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278 of Australia and California, who were gathering their golden harvest with its aid, and in the two succeeding decades the silver miner also impressed it extensively into his service. But as the various great precious-metal mining districts of the world became connected with fuel and labor centers by rail, the smelting industry arose and gradually supplanted most of the amalgamation process in which quicksilver was the prime factor, and so the demand for it slowly declined. The largest recorded yield occurred in the year 1877, when the output amounted to 5,308 tons. In 1906 the world's production was only 3,964 tons. For many years now the silver miner has given up its use almost altogether, but the Alaskan placer miner must still have it, and there is yet a considerable consumption in those gold districts of Africa and Australia, where smelters do not exist, and even in our own west, at isolated or very low grade mines. At present the principal demand is for the manufacture of mirrors, and certain scientific instruments like thermometers and barometers. There is good reason to believe that there yet remains, undiscovered, in Asia, Africa and South America, one or more great gold placer regions. When these come to light the market for mercury will revive, and remain active until the new fields are exhausted. There is no lack of its ores in the crust of the earth. The metal has been produced in Spain for at least three millenniums; the California deposits are far from being exhausted, though they have been worked more energetically in the last fifty or sixty years than the Spanish deposits since their discovery, and the great mines of Huancavelica in Peru have hardly been touched. So when the demand again arises, mother earth is prepared to meet the drafts of her children, as usual.

Fifty years ago this metal was practically unknown, except to the scientist. Its successful production as an article of commerce began in the United States about 1863, when it was detected in some copper ore coming from the Lancaster Gap Mine in Pennsylvania. For the next ten years, practically the entire world's output came from this mine. At its best, however, the yield never exceeded 100 tons per year, the metal commanding a price of $2.50 to $3 per pound, which of course severely restricted its use. In 1867 one of its ores was found in comparative abundance in the island of New Caledonia, a French possession, lying to the northeast of Australia, and commercial production from there began about 1874. In 1880 the metal was discovered in copper ores coming from Sudbury district, Canada, on the north shore of Lake Huron, and by 1886, a production began which has since steadily increased until at the present time two thirds of the annual world's crop of the metal comes from the later locality.