496 Intelligence and Miscellaneous Articles. 



(6) But if the kathode is platinized the maxima and minima 

 disappear almost entirely, and the polarization, which at first is 

 only 2*1 volts, rises with increasing concentration pretty regularly 

 to 2*8 to 2*9 volts, with a concentration of 65 percent. 



(7) If, on the other hand, the anode is platinized, the maxima 

 and minima do not disappear in the strongly dilute acids, but the 

 constant and small polarization remains in the concentrated acids 

 (of 20 to 25 per cent.). 



(8) The most regular course, and that which depends least on 

 the concentration, and in accordance with 3 and 4 the smallest 

 values of the polarization, is obtained by platinizing both electrodes. 



(9) The high polarization of bright electrodes in comparison with 

 the small one of platinized electrodes, if the acid is of small con- 

 centration, is therefore due in a great part to the polished condition 

 of the kathode, and the occurrence of maxima and minima is due 

 exclusively to this cause. On the other hand, the high values in the 

 more concentrated acids are to be ascribed almost exclusively to the 

 polished condition of the anode. 



The explanation of these conditions results from the more ready 

 formation of gas-bubbles on platinized as well as on polished elec- 

 trodes, especially in the more dilute acids, as well as from the forma- 

 tion and accumulation of secondary products (persulphuric acid and 

 hydrogen peroxide) at the bright anode in more concentrated acids. 



(10) The simple relations of platinized electrodes and their small 

 values of polarization are not manifested by bright electrodes e /en 

 when their surface is materially increased. 



(11) The polarization of bright electrodes varies somewhat with 

 the preparation of the mixtures of sulphuric acid ; that of platinized 

 is, however, independent thereof. 



(12) While half an hour to an hour frequently elapses before the 

 maximum of polarization is attained with bright electrodes, platinized 

 electrodes soon reach their maximum polarization. 



In the more dilute acids it is the bright kathode, and in the more 

 concentrated ones the bright anode which most slowly attains the 

 maximum polarization. The greater the maximum, the farther in 

 general is the polarization from it shortly after closing the current. 



(13) The polarization increases in general with decreasing cur- 

 rent strength, and to the greatest extent with bright electrodes. 

 The effect of platinizing the kathode is that polarization in the more 

 dilute acids is more independent of the strength of the current, 

 while that of platinizing the anode is that polarization in the 

 stronger acids is not so much affected by the strength of the cur- 

 rent. The explanation of this readily follows from (9). 



(14) The minimum resistance of the voltameter is at about that 

 concentration at which the conductivity of the sulphuric acid 

 attains its maximum. 



(15) The polarization of platinum electrodes is at most only 0-1 

 volt higher than the smallest electromotive force which with bright 

 platinum wires can disengage fresh gas under a pressure of one 

 atmosphere. — Wiedemann's Annalen, xxxviii. p. 362, 1889. 



