory, but in the case of the negative ion some considerable deviations were observed, if the gas is very dry, but these disappear as soon as some water vapour is added.