Pitch

Pitch. When the tar from wood or coal is distilled, volatile naphtha or 'spirit' is obtained at low temperatures, and as the heat is increased heavy oils and other products appear in the distillate. If the temperature reaches redness, coke or carbon is left as a residue, but if the fire is withdrawn before the distilling vessel becomes red—i.e. before the heavy oils in the tar begin to break up—the residue is pitch. A softer and tougher pitch is obtained if the fire is removed early than if the heat is continued till coking begins. In the latter case it is more black, glossy, and brittle. An elastic pitch is got from bone tar, and another from stearine residues, and both are valued by varnish and tarpaulin makers. Pitch is also obtained from natural petroleum. Wood-tar pitch is much more used in America than in England, chiefly for protecting timber from the weather and the attacks of insects. Coal-tar pitch is most largely employed in the manufacture of patent fuel, from 5 to 8 per cent. of it being required to form Briquettes (q.v.) of small coal or coke breeze. It has other applications, such as in the manufacture of black varnishes for coating iron, and to a less extent for protecting wood and other substances, in the preparation of artificial asphalt (see ASPHALT), and to yield lamp-black when burned. Burgundy Pitch is the subject of a separate article (see also PINE). In some parts of Persia and Afghanistan a kind of pitch is prepared by the destructive distillation of goat and sheep dung, which is applied as a remedy for sores or ulcers on sheep and some other animals.