A process first used in 1860 for the extraction of potash from sylvinite ore based on the differing solubilities of sodium and potassium chloride. The ore, which is a mixture of sodium and potassium chloride, is crushed and mixed with saturated sodium chloride. It is heated to boiling in which the potassium chloride dissolves but the sodium chloride does not. On cooling, the potassium chloride crystallizes and is separated.