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1. Coal-tar. This (patent) manufacture was in 1787 intro-duced into Scotland , by the Earl of Dundonald, a noblemanmuch attached to chemical pursuits.
This mineral tar, it has been said, possesses some advantagesover the vegetable tar in common use, for coating the bottomsof ships ; because it is a sure defence against those marine ani-mals, which in hot climates perforate the planks and timbers ofvessels not sheathed with copper.
This manufacture was first established at Enterkin, but after-wards removed to Muirkirk in Ayrshire, not far distant, whereit is now prosecuted with considerable energy.
It is obtained in most abundance from particular kinds of unc-tuous coal, by slow combustion, in circular brick kilns, of whichthe sides have a great number of perforations for admission ofsmall streams of air : These, however, are from time to timestopped up in course of the process, as found necessary. Thesmoke and vapour having ascended the chimney, before escap-ing, have to go a great way horizontally, backward and forward,in slightly inclined labyrinthal passages, in which are numbers ofprojecting tiles, the whole intended to detain the aeriform fluids,and rob them as much as possible of the tar. Besides, the roofof these flues being covered with lead, and a sheet of cold water16 inches deep, the condensation is rendered very complete;and accordingly, the tar, by its gravity, finds its way, in smallstreams, down channels prepared for its conveyance to receivingpits dug for the purpose ; whence it is taken and put into barrelsfor sale.
When the tar has all come over, the holes in the kiln areclosed. When cold, the coals, in a state of good coke, morevaluable than when they were put in, are withdrawn, and sentoff to the adjoining iron-works, to be used in smelting.— Beforethe tar is sold, it is most commonly boiled down to a very thickconsistency'.
There are forty-five of these kilns at present going ; and eachon an average is charged from ninety to a hundred times annual-ly. The whole produce is about 360 tons of tar, or one ton perday ; and it is sold at from 12s. to 14s. per cwt. The price isregulated by that of foreign tar, the former being always a fewshillings per cwt. lower
It is used, at some works, as a black pigment for both cast-iron goods and smith-work, laid on with a brush when the metalis a little hot, to cause it dry soon.
2. Lamp Black .—There are considerable quantities of coaltar converted, at Muirkirk, into this substance, by means of com-bustion. The process is conducted much in the same manner asat the works where lamp black is made from foreign pitch ; only,pere, no cloth is used for this soot to settle on, as it collects upon,
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