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Rh The most of these are as yet merely names to the general public, and some are certain to remain no more than chemical curiosities for years to come. There are good reasons to believe, moreover, that the list is still incomplete. But of the fifty-nine now known, eleven, aluminum, copper, gold, iron, lead, nickel, mercury, platinum, silver, tin and zinc, are, as metals, among the staple articles of commerce, which are being produced in large and ever increasing quantities, as the demand grows; while another list of six (manganese, tungsten, molybdenum, titanium, chromium and vanadium) are market staples in the form of alloys with iron, being largely used in the production of certain brands of steel. These are known in the trade as the ferro-metals. Again, there are six more (bismuth, arsenic, cobalt, uranium, thorium and cadmium) that are regularly produced, but not in the metallic state, for use mainly in the ceramic and electrical arts. Finally are iridium, osmium and palladium which find employment to a small but steadily increasing extent among makers of delicate instruments and tools of precision; tantalum, of which the electricians are now making incandescent light filaments, and magnesium, which for a number of years has been used by the photographers in the production of flash light. Thus nearly half of the total list may be said to be already among the indispensables of civilization, and already several of the remainder are under consideration by scientists, engineers and inventors—notably potassium, sodium and calcium—on account of the qualities they possess. Lithium, the featherweight of the metallic family, which will float in water, and has only one fifth the weight of aluminum, may before long be commandeered by the aeronauts, if a way can be found to protect it from the corroding action of air and water, while rubidium, that is as soft as fresh putty or wax at ordinary temperatures, zirconium, that possesses many of the qualities of thorium, and ruthenium, that is extremely infusible, are all certain to fill a want in the arts before long. In fact, each of the remaining known metals appears to possess some inherent and exclusive quality that will sooner or later be needed in our complex civilization. The most of those that are not yet exploited occur apparently in very small quantities in the crust of the earth, as, for instance, the last discovered, radium, which is so rare that but a few grains can be obtained from many tons of its ore. Yet it is one of the surprising facts of recent years that as soon as one of these rare metals is proved to be of real use to humanity, new sources of supply have quickly been found. We know little as yet as to the capacity of the wonderful storehouse we live upon. Nature seems to have provided a substance for every conceivable want of mankind, and beyond question, some of these substances that appear now to be useless are merely in reserve for wants not yet developed, while others that apparently are so scarce as to be