18 Mr. E. F. Herroun on the Electromotive 



Adding together the values obtained we get *189 + '335 

 = •524 volt for the zinc-tin cell, a result which shows a 

 striking agreement with the average value previously given, 

 viz. -525. 



The average E.M.F. of the cadmium-copper cell was also 

 determined and found to be # 744, Messrs. Wright and Thomp- 

 son finding '753 for the same cell, which gives ( — i.i-m = ) 



•73 volt; or, in other words, my value for the cadmium- 

 copper is as much above, as my zinc-cadmium is below, their 

 estimate, both values adding up correctly, 



*73 + '349 = 1-079, 

 and 



-744 4- '335 = 1-079. 



This discrepancy is no doubt due to the fact that the solutions 

 employed by me contained about 1*5 per cent, of free H 2 S0 4 

 in order to keep the conditions uniform with the tin cells. 



Subtracting the E.M.F. of cadmium-tin from that of cad- 

 mium-copper, we get the E.M.F. of tin-copper, thus : — 



•744 --189 = -555 volt; 



which accords fairly well with '56, but is, as would be antici- 

 pated, somewhat less. 



Cells the algebraic sum of whose E.M.F.'s should <equal 

 1-08, the standard DanielL 



Zinc-tin-sulpliate 

 •525 





tin-copper-sulphate. 



-56 



= 



1035. 



Zinc-cadmium 

 •335 



+ 



+ 



cadmium-tin + 

 •189 + 



tin-copper. 

 '56 = 



1-084, 



Zinc-tin 

 •525 



+ 



+ 



cadmium-copper — 

 •744 - 



cadmium-tin. 



•189 = 



1-08. 



Electromotive Force of Cells consisting of the Metals in Solutions 

 of their Chlorides of Equal Molecular Strength, 



I. Zinc-Tin Chloride Cell. 



A cell set up with amalgamated zinc opposed to tin in 

 solutions of their chlorides of the strength '5 M A/ C1 2 , 100 H 2 0, 

 containing 1 per cent. HC1, gave an E.M.F. of *544 to *553 

 volt, mean =*549 volt. 



Diluting the solutions equally with distilled water causes a 



