1877.] Contact of different Substances. 311 



Comparison of the difference of potential of zinc and copper in contact 

 with that of the terminals of the standard Darnell's cell before men- 

 tioned gave 



Zn | Cu=0-7892D; 



or, assuming Mr. Latimer Clark's measurement of D, viz. 1-079 volt, 



Zn j Cu= 0-8516 volt. 



This value shows that, on the occasion of the previous measures, 



C = 1-273 D = 1-374 volt. 



By using this value of Zn | Cu in the preceding results, the values con- 

 tained in the following Table are obtained : — 





D. 



Volt. 



Zn | Ye 



0-694 



0-749 



Pe | Cu 



0-095 



0-102 



Cu | Hg 



0-200 



0-216 



Zn | Cu 



0-789 



0-852 



Ye | Hg 



0-295 



0-318 



Zn | Hg 



0-989 



1-067 



The. experiments from which the above-mentioned ratios of Zn | Cu 

 to the difference of potential of the terminals of Clark's standard cell are 

 deduced were performed on January 5 and January 8, 1877. A series 

 of similar experiments had been previously made on December 15 and 

 December 16, 1876, which led to the following results, C representing 

 the difference of potential of the terminals of Clark's cell at that time : — 



Zn | Cu = 0-5863 C. 



0-5842 C. 

 0-5912 C. 

 0-5890 C. 



0-5877 C. (Mean.) 

 Hence, since Zn | Cu=0-7892 D = 0-8516 volt, 

 C = 1-343 D = 1-449 volts. 



