Charged Bodies at Moderate lemperatures. 105 



leak on heating. Only after thoroughly cleaning the zinc 

 plates was it possible to get them to hold electricity when 

 heat was applied. 



§ 6. Remits obtained with Iron Plates insulated in the Iron 

 Box. — The rate of leak Avith iron plates — no substance being 

 spread over them — charged to about 200 volts was about 

 1 volt per minute with the temperature about . 20° C. 

 The connexions, of course, were exactly as in previous 

 experiments. 



When the gas underneath was lit and kept alight for an 

 hour at a time, no increased leak was observed, the plates 

 still having no substance spread over them. 



With the insulated iron plates in the iron box covered 

 with potassium bichromate, common salt, ziuc sulphide, 

 potassium nitrate, barium sulphide, each substance being 

 taken either alone or with iodine, no increased rate of leak 

 was observed on heating. 



With potassium permanganate spread over the insulated 

 iron plates, an increased leak was observed after heat was 

 applied, the fall of potential increasing to 30 or 40 volts per 

 minute after a few minutes. When the apparatus was 

 allowed to cool the usual rate of leak was again observed ; 

 after heating a second time an increased fall of potential was 

 again obtained, but less than on the first occasion. 



Black oxide of manganese and potassium chlorate, when 

 placed together on the insulated iron plates, showed an 

 increased fall of potential after heating ; the experiment 

 being repeated a second time without a fresh supply of potas- 

 sium chlorate, no increased rate of leak was observed. On 

 the other hand, with another supply of chlorate the same 

 effect was produced after heating. 



With potassium chlorate and black oxide of manganese 

 as well as potassium permanganate, the increased rate of leak 

 was observed whether the charge was positive or negative. 

 This might quite well be the case, although the oxygen given 

 off from the potassium permanganate on heating, when tested 

 by means of an electric filter, was found to be positively 

 electrified : any difference in rate of leak due to different 

 charge would probably show itself at lower potentials. 



Potassium acetate was next placed on the iron plates, and 

 the leak per minute noted for a number of minutes when no 

 flame was lit. The leak in these circumstances was found to 

 be about 4 volts per minute. The flame was afterwards lit, 

 and after about 8 or 10 minutes' heating the leak had 

 increased to about 120 volts per minute. The experiment 

 was varied in the following manner : — Uranium acetate 



