[mclennan-treleaven] residual IONISATION IN GASES 



115 



the results which are given below it will be seen that while evidence 

 has been obtained which points to the existence of a spontaneous ionis- 

 ation in acetylene, there is no direct evidence of such an ionisation 

 in air, carbon dioxide, hydrogen, ethylene, or nitrous oxide. With 

 the last mentioned gases, however, the results point to the residual 

 ionisation being due to a feeble radiation from the walls of the zinc 

 electrometer consisting of alpha and beta and, possibly, gamma rays. 



II. 



APPARATUS. 



The Wolff electrometer used in this investigation is shewn in 

 Fig. 1, and a diagrammatic sketch of its electrical system is given in 

 Fig. 2. The instrument consisted of a cylindrical vessel of zinc 



Fig 1 



provided with plane sides and having a capacity of about two litres. 

 The electrical system consisted of two conducting silvered fused quartz 

 fibres attached at their upper ends to an insulating amber support 

 and at their lower ends to an non-conducting cross fibre also of fused 

 quartz and under tension. This cross fibre was attached to an insulat- 

 ing support of amber as shewn on the sketch. The instrument was 

 provided with a sliding tube SiSi which could be lowered so as to en- 

 close the electrical system, and so reduce to a minimum the volume 

 from which ions could be drawn. With the tube SiSi raised the effec- 

 tive volume of the chamber was 2021 • 1 c.c. and with it lowered 31-5 c.c. 

 The fibres were illuminated by light reflected into the instrument 



