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fifteen and sour tenths; with a third of silver, one in six-teen and two tenths; with a fourth, one in sixteen andseven tenths ; and with an eleventh of silver, which is thestandard proportion of alloy, one in eighteen and onetenth. On this principle, the specific gravity, or propor-tional loss in water, of gold alloyed with different quanti-ties of silver, copper, and mixtures of both, may be com-puted, and formed into tables, for abridging the trouble ofcalculation in the trial of given masses.

A person, said to have made large profits in the purchaseof gold from the Chinese, made use of this method forestimating the fineness of the gold. With the assistanceof tables, now in my hands, he could readily determineby the balance the quality of the whole compound, or thequantity of fine gold it contained ; without any danger ofbeing imposed on by a superficial coat, however thick,or by any baser materials, that were there known, beingincluded within the mass. The Chinese alloy being, asalready observed, almost always silver, contributed not alittle both to the facility and accuracy of the examination.

The above method of calculation supposes, that whenthe two metals are melted together, each of them stillretains its own proper gravity, as if they were joined onlyby simple apposition. In mixtures of gold with silver,this appears to be the cafe, but in mixtures of it withother metals there are some variations. Gold and copper,melted together, prove specifically lighter, or lose a greaterproportion of their weight in water, than if they wereweighed separately : Mr. Gellert, in a treatise of metallur-gic chemistry publissied in 1750, observes, that the famething happens in mixtures of gold with zinc, tin, andiron; but the reverse in mixtures of it with lead andbismuth. In some of the compositions of gold withpi atina, a dilatation of the volume (whence necessarily

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