The Romance of Modern Chemistry

METALS, COMMON AND UNCOMMON connecting the ends of the filament inside with the terminals outside. Thus it is that what may seem at first to be nothing more than a dry laboratory fact, without any practical bearing, may turn out to be of the greatest importance for the requirements of everyday life. Such a case of the discovery of a new use for a metal, and a consequent fresh demand for it, might be paralleled by what has happened recently in connection with tantalum. This is a rare metal, and up to within a year or two ago very little attention had been paid to it, as a glance at any chemical text-book will show. It has been discovered, however, that tantalum has certain properties of commercial value, and people are now on the look-out for fresh sources of this somewhat scarce material. The illuminating power of the electric glow lamp depends, as has been said already, on a carbon filament being raised to incandescence by an electric current. Now these carbon filaments are very fragile creations, and one might at first be inclined to wonder why fine metallic wires are not used instead; for it is well known that a metallic wire is similarly heated by the passage of a current. The explanation is simple; in order to get a respectable light from an incandescent metal wire, we should have to raise it to a temperature at which it would melt. This would happen even with platinum, for the temperature of the carbon filament in an electric glow lamp is several hundred degrees higher than the melting-point of that metal. It is just here that the valuable properties of tantalum come in. Briefly stated, they are these: tantalum can be drawn into very fine wire, about one-thousandth of 70