Scientific amusements . by washing. In Australiaand California nuggets are picked up of considerablesize. It is a rather soft metal, and, being likewise costly, isnever used in an absolutely pure state. Coins and jewel-lery are all alloyed with copper and silver to give themthe requisite hardness and durability. Gold is extremelyductile, and very malleable. One grain of gold may bedrawn into a wire five hundred feet in length; and the GOLD. I 5 5 metal may be beaten into almost transparent leaves ^o(/oooof an inch in thickness ! Aqua-regia, a mixture of hydro-chloric and nitricacids, is used t
Scientific amusements . by washing. In Australiaand California nuggets are picked up of considerablesize. It is a rather soft metal, and, being likewise costly, isnever used in an absolutely pure state. Coins and jewel-lery are all alloyed with copper and silver to give themthe requisite hardness and durability. Gold is extremelyductile, and very malleable. One grain of gold may bedrawn into a wire five hundred feet in length; and the GOLD. I 5 5 metal may be beaten into almost transparent leaves ^o(/oooof an inch in thickness ! Aqua-regia, a mixture of hydro-chloric and nitricacids, is used to dissolve gold, though free chlorine, orselenic acid individually, will dissolve it. Faraday mademany experiments as to the relation of gold to light.{See Phil. Trans., 1857, p. 145.) The various uses ofgold are so well known that we need not occupy time andspace in recording thenr. Gilding can be accomplishedby immersing the article in a hot solution of chloride ofgold and bicarbonate of potash mixed ; but the electro. Native gold. process is that now in use, by which the gold precipitateson the article to be plated. We have already described the process of electro-platingin the case of silvered articles, and we need only mentionthat electro-gilding is performed very much in the sameway. But gilding is also performed in other ways ; oneof which, the so-called water gilding, is managed as with the gold-leaf is merely a mechanical opera-tion, but water-gilding is effected by chemistry. Water-gilding is a process (in which, however, no wateris used) for covering the surface of metal with a thin 156 CHEMISTRY. coating of gold ; the best metal for water-gilding is eitherbrass, or a mixture of brass and copper. A mixture ofgold and mercury, in the proportion of one part of gold toeight of mercury, is made hot over a fire till they haveunited ; it is then put into a bag of chamois-leather, andthe superfluous mercury pressed out. What remains iscalled an amalgam ; it
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