A resinous substance, obtained by the inspissation of tar. There are two methods of obtaining it; one by simply boiling the' tar in large iron pots, or by setting it on fire and letting it burn until it obtains such a consistence as, by dipping a stick in it, and exposing it to the air, it readily solidifies. Two barrels of the best tar, or two and a half barrels of green tar, are thus convertible into one barrel of good pitch. The foregoing has reference only to tar obtained from the pine-tree and other vegetable matters; but a large quantity of tar and pitch are obtained in this country from coal. On the banks of the Grand Junction Canal, in the vicinity of the large iron and coal works, there were established some years ago several "tar-works," to which the iron masters sent their raw coal, gratis, and received, in return, the cokes produced by such coal; the proprietors of the tar-works being contented with the compensation afforded by the smoke alone: the following is the process of obtaining it: - A range of eighteen or twenty stoves is erected, and supplied with coal kept burning at the bottom; the smoke is conducted by proper horizontal tunnels into a capacious and close funnel, of one hundred or more yards in length: this funnel is built of brick, supported by brick arches, and covered on the top by a shallow pond of water, which pond is supplied with water, when wanted, by a steam engine belonging to the coal or iron works.
The coldness of the water gradually condenses the smoke, causing the tar to fall on the floor of the funnel, whence it is conveyed by pipes into a receiver; from the latter it is pumped into a boiler, and evaporated to the required consistence, or otherwise inspissated into pitch: when the latter is the case, the volatile particles which arise during the inspis-wtion are again condensed into an oil used as a varnish. In this process the smoke is decomposed, nothing arising from the work but a white vapour from some small funnels (kept open to give draft to the fires), and a small evaporation of water from the pond, occasioned by the heat of the smoke underneath it. The process requires but little attendance, the principal labour being that of supplying the fuel. In a tar-work, where twenty tons of coal are consumed per day, three labourers and a foreman do the whole business; and the quantity of tar produced will be about 28 barrels of 2 1/2 cwt. each; or 21 barrels of pitch of the same weight, in six days.
Some coals are, however, so bituminous as to yield one-eighth of their weight of tar.