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quality destroyed, by strong fire. Hence furnaces made ofthese pots, as described at the beginning of this volume,after they have suffered strong fife, cease to discolour, thehands.

Black-lead in fine powder, stirred into melted sulphur,unites with it so uniformly, and in such quantity, in virtueperhaps of its own abounding with sulphur, that thoughthe compound remains fluid enough to be poured intomoulds, it looks nearly like the coarser sorts of black-leaditself. Probably the way which prince Rupert is said tohave had, mentioned in the third volume of Dr. Birch’sHistory of the Royal Society, of making black-lead run.like a metal in a mould, so as to serve for black-lead again,consisted in mixing with it sulphur or sulphureous bodies.

On this principle the German black-lead pencils aresaid to be made; and many of those which are hawkedabout by certain persons among us, are prepared in thesame manner : their melting or softening, when held in acandle, or applied to a red hot iron, and yielding a bluishflame, with a strong smell like that of burning brimstone,betrays their composition j for black-lead itself yields nosmell or fume, and suffers no apparent alteration, in thatheat. Pencils made. with such additions are of a very badkind : they are hard, brittle, and do not cast or make amark freely either on paper or wood, rather cutting orscratching them than leaving a coloured stroke.

The true English pencils (which Vogel in his MineralSystem, and some other foreign writers, imagine to be pre-pared also by melting the black-lead with some additionalsubstances, and casting it into a mould) are formed ofblack-lead alone, sawed into flips, which are fitted into agroove made in a pieqe of wood, and another flip of woodglued over them: the softest wood, as cedar, is madechoice of, that the pencil may be the easier cut; and a

part,