Juniper Tar, Pyroleum Oxycedri, Oleum Juniperi empyreumaticum, Oleum Cadinum, Huile de Cade.—This is a tar originally obtained by the destructive distillation of the wood of the Cade, Juniperus Oxycedrus L., a shrub or small tree, native of the countries bordering the Mediterranean. It was for centuries used in the South of France as an external remedy, chiefly for domestic animals, but had fallen into complete oblivion until ten years ago, when it began to be prescribed in skin complaints.
The Huile de Cade now in use, is transparent and devoid of crystals. It is somewhat thinner than Swedish tar, but closely agrees with it in other respects. It is imported from the Continent, but where made and from what wood we know not. Huile de Cade is mentioned by Olivier de Serres,[2316] a celebrated French writer on agriculture of the 16th century; it is named by Parkinson[2317] in 1640; also by Pomet,[2318] in whose time (1694) it was rarely genuine, common tar being sold in its place.
Beech Tar—Tar is also manufactured from the wood of the beech, Fagus silvatica L., and has a place in some pharmacopœias as the best source of creasote.
Birch Tar—is made to a small extent in Russia, where it is called Dagget, from the wood of Betula alba L. It contains an abundance of pyrocatechin, and is esteemed on account of its peculiar odour well known in the Russia leather. A purified oil of birch tar is sold by the Leipzig distillers.
PIX NIGRA.
Pix sicca vel solida vel navalis; Pitch, Black Pitch; F. Poix noire; G. Schiffspech, Schusterpech, Schwarzes Pech.
Botanical Origin—see Pix liquida.
Production—When the crude products of the dry distillation of pine wood, as described in the previous article, are submitted to re-distillation, the following results are obtained. The first 10 to 15 per cent. of volatile matter consists chiefly of methylic alcohol and acetone. A higher temperature causes the vaporization of the acetic acid, while the still retains the tar. This last, subjected to a further distillation, may be separated into a liquid portion called Oil of Tar (Oleum Picis liquidæ), and a residuum which, on cooling, hardens and forms the product under notice, namely Black Pitch. Again heated to a very elevated temperature, it is capable of yielding paraffin, anthracene and naphthalene.
Description—Pitch is an opaque-looking, black substance, breaking with a shining conchoidal fracture, the fragments showing at the thin translucent edges a brownish colour. No trace of distinct crystallization is observable when very thin fragments are examined, even by polarized light. Pitch has a peculiar disagreeable odour, rather different from that of tar. Its alcoholic solution has a feeble taste somewhat like that of tar, but pitch itself when masticated is almost tasteless. It softens by the warmth of the hand, and may then be kneaded. It readily dissolves in those liquids which are solvents of tar. Alcohol of 75 per cent. acts freely on it, leaving behind in small proportion a dark viscid residue. The brown solution reddens litmus paper, and yields a dingy brownish precipitate with perchloride of iron, and whitish precipitates with alcoholic solution of neutral acetate of lead, or with pure water. Pitch dissolves in solution of caustic potash, evolving an offensive odour.
Chemical Composition—From the method in which pitch is prepared, we may infer that it contains some of the less volatile and less crystallizable compounds found in tar. Ekstrand (1875) extracted from it Retene, C₁₈H₁₈, a colourless, inodorous crystalline substance, melting at 90° C.