sides, thus exposing the bottom more, and with a wire brush remove the adhering particles of litharge, and dust of the cupel. Turning them half round so as to make the base a square, we repeat the operation, and then weigh, but only when quite cold, since otherwise the heat, by increasing the bulk, might tend to create a variation.

The silver produced in this manner, it should be remarked, is not perfectly pure, chemically speaking, but the slight impurities are too insignificant to deserve any attention from an assayer, who has nothing but technical purposes in view, though they might require it from a scientific chemist; and for this latter reason, I have thought proper in the third chapter to suggest a method to ascertain the exact amount of silver in this button, should it be deemed necessary, though, I must add, that such precision can only be required at mints, if the investigations are not con

ducted for science' sake, in which case, the wet process would, of course, be preferred from the beginning.

Besides this, small inaccuracies in the shape of losses, as has already been remarked, cannot be averted, even though the assay be performed with the greatest care, as the evaporating, or rather oxidizing lead probably carries off small particles of silver, particularly when too much heat is used during that process. It is impossible to give any perfect rules how to obviate such faults, since so much depends on the care and attention paid, as well as on the acquired practice and innate practical skill of the assayer; yet, pre-supposing all this as perfect, the Parisian mint has established a table to regulate their assays, which will be found on pages 52 and 53. From this it is seen that the different losses with different quantities of silver vary considerably, nor is the loss a per-centage, being greatest where the original or true

amount of silver in the ore or alloy is seven hundred.

This table should always be referred to, as it enables us to calculate the true amount of silver, and to rectify those unavoidable faults which may be occasioned by the lead carrying off portions of the silver entirely, or else drawing them along with it into the pores of the crucible.