with it other metals, and when it can be produced at a price not more than two or three times that of iron, it will certainly replace it very extensively. For it is far more ductile and malleable, it melts at half the temperature, and so may be cut or forged into bars, sheets and tubes at much less cost; it is practically unalterable in the air or water, while iron and steel disappear in rust in a very few years, unless very carefully protected by paint or grease or cement. As yet there is but one ore from which the metal can be produced with reasonable economy, the mineral known as bauxite, which has been found at only a few places, and in masses of comparatively small extent. The rate at which the demand for the metal is now growing will result in their exhaustion in a few years. The great metallurgical problem of the day, therefore, is to devise a means for the extraction of aluminum cheaply from its most abundant ore, ordinary clay. This problem is perhaps on the verge of solution. In another decade we are almost certain to see the metal a staple on the markets of the world at not to exceed five to ten cents per pound. When that day arrives a revolution will have occurred in the industries that it is difficult now to apprehend.
Copper
Accurate statistics of the world's output of copper do not go back much further than the year 1879, when the amount was 170,199 tons. But fairly close approximations have been made for many previous years, and from these it appears that in 1856 the production throughout the world was about 47,300 tons. In 1906 it amounted to 786,794tons. This is a marvelous increase in the case of a metal that is yet used as a coin by more than half the population of the globe. That the annual product now should be nearly seventeen times what it was about half a century ago, while at the same time the price should be less, explains why civilized nations have abandoned its use as a coin and for ornamentation, and indicates that modern man has acquired! much greater facility than his immediate ancestors in extracting it from its ores, which are by no means abundant, nor easy to work. Those of us who have reached middle age can easily remember when a copper kettle was almost a family heirloom, to be kept under lock and key when not in actual use, and whose burnished sides and interior were the pride of the housewife. Nor in those days did we refer disrespectfully to pennies and cents as "chicken feed."
Gold and Silver
The story of the two money metals is much the same as that of copper. A half century ago we used to talk of their production in terms of Troy ounces. During the eighties the kilogram (2.2 lbs.) began to be used as a more convenient unit, and now that has become
