Sulphur and Arsenic are the substances to which Silver and the other metals usually owe their mineral state. These two matters are never very closely united with Silver; but may be pretty easily separated from it by the action of fire, and the addition of Lead. If Arsenic be predominant in a Silver ore, it will unite with the Lead by the help of a pretty moderate heat, and quickly convert a considerable quantity thereof into a penetrating fusible glass, which has the property of scorifying with ease all substances that are capable of scorification. When Sulphur predominates, the scorification proceeds more slowly, and doth not always succeed; because that mineral combined with Lead lessens its fusibility, and retards its vitrification. In this case, part of the Sulphur must be dissipated by roasting: the other part unites with the Lead; and that, being rendered lighter by this union, floats on the rest of the mixture, which chiefly contains the Silver. At last, the joint action of the air and of the fire dissipates the portion of Sulphur that had united with the Lead: the Lead vitrifies and reduces to a scoria whatever is not either Silver or Gold: and thus the Silver being disentangled from the heterogeneous matters with which it was united, one part thereof being dissipated and the other vitrified, combines with the portion of Lead which is not vitrified, and falls through the scoria, which, to favour its descent, must be in perfect fusion. The whole process, therefore, consists of three distinct operations. The first is Roasting, which dissipates some of the volatile substances found united with the Silver: the second is Scorification, or the Vitrification of the fixed matters also united with the Silver, such as sand, stones, metals, _&c._ and the third is precipitation, or the separation of the Silver from the scoria. The two first are, as hath been shewn, preparatives for the last, and indeed produce it. As every thing we said concerning Gold, when we treated of the process of Amalgamation, is to be applied to Silver, which may be extracted by the same method when it is in its metalline form; in the same manner, all we now advance touching the method of extracting Silver by Scorification, when it is depraved with a mixture of heterogenous matters, is equally applicable to Gold in the same circumstances: and indeed Silver almost always contains more or less Gold naturally. In the process we directed, that the ore should be pulverized before it be exposed to the fire, with a view to enlarge its surface, and by that means facilitate the action of the Lead upon it, as well as the evaporation of its volatile parts.