Benzene and Toluene

Benzene is employed not only as a solvent, but as a diluent of the medium or oil employed in painting. It is obtained from the lighter naphtha separated in the fractional distillation of coal-tar. The benzene (also called benzol) of commerce is rarely pure. The presence of small quantities of higher hydrocarbons of the same series is of little moment, but it also contains about one half percent of a sulphur compound called thiophene (C4H4S), to which the offensive odour of ordinary benzene is partly due. Thiophene is, however, much more soluble in cold oil of vitriol than is benzene, and may be removed by several treatments of the benzene with small quantities of this powerful acid. Benzene thus purified can now be purchased. Benzene is a mobile liquid, not miscible with water, but dissolving readily in all proportions in most if not all of the liquids now being described. It dissolves oils and very many of the harder as well as all the softer resins.

Toluene, commercially known as toluol, much resembles benzene, and may be used for the same purposes, although it is less volatile. Commercial toluene has a disagreeable smell, arising from the presence of a sulphur compound (thiotolene), which is more difficult to remove from the liquid than the thiophene from benzene.

Toluene of good quality and at a moderate price may be obtained from Kahlbaum of Berlin. It constitutes a useful diluent and solvent when used with the spirit-fresco medium.