US 



Mr. J, A. Fleming on the Polarization of 



Table II. — Polarization in Acidulated Water thoroughly well 



aerated. 



Bridge- 

 reading. 



Electromotive 

 force. 



Excursion of needle in 

 degrees or fractions. 



Direct current. 



Polarization 

 current. 



275 



280 

 285 

 290 

 300 

 310 

 320 

 330 

 340 

 350 

 400 

 450 

 500 



12110 



18165 



24220 



30275 



42385 



54495 



66605 



78715 



90825 



102935 



115045 



224035 



284585 



o 



^ barely. 



1 

 1 



1| 



2 barely. 

 2 



3* 

 5 



7 

 10 



o 



ft 



ft 



£ barely. 

 | barely. 



5 



| barely. 



"i 



i 



H 



An examination of these two Tables shows that there is very 

 little difference between them which cannot properly be ascribed 

 to errors in observation. There is no difference in the mini- 

 mum electromotive force which could give in each case a visible 

 polarization with the galvanometer employed. But now there 

 was one very striking difference between the two sets of expe- 

 riments, not shown in the Tables, viz. the time required after 

 each experiment for the polarization to subside. In the case 

 of the aerated water, the polarization disappears very much 

 more quickly when the plates are short, circuited than in the 

 case of the air-free water. With this latter it was most trouble- 

 some to get rid of the last traces, even with the smallest pola- 

 rizing currents. This has been previously noticed and ex- 

 plained by Helmholtz *. It is, however, a point not involved 

 in our present considerations. 



A consideration of these observations leads apparently to the 

 conclusion that the presence of air in the water has no effect in 

 creating or assisting the polarization of the electrodes under a 

 feeble electromotive force (it is difficult to see any reason 

 why it should), although it has a great effect in removing it 

 when once formed. The process called by Helmholtz electro- 

 lytic convection, and in which dissolved air is essential, is the 

 consequence and not the cause of polarization. 



* Phil. Mag. [IV.] vol. xlvii. p. 152, Dr. 

 Polarization in Liquids free from Gas." 



Helmholtz "On Galvanic 



