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SECT. IX.

Of the refining of gold ; and the separation of small portions

of gold from other metals.

H E processes described in the preceding section,

for the assaying of gold, are used also for refiningit in the way of business; with such variations, in themanner of conducting them, as the greater quantitiesoperated upon, and the requisite cheapness and dispatch,render necessary.

The test is a large kind of cupel, formed of the samematerials with the small ones. Some of the Germanwriters recommend, both for tests and cupels, a sort offriable opake stone, called white spath, which appears tobe a species of gypsum, or of the stones from which plaster-of-paris is prepared. The spath is directed to be calcinedwith a gentle fire, in a covered vessel, till the flight crack-ling, which happens at first, has ceased, and the stone hasfallen in part into powder : the whole is then reduced intosubtile powder, which is passed through a fine sieve, andmoistened with so much of a weak solution of green vitriol,as is sufficient for making it hold together : Gellert how-ever finds, that is the stone is of the proper kind, whichcan be known only by trials, calcination is not necessary.Schesser observes, that these kinds of tests are liable to softenor fall asunder in the fire, and that this inconvenience maybe remedied, by mixing with the uncalcined stone some-what less than equal its weight, as eight ninths of such ashas been already used and is penetrated by the scoria of thelead, taking only that part of the old test which appearsof a green-grey colour, and rejecting the red crust on thetop. Tests or cupels made of the spath are said not to

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require