Transactions of The Royal Society of Canada 



SECTION III 

 Series III DECEMBER 1915 Vol. IX 



On the Mobilities of Ions in Air at High Pressures. 



By Professor J. C. McLennan, F.R.S. and David A. Keys, 

 B.A., University of Toronto. 



(Read May Meeting, 1915.) 



I. Introduction. 



In a paper by the writers, "On the electrical conductivity 

 imparted to Liquid Air by alpha rays," attention was called to 

 the exceedingly high insulating properties possessed by liquid air. 

 The paper also included some measurements on the saturation currents 

 in liquid air and in air at high pressures, when these were ionised by 

 alpha rays. In the discussion of some phenomena connected with 

 these currents, attention was drawn to the necessity of making measure- 

 ments^ on the mobilities of ions both in liquid air and in air at very 

 high pressures. Since the publication of that paper we have on several 

 occasions made attempts to measure the mobilities of ions produced 

 in liquid air; but up to the present have not succeeded in getting any 

 trustworthy results. Convection currents due to the motion of air 

 bubbles formed in the liquid air and the contamination of the liquid 

 air by ice crystals formed from condensed atmospheric water vapour, 

 have been two disturbing factors which we have not as yet been able 

 to satisfactorily eliminate. It has been difficult, too, to reduce the 

 size of the ionisation chamber of the measuring apparatus to dimensions 

 small enough to permit of its use in a mass of liquid air small enough 

 to be jacketted and kept at a low temperature by an outside vessel 

 of liquid air maintained at a low temperature by rapid evaporation. 



With regard to measurements on the mobilities of ions in air at 

 high pressures, however, it has been quite different, for it has been 

 found easy to make measurements on the mobilities at all pressures 

 up to as high as approximately one hundred and ninety atmospheres, 

 for such high pressures were obtained quite readily by the use of a 

 liquid air compressor. 



Sec. Ill, 1915—10 



