The principal Mint (or coin manufactory) in the United States is in Philadelphia, Pa. Another large one is in San Francisco, Cal. Nearly all the work is done by machinery, and that of the most ingenious and delicate nature. In converting the metals, silver, copper, (or copper and nickel), into coin the process is almost precisely the same as that or minting gold; so we will confine ourselves to the latter metal. Standard gold in the United States is nine-tenths pure gold, one-tenth alloy. It goes through a course of treatment to anneal it, after which it is drawn to the required thickness of the coin. The "drawings" or ribbons are then cut by machinery into rude circles a little larger than the intended coin. The next thing is to raise the slight rim on the edge. This is done at the rate of 120 double eagles a minute. Again they are annealed and thoroughly cleaned. They are then ready to be struck, the dies being previously prepared. A diagram would be necessary to fully describe the wonderfully ingenious machinery by which coin is struck. It is nearly a perfect automaton, which, when the blanks are fed to it through a tube, takes each blank piece in succession with a "hand," and lays it upon the face of the lower die. Both faces of the coin and the fluted edges which are given to all coin (as a guard against filling) are struck at one blow. Then the automaton hand displaces the coin and puts another blank in its place. The pressure for a double eagle is equal to 75 tons. 20,000 pieces can be struck in an hour by the 20 presses at work in one room at the Philadelphia Mint, only one girl and one boy being necessary to each press. From the press-rooms the coins are transferred to the chief coiner's rooms, where they are weighed, examined, and, if found perfect, put into suitable packages for transmission to points of circulation. The double eagles ($20) weigh 516 grains, and lesser coins in proportion: they are eagles, ($10), $5, $3, $2.50, and $1.

A silver dollar weighs 384 grains. Halves, quarters, dimes, and half-dimes in proportion.

The nickel cent - 88 parts copper and 12 parts nickel - weighs 72 grains.

The United States Mint was established in 1793.