Cohobation
In pre-modern chemistry and alchemy Alchemy (from the Arabic word , ) is an ancient branch of natural philosophy, a philosophical and protoscientific tradition that was historically practised in China, India, the Muslim world, and Europe. In its Western form, alchemy is first ..., cohobation was the process of repeated distillation of the same matter, with the liquid drawn from it (successive redistillation); that liquid being poured again and again upon the matter left at the bottom of the vessel. Cohobation is a kind of circulation, only differing from it in this, that the liquid is drawn off in cohobation, as in common distillation, and thrown back again; whereas in circulation, it rises and falls in the same vessel, without ever being drawn out. Cohobation is not recognized as a useful process in modern chemistry. Indeed, it is equivalent to performing the same distillation a number of times and does not increase the purity of the distillate or alter the residue any m ...
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