S02
5s., according to the degree of finishing, or work bestowed uponthem. Both combs and spoons are generally stained, to imitatetortoise-shell, &c. by certain applications of acids, metallic oxyds,and lime. The shaving and chips of ivory are used in the com-position of Frankfort black, and those of horn are mostly sold formanure at the rate of about 2s. per stone.
17. Coal, Lime, and Mahble.
These minerals, as. connected with manufactures, have beenalready treated of in a former part of this work, (Chap. I. Sect.S.) ; but some additional particulars, connected with the subjectuf manufactures, may be here explained.
1. Coal .—This valuable mineral is found in the greatest abun-dance in several districts of Scotland : the quantity indeed is sogreat, that it may be deemed almost inexhaustible. Its utilityin domestic purposes and in the arts, is well known; and it is nowproposed to give an account of a new application of coal to pro-duce light, which, from its novelty, and importance, requires aparticular discussion.
In several parts of Persia , where the soil is bituminous, thereissues copiously from the earth a vapour, which, being kindledby the natives, burns with great vividity, yielding heat sufficientto dress victuals. In several of the Pyrenees , the same pheno-menon has been observed; also in various parts of Lancashire ,Worcestershire , &c.; in the vicinity of coal mines, particularlynear Wigan , where, in dry weather, eggs have been boiled bythe inflammation of the vapour. From this Dr Clayton appearsto have taken the hint; as, having visited the latter place in 1736,he produced the same effect in 1739, * by the distillation of coalin a close retort. The idea, however, seems to have lain dor-mant 52 years; as it was not until about the year 1791 that MrMurdoch began his experiments on coal gas, with a view to ap-ply it to the purposes of giving light in manufactories, &c.—be-ing then ignorant of what Dr Clayton had done, -j-
Within these four or five years, several cotton, and one print-work, near Glasgow , and two or three other works on the eastcoast, have been lighted up with coal gas, which answers the pur-pose extremely well.
This process being new, it may be cursorily described, as prac-tised on the large scale.
The coals from which the light is to be obtained, are put intoa cast-iron retort, sufficient to contain about two or three hundredweight; this retort having previously been placed in a furnace,with fuel below it, ready to be kindled.
The gazomeler is an oblong square vessel, about 16 feet inlength, 10 broad, and 9 deep, with a bottom, and no top, g e ‘
* X^hil. Trans,
f Ibid. 1808.