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is to be regretted, that their affected mysterioufnefs, andpeculiar mode of philosophizing, have rendered theirwritings so forbidding, that many useful facts, scatteredthrough them, lie still unknown.

SECT. XIII.

Imitations of gold.

I. Gold coloured' metal.

ROM the general estimation of the colour of gold.

H which has attracted the notice of the most barbarousnations, the communication of the fame admired colour tometals of low price, for uses where the other qualities ofgold are not required, becomes an important object. Theproduction of a kindred colour, by artificial composition*in the common metal brass, affords a principle for thisimitation.

Brass is prepared by melting copper with the mineralcalled calamine, from which it receives an increase of onethird or one half its weight. The matter, which thecopper imbibes from the calamine, is found to be zinc, ofwhich that mineral is properly an ore; and accordinglyzinc itself, melted with copper, communicates a colour ofthe same kind. According to the purity of the zinc andcopper, the proportions in which they are mixed, and theintimacy of their union, the compound metal proves moreor less malleable, and approaches more or less to the colourof gold.

Those who have given receits for making a gold colouredmetal, differ greatly in the proportion of the two in-gredients; some directing the zinc to be taken only in afifth or a sixth part of the weight of the copper, andothers in an equal weight or more. From a. set of ex-

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perimeats