The Wealth of Nations by Part 1 Chapter 11 Page 81

the king’s tax amounts only to a twentieth part of the standard metal.

It was once a fifth, and afterwards a tenth, as in silver; but it was found that the work could not bear even the lowest of these two taxes. If it is rare, however, say the same authors, Frezier and Ulloa, to find a person who has made his fortune by a silver, it is still much rarer to find one who has done so by a gold mine. This twentieth part seems to be the whole rent which is paid by the greater part of the gold mines in Chili and Peru. Gold, too, is much more liable to be smuggled than even silver; not only on account of the superior value of the metal in proportion to its bulk, but on account of the peculiar way in which nature produces it.

Silver is very seldom found virgin, but, like most other metals,