Dictionary.net

The Pearlash of commerce, is prepared from the ashes of landplants by calcination, solution in water, filtration, and evaporation. It usually consists of subcarbonate of potassa, sulphate of potassa, chloride of potassium, silex, oxide of iron, &c. From the ashes of lees of wine, and from vine-twigs, a much purer alkali is obtained. It is called Cinis infecto'rius seu faecum, Cin'eres clavella'ti seu gravella'ti, Alu'men faecum, (F.) Cendres gravelees ou de sarment. Another variety of the alkali is afforded by burning argol in a crucible; afterwards powdering and calcining it, till it is nearly white; then dissolving in water, filtering, and evaporating. It is called Salt of Tartar, Sal Tar'tari, Kali praepara'tum e tar'taro, K. e tartaro, Subcar'bonas potassae puris'simus, Potas'sae subcar'bonas e tar'taro. Lastly, when wormwood is burnt to ashes, dissolved in water, filtered, and evaporated to dryness, it affords another variety of vegetable alkali, the Sal absin'thii or Salt of wormwood. Impure potash is used for preparing the subcarbonate for medical use.