Charged Bodies at Moderate Temperatures. 451 



§ 12. In experiments where the quadrant-electrometer was 

 used it was noticed that there was, in those cases where an 

 increased leak due to heating was observed, a more rapid 

 leak of positive or of negative electricity according as the 

 substance experimented with was insulated or was connected 

 to the case of the electrometer. This same difference of 

 leak depending on the nature of the charge obtains also 

 in the case of thorium and of uranium salts. A difference, 

 however, comes in when higher voltages are used. In the 

 case of thorium oxide and uranium nitrate no difference 

 in rate of leak could be observed, with the experimental 

 arrangement used, depending on the nature of the charge. 

 No flame was used with these two salts. 



On the other hand, with common salt and iodine or with 

 lithium chloride and bromine on zinc strips lying on the iron 

 plates insulated inside the iron box, a leakage was observed 

 on heating when the insulated substances were charged posi- 

 tively. The leakage was such that a multicellular indicated 

 a drop of as much as 100 volts per minute, whereas with 

 a negative charge the leak remained the same, to within a 

 couple of volts, as when no flame was applied. 



Again, when the zinc strips on which the substances had 

 been spread were placed on the bottom of the iron box so 

 that they were in connexion with the case of the instrument, 

 it was found that, on heating, the insulated iron plates 

 retained a positive charge almost as well as when no heat 

 was applied, but lost a negative one. 



The following figures will give some idea of the behaviour 

 at voltages between 200 and 100 ; other figures will be found 

 in § 5. It may be noted that the substances given there as 

 showing an increased leak show it for positive charges only 

 with the arrangement there used. So far as negative charge 

 goes, their behaviour when insulated is the same as that 

 described below for salt and iodine insulated on zinc strips. 



The iron plates were insulated in the iron box and con- 

 nected to the insulated terminal of the multicellular, the 

 iron box being itself in metallic connexion with the case. 

 It was found that on heating the apparatus for more than 

 an hour, the leakage of electricity was the same for positive 

 or for negative charges, the fall of potential being from 1 to 

 3 volts per minute, according to the day. A strip of zinc 

 was then laid on the insulated iron plates ; it was found 

 that a positive charge leaked away a little more readily 

 than a negative one : in one experiment the leak for a 

 positive charge of 200 volts was 10 volts per minute, for a 

 negative charge of 200 volts it was 1 volts per minute ; in 



