The Wealth of Nations by Part 1 Chapter 5 Page 33

considered as the metal which was peculiarly the standard or measure of value.

In reality, during the continuance of any one regulated proportion between the respective values of the different metals in coin, the value of the most precious metal regulates the value of the whole coin. Twelve copper pence contain half a pound, avoirdupois, of copper, of not the best quality, which, before it is coined, is seldom worth sevenpence in silver. But as by the regulation twelve such pence are ordered to exchange for a shilling, they are in the market considered as worth a shilling, and a shilling can at any time be had for them. Even before the late reformation of the gold coin of Great Britain, the gold, that part of it at least which circulated in London and its neighbourhood, was in general less degraded below its standard weight than the greater part of the silver.