222 I*rof. E. F. Herroun on the Divergence of 



Mean rise of Temp. 



o 



Direct current of "2 ampere for 20 minutes . . 0*6 C. 



Adverse current „ „ . . 0*1 C. 



Direct current „ „ • . 0"35 C. 



Adverse current „ „ . . O'OO C. 



Direct current „ „ . • 0'45 C. 



Adverse current „ *■„ . • O'OO C. 



Mean rise with direct currents =0°'466 0. 

 Mean rise with adverse currents = 0°* 03. 

 (Commonly = 0) . 



The thermal capacity of the cell was determined and found 

 to be equal to 68 grms. of water ; so that 



68 X -466 = 31-688 grms.°C. 



represents the total mean heat evolved when the cell was 

 worked forwards, and due to 



c^r t + ec 

 J • 

 The mean resistance of the cell was found to be 1*4 ohm, 

 and taking e, the difference between E and E^, as '34 volt, we 

 get 



^!li=.04x 1-4 X 1200" X •24 = 16-1 grms.° C. 



and 



^^^=-34x-2xl200"x-24 = 19-58grms.°C. 



Hence the sum of these amounts, 35-68 grms.° C, and their 

 difference, — 3-48 grms.° C, represent the total amounts of heat 

 evolved with direct and with adverse currents respectively, 

 with which the experimental results of 31-69, and practically 

 0, accord within the limits of experimental error. 



Hence it results that a copper-silver nitrate cell gives an 

 electromotive force below the calculated value, and when it 

 sends a current a portion of the energy due to the replace- 

 ment of silver by copper appears as heat in the cell, and its 

 equivalent in E.M.F. is therefore wanting. Consequently, 

 when the cell is worked backwards, a smaller amount of work 

 than that represented by the negative heat of substituting 

 silver for copper is capable of producing the required electro- 

 lysis, the difference being supplied at the expense of sensible 

 heat. 



In view of the great difference in the heat of formation 

 of mercury salts found by me, and the previously recorded 



