Mint

Alloys Used in Coinage.

The earliest gold and silver coins made by the Greeks consisted of the pure metals (99o-997 fine, i.e., 99o-997 parts in i,000) or of electrum. After electrum had fallen into disuse, pure gold continued to be used, but under the Roman emperors copper was intentionally added and in the two centuries preceding the fall of Rome very base alloys of gold were coined, some containing only 2% of gold or even less. In the middle ages these base alloys were discarded and the "byzant" of Constantinople and the early coins of Western Europe were in tended to be absolutely fine. The gold standard of or 916.6 (22 carats fine) was adopted in England in 1526 and remains unchanged.

The silver standard of 925 (II oz. 2dwt. of silver and i8dwt. of alloy) was probably first introduced in England by the Saxons but has not been maintained continuously. Henry VIII. reduced it to 1 o oz. silver and 2 oz. alloy and afterwards to 4 oz. silver and 8 oz. alloy. Under Edward VI. the standard, at first debased further to 3 oz. silver and 9 oz. alloy, was afterwards raised again, and the standard of 925 was restored by Elizabeth. In 1920 it was reduced to Soo, but the name "standard silver" generally means silver 925 fine. The goo standard for both gold and silver coins was introduced in France soon after the Revolution and was later adopted in most other countries. The standard in India is 916.6 for both gold and silver.

Copper was originally added to gold in coins to reduce the cost of metal, but it has long been recognized that gold-copper and silver-copper last longer in circulation than pure metals owing to their greater hardness. Rate of wear, however, does not depend entirely on hardness, but also on the resistance of coins to cor rosion. Coins become greasy in circulation and the fatty acids corrode the copper, forming a friable crust on the surface which is easily rubbed off. Accordingly coins containing much copper are not so resistant to wear as those of higher standard and more often present a dirty appearance in circulation. The average life of silver coins of the 925 standard in circulation in Great Britain was about 4o years in the 19th century, the larger coins lasting longer and the smaller ones for a shorter time.

Subsidiary coins have in the past generally consisted of cop per, but in France soon after the Revolution of 1789 copper be came scarce and the church bells were melted down to eke out the supply. The bells consisted of an alloy of copper and tin with a little zinc and the coins containing some of it were found to have advantages over those of pure copper. A mixture of these metals

in the proportion of copper 95%, tin 4%, zinc 1% ("coinage bronze") was adopted in 1851 by France for subsidiary coins and afterwards by almost every country in the world.

The copper-nickel alloy or "nickel-bronze" (consisting of cop per 75%, nickel 25%) has been used since its introduction in Belgium in 1861. Aluminium-bronze (copper 91%, aluminium 9%) has been used instead of silver for francs and two-franc pieces in France since 1921 and has been adopted elsewhere.

Manufacture of Coins.

Until the middle ages coins were struck between engraved dies by hand hammers and hand minting persisted in the native States of India until the 19th century. The Romans cast their larger copper coins. Modern methods may be said to date from 1553 when rolls for reducing the thickness of cast bars, machines for punching-out round discs from sheets of metal, and screw presses for striking coins were introduced in Paris. In England the new machinery was tried in 1561 and finally adopted in 1662. (For a detailed account of the history of minting, see NUMISMATICS.) The operations employed in the manufacture of gold and silver coin are as follows :—( I) Refining the metal to make it fit for coinage. Gold is refined at only a few mints and very little silver is refined even by these. (For a description of the processes, see GOLD : Mining and Metallurgy and SILVER : Metallurgy, etc.) (2) Melting the metal and casting it into bars. (3) Rolling the bars into strips or "fillets." (4) Cutting out discs or blanks from the strips. (5) Adjusting the weight of the blanks. (This is omitted in some mints.) (6) "Marking" or edge-rolling the blanks to produce a raised rim or to impress a design on the edge. (7) Annealing the blanks and, in some mints, cleaning them in acid. (8) Striking the blanks between dies. (9) Weighing each coin.

Among the incidental operations are : (a) The valuation of the bullion, by weighing and assaying it. (b) "Rating" the bullion, or calculating the amount of copper to be added to make up the standard alloy. (c) Recovering the values from ground-up cruci bles, ashes and floor sweepings (the mint "sweep"). (d) Assay ing the melted bars. (e) "Pyxing" the finished coin, or selecting specimens to be weighed and assayed. (f) "Telling" or counting.