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leather, which sags about one hand’s breadth ; next, the leather is foldedover and tied with a waxed string, and the dish catches the quicksilverwhich is squeezed through it. As for the gold which remains in the leather,it is placed in a scorifier and purified by being placed near glowing coals. Othersdo not wash away the dirt with warm water, but with strong lye and vinegar,for they pour these liquids into the pot, and also throw into it the quicksilvermixed with the concentrates made by washing. Then they set the pot in awarm place, and after twenty-four hours pour out the liquids with the dirt, andseparate the quicksilver from the gold in the manner which I have described.Then they pour urine into a jar set in the ground, and in the jar place apot with holes in the bottom, and in the pot they place the gold ; then thelid is put on and cemented, and it is joined with the jar; they afterward heatit till the pot glows red. After it has cooled, if there is copper in the goldthey melt it with lead in a cupel, that the copper may be separated from it ;but if there is silver in the gold they separate them by means of the aquawhich has the power of parting these two metals. There are some who,when they separate gold from quicksilver, do not pour the amalgam intoa leather, but put it into a gourd-shaped earthen vessel, which they placein the furnace and heat gradually over burning charcoal; next, with an ironplate, they cover the opening of the operculum, which exudes vapour, and assoon as it has ceased to exude, they smear it with lute and heat it for a shorttime ; then they remove the operculum from the pot, and wipe off thequicksilver which adheres to it with a hare’s foot, and preserve it for futureuse. By the latter method, a greater quantity of quicksilver is lost, and bythe former method, a smaller quantity.
If an ore is rich in silver, as is rudis silver 29 , frequently silver glance,or rarely ruby silver, gray silver, black silver, brown silver, or yellow silver,as soon as it is cleansed and heated, a centumfiondium (of the lesser weights) ofit is placed in an uncia of molten lead in a cupel, and is heated until the leadexhales. But if the ore is of poor or moderate quality, it must first be dried,then crushed, and then to a centumpondium (of the lesser weights) an unciaof lead is added, and it is heated in the scorifier until it melts. If it is notsoon melted by the fire, it should be sprinkled with a little powder of thefirst order of fluxes, and if then it does not melt, more is added little by littleuntil it melts and exudes its slag; that this result may be reached sooner,the powder which has been sprinkled over it should be stirred in with an ironrod. When the scorifier has been taken out of the assay furnace, the alloyshould be poured into a hole in a baked brick ; and when it has cooled and beencleansed of the slag, it should be placed in a cupel and heated until it exhalesall its lead; the weight of silver which remains in the cupel indicates whatproportion of silver is contained in the ore.
We assay copper ore without lead, for if it is melted with it, the copperusually exhales and is lost. Therefore, a certain weight of such an ore
a9 For discussion of the silver ores, see note 8, p. 108. Rudis silver was a fairlypure silver mineral, the various coloured silvers were partly horn-silver and partly alterationproducts.