Page:Popular Science Monthly Volume 34.djvu/529

Rh denote the intervention of this interior water. Thus, in this order of geological phenomena, when we might have believed that heat, accompanied by certain chemical actions, was the sole agent, subterranean water has also had its part to play.

This conclusion regarding the fundamental cause of metamorphism, although it had been justified by observation, still needed an experimental sanction. For that, the investigator should put himself in circumstances as nearly as possible like those in which Nature seems to have acted, and obtain the reproduction of characteristic minerals. I have tried to realize this. The principal difficulty in operating under the enormous pressure acquired by the vapor of water when the temperature approaches the point of dull redness is to find walls capable of resisting it. Water having been placed in a glass tube, which was then sealed by a lamp, this tube was introduced into a second tube of iron, with very thick walls, which was also closed, but not without difficulty, at the forge. In order to counterbalance the tension of the vapor in the interior of the glass tube, which might cause it to burst, care was taken to pour water outside of this tube, between its walls and those of the iron tube. The apparatus was set upon the dome of the furnace of a gas-factory in contact with masonry at a dull-red heat, in a thick bed of sand, where it remained for several weeks. Under these conditions, explosions of extreme violence took place. The most strongly resistant tubes were thrown into the air, bursting with a noise comparable to that of a cannon-shot. It was not possible to multiply the proofs to the extent that was desirable; but those that were made were sufficient to reveal facts quite different from those which we had deduced in laboratories under ordinary conditions.

The water acted very energetically upon the glass, which underwent a complete transformation, in composition and appearance. It was replaced by a white mass, quite opaque, resembling porcelain, with swellings and blisters, the results of softening. There had been developed, at the expense of a part of the substance, numbers of minute crystals, colorless and limpid like rock-crystal, with which they are identical, even to small details in the forms. These artificial crystals appeared, now isolated, now grouped into geodes which it was impossible to distinguish, except for the difference in dimensions, from those of nature. Another product of the same experiments deserves no less attention. It is pyroxene, which appears in little green, brilliant, and transparent crystals, exactly like those of the Alps. For the first time an anhydrous silicate had been seen to be produced by the action of water.