186 Dr. C. R. A. Wright and Mr. C. Thompson. [May 3, 



the nature of the fluid ; and similarly the quantity K 3 being inde- 

 pendent of the nature of the aeration plate used, but varying with 

 each kind of oxidisable metal employed, and to some extent also with 

 the nature of the fluid. 



For example, in one experiment four aeration plates, respectively 

 platinum sponge, gold sponge, silver sponge, and graphite, were 

 successively opposed, first to amalgamated zinc, and then to brightened 

 lead in a caustic soda solution of strength 3-45Na2O,100H 2 O, giving 

 the following average values after making a long series of readings 

 (Clark's cell = 1*435 at 15° C.) :— 





Zinc. 



Lead. 



Difference = K 2 . 





1-471 

 1435 

 1-619 

 1-400 



0-769 

 0-732 

 0-916 

 0-696 



-0-702 

 -0-703 

 -0-703 

 -0-704 





Mean. . 



-0-703 



Values of ~K X . 



Zinc. 



Lead. 



Mean. 



Platinum, sponge replaced by gold 











-0-036 



-0-037 



-0-0365 



Platinum sponge replaced by silver 











+ 0-148 



+ 0-147 



+ 0-1475 



Platinum sponge replaced by graphite 



-0-071 



-0-073 



-0-072 



Grold sponge replaced by silver 











+ 0-184 



+ 0-184 



+ 0-184 



G-old sponge replaced by graphite . . . 



-0-035 



-0-036 



-0-0355 



Silver sponge replaced by graphite,. . 



-0-219 



-0 220 



-0-2195 



Numerous other experiments of the same kind were made with 

 analogous results in all cases ; the values for K T and K 2 respectively 

 found in any given set of observations never differing by quantities 

 outside the limits of experimental error. The average values of K x 

 or K 2 thus deduced for a given fluid, however, always differed 

 measurably from those similarly deduced for a different fluid, even 

 when that was a similar solution but of different strength. The 

 tables hereafter described illustrate these differences more fully. 



