white. The color variations are obtained by changing the proportions of copper, nickel, zinc and silver in the alloy, without changing the proportion of pure gold.

Being a world-wide standard of value, gold is used principally for monetary purposes. The United States' gold coinage, containing 90% by weight of pure gold, was withdrawn from circulation shortly before suspension of the gold standard on April 19, 1933.

THE PLATINUM METALS

Platinum metals are recovered from the beds of certain rivers of Russia, Colombia and Alaska, and from ores mined in South Africa and Canada. Other countries produce small amounts. The most important source of platinum is the Canadian nickel industry which recovers platinum metals, gold and silver as by-products of the refining of nickel and copper.
In all these deposits, platinum occurs together with other platinum metals. It is seldom, if ever, true that one platinum metal is found alone without some of the other platinum metals.

The world produces more platinum than all of the other platinum metals combined, the proportions being roughly 60% platinum, 30% palladium, 4% rhodium, 3% ruthenium, 2% iridium, and 1 % osmium. The production of osmium, the rarest of these metals, amounts to only a few hundred pounds annually.

PLATINUM

Pure platinum is a white, ductile metal having a high melting point at 3224°F. It weighs 0.775 lb. or 226 dwt. per cu. in., being therefore a heavier element than gold.

For the production of jewelry, manufacturers usually employ an alloy of 90% platinum and 10% iridium, or alternately 95% platinum and 5% ruthenium. For some purposes they use a softer alloy of 95% platinum and 5% iridium. These unsurpassed, valuable alloys have excellent strength and fabricating properties. They generally are chosen for jewelry set with large diamonds, as metal cost is a minor item in such cases.

The quality of platinum and platinum alloys is maintained at a very high level. The materials supplied for jewelry in the U. S. seldom