Xylene, any of three isomeric dimethylbenzenes [which have the same chemical formula, C6H4(CH3)2, but different molecular structure], used as solvents, as components of aviation fuel, and as raw materials for the manufacture of dyes, fibres, and films. The three isomers, designated ortho (o), meta (m), and para (p), differ structurally only in the location of the methyl groups. All three are obtained from coal-tar distillate and petroleum as a mixture containing 50–60 percent by volume of m-xylene and 20–25 percent of each of the other isomers. Fractional distillation of the mixture removes the meta and para isomers, which have very similar boiling points, from the less volatile ortho isomer. Upon cooling the mixture of meta and para isomers, much of the p-xylene crystallizes in nearly pure form. The meta isomer, ...