In a general way, according to the later authors, they were largely lead oxide, and contained from 5% to 20% cuprous oxide. If a calculation be made backward from the products given as the result of the charge described, it would appear that in this case they must have contained at least one-fifth copper. The silver in these liquation cakes would run about 24 ozs. per ton, in the liquated lead about 36 ozs. per ton, and in the liquation thorns 24 ozs. per ton. The extraction into the liquated lead would be about 80% of the silver.
[Pg 540][29] The "ash-coloured copper" is a cuprous oxide, containing some 3% lead oxide; and if Agricola means they contained two unciae of silver to the centumpondium, then they ran about 48 ozs. per ton, and would contain much more silver than the mass.
[Pg 541][30] There are three principal "slags" mentioned—
| 1st. | Slag from "leading." |
| 2nd. | Slag from "drying." |
| 3rd. | Slag from refining the copper. |
From the analyses quoted by various authors these ran from 52% to 85% lead oxide, 5% to 30% cuprous oxide, and considerable silica from the furnace bottoms. They were reduced in the main into liquation cakes, although Agricola mentions instances of the metal reduced from "slags" being taken directly to the "drying" furnace. Such liquation cakes would run very low in silver, and at the values given only averaged 12 ozs. per ton; therefore the liquated lead running the same value as the cakes, or less than half that of the "poor" lead mentioned in [Note 17, p. 512], could not have been cupelled directly.
[Pg 542][31] See [Note 16, p. 511], for discussion of yellow and caldarium copper.
[32] This cadmia is given in the Glossary and the German translation as kobelt. A discussion of this substance is given in the note on p. [112]; and it is sufficient to state here that in Agricola's time the metal cobalt was unknown, and the substances designated cadmia and cobaltum were arsenical-cobalt-zinc minerals. A metal made from "slag" from refining, together with "base" thorns, would be very impure; for the latter, according to the paragraph on concentrates a little later on, would contain the furnace accretions, and would thus be undoubtedly zincky. It is just possible that the term kobelt was used by the German smelters at this time in the sense of an epithet—"black devil" (see [Note 21, p. 214]).
[33] It is somewhat difficult to see exactly the meaning of base (vile) and precious (preciosum) in this connection. While "base" could mean impure, "precious" could hardly mean pure, and while "precious" could mean high value in silver, the reverse does not seem entirely apropos. It is possible that "bad" and "good" would be more appropriate terms.
[Pg 543][34] The skimmings from the molten lead in the early stages of cupellation have been discussed in [Note 28, p. 539]. They are probably called thorns here because of the large amount of copper in them. The lead from liquation would contain 2% to 3% of copper, and this would be largely recovered in these skimmings, although there would be some copper in the furnace bottoms—hearth-lead—and the litharge. These "thorns" are apparently fairly rich, four unciae to the centumpondium being equivalent to about 97 ozs. per ton, and they are only added to low-grade liquation material.
[Pg 544][35] Particulis aeris tusi. Unless this be the fine concentrates from crushing the material mentioned, we are unable to explain the expression.