1888.] Development of Electricity by Atmospheric Oxidation. 187 



Cells set up with Caustic Soda Solution as Electrolytic Fluid, and 

 various Aeration Plates opposed to Zinc. 



When steadiness was once obtained, we fonnd that the fluctuations 

 observed from day to day in a given cell set up with amalgamated 

 zinc as oxidisable metal (freshly amalgamated each day) rarely ex- 

 ceeded + - 003 to 0*004 volt difference from the mean of several days 

 (sometimes some weeks) readings. Duplicate cells, however, gave 

 average readings exhibiting greater differences up to + 0*025 or 

 tt 0*030 volt : thus eighteen different cells set up with platinum-foil 

 or thin leaf, caustic soda solution of strength 3*45Na 2 0, 100H 2 O, and 

 amalgamated zinc gave the following results : — 



Maximum mean reading of any given cell 1*445 



Minimum mean reading of any given cell 1*403 



Average reading of all 1*423 



Probable error of average +0*0019 



Even with a much smaller number of cells, the probable error was 

 usually well within + 0*005 volt, the differences observed with dif- 

 ferent cells mainly depending on the unavoidably slight differences in 

 the surface of the metal, &c, constituting the aeration plate. 



On substituting a stronger solution of caustic soda for a weaker 

 one, as a rule an increment in average value was observed, and vice 

 versa; but the extent of the alteration varied considerably with 

 different kinds of aeration plates : with solutions of strength 

 0*05Na 2 O,100H 2 O the readings fluctuated so irregularly as to 

 prevent any approach to an accurate average valuation ; but with 

 stronger solutions the readings were sufficiently concordant to reduce 

 the probable error of the final average to only + a few millivolts. 



Cells set up with 3*45Na 2 O,100H 2 O. 



Aeration plate. 



No. of 

 cells. 



Maximum. 



Minimum. 



Average. 



Silver sponge (from acetate) . . 



8 



1-624 



1-615 



1-618 





4 



1-569 



1-549 



1-563 



Silver sponge (from chloride) . 



4 



1551 



1 "455 



1 -484 





14 



1-491 



1-450 



1-463 





4 



1-468 



1-422 



1-448 





10 



1 -450 



1-433 



1-443 





9 



1-465 



1-392 



1-428 





16 



1 -449 



1-402 



1-426 





18 



1-445 



1 -403 



1 -423 





21 



1-425 



1-367 



1-396 





4 



1 -383 



1-344 



1 -365 





4 



1-307 



1-269 



1 -2S7 



