Crude potash is used for the manufacture of glass, and, after being causticized, for the making of soft soap. For many other purposes it must be refined, which is done by treating the crude product with the minimum of cold water required to dissolve the carbonate, removing the undissolved part (which consists chiefly of sulphate), and evaporating the clear liquor to dryness in an iron pan.
Potassium carbonate, K 2 CO 3, popularly known as "potashes," was originally obtained in countries where wood was cheap by lixiviating wood ashes in wooden tubs, evaporating the solution to dryness in iron pots and calcining the residue; in more recent practice the calcination is carried out in reverberatory furnaces.
The charge was distilled almost to dryness, though the operation was not carried far enough to cause the residue to " coke."
From November to April there are usually constant dryness, a clear sky, and considerable, though by no means oppressive, heat.
Schimperl made a distinct advance when he distinguished between physical and physiological dryness or wetness of the soil.