1886.] NEW YORK ACADEMY OF SCIENCES. 9 



De Senarmont (C. R., 1851, t. XXXIL, p. 762.— L'Inst., 1851, 

 p. 165. — Ann. Chem. Pliarm., t. LXXX., p. 214. — Pharm. 

 ■Centr., 1851, p. 518) has applied the wet way to the crystalliza- 

 tion of alumina. He heated in a sealed tube, at 350° C, a solu- 

 tion of chloride of aluminum, or of nitrate of alumina, and 

 produced rhombohedrons with truncated edges. 



Almost at the same time Ebelmann obtained corundum (Ann. 

 de Phys. et de Chim., 1851, t. XXXIII. , p. 34) by a totally differ- 

 ent process. He heated in a porcelain kiln a platinum crucible 

 containing one part of amorphous alumina with three or four 

 parts of borax. After a few days of heating all the borax was 

 volatilized, and at the bottom of the crucible crystals of corun- 

 dum were found, and on the edges long bluish needles of borate 

 of alumina, which he separated by the action of chlorohydric 

 acid. The corundum thus obtained was in hexagonal plates like 

 specular iron of volcanic origin, and was quite similar to that 

 obtained by Gaudin. 



The base is striated by three systems of lines parallel to the 

 sides. Numbers of very irregular vitreous inclusions were 

 noticed in them, as well as microliths resembling sillimanite. 

 The density of the crystals was 3.98, and, like the natural stone, 

 they scratched topaz ; they have, as in natural specimens, 

 a ' p. = 122° 35'. 



Carbonate of baryta added to the mixture facilitates the 

 formation of the crystals and the development of rhombohedral 

 faces, which thus attain a length of several mm. Carbonate of 

 lime may be added or the borax wholly replaced by carbonate of 

 soda, but hexagonal or dodecahedral plates will still be obtained. 

 Ebelmann colored his product by small quantities of metallic 

 oxides. For example, violet was obtained by oxide of manganese 

 (Oriental amethysts). It was noted that boracic acid alone could 

 not replace the borax. Sainte-Claire Deville and Caron (C. E., 

 1858, t. XLVL, p. 764.— L'Inst., 1858, p. 133.— Ann. Chem. 

 Pharm., t. CVIIL, p. 55.— Dingl. pol. J., t. CXLVIIL, p. 372.— 

 J. pr. Chem., t. LXXI V., p. 157) obtained magnificent specimens 

 of corundum by a different method. They placed anhydrous 

 fluoride of aluminum (Al„ FJ at the bottom of a charcoal cruci- 

 ble, and suspended in the centre of this a cupel of the same 

 substance filled with boracic acid. The whole apparatus was 

 allowed to remain at white heat for an hour, and on opening the 

 crucible they found the interior lined with large thin hexagonal 

 plates of corundum, presenting the combination a' p e''. There 

 were no striae on the bases, but only hexagonal rosettes project- 

 ing, and brown arborescences. Vitreous inclusions of boracic 

 ^cid with bubbles of gas were observed, often arranged in 

 <3rowns, and fine microliths were also noticed, as already men- 



