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



Effect of Substituting Oxygen for Air. 



In order to see if any material improvement in the E.M.F. of 

 aeration cells could be effected by substituting tolerably pure oxygen 

 for atmospheric air, we carried out a number of observations with 

 plates under a bell-jar supplied with purified oxygen from a reservoir 

 by means of tubes passing through a cork in the narrow mouth. 

 Readings were first taken for a few days with ordinary air in the jar ; 

 oxygen was then admitted and passed through till gradually all air 

 was displaced, and after a day or two when the readings had become 

 constant another series of readings for some days was taken. The 

 oxygen was then displaced by air and another series taken, and so on 

 alternately several times. The following average values were ulti- 

 mately obtained showing a small, though decided, increment in 

 E.M.F. when atmospheric air was replaced by oxygen. 



Increment in E.M.F. in Oxygen. 





Caustic soda, 

 7 '15Na 2 O 5 100H 2 O. 



Sulphuric acid, 

 10H 2 SO 4 ,100H 2 O. 





016 



0-028 





0-012 



o-ooi 







0-032 



Gold foil 



0*'012 



O-002 







033 





-013 







016 







0-016 







-015 



o'-002 



Aeration Plates in Contact with Oxidisable Atmospheres. 



Some analogous experiments were made with aeration plates in 

 contact with an oxidisable atmosphere (hydrogen or coal-gas), and 

 an electrolytic fluid united by means of a siphon with an external 

 vessel containing an oxidising solution (alkaline permanganate, 

 sulphuric acid containing chromic acid, -nitric acid, Ac.) in which a 

 plate of platinum foil was immersed. The readings thus obtained 

 were nothing like as concordant as those above described (probably 

 from the difficulty of excluding air completely), showing a tendency 

 to rise continually. The following readings were obtained after 

 several days when the rise had either ceased or greatly slackened in 

 most cases ; little difference was observed whether pure hydrogen or 

 coal-gas was used. 



A. Cells set up with 7-loNa 2 O,100H 2 O in contact with the aeration 

 plates, opposed to platinum foil immersed in a solution of the same 



