BRITISH ORES. 
71 
employment as a decolouring agent in glass manufacture, and 
for the same reason it has been called " glass makers’ soap.” 
Manganite , or grey manganese ore, is a hydrous sesquioxide, of 
much rarer occurrence in this country than pyrolusite ; whilst 
the somewhat ill-defined species Psilomelane is an impure 
hydrous oxide, usually found in botryoidal or stalactitic forms, 
which from their smooth surface and black colour have given the 
name to this species. 
Uranium. 
Case 13 . — Of this rare metal several ores are here exhibited. 
The oxide called Pitchblende is interesting as being the mineral 
in which uranium was first detected ; whilst the species called 
Chalcolite and uranite are attractive by the brilliant colours of 
their crystals ; the former of these minerals contains phosphate 
of copper, and the latter phosphate of lime, associated in both 
cases with a phosphate of uranium. Uranium ores are at present 
worked near Grampound in Cornwall. 
Titanium. 
Case 13 . — In the state of oxide, titanium occurs in three 
totally distinct forms, of which specimens are here exhibited. 
The long prisms of Rutile running through the quartz of Perth- 
shire, the fine tabular crystals of Brookite, associated with 
albite- felspar, near Tremadoc, and the small pyramidal crystals 
of Anatase, are simply different forms of the same oxide of 
titanium ; the chemical composition being in all cases identical. 
Titanium has been employed for improving the quality of iron 
-and steel, and for the preparation of certain pigments. 
Vanadium. 
Case 13 . — The vanadate of lead called Vanadinite , found not 
unfrequently in the lead mines of Wanlock Head in Dumfries- 
shire, will be again noticed among the lead ores (p. 75). 
Vanadium has been found in the copper-bearing sandstone of 
Alderley Edge in Cheshire, and appears indeed to enjoy a much 
wider diffusion than was formerly supposed. 
Molybdenum. 
Case 13 . — The chief source of this rare metal is the mineral 
called Molybdenite, a sulphide of molybdenum, somewhat 
resembling plumbago in appearance. Specimens are exhibited 
from Perthshire, and from the granite rocks of Charnwood 
Forest in Leicestershire. 
Chromium. 
Case 13 . — This metal is tolerably abundant in the form of 
chromate of iron, constituting the mineral called Chromite or 
