59G ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



attempt has been made to use the toughened glass as a sub- 

 stitute for metal in making printer's type, though with what 

 success does not appear. 



ARTIFICIAL PRODUCTION OF CORUNDUM GEMS. 



Considerable interest was attracted during the past year 

 by the success of Messrs. Fremy and Feil (the first a chem- 

 ist of celebrity, and the last a leading glass- maker) in pro- 

 ducing, by artificial means, considerable masses of the precious 

 stones known as the ruby and sapphire, which rank next in 

 value to the diamond, in such quantity and quality that the 

 value of these hitherto costly products of nature threatens to 

 be seriously impaired, and sufficient to meet the future wants 

 of the jeweller and watchmaker. The experimenters above 

 named are not the first who have succeeded in producing 

 these colored varieties of corundum by artificial means, but 

 all previous efforts in this direction have been failures, 

 because of the microscopic minuteness of the crystals pro- 

 duced. 



In their experimental operations Messrs. Fremy and Feil op- 

 erated upon from fifty to seventy-five pounds of material, and 

 subjected it for a lengthened period (about three weeks) to the 

 highest temperature attainable in a glass-furnace. The re- 

 action they designed to accomplish was the decomposition 

 of an aluminous silicate (pure porcelain earth) by means of 

 a metallic oxide (oxide of lead). As carried out at the glass- 

 works of Mr. Feil, a mixture of equal parts of porcelain clay 

 and red-lead was subjected in a fire-clay crucible to the heat 

 of the glass-furnace for several weeks. To prevent the loss 

 of the charge, from the effect of the lead oxide on the silica 

 of the crucible, this was placed, for precaution, within anoth- 

 er. At the close of the operation, and on the cooling of the 

 charge, the contents of the crucible was found to consist of 

 two layers, the upper one vitreous, and consisting chiefly of 

 silicate of lead ; the lower one crystalline, and containing 

 clusters of geodes made up of beautiful crystals of alumina. 

 By the addition to the charge of bichromate of potassa, 

 these crystals were obtained of the rose or deep -red color 

 of the ruby, while the blue of the sapphire was perfectly 

 obtained by the addition of a slight percentage of cobalt 

 oxide. 



