PHYSICAL CHEMISTRY 13 



and chromium. These phenomena, which occur at both the 

 anode and the cathode, are usually explained as due to an 

 alternation between an active and a passive state of the 

 electrode. As was shown by Nernst, the potential between the 

 electrodes could in many cases be altered by shaking or moving 

 the electrodes. 



Kistiakowski had previously investigated the electrolysis 

 of chromic acid using irone lectrodes and obtained periodic 

 phenomena both at the anode and cathode. In order to 

 eliminate the anodic disturbance and to study the cathodic 

 processes, Liebreich used a platinum anode. He finds that 

 there are four distinct processes which occur at the cathode : 



I. Cr ->Cr- •• +30 



II. 2Cr03 + 6H'->Cr203 + 3H2O + 6 © 



III. CraOg + 2H-->2CrO + HgO + 20 



IV. 2H-->H2 + 2 ©and CrO + 2H'->Cr + H2O +2© 



No hydrogen is evolved in stages I and II, a slight evolution 

 occurs in III, and a vigorous evolution in IV. To each of these 

 processes corresponds a definite decomposition potential curve, 

 which can be realised between certain limits of current density 

 and voltage. Which of these processes is taking place at a 

 given time is determined partly by the applied E.M.F. and 

 partly by chance. Within certain ranges of current density, the 

 voltage suddenly changes from one curve to another, and it is the 

 repetition of this process which gives rise to a periodic change in 

 the voltage, which is accompanied by a corresponding change in 

 the products liberated at the electrode. The order of the voltage 

 change is 0*3 V. In addition to these large changes pulsating 

 phenomena were observed of the order of 0-005 V. 



These periodic occurrences correspond with a reduction or 

 oxidation of the electrode deposits, and the duration of the period 

 depends on the nature and the thickness of these deposits. 

 No steady conditions of current density and voltage were found 

 except those corresponding to points on the four curves. 



Ultramicroscopic Structure of Soaps. — W. F. Darke, J. W. 

 McBain, and C. S. Salmon {Proc. Roy. Soc, 1921, [A], 98, 395) 

 have applied the cinematograph to the study of the " life- 

 history " of the ultramicroscopic structures which are formed 

 on cooling soap solutions, and have extended the work of 

 Bachman and Zsigmondy in this field. Both soap sols and 

 soap gels were found to be transparent under the ultramicro- 

 scope. The ionic micelle is invisible, but on cooling slowly 

 Brownian particles appear. These are followed, in the sodium 

 soaps, by long thin fibres of characteristic curvature, which 

 grow slowly into the field, and in many cases it appeared that 

 the fibres had attained their full length before becoming visible. 



