contracting combinations with them, and capable of being reduced to vapour at a still higher temperature.
Experiment taught him that boric acid possessed the requisite properties in a high degree.
Being
director of the manufactory of porcelain at Sèvres, he profited by the
high temperatures developed in the furnaces to make some very
interesting experiments, which were afterwards produced with still
greater success at the continuous fires of furnaces placed at M.
Ebelman's disposal by M. Bapterosses, fabricator of buttons of ceramic
paste.
Mixtures
in proportions corresponding to the composition of the stones to be
produced were placed in capsules of platina along with boric acid, and
the whole was submitted to a high temperature. The boric acid first
melted, and afterwards volatilized, and, as Ebelman had anticipated,
the substances that it held in solution crystallized.
In
this way he produced the spinel ruby so perfectly that it could not be
distinguished by Dufré-noy from the natural stone. This was effected by
subjecting a compound consisting of proper proportions of alumina,
magnesia, the green oxide of chromium and boric acid to a high
temperature in the muffle of a furnace for eight days. He obtained
crystals measuring 0.197 inch on a side.
