48 MM. Fremy and Feil on the Artificial Production of 



we have often acted on 20 or 30 kilograms of material, which 

 we kept heated uninterruptedly for twenty days. 



It was in the oven of Feil's works that we conducted the 

 experiments which required the highest temperature. When 

 our trials demanded prolonged calcination, we had recourse to 

 a glass-furnace which was generously placed at our disposal 

 by the Company of Saint-Gobain. In this case our essays were 

 directed by an eminent chemist, M. Henrivaux, whose intelli- 

 gent supervision secured their success, for which we here render 

 him all our thanks. 



The following is the method which permitted us to produce 

 the largest quantity of crystallized alumina : — 



We commence by forming a fusible aluminate, and then 

 heat it to bright redness with a siliceous substance. In this 

 case the alumina is slowly separated from its saline combination 

 in presence of a flux, and crystallizes. 



We attribute the crystallization of the alumina to various 

 causes : — either the volatilization of the base with which the 

 alumina is united ; or the reduction of this base by the gases 

 of the furnace ; or the formation of a fusible silicate which, by 

 the combination of its silica with the base, isolates the alumina ; 

 or, finally, a phenomenon of liquidation which produces a very 

 fusible silicate and some hardly fusible alumina. All these 

 cases presented themselves in our essays ; but the displacement 

 of alumina by silica appears to us the surest process for effect- 

 ing its crystallization. 



Several fusible aluminates lend themselves to these different 

 kinds of decomposition ; that which, up to the present, has 

 given us the neatest results is the aluminate of lead. When 

 a mixture of equal weights of alumina and minium is placed 

 in a crucible of fire-clay, and calcined at a bright-red heat for 

 a sufficient time, two different layers are found in the crucible 

 after cooling : the one is vitreous, and formed chiefly of silicate 

 of lead ; the other is crystalline, often presenting geodes filled 

 with beautiful crystals of alumina. In this operation the sides 

 of the crucible act by the silica which they contain. They 

 are always made thinner, and often perforated, by the action 

 of the lead-oxide ; therefore, to avoid loss of the product, we 

 usually conduct the operation in a double crucible. 



The experiment just described gives white crystals of co- 

 rundum ; when we would obtain crystals presenting the rose- 

 colour of the ruby, we add from 2 to 3 per cent, of bichromate 

 of potass to the mixture of alumina and minium. The blue 

 coloration of sapphire is produced by employing a small 

 quantity of oxide of cobalt mixed with a trace of bichromate 

 of potass. The ruby crystals thus obtained are ordinarily 



