Bredig-Arc method:
Colloidal solutions of metals are obtained by this method. The metal, whose sol is to be prepared, is made as two electrodes immersed in dispersion medium such as water. The dispersion medium is kept cool by surrounding it with a freezing mixture.
An electric arc is struck between the electrodes. The tremendous heat generated by the arc vaporises the metals which are condensed immediately in the liquid to give colloidal solution. The colloidal solution of the metals are water repellant so small quantity of KOH is mixed for their stability.
