CHEMICAL SCIENCE. 291 



and is unalterable in presence of sulphuretted hydrogen. One part of alu- 

 minium and one part of silver give a material as hard as bronze. An alloy 

 of ninety-nine gold and one aluminium is very hard, but malleable ; its color 

 is that of green gold. The alloy of ten aluminium is colorless, crystalline, 

 and consequently brittle. 



AirriFICIAL WHITE SAPPHIRES. 



Some ten years ago, the late M. Ebclman, then director of the govern- 

 ment Porcelain Manufactory at Sevres, succeeded in crystallizing alumina 

 by slowly evaporating a solution of this substance in boracic acid, by the 

 heat of his furnaces. The crystals thus produced were microscopic but pos- 

 sessed all the properties of the snpphire, ruby, &c\, except the color. A few 

 years after, Mons de Senarmont obtained crystals of alumina and of silica, 

 by exposing closed glass tubes, containing water and hydrates of alumina 

 and silica, to a temperature of ISO (leg. centigrade. The heat drove off the 

 water from these earths, and converted them into insulated, anhydrous, and 

 microscopical crystals, of rare beauty, and quite perfect. 



M. Gaudin, in a communication made during the past year, to the French 

 Academy, states that during the last twenty years he has directed his atten- 

 tion to the production of precious stones, but more particularly to rubies, 

 and that he had succeeded in making rubies artificially by calcining ammo- 

 nia-alum with the addition of five-thousandths of chromate of potassa, by 

 the oxyhyclrogen blowpipe but that the large globules were deficient in 

 limpidity, owing to partial crystallization. 



Recent experiments have, however, proved more successful, and he has 

 been enabled to obtain in a quarter of an hour, with a common forge fire, 

 thousands of crystals, the size of which is proportionate to the volume and 

 duration of the fire. For this purpose he proposes the following process. 

 Into an ordinary crucible lined with lampblack, he introduces equal parts of 

 alum and sulphate of potassa, previously calcined and powdered ; the cru- 

 cible is then submitted to a violent forge heat for a quarter of an hour. If 

 the heat has been sufficient there will be found in breaking the crucible a 

 small black concretion sulphuret of potassium covered with brilliant 

 points crystals of alumina. If this mass be placed in a capsule filled 

 with acidulated water, and submitted to heat, the sulphuret will be dissolved 

 out with effervescence, leaving at the bottom white sapphires, that at first 

 sight appear like diamond powder. Under the microscope each grain ap- 

 peared to be a crystal of marvellous limpidity. 



Although coloring agents were introduced into the crucible, the sapphires 

 have generally remained colorless, (owing to the reducing action of the car- 

 bon, which transforms all the coloring oxides into metallic globules), but in 

 one experiment small colored crystals were deposited on the colorless crys- 

 tals, and on one of the facets of a sapphire were found three hundred small 

 rubies. 



The greater the mass operated on, the larger the crystals . Those ob- 

 tained by M. Gaudin were one mm. (^ in ) in length; and about one-third 



