288 Messrs. Wright and Thompson on the Determination of 



Bright Zinc Plates. 



Molecular strength 



of solution, per 



100 H 2 0. 



Near 5 MS0 4 . 



MS0 4 to 2 MS0 4 . 



•25 MS0 4 to 

 •5 MS0 4 . 



Maximum .. 

 Minimum .. 

 Average 





1-49 

 •07 



•69 



3-65 



•32 



213 



12*5 

 •32 

 5-45 









Amalgamated Zinc Plates. 



Maximum .. 

 Minimum .. 

 Average 





•11 

 •01 

 •07 



15 

 •02 



•09 



1-55 

 •01 

 •69 









Bright Copper Plates. 



Maximum . 

 Minimum . 

 Average .... 







3-15 



•65 



1-95 



2-6 

 •48 

 1-53 









Recently coated Electro-copper Plates. 



Maximum . 

 Minimum . 

 Average .... 







•66 

 •03 

 •21 



•22 

 •03 

 •14 









Amalgamated Copper Plates. 



Maximum . 

 Minimum . 

 Average .... 







•54 



•08 



•28 



1-4 



•27 

 1-0 









As a general rule the weaker the solution the greater is 

 the average difference of potential set up between two plates, 

 as alike as practicable, immersed in the same fluid : ceteris 

 paribus, bright plates show much wider limits of variation 

 than amalgamated or electro plates. 



It being impossible to ensure equality of surface-conditions 

 by simply taking pains to make plates as alike as practicable, 

 an approximation to the value that would have been obtained, 

 had the plates been equal in surface-conditions, was arrived 

 at in each experiment by the simple device of exchanging the 

 plates after one series of readings had been taken, and taking 

 another series of readings, averaging the two mean values thus 

 obtained. In many cases the plates were exchanged twice more, 

 and the general mean of all four sets of readings taken. To 

 prevent alteration of solution-strength, the plates exchanged 

 were always rinsed with the solution into which they were 



