[ 2I 5 J

whether made by myself or others, how nearly soever theyapproached to gold in the mass, were very different fromit on the touchstone.

The colour of these compounds is improved by a finalsadmixture of certain other metallic bodies. Cramer ob-serves, that when copper is melted with a fourth or a sixthof zinc, and a little pure tin; the compound metal, wellcleaned and laid in the air for some days, acquires on thesurface the colour of fine gold : this teint, though merelysuperficial, is not the less valuable; for though it shouldbe discharged by cleaning, the piece soon recovers it again,every fresh surface tarnishing as it were to a like colour.Geoffroy relates, in the French memoirs for the year1725, that on trying different metals, iron seemed to havethe best effect; equal parts of copper and zinc beingbrought into fusion, he threw, in some iron filings,amounting to an eight part of each of the other metals:the mixt turned out of a beautiful yellow colour, and a.fine smooth grain, not at all fibrous, as mixtures ofcopper and zinc in this proportion by themselves alwaysare, yet very brittle: on repeating the experiment with-a fourth more of zinc, the proportions being ten parts ofzinc, eight of copper, and one of iron filings, the metal,proved of a grain like the former, but more compact,harder, brighter, and in colour still more like gold. Hefays the commixture of the iron with the other ingredientsrequires a particular management, which I cannot findthat he has any where communicated.

It has been said, that the mixtures of zinc and coppermay be made tough, by injecting upon them in fusion . alittle mercury-fublimate, as also by nitre, sal ammoniac,borax, and different kinds of inflammable bodies: butthese additions, as I have often found, from experience,,and as, P.ott also 1 observes; in a dissertation de zinco t

1 will