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Page:Popular Science Monthly Volume 32.djvu/838

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THE POPULAR SCIENCE MONTHLY.

According to recent investigations, the almost boiling Steamboat Springs in the United States precipitate, besides sulphur, small quantities of gold, mercury, silver, lead, copper, and zinc, which, by the aid of certain salts and their high temperature, they hold in solution. These deposits appear to be the continuation of those which in the same region, as at Sulphur-bank, have formed beds which are mined for their mercury.

What we have been able to observe from the surface of the ground gives a very limited and imperfect idea of the actions which excavations made to secure some particular thermal waters have revealed to us. The bottom of the basin of the principal spring at Bourbonne-les-Bains, where the temperature reaches 68° C, has furnished some very remarkable facts relative to the formation of minerals. The place was a flourishing station in the Roman period. In draining an ancient well a blackish mud was reached which contained fragments of wood, acorns, thousands of filberts which had become black like lignite, and numerous medals. The washing of four cubic metres of the mud yielded more than five thousand pieces of money, mostly of bronze or tin, but some of silver and gold. The four coins of the last metal bore the images of Nero, Hadrian, Faustina the younger, and Honorius. Twenty of the silver pieces belonged to the Gallico-Roman period, while the other coins were consular or imperial pieces, mostly of the first centuries of the empire; but some were as recent as the Lower Empire. The bronze pieces of the medium and smaller sorts were likewise of different ages, but three types of Augustan coins predominated. Many of them had been cut in two, doubtless to prevent their being taken out and used again, they having been cast in as offerings to the health-giving fountains. Ex-voto offerings were also recovered, including a bronze statuette of a man whose leg had been hurt.

Some of the coins had been so corroded by the action of the hot water that the figure on them could not be discerned. Others had been further corroded into holes and notches. Many others had been wholly dissolved, but had engendered, at the expense of their bronze, new and solidly agglutinated combinations. The species thus originated were identical in their crystalline forms and general characters with similar natural minerals—sulphuret of copper, copper pyrites, and variegated copper-ore. The most numerous crystals are regular tetrahedrons, like those of the mineral called gray antimonial copper, of which they have also the composition, the luster, and other properties. In some of the coins the tin of the bronze has passed into the state of an oxide, and has formed a white superficial crust. A real separation has therefore been produced between the metals of the alloy by the different workings of their chemical affinities. It seems as if in all of these transformations Nature, claiming her rights upon what human industry had taken out of her domain, had been pleased, with the aid of the mineral water, to recover her property, and reconstitute exactly the