POLAROGRAPHY OF CARBON SUSPENSIONS

The polarographic behaviour of activated charcoal and two other forms of carbon have been studied. Activated charcoal suspensions give rise to a high cathodic current peak which is greatly enhanced by stirring. The diminished current on each side of the peak is shown to be due to the inability of particles to make contact with the DME at potentials removed from the electrocapillary zero of mercury. This inability arises from a boundary layer effect, produced by vigorous movement of the mercury surface and the liquid in contact with it. The reducible groups on the charcoal surface can be reduced by sodium dithionite and also by bulk electroreduction. The cathodic current is then replaced on the polarogram by anodic current. The quantities of electricity, calculated from oscillographic recordings of current pulses for single charcoal particles, show a very high surface concentration of reducible groups. The form of the pulses and the quantities of electricity they represent are pH-dependent, suggesting participation of hydrogen ions in the electroreduction process. © 1969.