CXV1 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 
atom of metal and 1 of oxygen, a class of minerals for the most part 
very hard, and some of which are gems. By mixing together 
Alemiia ? st os een Ha aes 6-00 
Ningmesia \.:2.)50% 2s ae cts oetaeeie 3°00 
Green oxide of chromium........ 0°10 to 0°15 
Fused boracic acid .......e.00. 6:00 
he obtained, after the mass had been fused, and the boracic acid had 
been volatilized, rose-coloured spinels in every respect identical with 
the natural ruby spinel in form, hardness and chemical composi- 
tion, analysis giving for the latter the formula Al? O? MgO. The blue 
spinel sapphire (octahedral) was obtained by mingling 
Albonmmag? piace Gustes 5:00 
Maenesia oce es is2 3.2 2°40 
Oxide of cobalt ...... 0°20 
Fused boracic acid.... 4°70 
The crystals arising from the treatment of his compound were suffi- 
ciently large to be seen by the naked eye, while those of the rose- 
coloured ruby spinel required a lens ; they were hard, readily seratch-_ 
ing quartz. Analysis gave the formula Al’ O* (MgO, CoO), that of 
the natural sapphire blue spinel. By employing the proper com- 
binations, M. Ebelmen obtained the black and colourless spinels. 
Referring to the analyses of M. Awdejew and M. Damour, as show- 
ing chrysobery! to be an aluminate of glucina, he mixed together 
gr. 
Alumina, slightly ferrugmous .. 6°00 
Giuetnae. 22". 4). 2) eet Oe ee 1°62 
Fused boracic acid............ 5°00 
The form of the crystals obtamed resembled some from the Brazils ; 
they scratched quartz and topaz, were infusible before the blowpipe, 
and their analysis gave the formula Al’ O%, GIO, that for chrysoberyl. 
To complete the investigation for this substance its optical properties 
were tried, and were found to accord with the natural mineral. 
Many other aluminates were obtained by the same method, such 
as the aluminate of manganese, the alumimate of iron, the aluminate 
of cobalt, the aluminate of lime, and the aluminate of baryta. 
Many combinations of the sesquioxide of chromium with bases may 
in this manner be formed, and among them M. Ebelmen obtained an 
artificial chromate of iron by mixing 
gr. 
Green oxide of chromium 7°50 
PaNITUCtHt cP Renee ee roma TaN 8 1:60 
Peroxide of iron ....... 3°00 
Moacnesia if tc eis Jeet 1-10 
Boracic acidyad oak. £3 2 8:00 
Partavie debe 22h. b4 Nes 1°50 
The tartaric acid was employed for the reduction of the peroxide 
