It is highly desirable in vacuum distillation for the purification of materials to be able to split the fractions of distillate without interrupting the distillation itself. Inasmuch as only the two fractions are required, the low boiling and the pure material fractions, the apparatus illustrated in the accompanying diagram serves the purpose exceedingly well: a distilling flask,F, with two side arms. Two additional arms could be provided rather easily, however, in order to increase the number of fractions which could be collected without interruption.