444 Dr. Beattie on Leakage of Electricity from 



seconds to a reading at which it remained steady. When D 

 was charged positively or negatively, the charge leaked away 

 till this reading was reached. The difference between this 

 reading and the metallic zero did not vary with the distance 

 between the two mutually insulated disks either for salts of 

 thorium or of uranium. 



The difference was the same to within a small fraction of a 

 volt, whether thorium oxide, thorium nitrate, or thorium 

 sulphate was used. 



It was found that the difference of potential with the zinc D 

 connected to the insulated pair of quadrants and with polished 

 copper covered with a thorium salt on the zinc B — this latter 

 being of course connected to the electrometer-case — was 

 about *5 of a volt negative. This difference was considerably 

 increased after the copper had been oxidized by heating in air 

 and again used. 



With amalgamated zinc or aluminium used in the same 

 manner, the difference of potential was a fraction of a volt 

 positive. The difference, it was found, depended very greatly 

 on the polish of the mutually insulated metals. 



§ 9. It has already been stated that when zinc covered 

 with salt on which iodine had been sprinkled is insulated in 

 an iron box, and heated, a positive charge leaks away when 

 the temperature is raised to between 300° C. and 400° C. 

 With the arrangement described in § 2, Phil. Mag. xlviii. 

 p. 98 (July 1899), which was again used in the experiments 

 to be described — with a quadrant-electrometer instead of a 

 multicellular in many cases — results of an analogous nature 

 were obtained. These will be described more particularly 

 in a later paragraph. 



The insulated plates were in most instances of iron ; zinc 

 strips on which common salt sprinkled with iodine was 

 spread were laid on these iron plates, and the latter joined to 

 the insulated terminal of the quadrant-electrometer, the box 

 (of iron) surrounding these insulated plates was connected 

 to the case of the electrometer. When heat was applied to the 

 outside of this box, as described in § 2, it was found that the 

 electrometer-reading deviated from the metallic zero to a 

 steady position, indicating a difference of potential between 

 the insulated plates and the surrounding disinsulated box of 

 about *6 of a volt negative. When the plates were charged 

 positively, the charge leaked away till the final reading was 

 again *6 of a volt negative : a negative charge less than 

 this increased, while one greater leaked away till the same 

 steady reading was obtained. 



