485 
FOUEIGN COEKE SPONDENCE. 
By De. T. L. PnirsoN, of Paeis. 
NeiD method of oMaining Artificial Minerals and Precious Stones— WJiife Cor- 
undum — Ruhij — Sapphire — Gr-een Corundum — Zircone — Cymophane 
—Oahnite — Staurotide — Silicate of Zircone— Emerald— Curious De- 
compositions-Action of Fluor— Compounds in the Natural Formation 
oj Minerals— Rutile— Mode of Workiiig the Sub-Alpine Tunnel between 
Modane and Bardoneche — Employment of Compressed Air as a Motive 
Power for Boring and for Ventilation— Curious Phenomenon observed 
during these Works — Hate at which the Alpine Tunnel is Progressing 
— Thickness of the Alps — Ascent of the Muladetta and the three kinds 
of Granite in the Pyrenees and the Haute-Garonne. 
Messes. H. Ste. Claire Deville and H. Caeon have lately published 
a remarkable memoir On a new 3Iethod of producing, in a Crystalline state, 
a certain number of Chemical and Mineralogical Species." It will be suffi- 
cient to state that sapphires, rubies, and other stones of the corundum 
kind, staurotide, cymophane, &c., have been obtained to make it imme- 
diately understood how great an interest is attached to these new inves- 
tigations. 
One of the most successful methods employed by those chemists, to 
obtain the artificial crystals in question, consists in the mutual action 
of certain volatile metallic fluorides on fixed or volatile oxygenized 
compounds. Now, as very few of the metallic fluorides are not able to 
be volatilized more or less completely, this method of experimentation is 
almost always applicable. We shall here enumerate successively the 
mineralogical species obtained by the authors, and the exact process 
they have employed to produce them : — 
1. White Corundum. This substance was produced in very fine 
crystals by the following means: — Into a charcoal crucible a certain 
quantity of fluoride of aluminium is placed, over which is fixed a little 
charcoal cupel, filled with boric acid. The crucible, covered by its lid, 
and carefully protected from the contact of the atmosphere, is then 
heated to a white heat for about one hour — not more. The vapours of 
fluoride of aluminium and boric acid come in contact and mix together 
in the empty part of the crucible, and are mutually decomposed, pro- 
ducing corundum and fluoride of boron. Corundum — which, as our 
readers are aware, is nothing more than a peculiar state of alumina — is 
found, after the operation, crystallized in rhombohedrons, with the 
faces of the hexagonal prism. They possess all the optical, crystallo- 
graphical, and chemical properties of the corundum found in nature, 
whose hardness they possess also. 
By the above method, crystals as much as one centimetre in length, 
and at the same time very broad, can be produced ; but they are gene- 
rally wanting in thickness. 
2. Ruby. — To obtain the ruby, or red corundum, the same process 
is resorted to, merely adding a small quantity of fluoride of chromium 
to the fluoride of aluminium employed. There is, however, another 
