fractional precipitation[¦frak·shən·əl prə‚sip·ə′tā·shən]
a method of separating a mixture of substances by means of their gradual precipitation from a solution. The possibility of quantitative separation of a mixture depends on the ratio of the original concentrations of compounds being precipitated and on the values of their solubility product. Coprecipitation of a more soluble compound with a less soluble one is possible in the process of fractional precipitation. The methods of fractional precipitation, which are generally used for separation of mixtures of substances that are close in terms of chemical properties and solubility, are extremely labor-intensive.