BOOK VII.

247

In assaying bismuth ore, place pieces of ore in the scorifier, and putit under the muffle in a hot furnace ; as soon as they are heated, theydrip with bismuth, which runs together into a button.

Quicksilver ore is usually tested by mixing one part of broken orewith three-parts of charcoal dust and a handful of salt. Put the mixture intoa crucible or a pot or a jar, cover it with a lid, seal it with lute, place it onglowing charcoal, and as soon as a burnt cinnabar colour shows in it, takeout the vessel; for if you continue the heat too long the mixture exhales thequicksilver with the fumes. The quicksilver itself, when it has become cool, isfound in the bottom of the crucible or other vessel. Another way is to placebroken ore in a gourd-shaped earthen vessel, put it in the assay furnace,and cover with an operculum which has a long spout; under the spout, putan ampulla to receive the quicksilver which distills. Cold water should bepoured into the ampulla, so that the quicksilver which has been heated by thefire may be continuously cooled and gathered together, for the quicksilveris borne over by the force of the fire, and flows down through the spout ofthe operculum into the ampulla. We also assay quicksilver ore in the verysame way in which we smelt it. This I will explain in its proper place.

Lastly, we assay iron ore in the forge of a blacksmith. Such ore is burned,crushed, washed, and dried ; a magnet is laid over the concentrates, andthe particles of iron are attracted to it; these are wiped off with a brush,and are caught in a crucible, the magnet being continually passed over theconcentrates and the particles wiped off, so long as there remain any particleswhich the magnet can attract to it. These particles are heated in the cruciblewith saltpetre until they melt, and an iron button is melted out of them.If the magnet easily and quickly attracts the particles to it, we infer that theore is rich in iron ; if slowly, that it is poor ; if it appears actually to repelthe ore, then it contains little or no iron. This is enough for the assaying ofores.

I will now speak of the assaying of the metal alloys. This is done bothby coiners and merchants who buy and sell metal, and by miners, but mostof all by the owners and mine masters, and by the owners and masters ofthe works in which the metals are smelted, or in which one metal is partedfrom another.

First I will describe the way assays are usually made to ascertain whatportion of precious metal is contained in base metal. Gold and silver arenow reckoned as precious metals and all the others as base metals. Onceupon a time the base metals were burned up, in order that the precious metalsshould be left pure ; the Ancients even discovered by such burning whatportion of gold was contained in silver, and in this way all the silver wasconsumed, which was no small loss. However, the famous mathematician,Archimedes 31 , to gratify King Hiero, invented a method of testing the silver,

sl This old story runs that Hiero, King of Syracuse, asked Archimedes to tell himwhether a crown made for him was pure gold or whether it contained some proportion ofsilver. Archimedes is said to have puzzled over it until he noticed the increase in water-level upon entering his bath. Whereupon he determined the matter by immersing bars ofpure gold and pure silver, and thus determining the relative specific weights. The best