BOOK VII. 247 



In assaying bismuth ore, place pieces of ore in the scorifier, and put 

 it under the muffle in a hot furnace ; as soon as they are heated, they 

 drip with bismuth, which runs together into a button. 



Quicksilver ore is usually tested by mixing one part of broken ore 

 with three-parts of charcoal dust and a handful of salt. Put the mixture into 

 a crucible or a pot or a jar, cover it with a lid, seal it with lute, place it on 

 glowing charcoal, and as soon as a burnt cinnabar colour shows in it, take 

 out the vessel ; for if you continue the heat too long the mixture exhales the 

 quicksilver with the fumes. The quicksilver itself, when it has become cool, is 

 found in the bottom of the crucible or other vessel. Another way is to place 

 broken 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, put 

 an ampulla to receive the quicksilver which distills. Cold water should be 

 poured into the ampulla, so that the quicksilver which has been heated by the 

 fire may be continuously cooled and gathered together, for the quicksilver 

 is borne over by the force of the fire, and flows down through the spout of 

 the operculum into the ampulla. We also assay quicksilver ore in the very 

 same way in which we smelt it. This I will explain in its projjer place. 



Lastly, we assay iron ore in the forge of a blacksmith. Such ore is burned, 

 crushed, washed, and dried ; a magnet is laiid over the concentrates, and 

 the 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 the 

 concentrates and the particles wiped off, so long as there remain any particles 

 which the magnet can attract to it. These particles are heated in the crucible 

 with saltpetre imtil 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 the 

 ore is rich in iron ; if slowly, that it is poor ; if it appears actually to repel 

 the ore, then it contains httle or no iron. This is enough for the assaying of 

 ores. 



I will now speak of the assaying of the metal alloys. This is done both 

 by coiners and merchants who buy and sell metal, and bj' miners, but most 

 of all by the owners and mine masters, and by the owners and masters of 

 the works in which the metals are smelted, or in which one metal is parted 

 from another. 



First I will describe the way assays are usually made to ascertain what 

 portion of precious metal is contained in base metaJ. Gold and silver are 

 now reckoned as precious metals and all the others as base metals. Once 

 upon a time the base metals were burned up, in order that the precious metals 

 should be left pure ; the Ancients even discovered by such burning what 

 portion of gold was contained in silver, and in this way all the silver was 

 consumed, which was no small loss. However, the famous mathematician, 

 Archimedes*^, to gratify King Hiero, invented a method of testing the silver, 



"This old story runs that Hiero, King of Syracuse, asked Archimedes to tell him 

 whether a crown made for him was pure gold or whether it contained some proportion of 

 silver. 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 of 

 pure gold and pure silver, and thus determining the relative specific weights. The best 



