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and is scraped from, the walls of the houses built for that purpose.This black is used for almost all the purposes for which the com-man lamp black is employed ; but, being a little coarser, it issold somewhat cheaper.
3. Coal Tar Oil is produced by distillation. The tar, as itcomes from the kilns, being put into a cast-iron retort, and heatapplied, the vapour rising is condensed in a common worm con-tained in a refrigeratory. What remains, after the oil, &e. comesover, is very thick ; and then answers most purposes better thanbefore it underwent this process.
This oil is of a dark amber colour, and very volatile ; its spe-cific gravity is usually tried by the graduated hydrometric glassbeads used for ascertaining the strength of spirits. Proof rumsinks bead 28 ; spirits of turpentine 22 or 23 ; and coal tar oilonly 18 or 20.
At a work in Glasgow it is used, together with coal tar andochre, in making a cheap brown paint, which is sold for Ss. thegallon.
At Muirkirk, the bands employed at the tar, the tar oil, andthe lamp black making, amount to about twenty.
4'. Wood Tar is obtained while distilling pyroligneous acid,already mentioned, in the proportion of about ten gallons forevery ton of wood submitted to that process.
This substance not being quite water proof, lias not yet beenapplied to any particular purpose, farther than coating courseout-door wood work ; for which even, from the above cause, itis not very applicable. At some of the manufactories where pro-duced, large accumulations of it are kept, in expectation of oneday being able to find an economical purpose to which it may beapplied.
At a recently established chemical work in Glasgow , the onlyone of the kind in Scotland , and belonging to the same compa-ny who make the coal tar at Muirkirk, the following articles aremanufactured; for which, and other purposes, a steam engine of21 horses’ power is on the premises, together with from a dozento twenty hands.
1. Ivory Black .—Produced from animal bones put into cover-ed cast-iron crucibles, and exposed to violent heat in a kiln, sons to produce incineration;—they are afterwards pulverized be-tween rollers and grindstones. The bones are collected in thecity and suburbs, and cost the manufacturer from a guinea anda half to forty shillings per ton. Ivory Black, which is chieflyused by painters, is troublesome to manufacture pure, as the en-amel of the teeth, when any happens to be ground along withthe bones, produces a lighter colour, and consequently deterioratesthe quality of the article. Considerable circumspection is also