10 TRANSACTIONS OF THE [OCT. 4, 



tioned. They found that by adding a little fluoride of chrom- 

 ium to that of aluminum, and using a clay crucible with cupels 

 of platinum, they could produce rubies together with a little 

 sapphire. When they increased the quantity of fluoride of 

 chromium they obtained green crystals (Oriental emeralds). 



Debray (C. R., 1861, t. LIl., p. 9t<5.— L'Inst., 1861, p. 165.— 

 Ann. Chem. Pharm., t. CXX., p. 184.— Jahrb. f. Min., 1861, p. 

 702. — Bull. Soc. Chim., 1865) describes several methods of ob- 

 taining corundum. He passed a slow current of chlorohydric 

 acid over aluminate of soda at a red heat or over a mixture of 

 phosphate of alumina and lime. In the latter case calcic wag- 

 nerite was also produced. M. Debray has also produced crystals 

 of alumina by melting phosphate of alumina with three or four 

 times its weight of sulphate of potash or soda, and thus produc- 

 ing an alkaline phosphate. 



Quite recently H. Grandeau (C. R., 1882, t. XCV., p. 921) has 

 had occasion to apply the preceding method to various oxides, 

 and has found that particularly with alumina, after several 

 hours of heating, a crystallized double phosphate of alumina 

 and potash is obtained at the same time as the corundum. 



The mineral-producing qualities of fluohydric acid have been 

 well employed by M. Hautefeuille in reference to alumina. It 

 was only necessarv to make the vapor of this acid (Ann. Chim. 

 Phys.. 1865, t. IV., p. 153.— Jahresb., 1814, p. 206) pass slowly 

 over the amorphous alumina heated to a bright red heat in a 

 platinum tube, previously diluting it with nitrogen and steam. 

 On the hottest part of the tube foliated hexagonal plates of 

 corundum will form, resembling very much specular iron of vol- 

 canic origin. The more the operation is prolonged the more 

 beautiful these become, for the smaller crystals are destroyed to 

 make way for larger ones. 



M. Gaudin (C. R., 1869, t. LXIX., p. 1343), in 1869, gave a 

 second method of producing corundum by exposing amorphous 

 alumina to the flames of the oxyhydrogen blowpipe. This oxide 

 melts into a very clear, fluid glass, wliicli in cooling hardens 

 into a crystalline globule as hard as corundum. 



MM. Fremy and Feil (U. R., 1877, t. LXXXV., p. 1029) have 

 produced specimens of corundum remai'kable for the size of the 

 individual crystals and the weight of the crystalline masses, by 

 means of a double decomposition in a dry way. They melted 

 at a bright red heat in a large crucible of very siliceous material 

 equal weights of alumina and minium, producing thereby a 

 fusible aluminate of lead, which is soon destroyed by the silica 

 of the crucible, giving place to a still more fusible silicate 

 and liberating the alumina, which crystallizes in the body of the 

 liquid. Part of the lead is also volatilized or reduced by the gas 



