When you see the marks on a watch-case or the inside of a gold ring they read 18 K or 14 K, or whatever number of carats the maker wishes to indicate. A piece of gold jewelry marked 18 K or 18 carats means that it is three-fourths pure gold. In arranging this basis of marking things made of gold, absolutely pure gold is called 24 carats. Then if two, six or ten twenty-fourths of alloy has been added, the amount of the alloy is deducted from twenty-four, and the result is either 22, 18 or 14 carats fine, and so on. On ordinary articles made by jewelers the amount of pure gold used is seldom over 18 carats, or three-fourths. Weddings rings (and these are considered solid gold) are generally made 22 carats fine, that is, there are only two twenty-fourth parts of alloy in them. Why Does Silver Tarnish? Silver is a remarkably white metal, which is associated with gold as one of the precious metals. It is harder than gold and will not rust, although it will tarnish, which gold will not, when exposed to certain kinds of air. The silver tarnishes when it is exposed to any kind of air that has sulphur mixed in it. It ranks below gold as a precious metal for use in making ornaments and is not so costly, because there is a great deal more of it to be found in the world. While silver is somewhat harder than gold, it is still not sufficiently hard to use pure for making coins, so, as in the case of the gold coins, it is mixed with something else--copper--to harden it. Otherwise our dimes and quarters would wear out too rapidly. Our silver coins are made of nine parts of silver to one of copper. The coins of France are in the same proportion, while the silver coins of England are made of 92¹⁄₂ parts of silver to 7¹⁄₂ parts of copper. German silver coins are made of three parts of silver and one of copper. Why Do We Use Copper Telegraph Wires?