The same mines also furnish us with the preparation known as “scum of silver.”[989] There are three[990] varieties of it; the best, known as “chrysitis;” the second best, the name of which is “argyritis;” and a third kind, which is called “molybditis.” In most instances, too, all these tints are to be found in the same cake.[991] The most approved kind is that of Attica; the next being that which comes from Spain. Chrysitis is the produce of the metallic vein,[992] argyritis is obtained from the silver itself, and molybditis is the result of the smelting of lead,[993] a work that is done at Puteoli; to which last circumstance, in fact, molybditis owes its name.[994] All these substances are prepared in the following manner: the metal is first melted, and then allowed to flow from a more elevated receiver into a lower. From this last it is lifted by the aid of iron spits, and is then twirled round at the end of the spit in the midst of the flames, in order to make it all the lighter. Thus, as may be easily perceived from the name, it is in reality the scum of a substance in a state of fusion—of the future metal, in fact. It differs from scoria in the same way that the scum of a liquid differs from the lees, the one[995] being an excretion thrown out by the metal while purifying itself, the other[996] an excretion of the metal when purified. Some persons distinguish two kinds of scum of silver, and give them the names of “scirerytis” and “peumene;”[997] a third variety being molybdæna, of which we shall have to make further mention when treating of lead.[998] To make this scum fit for use, the cakes are again broken into pieces the size of a hazel-nut, and then melted, the fire being briskly blown with the bellows. For the purpose of separating the charcoal and ashes from it, it is then rinsed with vinegar or with wine, and is so quenched. In the case of argyritis, it is recommended, in order to blanch it, to break it into pieces the size of a bean, and then to boil it with water in an earthen vessel, first putting with it, wrapped in linen cloths, some new wheat and barley, which are left there till they have lost the outer coat. This done, they bruise the whole in mortars for six consecutive days, taking care to rinse the mixture in cold water three times a day, and after that, in an infusion of hot water and fossil salt, one obolus of the latter to every pound of scum: at the end of the six days it is put away for keeping in a vessel of lead.