This first fusion may also be performed amidst the coals, by casting the ore upon them in the furnace, without using a crucible; and then an earthen vessel, thoroughly heated, or even made red-hot, must be placed under the grate of the fire-place, to receive the metal as it runs from the ore.
The Regulus obtained by this means is much more impure and brittle than Black Copper, because it contains moreover a large quantity of Sulphur and Arsenic; as these volatile substances have not time to evaporate during the short space requisite to melt the ore, and as they cannot be carried off by the action of the fire after the ore is once melted, whatever time be allowed for that purpose. However, some part thereof is dissipated; and the Iron which is in pyritose ores, having a much greater affinity than Copper, and indeed than any other metallic substance, with Sulphur and Arsenic, absorbs another part thereof, and separates it from the Regulus.
This Regulus, it is plain, still contains all the same parts that were in the ore, but in different proportions; there being more Copper, combined with less Sulphur, Arsenic, and unmetallic earth, which have been either dissipated or turned to slag. Therefore, if you would make it like Black Copper, you must pound it, roast it over and over, to free it from its Sulphur and Arsenic, and then melt it with the black flux.
If this Regulus contain much Iron, it will be adviseable to melt it once or twice more, before all the Sulphur and Arsenic are separated from it by roasting; for as the Iron, by uniting with these volatile substances, separates them from the Copper, with which they have not so great an affinity; so also the Sulphur and Arsenic, by uniting with the Iron, help in their turn to separate it from the Copper.
PROCESS II.
To purify Black Copper, and render it malleable.
Break into small bits the Black Copper you intend to purify; mix therewith a third part in weight of granulated Lead, and put the whole into a cupel set under the muffle in a cupelling furnace, and previously heated quite red. As soon as the metals are in the cupel raise the fire considerably, making use, if it be needful, of a pair of perpetual bellows, to melt the Copper speedily. When it is thoroughly melted, lower the fire a little, and continue it just high enough to keep the metalline mass in perfect fusion. The melted matter will then boil, and throw up some scoriæ, which will be absorbed by the cupel.
When most of the Lead is consumed, raise the fire again, till the face of the Copper become bright and shining, thereby shewing that all its alloy is separated. As soon as your Copper comes to this state, cover it with charcoal-dust conveyed into the cupel with an iron ladle: then take the cupel out of the furnace and let it cool.
OBSERVATIONS.