Source, Etc

Coal-tar is obtained by the destructive distillation of coal in iron or clay retorts. The gaseous products that are formed during the process constitute ordinary illuminating gas; the liquid products are a watery solution of ammonium carbonate, sulphide, etc, and a heavy, dark, viscid, tarry liquid, coal-tar. The retort contains a porous, carbonaceous residue, coke.


Coal-tar is a nearly black, viscid liquid, with a strong, penetrating, disagreeable odour; it is heavier than water, its specific gravity varying from 1.1 to 1.2. It is only slightly soluble in water, to which it imparts an alkaline reaction (distinction from wood-tar). It consists of a large number of substances, amongst which benzene, toluene, xylene, phenol, cresol, naphthalene, anthracene, and pitch may be mentioned. For further details see Martin, ' Industrial Chemistry, Organic,' p. 415.


The chief medicinal use of coal-tar is as an antiseptic application in certain skin diseases.