Thin Metal Partition in a Voltameter. 199 



dissipated, (b) Quite different is the case for " thin " plates, 

 where, within the limits of current and thickness prescribed, 

 the polarization is dependent upon the current, and gives 

 for each thickness a different curve, or rather straight line, 

 for they are all straight lines converging to the origin, and 

 differing only in slope. The current-strength at which the 

 polarization on very thin plates would reach a maximum is 

 far above that used, being, perhaps, expressed in amperes 

 instead of tenths and hundredths. 



By thick plates are denned those above the " upper critical 

 limit ;" by thin plates those below this limit of thickness. 



(6) Inspection of Table III., which gives the time-change 

 of the polarization, will show a similar distinction between 

 " thick " plates and " thin " to that noted in the last paragraph, 

 viz., that for thick plates the change is considerable and con- 

 tinues slowly for hours ; for thin plates, the change of 

 polarization with time is both less pronounced and extends 

 over much less time. 



(7) It was noted, especially in the case of CuS0 4 as elec- 

 trolyte, that there was polarization on gold-leaf if the gold 

 exposed contact with the solution some distance beyond the 

 edge of the hole in the glass plaice to which it was sealed. 

 Thus in CuS0 4 , for the stronger current used there was a 

 symmetrical deposit of Cu, decreasing in thickness from the 

 outside toward the centre, and vanishing at a small distance 

 ftOin the edge of the hole, this distance being less the stronger 

 the current. If only one corner was left exposed, the Cu 

 was deposited there. This phenomenon was further tested 

 by bending a thick strip of aluminium 4 centim. long into 

 the shape of a narrow U and simply hanging this U in the 

 open hole of the glass partition, in CuS0 4 , and closing the 

 circuit on the voltameter ; the two ends of the metal strip 

 being thus in contact with the CuS0 4 on opposite sides of 

 the glass,* two centim. from the edge of the opening, there 

 was decided deposit of Qu on one end and escape of oxygen 

 from the other end. 



(8) In CuS0 4 all the plates except those below the critical 

 thickness were destroyed by oxidation. #1 silver was destroyed 

 in less than one minute. Of course gold and silver above the 

 critical thickness could not be used in KaCl because of 

 chemical action, though the thinnest plates were quite un- 

 affected. Only the # 7 gold was tested in KOH, as it dissolved 

 the sealing-wax. 



(9) Thick plates of gold were strongly oxidized in H 2 S0 4 , 

 especially with strong currents. Thin gold plates were 

 apparently only oxidized under action of strong or long 



P2 



