. A dictionary of arts, manufactures and mines : containing a clear exposition of their principles and practice. mplete fusion the silver and the scoriae, and to effect theircomplete separation. In case it should be supposed t^at the whole of the silver hadnot been reduced by the iron or zinc, a little carbonate of potash should be added to theborax. The silver may also be reduced by exposing the chloride to a strong heat, incontact with chalk and charcoal. The following remarks by M. Gay Lussac, the author of the above method, upon theeffect of a little mercury in the humid assay, are importa
. A dictionary of arts, manufactures and mines : containing a clear exposition of their principles and practice. mplete fusion the silver and the scoriae, and to effect theircomplete separation. In case it should be supposed t^at the whole of the silver hadnot been reduced by the iron or zinc, a little carbonate of potash should be added to theborax. The silver may also be reduced by exposing the chloride to a strong heat, incontact with chalk and charcoal. The following remarks by M. Gay Lussac, the author of the above method, upon theeffect of a little mercury in the humid assay, are important:— It is well known that chloride of silver blackens the more readily as it is exposedto an intense light, and that even in the diffused light of a room, it becomes soonsensibly colored. If it contains four to five thousandths of mercury, it does not blacken;It remains of a dead white: with three thousandths of mercury, there is no markeddiscoloring in diffused light; with two thousandths it is slight; with one it is muchmore marked, but still it is much less intense than with pure chloride. With half a. 80 ASSAY. thousandth of mercury the difference of color is not remarkable, and is perceived onlyin a very moderate light. But when the quantity of mercury is so small that it cannot be detected by thedifference of color in the chloride of silver, it may be rendered quite evident by a verysimple process of concentration. Dissolve one gramme of the silver supposed to containJ of a thousandth of mercury, and let only f of it be precipitated, by adding only | ofthe common salt necessary to precipitate it entirely. In thus operating, the J thou-sandth of mercury is concentrated in a quantity of chloride of silver four times smaller:it is as if the silver having been entirely precipitated, four times as much mercurj,equal to two thousandths, had been precipitated with it. In taking two grammes of silver, and precipitating only | by common salt, theprecipitate would be, with respe
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