40 THE ROYAL SOCIETY OF CANADA 



In view of this continuity in the dielectric property of oxygen 

 in passing through the stage of liquefaction, it was thought to be of 

 interest by the writers to see if any indication of a similar continuity 

 could be obtained in the ionisation of air by alpha rays when passing 

 from the gaseous to the liquid state. P. Curie,* Jaffe,t Càcilia Bôhm- 

 Wendt and E. von Schweidler| and Bialobjeski,* have shewn that a 

 conductivity can be impressed on certain dielectric liquids by gamma- 

 rays, but Greinacher* appears to have been the only investigator 

 who has studied the ionasation produced in such liquids by alpha 

 rays. His experiments were made with paraffin oil and petrol ether. 



Among other results he found : — 



1. That the conductivity so impressed wa ■• independent of the 



direction of the current and that therefore the molsilities 

 of the positive and negative ions produced in these liquids 

 by the alpha rays were practically identical. 



2. That with petrol ether a saturation current was obtained with 



a field of about 400 volts per cm., but that in the case of 

 petroleum oil complete saturation was not obtained even 

 when fields as high as 10,000 volts per cm. were applied, and 



3. That the total ionization produced in air at atmospheric 



pressure when the alpha-rays from a sample of polonium 

 were completely absorbed, was about 2,000 times as great 

 as the total ionisation produced in petrol ether when the 

 radiation from the same polonium was completely ab- 

 sorbed by that liquid. 



In the following paper an account is given of some preliminary 

 experiments made on the ionisation of liquid air by alpha rays, and 

 from the results which are given below, it will be seen that the findings 

 of others are confirmed in regard to the high insulating power of liquid 

 air. It will be shewn too that the conductivity impressed by alpha 

 rays on liquid air is similar in some regards to that obtained by Grein- 

 acher in his experiments with petroleum and petrol ether traversed 

 by alpha rays. 



II. Preliminary Experiments. 



In order to obtain an estimate of the insulating power of liquid 

 air, a clean copper wire A was connected to earth and suspended in 



*Curie, C.R., 134, 1902, p. 420. 



tJaffe, Ann. d. Phys., 28, p. 326, 1909. 



JBohm-Wendt & Scliweidler, Phys. Zeit. 10, 1909, p. 379. 



* Bialobjeski, J.c Radium, p. 293, Aug. 1911. 



* Greinachor, Phys. Zoit. 10 .lahr. No. 2.5. p. 9IS«. 



