198 Mr. J. Daniel on the Polarization upon a 



Table IV. (PI. IV. fig. 1.) 



Relation of Polarization to Thickness ; 30 per cent. H 2 S0 4 ; 



gold plates. 



Thickness in 1 

 millimetres J " 



#6. 

 0-00038 



8 5. 

 0-00059. 



#3. 

 0-0043. 



Eatio. 



d 2 : x. 



Current. 

 I=-01 



X ... 



•04 



•09 



0-40 



441 .: 484 



I = -02 



X ... 



•09 



•26 



0-77 



1274 : 1081 



I =-03 



X ... 



•13 



•39 



113 



1911 : 1694 



1=04 



X ... 



•19 



•50 



1-48 



2450 : 2299 



1 1 1=05 



X ... 



•28 



•76 



2-02 



3724 : 3388 



_ I=, io. 



X ... 



•47 



1-23 



2-35 



6027 : 6681 



BB 'SBur 



X ... 



•71 



1-76 



2-35 



8624 : 8591 



We may now briefly summarize the experimental observa- 

 tions : — 



(1) The polarization on a gold-leaf partition in good- 

 conducting H 2 S0 4 is zero, or too small to detect with our 

 apparatus, for the range of current used. 



(2) The " critical thickness " in good-conducting solutions 

 of H 2 S0 4 , CuS0 4 , and NaCl is greater than '00009 millim. 

 for gold ; '00015 millim. for platinum ; and '0005 millim. 

 for aluminium, under the above conditions. It is less than 

 •0004 millim. for gold ; '002 millim. for Pt ; and '002 

 for Ag. 



(3) The "upper critical limit" of thickness under these 

 conditions seems to be about '004 millim., rather less than 

 #3 gold. 



(4) Tables I., II., and III. all point to the conclusion that 

 between the " critical limits " of thickness the polarization for 

 a given current increases with the thickness. 



(5) Table IE., showing relation of polarization to current, 

 expresses two interesting facts : — (a) That the polarization on 

 " thick " plates is about the same, in this voltameter, for all 

 currents between '2 amp. and, say, '01 amp., provided time 

 enough be allowed in each case for the current to become 

 constant : i. e. between the upper limit of current at which 

 the development of gas is so profuse as by mechanical ob- 

 struction and irregular escape to interfere, and the lower 

 limit, at which the formation of gas is no faster than it can be 



