Page:Popular Science Monthly Volume 74.djvu/275

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OME one has characterized the present as the "age of metals." There are at least fifty-nine of these useful substances known to the chemist of to-day, yet if the average well-educated man was asked to name them, it is doubtful if he could enumerate more than a score. In that far distant period called by the archeologists the "dawn of history" (say 8,000 to 10,000 years ago), only four appear to have been recognized, viz., copper, tin, gold and silver. Sometime later, iron, lead and mercury were added to the list. These seven constituted the metallic stock in trade of the ancients, and of the moderns for the first thousand years of the Christian era. In the opinion of most historians, copper, as the metal that is found most abundantly in the native or pure state, was the first to attract the attention of primitive man, and it is likely that tin was recognized very soon thereafter, for the latter, though far from abundant, and never existing naturally in the metallic state, yet occurs under conditions where it would be easily noted by its weight as a substance very different from ordinary stone, and in a chemical combination from which it can be smelted by the simplest of fire processes. Moreover, the greatest tin-producing district in the world lies in a part of the globe that has been inhabited from most ancient times. Both copper and tin are alone too soft to be utilized as weapons or tools, and humanity at a very early period in the progress of civilization learned to produce, by combining the two, that most serviceable alloy we know as "bronze," which can be forged and tempered to a keen edge and point, and which is so resistant to the attacks of air and water that great numbers of the implements made by the ancient smiths are preserved in the museums of the present day. Gold and silver were doubtless recognized as separate entities at a very early date, and their rarity and beauty set them apart at once as suitable measures of the value of other things. It is thought that iron, though the most abundant of all the common metals, did not come into general use until 1500 or 1000 B.C. for a long time lead was regarded as another form of tin. It does not occur in a metallic condition in nature, only one of its ores (cerrusite) is easily smelted, and most of them are associated with ores of antimony, arsenic and zinc, from which it is separable only with considerable skill. Mercury, on the other hand, comes from its ore with much ease, but it was a puzzle