200 ANNUAL OF SCIENTIFIC DISCOVERY. 



ARTIFICIAL GEMS. 



M. Becquerel lias succeeded in producing opals and other crystal- 

 line minerals, in a short space of time, by strong currents of electri- 

 city. In order to succeed in these experiments, the solution must be 

 pure, and of a particular strength, while the intensity of the current 

 must be regulated by the nature of the materials. From a solution 

 of sulphate of alumina he obtained, in the course of a few hours, a 

 hydrate of alumina, like diopside, hard enough to scratch quartz. In 

 like manner he has hopes of ultimately producing topazes and sap- 

 phires. 



A recent English writer, J\Ir. Howgraye, thus reviews the various 

 attempts that have been made by chemists, from time to time, to pro- 

 duce, by artificial means, the diamond and other precious stones. As 

 regards the production of the diamond, but little progress has yet 

 been made, and chemists have been completely baffled in all their 

 efforts to find a substance capable of dissolving carbon, the chief 

 constituent of that crystal ; and, indeed, until Despretz succeeded, 

 by the agency of electricity, in actually producing minute diamonds, 

 the manufacture of this precious stone seemed as chimerical as that 

 of the philosopher's stone, so perseveringly sought after by the 

 ancient alchemists. Despretz found that by passing a powerful gal- 

 vanic current through a point of charcoal over which a platinum 

 wire was suspended, the charcoal was volatilized and deposited on the 

 wire in the form of minute crystals, which, on examination under the 

 microscope, proved to be true diamonds. Since the discovery, no 

 further advance has been made toward the solution of this interesting 

 problem. 



The search after the diamond having proved so unsatisfactory in 

 its results, attention was directed to a class of stones almost as simple 

 in their composition, going under the generic name of corundum. In 

 order to understand the experiments that were made, and the difficul- 

 ties attending them, it is necessary that a clear idea should be obtained 

 of the compositions and distinctive characteristics of the stones 

 belonging to this class. 



The ruby, sapphire, oriental topaz, and several other precious 

 stones, are all merely colored varieties of a mineral called corundum, 

 or white sapphire, the composition of which was stated by Chenevix 

 to be alumina, mixed with a small proportion of silica and oxide of 

 iron. Dr. Muir and others proved, however, that it was pure alumina, 

 the silica found by Chenevix being abraded from the substance 

 in which the stones were imbedded. All the varieties of corundum 

 crystallize in six-sided prisms, and have the curious property of 

 double refraction, that is, causing everything that is looked at 

 through them to appear double. Alumina, the oxide of the metal 

 aluminum, now coming into such frequent use in the manufacture of 

 articles of jewelry, etc., was, until the invention of the oxyhydrogen 

 blow-pipe, supposed to be, like carbon, infusible by any degree of 

 heat. In 1837, however, M. Gaudin, who had given much attention 

 to the effects produced by this then newly-invented means of gener- 

 ating heat on various metallic oxides formerly thought unsusceptible 

 of fusion, attempted with some success to convert, by its aid, the 



