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to yield more easily to the menstruum. The coiled plateis put into a small glass vessel, called a parting glass,broad at the bottom and tapering upwards; with twiceits weight or more of the prepared aqua sortis. Thevessel is set in a sand-bath or other moderate heat, notexceeding that of boiling water; and its mouth stoptlightly with paper, or covered with a plate of glass, soas to keep out dust, without preventing the escape of theelastic vapours which rife during the dissolution. So longas the acid continues to act, the metal appears everywhere encompassed with minute bubbles, which issuefrom it in jets : the disappearance of these, or their uni-ting into a few large ones, is a mark that the acid is sa-tiated.

The coiled plate, aster the silver is thus eaten out fromit, should still retain its original form : for if the goldfalls into powder, it can scarcely be collected without theloss of some particles, which, though small in bulk, mayamount to a considerable proportion of the little quantityof metal made use of. This cohesion of the gold depends,partly, upon the quantity of silver not being so large as toleave the golden particles discontinued ; and partly on theaction of the acid not being so violent, as to divide anddisunite the gold by its impetuous extraction of the silver.The strength of the acid is to be ascertained by previoustrials on gold and silver mixed together in the assay pro-portions : if it is found to disunite the gold, it must belowered with water till it leaves the plates entire. Thesetrials are to be made exactly in the same manner as the assayprocess itself.

The liquor is poured off whilst hot, lest some of thedissolved silver should crystallize in cooling upon the re-remaining gold. To the golden plate, which appearsspongy and of a dark reddish brown colour, a little fresh

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