200 Polarization upon a Metal Partition in a Voltameter, 



continued currents. Compare Tables II. and III. Silver was 

 even more easily oxidized than gold. Aluminium was so 

 intensely oxidized by the current that no satisfactory measure- 

 ments could be made for this metal, though the thin foil was 

 unaffected. 



(10) With H 2 S0 4 as electrolyte, after a thick plate of 

 pure gold had been used as partition for the time-change of 

 Table III., the end kathode was found to be gilded. A thick 

 Pt plate being then substituted for the gold in the same 

 solution for the results of # 1 Pt in Table III., the Pt par- 

 tition was found on removal to be gilded. The polarization 

 for # 1 Pt in this case was somewhat less than for the same 

 Pt after both it and the end electrodes had been thoroughly 

 cleansed, the electrodes re-platinized, and a fresh solution 

 made. 



(11) The polarization in CuS0 4 , using Cu electrodes, 

 reached a maximum almost immediately and remained very 

 constant. The maximum polarization for thick Pt in CuS0 4 

 was hardly 75 per cent, of that for the same in H 2 S0 4 . In 

 NaCl the polarization became constant very quickly also, but 

 its value was decidedly greater, especially on thin plates, than 

 in H 2 S0 4 ; though the same distinctive behaviour of thick 

 and thin plates maintained. 



(12) In H 2 S0 4 of different concentrations the maximum 

 polarization for a partition was of the same order of magnitude ; 

 but its value for very weak currents was decidedly greater in 

 weak solutions than for the same current in stronger solutions, 

 up to 30 per cent. This shows itself especially with thin 

 plates, and also in the shorter time required for thick plates 

 to reach a maximum polarization with weak currents. The 

 greater change in temperature and the greater change in 

 concentration of weak solutions may account for this. For 

 currents between 0*1 and 0*2 ampere, the polarization on 

 the end electrodes was, 



forH 2 S0 4 . . . 1-84 

 „ NaCl .... 1*98 

 „ CuS0 4 . . . 0-00, 



with Cu electrodes, though if the current-density was too 

 great or the time long, the anode would oxidize and become 

 irregular. C. Fromme, in a paper " Ueber das Maximum der 

 galvanischen Polarization von Platinelektroden in Schwefel- 

 s'aure " (Annalen d. Physik u. Chemie, xxxiii. pp. 80-126), 

 states that the maximum polarization varies both with the 

 concentration and the relative size of the electrodes, the 

 extreme limits being given as 1*45 to 4*31 volts — the mini- 

 mum polarization coinciding with maximum conductivity. 



