ars doctrinistica, in its extent, comprehends particular manners of examining every ore, or mixed metal, according to its nature, with the best-adapted fluxes; so as to discover, not only what metals, and what proportions of metal, are contained in ores; but likewise how much sulphur, vitriol, alum, arsenic, smelt, &c. may be obtained from every one respectively. See Blow-pipe, Metallurgy, and Mineralogy.

Assaying is more particularly used by moneyers and goldsmiths, for the making a proof or trial by the cup-pel, or test, of the fineness or purity of the gold and silver to be used in the coining of money, and manufacture of plate, &c. or that have been already used therein.

There are two kinds of assaying; the one before metals are melted, in order to bring them to their proper fineness; the other after they are struck, to see that the species be standard. For the first assay, the assayers use to take 14 or 15 grains of gold, and half a dram of silver, if it be for money; and 18 grains of the one, and a dram of the other, if for other occasions. As to the second assay, it is made of one of the pieces of money already coined, which they cut in four parts. The quantity of gold for an assay among us is six grains; in France, nearly the same; and in Germany, about three times as much.

The proper spelling of that word, however, is essay; under which article, therefore, the reader will find the subject more particularly treated.

Assay-Balance, or Essay-Balance, the flat pieces of glass often placed under the scales of an assay-balance, seem, by their power of electricity, capable of attracting, and thereby making the lighter scale preponderate, where the whole matter weighed is so very small. See Essay-Balance.

The electricity of a flat surface of about three inches square has been known to hold down one scale, when there were about 200 grains weight in the other. See Balance.