_United States coinage._—A brief statement of the system of coinage now established in the United States may illustrate the definiteness of the standards of value. The United States mint at Philadelphia and its branches at New Orleans, Denver, San Francisco and Carson have the sole authority for making coins. Any effort at coinage by outside parties is criminal. The mint receives the gold and silver by weight and assay of purity, melts and refines and mixes with alloy, to bring the mass to required fineness, nine-tenths pure, and casts the metal into bars called bullion. These bars are then most carefully assayed, and, if found of exact standard purity, are rolled and drawn into plates the thickness of the coins desired. From these plates disks are punched by machinery, each disk being weighed, and if found too light thrown aside, if too heavy reduced by filing, until every disk represents exactly the required weight of the coin desired. The disks then pass through a milling machine which raises the edges, and when cleaned by dilute acid and carefully dried, are stamped by a steel die with some device covering both surfaces completely. This effectually gives the seal of the nation to the purity and weight of the coin, and, since it covers the whole surface, prevents the possibility of reducing that weight without marring the coin. _United States standards._—The system of coinage in the United States since 1873 embraces standard coins of gold, silver, nickel and copper, but gold alone actually furnishes the standards of value, all other coins being at present subsidiary. Gold is coined for individuals free; that is, a certain weight of metal presented at the mint is assayed, to determine the exact weight of pure gold, and an equal weight of pure gold is returned to the owner in coin. Sometimes a slight charge for the expense of coinage is made and called seigniorage. At present no such charge is made, for the reason that when a nation bears the cost of coinage, foreign coins are kept from circulation, and its own coins are current everywhere. The standard unit of value for the United States is 25.8 grains of gold nine-tenths fine, and this is called a dollar, although no coin of this weight is at present struck. In actual practice, the standard is shown in the ten-dollar piece, or eagle, weighing 258 grains. The half eagle (five dollars) and the quarter eagle (two dollars and fifty cents) indicate upon their face their relation to the principal coin. The double eagle, or twenty-dollar piece, is coined for greater convenience. These coins connect all the currency of the country directly with the market value of commodities in the world, through gaining their value directly from the market value of gold, where gold is bought and sold. Thus gold furnishes the standard of value with which all other values are compared.