Prof. Franz Exner on Contact Electricity. 



291 



as the interior of the glass tube was filled with dry chlo- 

 rine gas, evolved from potassium bichromate and hydrochloric 

 acid, the condenser showed at once a considerable and quite 

 constant tension. At the same time the inner side of the 

 lower silver plate blackened. The difference of potential 

 lasted, however, only so long as the combination of the chlo- 

 rine with the silver went on. If the chlorine was driven out 

 of the vessel by dry air, and time allowed for the silver to 

 completely consume the remaining traces of chlorine clinging 

 to it, no further difference of potential between the clean and 

 the attacked plates was apparent. 



Below I give the results of these experiments : — 



IV. Silver in Air with Silver in Chlorine, 

 is ap-ain the same as before. 



The notation 





A. 



E. 



C. 



D. 



E. 



F. 



G. 



1. 



N = 800 

 a =789 



N = 800 

 a =840 



x =14*5 

 D=25-5 



N=800 

 a =815 



x = lb 



■r = 14'7 



x=-&1 



2. 



N = 803 

 a =792 



N = 802 



a =842 



x =14-5 

 D=255 



N=802 

 a =816 



x=U 



^=14-2 



x = -56 



3. 



N = 690 

 a =676 



N = 690 

 a =734 



j? =15 

 D=29 



N = 690 

 a =704 



a: =14 



x = 14*5 



x = -50 



It will be seen from the figures under A, B, and D that the 

 deflections are now all in the direction opposite to that of the 

 former experiments, because now, instead of connecting, as at 

 first, the more strongly attacked plate to the electrometer, the 

 less strongly attacked one was connected. 



Yet another experiment was arranged as follows : — The 

 plate which closed the tube was taken out, cleaned perfectly, 

 newly polished, and replaced. Again the two plates gave 

 no trace of a difference of potential. The lower plate was 

 now allowed to remain in contact with air, but the movable 

 one was held for a short time in a stream of chlorine and imme- 

 diately examined. The following values were found: — 



A. 



B. 



C. 



D. 



E. 



F. 



G. 



N=658 

 a =683 



N=658 



a =573 



x =30 

 D=55 



ff=658 



a =628 



x=2>0 



a- = 30 



a? =-64 



The deflections are here again in the same direction as 

 those of the Zn | Pt condenser, since now again the more 

 strongly attacked plate is connected to the electrometer. The 

 mean of the foregoing experiments is '542. 



According to Thomsen, the heat of oxidation of silver is 

 3000 calories, and the heat of combination of chlorine and 



