It is proper to observe, that there is scarce any Lead that does not contain some Silver; too little perhaps to defray the charges necessary to separate it, yet considerable enough to lead us into an error, by mixing with the Silver obtained from an ore, and increasing its weight. And therefore, when the operations above described are applied to the assaying of an ore, in order to know how much Silver it yields, it is previously necessary to examine the Lead to be used, and to ascertain the quantity of Silver it contains, which must be deducted from the total weight of the bead of Silver obtained by purifying it in this manner. Silver may be separated from its ore, and at the same time refined, by the single operation of the cupel, without any previous scorification with Lead. In order to do this, you must pound the ore; roast it, to dissipate all its volatile parts; mix it with an equal quantity of litharge, if it be refractory; divide it into five or six parcels, wrapping each in a bit of paper; weigh out eight parts of granulated Lead for one of ore, if it be fusible, and from twelve to sixteen, if it be refractory; put one half of the Lead into a very large cupel under the muffle; add thereto one of the little parcels of ore, when the Lead begins to smoke and boil; immediately slacken the fire a little; continue the same degree of heat till you perceive that the litharge formed round the metal, and on its surface, begins to look bright; then raise the fire; add a fresh parcel of ore; continue proceeding in the same manner till you have put in all the ore; then add the remaining half of the granulated Lead, and conduct the succeeding part of the operation in the same manner as that of cupelling. In this operation it is necessary that the fire be not too strongly urged, and that it be diminished every time you add a fresh parcel of ore; that so the Lead and the litharge may have time to dissolve, scorify, and carry off into the pores of the cupel, all the adventitious matters with which your Silver may be mixed. Notwithstanding this precaution, when the ore is refractory, there often gathers in the cupel a great quantity of scoria, together also with some of the ore that could not be dissolved and scorified. It is with a view to remedy this inconvenience that the second moiety of the Lead is added towards the end, which completes the dissolution and scorification of the whole; so that by means thereof no scoria, or very little, is left in the cupel at the end of the operation.