Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/12

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Dr. Mac Culloch on certain products

As it is commonly called tar by the workmen, I shall use this term for want of a better.

This tar is very inflammable, and so liquid that it may be burnt in a lamp.

Although it appears to be an uniform fluid, it contains a great quantity of acetic acid, in a state of loose combination or mixture. For, by washing with water, a great part of this is separated; the water at the same time acquiring a colour from a portion of the tar which is retained in solution by the acid. Boiling water takes up a larger portion, and the tar acquires from this operation a thicker and more pitchy consistence.

Lime and the carbonated alkalies separate the acid with ease, carrying away also a portion of the tar which continues united to the solution. With subcarbonate of potash it thus forms in the first instance an uniform solution of a brown colour, but a continuance of trituration or boiling renders it pitchy and tenacious, after which it forms no further union with the mild alkalies.

It is perfectly and readily soluble in alcohol, in ether, in the pure alkaline lixivia, in acetic acid and in the mineral acids. The fat oils and the new essential oils dissolve only a small portion of it; but the drying oils and the latter when thickened by age act more readily. Coloured oil of turpentine dissolves a good deal of it. Naphtha hardly exerts any action, acquiring a scarcely sensible brown colour. If heat be applied to assist the solution, the portion taken up is deposited on cooling.

When it is subjected to distillation in a heat sufficient to keep it in a gentle ebullition, an oily looking matter passes over in considerable proportion, which sinks to the bottom of the water into which the tube is inserted. It is first of a pale colour, resembling oil of peppermint, but becomes gradually darker as the operation advances, till it acquires a deep brown hue.