Gold is separated from gravel (placer mines) by washing with water. The particles of metal, being heavy, sink and can be collected. Rock containing gold is crushed to fine powder and the gold combined with mercury (amalgamation). Low-grade ores are treated with a solution of cyanide of potassium which dissolves the gold and the metal is later separated.
_Chloride of gold_, used in photographic work, is its only important compound. Pure gold is called twenty-four carats fine. A smaller figure indicates that the metal is alloyed to harden it.
Gold is used for money, jewelry, gold leaf (gilding) and in dentistry. It is almost always alloyed with copper and silver. Gold is the world’s accepted standard of value. Shipments of gold go from one country to another chiefly to balance international business dealings. Government treasuries and bank vaults are the chief storehouses for gold, either as bullion or coin.
=Graphite= is almost pure carbon. It is produced in Bohemia, Ceylon, Italy, Germany, Mexico and the United States. The deposits in Ceylon are the largest in the world. Much of that mined in New York and Alabama is of very high grade.
_Plumbago_ or _black lead_ is used in making crucibles, lead pencils, lubricants for heavy machinery, stove polish, foundry facings, paint, etc.
_Artificial graphite_ is made from coal or coke by an electric process.
Powdered graphite is mixed with fine clay in greater or less proportion and then molded and baked to form such articles as crucibles and lead for pencils. Graphite is imported from Ceylon to the United States, and lead pencils from Europe.
=Iron= is the most useful of all metals. The United States, Germany, Great Britain, Spain and France are the greatest producers of iron. Its ores occur in almost all parts of the world. Hematite is mined in Minnesota, Michigan, Alabama and other parts of the United States and in Germany, England, France, Spain, Russia, etc. Limonite is also widely distributed. Pig iron is made by smelting iron ore in a blast furnace. The ore, mixed with limestone, is melted by burning coke, coal or charcoal.
_Pyrite_ (iron pyrites, or fool’s gold) is found in Spain and many other parts of the world and is valuable in the preparation of sulphuric acid (oil of vitriol), but useless as an iron ore.
