28 • VITRIFICATI0N\ [ll. 



It should be mentioned that some chemists hold that the 

 red color is due to the precipitation of metallic gold. 



Hydrated Silicic Acid. — Ebelmen's neutral silicic ether (si- 

 licate of oxide of ethyl) is slowly decomposed by the moisture 

 of the air, yielding alcohol, and hydrated silicic acid (2Si03, 

 8H0), which resembles natural silica, scratches glass, and has 

 a spec. grav. of 1.77. By mixing colored tinctures with the 

 ether, the silica may be obtained of various colors. 



Artificial Brilliants. — Those from Austrich in Paris, analysed 

 by Kcittig (Journ. f. Pract. Chem. xxxiv. 458), consist of 

 38.8 silica, 53 oxide of lead, and 8.2 potassa and soda, with 

 traces of iron and alumina. They are therefore similar to 

 paste (or strass), and exhibit much brilliancy and refraction. 



Artificial Cfems. — To make gems, Ebelmen avails himself 

 of the two properties of boracic acid, of dissolving metallic 

 oxides by fusion, and volatilizing at a higher heat. His pro- 

 cess resembles the solution of substances in water and the 

 evaporation of that water to obtain crystals. Having made 

 a mixture of alumina and magnesia, in the same proportion as 

 they exist in spinel], and added J-1 per cent, bichromate of 

 potash, he added to 2 pts. of this mixture 1 pt. fused boracic 

 acid, and exposed it in platinum resting in porcelain to the 

 heat of the porcelain furnace of Sevres. The product con- 

 tained cavities lined with minute, rose-red, octahedral crystals, 

 harder than quartz and infusible before the blowpipe. They 

 had all the characters of ruby. The constituents of emerald, 

 treated in the same way, yielded small hexagonal crystals, 

 harder than quartz, and therefore agreeing with true emerald. 



Cfrinding and Gutting. — For a full account of the emery 

 localities of Asia Minor, see J. L. Smith, in Araer. Journ. 2d 

 ser. X. 354, &c., and in Lond. Journ. Oct. 1850. 



Diamond Carlon. — For an account of this curious sub- 

 stance, see Journ. Fr. Inst. (3) xvii. 47. 



Coke. — According to J. Nasmyth (Ch. Gaz. vi.), common 

 coke possesses the property of cutting glass in as clean and 

 perfect a manner as the diamond. 



Silvering. — Glass vessels may be beautifully ornamented by 



