294 Dr. C. R. A. Wright on the Determination of 



(4) with the smaller zinc and larger copper plates opposed. 

 By interpolation from the direct observational results, the 

 differences of potential between the plates for any constant 

 current-value were then calculated in each of the four cases. 

 By comparing the values thus obtained in cases (1) and (2) 

 and in (4) and (3), two sets of differences were obtained, 

 indicating the effects produced by halving the area of the 

 copper plate, every thing else being the same throughout, 

 saving that with results (1) and (2) the larger zinc plate, 

 and Avith the other pair of results the smaller zinc plate, was 

 opposed to the two copper plates respectively : although this 

 modified the actual values obtained in each of the original 

 sets of readings, yet it produced practically no effect on the 

 differences. In just the same way, by comparing the inter- 

 polation values in cases (1) and (4) and in (2) and (3), two 

 corresponding sets of differences were obtained, indicating 

 the effects produced by halving the area of the zinc plate ; 

 as before, the two sets substantially coincided. Various 

 experiments of this kind were made with different plate- 

 materials and fluids surrounding them : whilst the numerical 

 values obtained were found to be to some extent variable 

 with these conditions, yet, on the whole, it was always found 

 that the effect of halving the area of the copper plate notably 

 exceeded that of halving the area of the zinc plate. For 

 instance, the following numbers were obtained in one set of 

 observations with a cell containing bright pure zinc plates 

 surrounded by zinc-sulphate solution of sp. gr. 1-42, and 

 freshly- coated electro-copper plates surrounded by copper- 

 sulphate solutions of sp. gr. 1-175, the larger plates exposing 

 a surface of 5*0 square centimetres, and the smaller ones expo- 

 sing 2*5 square centimetres. 







Effect of halving 



the area o 



f tbe copper plate. 







Larger zinc plate opposed. 



Smaller zinc plate opposed. 





Current, 

 in micro- 















Mean 

 differ- 















amperes. 



(1) 

 Larger 



« (2) 



Smaller 



Differ- 



T (4) 



-Larger 



(3) 

 Smaller 



Differ- 

 ence. 



ence. 





copper. 



copper. 





copper. 



copper. 





100 



1-082 



1-078 



•004 



1-076 



1-073 



•003 



•0035 



200 



1-071 



1-066 



•005 



1-064 



1-060 



•004 



0045 



500 



1-061 



1055 



•006 



1-052 



1047 



•005 



•0055 



1,000 



1-045 



1-036 



•009 



1-035 



1026 



•009 



•0090 



2,000 



1026 



1015 



•011 



1011 



•999 



•012 



•0115 



5,000 



•964 



•947 



•017 



•950 



•929 



021 



•0190 



10,000 



•876 



•843 



•033 



•854 



•820 



034 



0335 



20,000 



•729 



•672 



•057 



•698 



•639 



•059 



•0580 



