184 ]\fiscellaneous Intelligence. 



This process belongs to M. M. Dubois and Silveira. See 

 Annates de Chim. XIV. p. 110. 



14. Oji Artificial Gems — M. Douault-Wieland, in an experi- 

 mental memoir on the preparation of artificial coloured stones, 

 has given the following directions and proportions, as better 

 than those before known; 



The base of all artificial stones is the strass (paste), which he 

 cdMed fondant j when uniting it to metallic oxides to form the 

 imitations. When worked alone it imitates brilliant and 

 rose diamonds. 



The paste is composed of silex, potash, borax, oxide of lead, 

 and sometimes arsenic. The silex should be perfectly pure ; if 

 obtained from rock crystal that is the case ; if obtained from 

 sand, though of the whitest kind, it ought first to be washed 

 "with muriatic acid, and then with water. The crystal, sand, 

 or flint, should be heated red hot, quenched in water, dried, 

 powdered fine, and sifted. The potash should not be mixed 

 with other salt ; it ought to be the finest pearlash, or else pure 

 potash, by alcohol. The borax of the markets gives a brown 

 glass ; the crystallized boracic acid, from the borax of Tus- 

 cany, should be preferred. The oxide of lead should be per- 

 fectly pure ; if it contains an atom of tin, the glass will be 

 milky. Red lead is preferable to the best litharge, or even to 

 the ceruse of Clichy. It should be analyzed before being 

 used.^ The arsenic should also be pure. 

 Hessian crucibles are better than those of porcelain, for though 

 they sometimes colour the matter more, they do not break or 

 run so soon. Either a potter's or a porcelain furnace, may be 

 used, and the fusion should be continued 24 hours ; the more 

 tranquil and continued it is, the denser the paste, and the 

 greater its beauty. The four following receipts have given 

 good paste : 



No. I; 



Grains. Grains. 



Hock crystal .... 4056 Borax 276 



Minium 6300 *Arsenic. ..,,.. . 12 



Pure potash ,,,. 2154 



