RECENT SCIENCE. 625 



upon the great questions raised by Mendele'eff as regards the prob- 

 able 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.* 



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 min- 

 erals, 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, Haute- 

 feuille, 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. Chrust- 

 choff, after he had spent seven years in unsuccessful attempts ; f 

 but in order to reproduce it he had to heat its constituent ele- 

 ments 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 Freiny'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, Fre'my 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 num- 

 bers to have a collar made of them. And, finally, the investiga- 

 tion of Friedel, Le Chatelier, and especially F. Fouque' 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 con- 

 dition for further progress in the reproduction of minerals and 

 gems. But the measurement of high temperatures is a very diffi- 

 cult 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 



* See, in Mendel6effs Principles of Chemistry, the footnotes to the chapters on carbon 

 and iron. f Comptes Rendus, 1891, tome cxii. 



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