Abstract: A method of evaporating liquids to separate solid substances contained therein to form a residue of the substances characterized by applying subatmospheric pressure to at least one discrete portion of the liquid at a first pressure level and subsequently applying subatmospheric pressure to the discrete portion at a second pressure level lower than the first level to gradually evaporate the liquid from the discrete portion thereby leaving a residue of solid substances. Apparatus for performing the foregoing method preferably comprises an enclosure within which a support means is used for supporting at least one discrete portion of the liquid to be separated, a vacuum pump connected to the enclosure for evacuating atmosphere from within the enclosure, and a valve means between the pump and enclosure operable automatically to apply first and second subatmospheric pressure levels to within the enclosure.