f 89 ]

be brought to by other means : by long continuance of amoderate fire, the calx acquires more or less of a purplehue, according to the quantity of the gold and the naturalcolour of the calx of the metal it is mixed with.

Tin, which when calcined by itself is neither vitresciblenor fusible in the fire, and which cannot be perfectly vi-trefied by the most active substances commonly made useof in this intention, is remarkably affected by the admix-ture of gold. Dr. Brandt relates, in the transactions ofthe Swedish academy for the year 1753, that two parts oftin, and three of gold, being melted together, reducedinto fine powder, and calcined only to an ash grey colour,the calx melted with ease into a yellow glass, at the bot-tom of which was found a metallic regulus. I shall exa-mine this curious experiment on another occasion.

Though gold, in the highly attenuated state intowhich it is thus reduced by calcination with base metals,is by some bodies otherwise acted upon than in its grosserform, as appears from its habitude to tin in the precedingparagraph, and to the marine acid in the following section,it is by no means divested of its metallic properties, orchanged into a calx. Mercury, which does not dissolvemetallic calces, any more than unmetallic earths andstones, on being triturated with the compound powder,imbibes the gold; and on this foundation, gold, blendedwith the base metals, may in some cases be advantageouslyextracted from them.

If mixtures of gold and lead be continued in a fire suffi-cient to keep them in perfect fusion, the lead, calciningand rising to the surface, changes into a fluid scoria, easilyseparable from the gold by means to be described here-after. Bismuth also scorifies and separates in the samemanner; and both these metals, promoting the scorifica-

N tion,