ON THE ARTIFICIAL PRODUCTION OF MINERALS 
AND PRECIOUS STONES, 
BY 
MM. FEIL anp FREMY. 
[Read January 21st, 1878.] 
THE artificial production of minerals presents, in a scientific point 
of view, an interest which everybody understands. It has long 
afforded a wide field of research to many scientific men, among 
whom may be mentioned Ebelman, Senarmont, Deville, &c. 
We thought it might be interesting, even after the works of 
these eminent scientific men, to publish the result of our researches 
on the crystallization of alumina and of divers silicates. 
If we place in a furnace, heated to a high temperature, a mix- 
ture of alumina and oxide of lead, we obtain white crystals 
alumina, and, by adding a metallic oxide as colouring matter, 
—either chromium for obtaining a red colour, or cobalt for blue—— 
we can produce rubies in the first case, and sapphires in the 
second, It is necessary, however, in order to procure chemically 
pure crystals, from the mass obtained to separate the lead 
which may yet remain in combination with the vitrifiable earth 
proceeding from the crucible, and which may itself have been 
combined during the fusion. We may separate these bodies 
by different processes, either by the action of hydrofluoric acid 
or by potash in fusion, or by prolonged calcination in hydrogen, 
and subsequent treatment with alkalies and acids. 
The following are the properties of the rubies we obtained :— 
They scratch quartz and topaz. Their density is 4°0041. 
They lose, like natural rubies, their pink coloration when they 
are strongly heated, and regain colour on cooling. They are as 
hard as natural rubies. 
When submitted to optical examination—that is to say, to 
the microscope of polarization of Amici—our rubies, which have 
the form of hexagonal prisms, present the characteristic black 
cross and coloured rings. 
The crystals we obtained, and which we had cut by a lapidary, 
have not yet the requisite limpidity for commercial pur- 
poses neither do they present to the lapidary favourable facets 
