The impure glycerin obtained as above is purified by redistillation in steam and evaporation in vacuum pans.
By careful redistillation F.
A redistilled zinc, from an ordinarily pure commercial zinc, is often called chemically pure, but redistillation is seldom practised except for the recovery of zinc from galvanizer's dross and from the skimmings and bottoms of the melting furnaces of zinc rolling mills.
It may be purified by redistillation over barium and silver nitrates, followed by treatment of the distillate with a stream of ozonized air.
This solid, on redistillation, gives the pure acid, which is a liquid boiling at 39° C. (under a pressure of 56 mm.) and of specific gravity 1.764 0,2').