ARTIFICIAL PRECIOUS STONES. 543 



tinued heat in porcelain furnaces. In fact, as soon as the larger por- 

 tion of the boric acid has evaporated, there are evolved from the fiery, 

 liquid mass small rubies, sapphires, or emeralds. This was discovered 

 some twenty years ago, but the crystals were too small to make the 

 process a remunerative one. 



Far more satisfactory were the results of Fr6my's recent experi- 

 ments. They are based upon a different principle, namely, that of 

 separating the argillaceous earth slowly from its usual combination 

 with silicic acid, as it is found in Nature everywhere, by bringing to 

 bear upon it a substance of stronger affinity for the acid. In conse- 

 quence, small crystals of argillaceous earth are formed in the fiery, 

 liquid " mother-liquor," which, in the course of further separation, grow 

 slowly. In the glass-factories of M. Feil, quantities of this " mother- 

 liquor" of precious stones, weighing from twenty-five to fifty pounds, 

 were Basil}' kept in a fieiy, liquid state for two and three weeks, and in 

 this way very favorable results were obtained. The most advantageous 

 process turned out to be the separation of the argillaceous earth from 

 the silicic acid by means of oxide of lead, for which purpose a mixture 

 of equal parts of pure porcelain-clay and red-lead was placed in a large 

 crucible of fire-proof clay and exposed for weeks to an intense red heat. 

 Usually, the lead also extracts the silicic acid which the walls of the 

 crucible contain, and eats holes through them. Hence, to avoid losses, 

 the precious-stone crucible should be placed in another. 



After several weeks of patient waiting, vividly recalling the expect- 

 ant watching of the old alchemists at their crucibles in which the phi- 

 losopher's stone was to be created, the crucible is taken out and cooled. 

 After destroying the crucible, the contents are found to consist of two 

 strata, above a glassy one, consisting principally of silicate of lead, and 

 below a crystalline one, containing the most beautiful crystals of argil- 

 laceous earth in round clusters. If nothing but argillaceous earth and 

 red-lead has been placed in the crucible, these crystals are as colorless 

 as glass. They will cut glass and rock-crystal, nay, even the very hard 

 topaz ; in short, they are precious corundums or diamond-spar, so called 

 because, next to the diamond and crystalline boron, it is the hardest of 

 all stones. 



Now rubies, sapphires, and Oriental emeralds, are nothing but colored 

 corundums, and the former two can be easily obtained by the addition 

 of the requisite quantities of the coloring metallic combinations. When 

 there was added to the mixture of argillaceous earth and red-lead two 

 or three per cent, of bichromate of potash, the c^stals showed the 

 beautiful rose-color of the ruby; when only a small quantity of that 

 salt was used, and simultaneously a still smaller quantity of oxide of 

 cobalt was added, sapphires were obtained. The precious stones thus 

 produced, as a rule, are covered with a firm crust of silicate of lead, which 

 is best removed chemically by melting it with oxide of lead or potash, 

 or by means of hydrate of fluor-spar. Among a number of pounds of 



