MECHANICS AND USEFUL ARTS. 81 



RESEARCHES ON MATERIALS FIT FOR RESISTING VERY HIGH 



TEMPERATURES. 



M. Audaiiin. — (^Cosmos. } — While engaged with other studies 

 on geology in the southern parts of France, the author found that 

 between Tarascon and Antibes there exists a very valuable and 

 extensive bed of bauxite (hydrate of alumina) , wlltch is occasion- 

 ally applied for the manufacture of sulphate of alumina. This 

 material has been applied, at the suggestion of Audouin, for the 

 manufacture of crucibles and fire-bricks ; and on having been 

 tested in comparison with the best products of the kind from 

 France, England, and Germany, it was found that even best fire- 

 bricks might be melted in bauxite-made crucibles heated by min- 

 eral oils and a blast. 



SILVER EXTRACTION ELECTRO-CHEMICAL TREATMENT. 



To do away with the tedious and expensive process of amalga- 

 mation in the production of pure silver is a feat which Becquerel, 

 Sen., of the French Academy of Sciences, asserts he has recently 

 accomplished, after having experimented on this subject since the 

 year 1835. 



The experiment was tried successfully on 40,000 lbs. of silver 

 ores from Peru, Mexico, and Chili, etc, 



A powerful battery, with double liquid voltaic elements sepa- 

 rated by porous diaphragms, was made to act on the j)repared ore, 

 from which the pure silver was thus obtained at once in a finely 

 divided state and in a crystalline form. Messrs. Wolf and Pioche 

 are at present, it is said, preparing for a trial of this system in 

 California. — Scientific American. 



ON THE GLASS USED FOR LIGHT-HOUSES. 



The special composition of the crown-glass used for the light 

 apparatus for light-houses was, until quite recently, kept a secret 

 by the manufacturers of Saint Gobain, in France, and some firms 

 in Birmingham, which had the monopoly of this branch of 

 trade. 



From the researches of David M. Henderson, C.E., published 

 in"Dingler's Journal," we are able to furnish the recipes for 

 both of these. 



The French glass is composed of: — 



Silicic acid, 72.1 parts. 



Soda, 12.2 " 



Limo, 15.7 " 



Alumina and oxide of iron, traces. 



