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VII. Chi the Artificial Production of Corundum, Muby, and 

 various Crystallized Silicates. By MM. E. Fremy and Feil*. 



SYNTHETIC mineralogy (that is to say, the artificial pro- 

 duction of minerals) presents, in a scientific point of view, 

 an interest which every one can understand ; for it throws the 

 greatest light upon the mode in which minerals are formed, 

 and permits us to solve certain questions, relative to their com- 

 position, which chemical analysis often leaves undecided. In 

 fact, a mineral which appears most pure contains almost always 

 foreign substances interposed which existed in the medium 

 that formed it ; analysis is then powerless to determine the 

 real composition of the mineral, while a synthetic reproduction 

 enables us to distinguish the constituent elements from those 

 which are merely accidental. 



A great number of minerals have been artificially produced 

 in the dry way, in the wet way, and by M. BecquerePs inge- 

 nious methods ; and synthetic reproduction is daily receiving- 

 some fresh extension, as is proved by the recent discoveries of 

 M. Hautefeuille. 



Corundum has, perhaps, more than any other mineral ex- 

 ercised the sagacity of chemists. The excellent investigations 

 on the different modes of crystallization of alumina which have 

 been published by Ebelmen, de Senarmont, and since by 

 MM. H. Sainte-Claire Deville and Caron, by M. Gaudin, and 

 by M. Debrayt, are known to every man of science. Even 

 after these remarkable researches, however, we have thought 

 we might still be permitted to interest the Academy by making 

 known the processes we employ for the production of differ- 

 ently coloured and' crystallized alumina (that is to say, ruby 

 and sapphire) in masses sufficiently large to be used in horo- 

 logy and to be cut by the lapidary. It will probably be pos- 

 sible to apply the methods we are about to describe to the 

 artificial production of other minerals ; in this respect they 

 seem to possess a true scientific interest. 



Wishing to approximate as nearly as possible to the natural 

 conditions which have probably determined the formation of 

 corundum, ruby, and sapphire, we have borrowed from industry 

 its most energetic heat-producing appliances, which permit an 

 elevated temperature to be produced, to be maintained for a 

 long time, and considerable masses to be operated on ; indeed 



* Translated from the Comptes Rendus de VAcademie des Sciences, Dec. 5, 

 1877, tonie lxxxv. pp. 1029-1035. 



t It is known that, by treating heated phosphate of alumina and lime 

 with chlorhydric acid, M. Debray has obtained at the same time apatite 

 and crystallized alumina. 



