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III. Gold with the Vitriolic acid.

The vitriolic acid, in whatever manner applied, hasnot been observed to have any action on gold, or to pro-mote the action of other acids. Hence, as oil of vitrioldissolves silver by a boiling heat, silver and gold may beparted from one another by this acid, as effectually, thoughnot so commodioufly, as by the nitrous. If the compoundbe reduced into grains or thin plates, and boiled in abouttwice its weight of oil of vitriol to dryness, the silver willbe so far corroded, as to be easily waffled off" by a littlemore of the acid ; or if the mass, after the corrosion, bemelted in a crucible, the gold will separate and subside,the silver forming a scoria above it. Gold may thus alsobe purified from several other metallic bodies : Mr.Scheffer fays, that this is the most direct way of sepa-rating tin from gold.

IV. Gold with compound menjlrua.

Gold is said to be dissolved by the marine acid mixedwith a small proportion of spirit of urine ; by a mixtureof the vitriolic acid with the fame urinous spirit; by amixture of the vitriolic acid with a little fixt alkaline salt jby the vapour, which arises during the effervescence ofthe vitriolic acid with fixt alkaline fait, collected by di-stillation ; in a spirit, prepared by saturating the vitriolicacid with volatile alkaline fait, exsiccating the mixture,dissolving it in twice or thrice its quantity of aqua fortis,and distilling the solution. In my experiments, not one ofthese liquors appeared to have any action on golfl.

The most effectual menstruum of gold is a mixture ofthe nitrous and marine acids, called aqua regia; which,in a moderate heat, readily and totally dissolves it into a

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