Silver is widely diffused but is rarely found in the native state.
Silver is originally as widespread as gold, occurring in nearly all of the volcanic rocks. Whereas gold remains unaltered by the action of the elements and is often carried long distances from its original place of occurrence, silver on the contrary is only to be found in the rocks where it originally occurs. When these rocks are broken down or worn away, the silver is either driven into new mineral combinations, or more often dissipated and lost. Silver, therefore, is only to be obtained by subterranean mining. Shafts are driven and the ore brought to the surface, and by use of various processes the silver is extracted, refined and made ready for commercial purposes.
An old process and one still employed extensively throughout Mexico where a large quantity of silver is produced, is to take the ore after it has been crushed or reduced to a fine mud or puddle and spread it about two feet deep over the floor of a large courtyard. Powered sulfate of copper is spread over the mass and then horses or mules are driven around in circle to tread the sulfate in and mix it thoroughly with the ore. After about one day's treading a quantity of common salt is added and after two days more treading quicksilver is added. This mass is trodden over for a period of about fifteen days, and is then shoveled into a large tank through which a rapid stream of water is passed. This washes away all but the silver and quicksilver, which is then poured into cone-shaped canvas bags. Most of the quicksilver runs out leaving the silver, which is then retorted. The quicksilver is used over and over again to assist in recovering the silver.
Pure silver has a beautiful white color and luster; it is almost as plastic as pure gold and like it very soft. Silver does not tarnish in natural air, but when it comes in contact with sulfur compounds it readily forms black silver sulfide. The sulfur compounds which act on silver are found in small quantities in the air as a result of burning coal and illuminating gas, while larger amounts occur in vulcanized rubber, wool, and foods like eggs.
Pure silver is too soft to make durable objects that require lightness and stability of form. This defect is overcome by alloying it with a little copper.
An alloy of 925 parts fine silver and 75 parts copper is called 925-1000 fine or what is commonly known as sterling silver. This alloy is used almost universally for jewelry and the best silverware.
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