The export trade in copper is very important, amounting at the close of the past century to about one hundred and seventy thousand short tons. Of this amount, half goes to Germany (most of it through ports of the Netherlands), and one-fifth each to France and Great Britain. The market price to the consumer during the ten years closing the century averaged about sixteen cents per pound. Most of the product is exported from New York and Baltimore. The head-quarters of the great copper-mining companies of America are at Boston. The imports of raw ores and partly reduced ores called "regulus," come mainly from Mexico to New York and Baltimore, and from Mexico and Japan to Puget Sound ports. The most important American refineries are at New York and Baltimore. A part of the copper is mixed with zinc to form brass, an alloy much used in light machinery. A considerable quantity is rolled into sheets to sheath building fronts and the iron hulls of vessels. By far the greater part, however, is drawn into wire for carrying electricity, and for this purpose it is surpassed by silver alone. The decrease in the price of copper in the past few years is due, not to a falling off in the demand, but to methods of reducing the ores and transporting the product more economically. =Aluminium.=--Aluminium is the base of clay, this mineral being its oxide. It occurs in the various feldspars and feldspathic rocks, and in mica. The expense of extracting the metal from these minerals has been so great as to prohibit its commercial use. In 1870 there were probably less than twenty pounds of the metal in existence, and it was to be found only as a curiosity in the chemical laboratories. The discovery that the metal could be extracted cheaply from cryolite, a mineral with an aluminium base, obtained from Ivigtut, Greenland, led to a sparing use of the metal in the economic arts. The chief step in the production of the metal dates from the time that the mineral _bauxite_, a hydroxide of aluminium and iron, was decomposed in the electric furnace. The process has been repeatedly improved, and under the patents covered by the Hall process the crude metal is now produced at a market price of about eighteen cents per pound. The entire production of the United States is controlled by the Pittsburg Reduction Company, which also manufactures much of the commercial product of England. The competitor of the Pittsburg Reduction Company is an establishment in Germany, near Bremen. Aluminium does not corrode; it is easily rolled, drawn, or cast; and, bulk for bulk, it is less than one-third as heavy as copper. Because of these properties it has a great and constantly growing economic value. Because of its greater size, a pound of aluminium wire will carry a greater electric current than a pound of copper wire of the same length. It therefore has an increasing use as a conductor of electricity.