It is the well known fact that the producing capacity of electrolytic zinc plant is much influenced by the technique of neutralization at neutral leach. The filtration velocity of the pulp after leaching varies at a wide range owing to the morphorogical and electrokinetic properties of ferric hydroxide particles.
The author has investigated this neutralization process to find out an end point which gives maximum filtration velocity, and has observed that the ferric hydroxide rapidly coagulated at a point near its isoelectric condition and that the filtration velocity of the pulp was almost inversely proportional to the apparent viscosity of it. He also studied the favourable effect of gelatine on the filtration efficiency and concluded that it is based on the amphoteric characteristics of hydrophilic gelatine and hydrophobic ferric hydroxide, i.e., the successive change of electric charges at their isoelectric points causes the. dehydration and coagulation of the latter.

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