1803.) 
amethyf?. The blue are the moft rare of 
thofe belonging to this fubftance ; by the 
union of the blue with the yellow is form- 
ed the green, which produces the oriental 
emerald ;—when the yellow is predomi- 
nant, the ftone becomes the oriental chry- 
folite. 
Having fettled the colour pertaining to 
each fpecies, the count difcuffes their other 
properties, as the tranf{parency, hardnefs, 
phofphorefcence, and {pecific gravity, of 
each ; and ke infers (1) that the fpeci- 
fic gravity of the imperfect corundum is 
always lefs confiderable than that .of the 
perfe& kind: (2) that this gravity varies 
accoriing to the degree of perfection of 
the cryftallization: (3) in general the 
blue corundum is of a greater fpecific 
gravity than that of any other colour. 
The cryftalline forms come next under 
review, which are examined under eight 
IMPERFECT 
From the Carnatic 
Silica - - - 5.0 
Adjumina +. 7 gi 
Tron - - = = 1.5 
Lols - - - = Bidk 
100.0 
PERFECT CORUNDUM. 
Blue or Red or 
Sapphire Oriental Ruby 
Silica - 5-25 7.0 
Alumina 92.0 go 
Tron- - 1 i 
Lofs Bap 7 & 1.8 
_ 100.0 100.0 
Hence it fhould feem that the analogy 
exifting between ftones hitherto known by 
the names of corundum, fapphire, orien- 
tal ruby, hyacinth, &c. is fo ftrong and 
complete, as to make us certain that they 
ought all to be confidered as varieties of 
the fame fubftance to which is given the 
general name of corundum. 
The Count de Bournon then proceeds 
to deferibe the compa corundum, inwhich 
there do not appear the fmalleft traces of 
eryftallization ; —the matrix of imper- 
Se corundum trom the Carnatic; and of 
Jubfiances which accompany it 3 ‘ach as 
felfpar, Fibrolite, Thallite, Hornblende, 
Quartz, Mica and Tale: belides thefe 
there are fometimes to be met with pieces 
ofreal fieative garnets and zircon, The 
Proceedings of Learned Societics. 
151 
different modifications. The primitive 
form of corundum is a rhomboid flightly 
acute, the obtufe angles of the vlanes 
meafuring 94°, and the acute one 86° ; ar 
is formed by the union of two triedral 
pyramids, united at their bafcs; the folid 
angle of the fummit will then be formed 
by the meeting of three of the more acute 
angles ; and its meafure taken upon one 
of its edges, and in the middle of the op. 
pofite face, will be nearly 95°.30/. 
In examining the fracture and texture of 
thefe ftones, the Count acknowledges that 
he never perfectly fucceeded in breaking a 
fapphire according to the direction of its 
lamine, but what art will not perform is 
executed by mature. The next fubje& 
difcuffed relates to the phenomena with re. 
fpect to light ; then the charater afforded 
by analyfis, from which it appears that 
the conftituent parts areas follow ; 
CORUNDUM, 
Malabar} China Ava. 
vite) 5.2 5 6.5 
36.5 30.50 87.0 
4:0 6.50 4:5 
pe T1715 2.0 
100.0 100.0 200.0 
fame minute defcription is given of fimilar 
fubftances from China and Ceylon. The. 
author regrets at:the clofe of this paper, 
which may be confidered as a complete 
mineralogical hiftory of ‘this ftone, thelofs 
of a confiderable colledtion of minerals in- 
tended exprefsly for the purpofes of ftudy, 
which was completely formed, and mot 
of the fpecimens had been colleéted in their 
native places, by his own hends. 
In conneétion with this valuable paper, 
the reader will be glad to know that the next 
communication in the fame work, is Ai 
Analyfis of ‘Corundum, and of fome fub- 
ftances which accompany it, with obfer- 
vations on the affinities which thefe earths 
have been fuppofed to have for each other 
in tbehumid way. By Richard Chenevix, 
Efg. F.R.S. &e. ) 
In this paper the mode of operation ss 
very exactly explained, as well as the re- 
fults given; and MrChenevixlaysdown as 
a general rule, with -re!peét to delicate ex- 
periments, that in the treatment of metallic 
fubftances, metallic erucibles mutt not be 
ufed;'but in thetreatment of earthy ‘bodies, 
they affine areto be-depended on. Metals 
eafily oxidizable canno: be ewpl. yed, but 
2 lilver 
