Note note 16, p. 511 — BOOK XI.

[Pg 511][16] The latter part of this paragraph presents great difficulties. The term "refining furnace" is given in the Latin as the "second furnace," an expression usually applied to the cupellation furnace. The whole question of refining is exhaustively discussed on pages 530 to 539. Exactly what material is meant by the term red (rubrum), yellow (fulvum) and caldarium copper is somewhat uncertain. They are given in the German text simply as rot, geel, and lebeter kupfer, and apparently all were "coarse" copper of different characters destined for the refinery. The author states in De Natura Fossilium (p. 334): "Copper has a red colour peculiar to itself; this colour in smelted copper is considered the most excellent. It, however, varies. In some it is red, as in the copper smelted at Neusohl.... Other copper is prepared in the smelters where silver is separated from copper, which is called yellow copper (luteum), and is regulare. In the same place a dark yellow copper is made which is called caldarium, taking its name among the Germans from a caldron.... Regulare differs from caldarium in that the former is not only fusible, but also malleable; while the latter is, indeed, fusible, but is not ductile, for it breaks when struck with the hammer." Later on in De Re Metallica (p. 542) he describes yellow copper as made from "baser" liquation thorns and from exhausted liquation cakes made from thorns. These products were necessarily impure, as they contained, among other things, the concentrates from furnace accretions. Therefore, there was ample source for zinc, arsenic or other metallics which would lighten the colour. Caldarium copper is described by Pliny (see note, p. 404), and was, no doubt, "coarse" copper, and apparently Agricola adopted this term from that source, as we have found it used nowhere else. On page 542 the author describes making caldarium copper from a mixture of yellow copper and a peculiar cadmia, which he describes as the "slags" from refining copper. These "slags," which are the result of oxidation and poling, would contain almost any of the metallic impurities of the original ore, antimony, lead, arsenic, zinc, cobalt, etc. Coming from these two sources the caldarium must have been, indeed, impure.