Tar
3 of the 7 encyclopedias on this shelf carry an entry for Tar. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
a product of the destructive distillation of various organic substances; but the tars of commerce are obtained 1st from the distillation of coal, etc., for gas (gas tar or coal tar), and 2d from the distillation of wood (wood tar). Gas or coal tar, which was formerly regarded as a troublesome and almost useless byproduct product of the gas manufacture, is now a substance of so much value that it is second only in importance to the gas itself. Its value has arisen almost entirely from the fact that it is the source of the wide range of important dyeing substances, which, derived from aniline, phenol (carbolic acid), and anthracene respectively, may all be classed as tar colors. Coal naphtha obtained by distillation from coal tar is a mixture of several hydrocarbons of different degrees of volatility, the lightest being benzol and toluol, and the earlier part of the distillate is composed of a mixture of these two, and that part is utilized for the preparation of aniline as the basis of the aniline colors. The material remaining in the retort after the light oils are distilled over constitutes artificial asphalt, but this on further distillation at a higher heat gives off "heavy oils," leaving in the retort pitch, a substance which when cold is hard, black, and shining, and breaks with a glassy fracture. The principal constituents of the heavy oil are carbolic acid (phenol), cresylic acid (cresol), and in the later stages of the distillatory process anthracene is obtained. All these substances are industrially important. Wood tar is obtained as a by-product the destructive distillation in of wood for the manufacture of pyroligneous acid (wood vinegar), and methyl alcohol (wood spirit). Wood tar has several constituents in common with coal tar; its most characteristic fluid ingredients being hydrocarbons with methylic acetate, acetone, eupione, and creosote, with solid resinous matters, paraffin, anthracene, chrysene, etc. It possesses valuable antiseptic properties, chiefly owing to the creosote it contains, whence its principal value for most purposes is derived. In addition to its various uses in the arts of coating and preserving timber and iron in exposed situations, and for impregnating ships' ropes and cordage, it has various applications for external use in medicine owing to its antiseptic properties.
Aiton's Encyclopedia (1910)
a dark, sticky liquid variously obtained by destructive distillation. The wood tar of the United States is produced chiefly in the southern Atlantic States from the long-leafed pine by a very crude method. A conical chamber or cave is excavated in the side of a steep bank. A large sheetiron pan is placed in the bottom, provided with a spout leading into a barrel outside. The cave is filled with logs of pine, and the face built up with sods to prevent the entrance of air. The mass of wood is then fired. It burns slowly without a flame, and literally roasts the tar out of the wood. The tar is caught in the pan, and trickles slowly out into the barrel. When one barrel is filled, another is put in its place. Wood tar is in use for tarring ropes, and covering timbers exposed to the weather. Tar is a cure for certain diseases of the skin. It is used in making tar soap and in compounding tar remedies for lung troubles. Charleston, South Carolina , Archangel, Russia, and Stockholm, Sweden, are noted centers of the tar trade. Coal tar is obtained--ten gallons to the ton--by a somewhat similar process of roasting coal in the manufacture of illuminating gas. It is used for preserving timber and in making tar paper. Coal tar also makes an excellent protective paint and, being waterproof, is much used in laying gravel roofs. Coal tar yields the oil known as benzine. It is the base also of the beautiful aniline colors now the dependence of the dyer's art. Owners of gasworks formerly considered coal tar an expensive nuisance. They now regard it as a by-product of substantial value. See Turpentine ; Aniline
The Encyclopedia of Founding (1892)
A viscid liquid, usually from brown to black in color, obtained in the destructive distillation of organic matters. Wood-tar is obtained in the manufacture of wood vinegar, and yields, on repeated fractional distillations, creosote, paraffine, picamar, etc. Stockholm-tar is obtained in the same manner from roots and other useless parts of resinous pines. Coal-tar comes from the destructive distillation of coal in the manufacture of coal-gas, and when distilled yields carbolic acid, cresylic alcohol, etc.; also the liquid hydrocarbons benzol, toluol, etc; the solid hydrocarbons paraffine, napthaline, and the compounds coridine, piciline, aniline, etc. See PITCH.