ARTIFICIAL. PRECIOUS STONES HEATON. 223 



Taking these two points in conjunction, and confining our atten- 

 tion for the moment to the transparent stones as summarized in 

 Table III, the diamond appears to offer the most promising field for 

 attack and corundum comes next, and we find that the main attempts 

 at artificial production center round these species. From the point 

 of view of composition alone, quartz is the most simple, but it is so 

 common in nature as to render its artificial production scarcely worth 

 while. The aluminate group offers some attraction, but the artificial 

 production of crystalline silicates on a large scale is a very difficult 

 problem, and, with the exception of the emerald, the stones com- 

 prised in this group are so freely distributed in nature as to render 

 their artificial production a matter of academic rather than industrial 

 interest. 



It is unnecessary to discuss at any length the artificial production 

 of the diamond 1 — the problem has been attacked by numerous 

 scientists, and was solved by Moissan some years ago. Some 15 

 years ago, on the occasion of a visit to Paris, I had the privilege of 

 witnessing the production of his diamonds, prepared, as all the 

 world knows, by saturating iron with carbon at the temperature 

 of the electric arc and plunging the molten mass into cold water. 

 The mass of iron is then dissolved in acid and the residue subjected 

 to a laborious process of extraction, the diamonds being picked out 

 by aid of the microscope. The largest diamond that has been pro- 

 duced in this way is barely visible to the naked eye, however, and 

 when I say that the problem of their production has been solved, 

 I mean from the scientific point of view. 



The artificial production of the diamond is, in fact, far more com- 

 plicated than it appears at first sight. If it were only a matter of 

 obtaining the necessary high temperature to fuse the carbon to obtain 

 it in the crystalline condition it would be simple — such high tempera- 

 tures are readily obtained nowadays by means of the electric furnace 

 and the oxy-acetylene flame — but carbon is one of those substances 

 which pass direct from the solid to the gaseous state under ordinary 

 atmospheric conditions, and only assumes the liquid condition 

 under enormous pressure. The combination of high temperature 

 and enormous pressure can be obtained momentarily by Moissan's 

 ingenious process, but to obtain crystals of any size it is necessary to 

 conduct the operation on a very large scale and to maintain the com- 

 bined temperature and pressure for a sufficient length of time to 

 allow the liquid carbon to separate out from its matrix; moreover, 

 the entire operation must be conducted out of contact with ah*, for 

 carbon rapidly combines with oxygen at high temperatures. 



i A complete account is given in "Diamonds," by Sir William Crookes (Harper's Library of Living 

 Thought). 



