ARTIFICIAL, PRECIOUS STONES HEATON. 225 



case fusion was obtained by the aid of a substance molting at a 

 lower temperature which acted as a solvent. Consequently the 

 alumina crystallized out in much the same manner as a salt crystallizes 

 from a saturated solution, and to obtain sufficiently large crystals 

 to be of practical use it would be necessary to conduct the experiment 

 on a very large scale, and subject the fused mass to very slow and 

 carefully regulated cooling. 



In 1877 Fremy and Feil attempted to get over this difficulty by 

 using lead oxide as the flux and employing a crucible composed of 

 highly acid clay. On heating up the mixture in such a crucible the 

 lead oxide melts and combines with the alumina to form lead alum- 

 inate, and on further heating this reacts with the silica of the fire 

 clay, forming lead silicate and setting free the alumina, which crys- 

 tallizes out. But although very much larger ciystals were obtained 

 by this ingenious process, they had the same form and were too thin 

 for industrial employment. 1 



Some time earlier than this, however, we hear of the oxj^-hydrogen 

 blowpipe again, for Gaudin had noticed (as Clarke did in 1819) that 

 by introducing alumina into the flame of an oxy-hydrogen blowpipe 

 he could obtain globules of fused alumina similar to the borax beads 

 one makes in the ordinary blowpipe. Gaudin appears to have taken 

 it for granted that these beads were amorphous — that is, an alumina 

 glass — and it was not realized until many years later that they were 

 really identical in all their properties with natural crystalline corun- 

 dum. When this was realized, the commercial production of corun- 

 dum became only a matter of detail. 



Having obtained this further point, the idea immediately suggests 

 itself of converting small and useless stones into valuable gems by 

 fusing them together into one, and, as a matter of fact, " reconstructed 

 rubies" — as stones produced by this method are now generally 

 called — made in this manner were the first artificial gems to be pre- 

 pared on a commercial scale. These were introduced some quarter 

 of a century ago under the name of "Geneva rubies," and were offered 

 as, and realized the price of, natural stones, until the method of their 

 production became apparent. 



It will, of course, be well understood that the experiments I have 

 briefly indicated toward the artificial production of corundum had 

 as their immediate objective the formation of ruby, that being by 

 far the most valuable variety. It had long been known that the color 

 of the ruby was due to a trace of chromium, and by adding a small 

 proportion of potassium or ammonium ehromate to their mixture 

 Fremy and Feil reproduced accurately the color of the ruby in their 

 crystalline flakes. 



1 For a full account of the history of these earlier attempts, see La Synthese du Rubis, by F. Fremy, 1891. 

 38734°— sm 1911 15 



