137 
trically disposed brown and yellow colours, is 
called toad’s eye wood-tin. 
In the next glass case begin the oxides of electro¬ 
negative bodies, and their various combinations. 
Case 18. Alumina and Aluminates. To the 
former belongs the corundum, comprehending the 
precious stones, commonly called oriental gems 
(the sapphire, ruby, oriental amethyst, oriental 
topaz, oriental emerald), of the crystallized forms 
of which the principal modifications are here de¬ 
posited ; and the common or imperfect corundum 
from Bengal, Mysore, China (Werner’s diamond 
spar), Lapland, Piedmont, &c. As appendix 
to these are added, the Jibrolite (bournonite of 
Lucas) one of the concomitant substances of 
the common corundum ; and the emery, which 
owes its hardness and consequent usefulness in 
polishing to an admixture of blue corundum.— 
The diaspore and the gibsite are hydrates of 
alumina.— Aluminates of magnesia —the spinel: 
© 
among its varieties is the blue spinel of Aker in 
Sudermannia. The ceylonite or pleonaste, and 
the automolite from Fahlun in Sweden and from 
Franklin in New Jersey, are, the former an 
aluminate of protoxide of iron and magnesia, 
the latter an aluminate of zinc.—The substance 
called plomb gomme , from Huelgoet in Britanny: 
a hydrous aluminate of lead. 
The five following glass cases contain silica or 
quartz, the numerous varieties of which, form- 
erly 
LONG 
GALLERY. 
