ARTIFICIAL PRECIOUS STONES—-HEATON. 295 
case fusion was obtained by the aid of a substance melting 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 crystals were obtained 
by this ingenious process, they had the same form and were too thin 
for industrial employment.! 
Some time earlier than this, however, we hear of the oxy-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 chromate 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 Synthése du Rubis, by F. Fremy, 1891. 
38734°—sm 1911——15 
