Of course, we can go another way as well. We can mix elements or even compounds together without chemical means so that they remain the substances they were but are now in a mixture. Clearly a mixture of pure substances is not a pure substance itself. Physical Separation Techniques of Mixtures Many are already well known to you. But while we have there the advantage of separate physical phases, it's certainly possible to separate pure liquids by boiling of the component of lower boiling point via distillation .
Chemists exploit other differences in property beside boiling point.
A difference in freezing points means one should be able to cool and precipitate out the higher melting compound. More subtle such differences include the dwelling time of a compound on some solid support within a fluid stream. The component less attracted to that support is eluted by the stream earlier than the others in a process called chromatography . Those subscripts imply that there is a fixed ratio of elemental atoms in a chemical compound. Fixed ratios of atoms make for fixed compounds.