BOOK VII

241

But it is better at first to add as much lead as is required to the ore whichneeds melting, rather than afterward when the melting has been half finished,that the whole quantity may not vanish in fumes, but part of it remainfast. When the heat of the fire has nearly consumed the lead, then is thetime when the gold and silver gleam in their varied colours, and when all thelead has been consumed the gold or silver settles in the cupel. Then assoon as possible remove the cupel out of the furnace, and take the button outof it while it is still warm, in order that it does not adhere to the ashes. Thisgenerally happens if the button is already cold when it is taken out. If theashes do adhere to it, do not scrape it with a knife, lest some of it be lost andthe assay be erroneous, but squeeze it with the iron tongs, so that the ashesdrop off through the pressure. Finally, it is of advantage to make two orthree assays of the same ore at the same time, in order that if by chanceone is not successful, the second, or in any event the third, may be certain.

While the assayer is assaying the ore, in order to prevent the great heatof the fire from injuring his eyes, it will be useful for him always to haveready a thin wooden tablet, two palms wide, with a handle by which it maybe held, and with a slit down the middle in order that he may look throughit as through a crack, since it is necessary for him to look frequently withinand carefully to consider everything.

A—Handle of tablet. B—Its crack.

Now the lead which has absorbed the silver from a metallic ore is con-sumed in the cupel by the heat in the space of three quarters of an hour. Whenthe assays are completed the muffle is taken out of the furnace, and theashes removed with an iron shovel, not only from the brick and iron furnaces,but also from the earthen one, so that the furnace need not be removed fromits foundation.

From ore placed in the triangular crucible a button is melted out, fromwhich metal is afterward made. First of all, glowing charcoal is put intothe iron hoop, then is put in the triangular crucible, which contains the oretogether with those things which can liquefy it and purge it of its dross ;then the fire is blown with the double bellows, and the ore is heated untilthe button settles in the bottom of the crucible. We have explained thatthere are two methods of assaying ore,—one, by which the lead is mixed