Charged Bodies at Moderate Temperatures. 453 



With zinc chloride on iron plates the effect continued even 

 after heating for three or four days. 



§ 14. A number of other experiments were made with the 

 same arrangement of apparatus and with the multicellular. 

 Those substances were chosen which were known to give off 

 a gas on moderate heating. In the following table some of 

 the results obtained are given. The iron box was connected 

 to the case, and the insulated plates (of iron) to the insulated 

 terminal of the electrometer. 



Substance. 



Nature of 

 charge. 



Leak. 



Manganese dioxide and caustic 



potash. 

 Manganese dioxide and sulphuric 



acid. 

 Bleaching - powder, water, and 



cobalt oxide 



Barium oxide 



Manganese dioxide and potassium 



chlorate 



Positive. 



Positive. 



f Positive. \ 

 \ Negative. J 



Positive. 

 1 Positive. "1 

 \ Negative. | 



Positive. 



Positive. 



Positive. 



f Positive. "1 

 \ Negative, j 



Normal. 

 Normal. 



Normal. 

 Normal. 

 Increased. 

 Normal. 



Increased. 



Increased. 



Increased. 



Potassium bichi-omate with sul- 

 phuric acid. 



Potassium bichromate with hydro- 

 chloric acid. 



Manganese dioxide with hydro- 

 chloric acid. 



pwiudngaiidw 



§ 15. An examination of the various results given for small 

 voltages shows that the effect produced in the heated atmo- 

 sphere surrounding certain insulated substances is of the same 

 nature as the effect produced in the atmosphere surrounding 

 bodies on which salts of thorium or of uranium are spread ; 

 the difference of potential between the mutually insulated 

 metals depends on the nature of the metals, but not on their 

 distance apart. The difference observed also changes sign 

 when the substance, instead of being on the one mutually 

 insulated metal, is placed on the other. 



With potentials of 200 volts there is a one-sidedness in the 

 discharge from certain heated substances which does not show 

 itself in the case of thorium or of uranium salts. This 

 peculiarity may be compared with the discharge due to ultra- 

 violet light, which has been so thoroughly investigated by 

 Elster and Greitel. Here, however, it is the positive charge 

 which leaks away, while the negative is retained. It may 

 also be compared with the behaviour of a heated metal, as 

 observed by Guthrie, Elster and Geitel, and others ; the 



