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"T HE dull red that dims the luster of polished iron or steel is, as you know, rust, or, in learned language, oxide of iron; that is, iron mixed with oxygen. As it comes from the mine, iron takes this form of rust mingled with stone. What an unprepossessing appearance it then wears, this most useful of all the metals! It is an earthy crust, a reddish lump, a shapeless mass, in which the presence of any kind of metal whatever can be divined only after painstaking research. And then it is by no means enough to determine that this rusty matter contains a metal; it is still necessary to find some means of decomposing the ore and extracting the iron in its true metallic state. What labor and experiment has it not required to attain this end, one of the most difficult imaginable! How many fruitless attempts, how many laborious trials!
"Other metals, the greater number of them, likewise rust, the color of the rust varying with the metal. Iron turns yellowish red; copper, green; lead and zinc, white. Take a knife and cut through a piece of lead. The cross-section shows a fine metallic luster, but before long it becomes tarnished and a sort of cloudy appearance is noticeable. This change begins as soon as there is contact with the air, and in course of time it extends, slowly indeed, but surely, until it penetrates to the very heart of the mass and ends by converting the lead into an earthy substance quite different in quality. And the greater number of metals undergo a similar deterioration under like conditions."
"Then that green stuff we see on old copper coins is rust?" asked Marie. "And the whitish coating on the water-pipe of the pump?"
"Yes, it is rust in each instance. But all metals are not equally subject to rust. Iron is one of those that rust most quickly; next come zinc and lead; in the third class are tin and copper; and in the fourth is silver, which remains free from rust with very little care; finally, gold is still more immune and never rusts.
"Gold coins and jewelry of the remotest antiquity come down to us as pure and brilliant as if made yesterday, despite a sojourn of long ages in a damp soil where other metals would have turned to shapeless rust. Since it has such a power of resistance to destructive agencies, gold ought to be found, and in fact is found, always retaining its metallic properties, especially its luster. In the bosom of the rocks where it is disseminated—in its ore, as we say—it forms scales, veins, and sometimes big nuggets, which shine like jewels just from the goldsmith's hands. Our ear-rings and finger-rings, carefully kept in their casket, are not more brilliant than the particles of this precious metal found in the heart of a rock. Just as it occurs in its natural state it can be put to immediate use; all that is needed is to hammer it and shape it. Hence it is the first of metals to be discovered and used by man; yet owing to its extreme rarity it has never, in our part of the world, been used for common tools, but has ever remained the preëminently precious metal, reserved for jewelry and coinage."