Assaying
the process of determining the quantity of metal, as gold, silver, copper, iron, or lead, present in a given quantity of ore or alloy. In mining countries assaying is a very important business. One contemplating buying a mine secures samples of ore from different places in the vein, and takes them to an assayer to find out how much gold or silver or copper, as the case may be, the ore will yield to the ton. Miners desiring to sell ores submit them to the company's assayer to determine their value per ton.
Three methods of assaying are in common use, the wet, the dry, and the streak method. In the wet method, the precious metal is separated by means of acids; in the dry method, grinding and heating are relied upon. In both of these methods, the weight of the button of precious metal finally obtained is compared with the amount of ore assayed. The streak method is employed in testing the fineness of silver plate or of other articles which would be damaged by detaching a piece of the metal. It consists in rubbing the article on a rough surface, especially that of the touchstone, and producing a streak, from the appearance of which experts are able to determine the fineness of the alloy. In Great Britain articles of gold or silver are tested in this way and stamped with an official hall-mark by the Goldsmiths' Company, denoting the place, date, and fineness of the manufacture. In this way the British public may know what it is buying. The term hall-mark comes from Goldsmiths' Hall, the traditional London office of the society.
Assay offices are maintained by the United States government in Boise, Idaho; Helena, Montana; Denver, Colorado; Charlotte, North Carolina; Seattle, Washington; San Francisco, California; St. Louis, Missouri; and in New York City. The New York office is situated in Wall Street on the site of the old Federal Hall, where Washington took the oath as the first president of the United States. These assay offices are public, and undertake to determine, for a nominal charge, the value of any bars, coins, jewelry, or tableware submitted. They are also purchasing offices for the United States government. Gold is accepted at any time at the fixed rate of $20.67 an ounce. Silver is purchased from time to time, under direction of Congress, at a price fluctuating with the market. During the year in which the last census was taken, over 60,000 tests were made in the various United States assay offices.
