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It is said, that the gold dust from Africa, in its pureststate, is from twenty-one to upwards of twenty-two caratsfine ; but that the natives frequently mix with it filingsof brass. This admixture may be distinguished by thehydrostatic balance, the specific gravity of brass not beinghalf so great as that of the gold dust : in this way ofexamination great care must be taken to make the waterpenetrate as perfectly as possible into all the interstices soas to come into close contact with every particle. A littleaqua fortis also, poured on the mixture, will immedi-ately discover the fraud, receiving, from the copper inthe brass, a blue tincture. It has been suspected, that ifthe gold be naturally alloyed with a little copper, this trialwill prove fallacious, and that the natural copper willtinge the menstruum equally with that which is addedby art : of this, however, there is no danger, the naturalalloy not being in distinct particles, but diffused througheach mass or particle of the gold, so as to be covered bythe gold, and protected from the action of the menstruum.There are several other means by which this abuse maybe discovered : if the dust be spread thin on a piece ofwhite paper, and moistened with any volatile alkalinespirit, as that of hartshorn, of sal ammoniac, or of urine,the spirit will in a few minutes diffolve so much of thecopper as to stain the paper blue : stale urine itself has alike effect, in an inferiour degree; and a solution ofcrude sal ammoniac, applied in the same manner, producesa greenish stain.

There are sundry European rivers which roll particlesof gold with their sands, in no great quantity, yet such,that the neighbouring inhabitants, at certain seasons, findtheir account in collecting them. M. de Reaumur, in anessay in the French memoirs for 1718, drawn up frommaterials furnished by the intendants of the several pro-vinces

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