298 Messrs. Wright and Thompson on the Determination of 













Average with 



Value of m. 



Electro- 

 meter. 



Two 



opposed 



cells. 



Diffusion- 

 cells. 



Average. 



zinc sulphate 

 and amalga- 

 mated zinc 

 plates. 



2-1 



-•5 











2-0 







6 















T972 





•2 









1-88 







•8 







1-0 



5-6 



5*5 



64 



5-8 



63 



•5 



11-7 



101 



110 



109 



11-5 



•227 



18-5 



18-2 



171 



179 



18-2 



•167 



20-0 



202 





201 



20-3 



•100 



21-7 



22-4 





220 



22-6 



•094 



21-8 



22-6 









It would hence result that the E.M.F. of a Daniell cell set 

 up with zinc- and copper-sulphate solutions of the same mole- 

 cular strength, and amalgamated-zinc and electro - copper 

 plates, cannot exhibit any very marked variation, whatever 

 the actual strength of the solutions, inasmuch as whatever 

 effect on the E.M.F. is produced by a given variation in the 

 strength of the zinc-sulphate solution must be very nearly 

 counterbalanced by the equal and opposite effect of the same 

 variation in the strength of the copper-sulphate solution. If, 

 however, electro- zinc or bright zinc plates be used, the E.M.F. 

 must rise with the strength of the solutions, the copper-sul- 

 phate variation effect overpowering the zinc-sulphate variation 

 effect. In other words, if e be the E.M.F. of the cell for a 

 given low strength of solution, and E that for a greater strength, 

 thenE = £-fa— b (§ 148): with amalgamated zinc and electro- 

 copper plates, a nearly = b; but with electro or bright zinc, 

 a<b. 



The following experiments show that the value of a, cceteris 

 paribus, is greater with amalgamated, but less with bright, 

 than with electro copper; so that with cells set up with amal- 

 gamated zinc plates, the value of the E.M.F. rises with the 

 strength of the solutions when amalgamated copper plates are 

 opposed, and falls when bright copper plates are used instead. 



2. Amalgamated Copper Plates. 



Observations with Diffusion-cells. Probable error not 

 exceeding +*75 millivolt. 





^=•940 



^=•461 



w=-094 



27-5 

 21-5 

 15-5 



™=1972 

 •940 

 •461 



60 



120 

 60 



