This metal is soluble in aqua regia; and being precipitated by a volatile alkali, makes a powder called aurum fulminans, which is one fourth heavier than the gold, and explodes with great violence in a heat something greater than that of boiling water.
Tin precipitates gold in the form of a purple powder, called the powder of Cassius, from the inventor of it, and is used in enamels, or the glassy coating which is given to metals by heat.
Gold unites with most of the metals, especially with mercury, and these mixtures are called amalgams. In gilding, the amalgam is applied to the surface of the metal to be gilded, and the mercury is driven off by heat, leaving the gold attached to the surface.
Gold mixed with iron, makes it harder, for the purpose of cutting instruments.
To separate gold from the imperfect metals, such as copper, &c. it is mixed with lead, and then exposed to a strong heat, which calcines the lead, and with it the imperfect metals, leaving the gold pure. This process is called cupellation, from being performed in a small crucible called a cupell. When the gold is mixed with silver, three parts more of silver are put to it, and then the silver is dissolved by nitrous acid, leaving the gold pure. This process is called quartation, from the gold being one fourth part of the mass.
The fineness of gold is generally estimated by dividing the gold into twenty-four parts, called carats. The phrase twenty-three carats fine means that the mass contains twenty-three parts out of twenty-four of pure gold, the remainder being alloy, of some baser metal. The fineness of gold may in some measure be discovered by the colour it leaves upon a touch-stone, or fine-grained basaltes.
Gold is generally found nearly pure, but mixed with earth, or diffused in fine grains through stones.