The mobility of ions in air

Abstract

In a previous paper I have described an experimental method of measuring ion mobilities in a gas, which yields accurate values for both upper and lower limits of a distribution range, and from which one can also derive a curve showing the general shape of the distribution band, with a calculable resolving power. It was found that negative ions in dry air at normal pressures had mobilities ranging from 2∙15 to 1∙45 cm. per second per volt per centimetre, while the distribution band showed a peak value about 1∙8 and a sharp upper limit at 2∙15. There was also some reason to believe that in the presence of water vapour the band was narrowed, the faster ions being eliminated in the manner found by other observers, and the slower ions remaining comparatively unaffected. In the experiments here described, an improved form of the apparatus is used to study in greater detail the effect of water and other vapours on the mobility distribution, for positive and negative ions in air.