This consists in putting the pure gold into a small, borons crucible, or cupel, and heating it to redness in the muffle. Weighing must be done with the utmost accuracy. The weight in grains troy, doubled or quadrupled as the case may be, gives the number of carats fins of the alloy examined, without calculation.

According to the old French method of assaying gold, the following quantities were taken: For the assay pound, 12 gr.; fine silver, 30 grs.; lead, 108 grs. These having been cupelled together, the perfect button is rolled into a leaf (l¼ by 5 inches), twisted on a quill, and submitted to parting with 2½ oz. and 1½. oz. of nitric acid, sp. gr., 1.16 (20° Baume). The remainder of the process is similar to that above described.

The usual weight of silver taken for the assay pound, when the fineness is reckoned in 1000ths, is 20 grs., every real grain of which represents 50-1000ths of fineness, and so on of smaller divisions.