Fractional distillation of oil. Glass beads in a glass column being used to distill fractions from crude oil. A fraction is part of a liquid mixture that is separated out from the rest of the liquid by boiling the liquid. Different fractions boil at different temperatures. The glass beads seen in the fractionating column provide a large and cool surface area on which the evaporating oil fraction has condensed to form the liquid seen. This liquid can then evaporate and recondense further up the column. This ensures a smooth temperature gradient up the column. The required fraction is collected in a condensing tube (not seen).