upon the great questions raised by Mendeléeff as regards the probable presence and prevalence of iron and carbon compounds in the interior of the globe, the formation of naphtha out of these compounds, and other extremely interesting geological questions.[1]
The artificial reproduction of the diamond must also be viewed as a further step in a long succession of researches which have been lately pursued for artificially reproducing all sorts of minerals, the formation of which had long remained a puzzle for mineralogists. The silicates which were formerly considered as impossible to reproduce in the laboratory have yielded within the last few years before the efforts of the chemists. Sarrasin, Hautefeuille, and especially Friedel, have reproduced different varieties of the chief constituent mineral of our crystalline rocks—feldspar—and the artificial crystals are absolutely identical with those found in Nature. Hornblende, which had long defied the efforts of the explorers, has been finally obtained in 1891 by K. Chrustchoff, after he had spent seven years in unsuccessful attempts;[2] but in order to reproduce it he had to heat its constituent elements for three months at a temperature of nearly 1,000°. The importance of a high temperature for further achievements was rendered still more evident in Frémy's successful reproduction of the ruby. The ruby is, of course, quite different from the diamond. Like the sapphire and the corundum, it is nothing but alumina—that is, a compound of two atoms of aluminium with three atoms of oxygen, colored by some impurities in red, in blue, or in brown. But for a long time alumina would not crystallize in our laboratories. Later on, Frémy obtained a very fine dust of rubies; but when he submitted the constituent parts of the ruby to a temperature of 2,700°, and maintained the same temperature for one hundred consecutive hours, he was rewarded by full-sized crystals of the precious stone, big enough and in sufficient numbers to have a collar made of them. And, finally, the investigation of Friedel, Le Chatelier, and especially F. Fouqué and Michel Levy, who reproduced a micaceous trachyte containing feldspar, spinel, and mica, demonstrated the necessity of resorting to a high pressure in addition to a high temperature.
To extend the range of high temperatures hitherto obtained, and to devise a means of measuring them, was thus the first condition for further progress in the reproduction of minerals and gems. But the measurement of high temperatures is a very difficult problem which has much occupied of late several prominent physicists and chemists. A thermo-electric thermometer, made of two very resistant metals (platinum and an alloy of platinum
