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POEEIGN COEEESPO]N'DEKCE. 



By De. T. L. Pnipsoiir, of Paeis. 



Neic method of obtaining Artificial Minerals and Precious Stones — White Cor- 

 undum — Ruhy — Sapphire — Green Corundum — Zircone — Cymophane 

 — Gahnite — Staurotide — Silicate of Zircone— Emerald — Curious De- 

 compositions—Action of Fluor — Compounds in the Natural Formation 

 of Minerals — Rutile — Mode of Working the Sut- Alpine Tunnel hetioeen 

 Modane and Bardoneche — Employment of Compressed Air as a Motive 

 Power for Boring and for Ventilation — Curious Phenomenon observed 

 during these Works — Rate 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. Claiee Detille akd H. Caeon have lately published 

 a remarkable memoir On a new Method of producing, in a Crystalline state, 

 a certain number of Chemical and Miner alogical 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. 



Ey 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, howeyer, another 



