Abstract: The invention relates to a rotary evaporator for carrying out a processor-controlled distilling operation. A rotary flask (5), a condenser (8) and a distillate collector receptacle (10) of the rotary evaporator (1) are continually kept under vacuum.According to the invention, the automatically controlled supply of a sample solution to the rotary flask is accomplished by means of a metering receptacle adapted to have the sample solution supplied thereto from a supply container for temporary transitory storage therein prior to transfer of the solution to the vacuum system, or the rotary flask (5), respectively. For discharging the distillate from the distillate collector receptacle (14), an outlet valve associated therewith is operable to connect the collector receptacle to a vacuum conduit (26) for the discharge of the distillate. This provision offers the advantage of permitting substantially discharge of the distillate without requiring the vacuum system to be vented.