1878.] 



Contact Tlieory of Voltaic Action. 

 Table XI. — Some Collected Results. 



217 



Zinc ■"' 



Copper 



Saturated pure cop- 

 per sulphate 



Saturated nearly 

 pure zinc sul- 

 phate 



Slightly impure cop- 

 per sulphate 



Very dilute zinc 

 sulphate 



Distilled water . . . . 



OriLLidJT water. . . . 



Zinc 



UjJCJL . 



Saturated pure 

 copper sulphate. 



Saturated nearly 

 pure zinc sulphate. 



Slightly impure 

 copper sulphate. 



Very dilute zinc 

 sulphate. 



Distilled water. 



Ordinary water. 





-0-75 





0-358 





0-177 



0-126 



0-118 



0'75 





-0-028 



0113 



" 



-0-024 



-0-074 







0-028 





0-033 







-0-071 





— 0*358 



— 0'113 



-0033 

























-0063 







-0-177 



0-024 







0063 









-0-126 



0-074 



0-071 













-0-118 

















A number of results have been collected in Table XI. The num- 

 bers in a vertical column below the name of a substance are the differ- 

 ences of potential in volts between that substance and the substance 

 in the same horizontal row as the number, the two substances being in 

 contact. Thus zinc is negative to saturated pure zinc sulphate, the 

 electromotive force of contact being 0"358 volt. 



IV. 



From Tables VI, VII, and VIII, we see that when zinc and copper 

 are connected by an electrolyte the zinc becomes negative to the 

 copper, the difference of potential seeming to be somewhat less than 

 0'2 volt for water, zinc sulphate, and dilute sulphuric acid. This dif- 

 ference of potential added to the electromotive force of contact of zinc 

 and copper ought to be equal to the electromotive force of a simple 

 cell. 



Pure saturated 

 zinc sulphate. 



Pure water .... 



From 

 Table VIII. 



ZC. 



Sum. 



Observed EMF of 

 ceU. 



0-191 to 0-182 

 0-168 



0-75 

 0-75 



-941 to -932 

 0-918 



"907, increasing to 

 -926, and still in- 

 creasing slowly. 



-832, increasing to 

 0-942, and still in- 

 creasing slowly. 



