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Assay of Gold by Cupellation

This process is divided into five operations.

Cupellation. Either 6 or 12 grains of the alloy is the weight usually taken for the assay, to which is added 16 parts of lead for every 1 part of copper that it is presumed to contain, though considerably more lead may be used when the sample does not contain any silver; but if the reverse be the case, an excess of lead would tend to the loss of the latter metal, which ought not to be separated until the operation of parting. When silver is present an additional allowance of lead, equal too of its weight, is made on that account.

When, however, the quantity of silver is small, or is not required to be estimated, it becomes of little consequence what weight of lead is employed, so long as enough be used to carry off the base metals, at the same time that the quantity is not too large for the

Iron treated with this solution takes a steel cupel. The sample is then submitted to cublue color; zinc, a brown color; in the case pellation. This process does not require so of copper objects the first gold color does not much care for gold as silver, as none of this appear; lead and zinc are entirely indifferent. metal is absorbed by the cupel, or lost by

If, instead of the acetate of lead, an equal evaporation, and it will safely bear the highweight of sulphuric acid be added to the hypo- est heat of the furnace without injury. In sulphite of soda, and the process carried on other respects the operation may be conductas before, the brass is covered with a very ed in exactly the same manner as for silver. beautiful red, which is followed by a green, and changes finally to a splendid brown with green and red iris-glitter; this last is a very durable coating, and may find special attention in manufactures. (See No. 3313.) Very beautiful marbleized designs can be (See No. 3206.) Quartation. After gold has passed the cupel, it may still retain either of the other perfect metals, particularly silver. To remove the latter it undergoes the operations. of quartation and parting. Quartation is GOLD.