88 SOME PRINCIPLES AND METHODS OF EOCK ANALYSIS, [bull. 176. 
clays, coals, iron ores, and those rocks in which vanadium has thus far 
been reported, for although it is usually certain of the most basic of 
the silicate rocks that are highest in chromium — as the peridotites — 
yet in these, so far as present experience teaches, vanadium is lacking, 
a fact doubtless Connected with the simultaneous absence from them 
of ferric-aluminous silicates. 
CONDITION OF VANADIUM IN ROCKS. 
The above and elsewhere mentioned connection of vanadium with 
the ferric-aluminous silicates of rocks, taken in connection with the 
existence of the mineral roscoelite, classed as a vanadium mica, indi- 
cates a condition of the vanadium corresponding to aluminum and 
ferric iron, and that it is to be regarded as replacing one or both of 
these elements. Hence it should be reported as V 2 3 and not as V 2 5 . 
What its condition may be in matter of secondary origin, like clays, 
limestones, sandstones, coals, and ores of iron, is yet open to discus- 
sion. It was the writer's opinion until recently, that it should then be 
regarded as in the pentavalent state (V 2 5 ), but his work upon certain 
remarkable vanadiferous sandstones 1 of western Colorado, in which it 
unquestionably occurs as trivalent vanadium (V 2 3 ), has led to a 
decided unsettling of this view. It is but proper to recall that 
Czudnowicz, 2 because of the extreme difficulty in completely extract- 
ing it from iron ores by an alkali-carbonate fusion and because of the 
easy reducibility of vanadic acid by ferrous salts, under the conditions 
in which brown iron ores are supposed to form, considered the 
vanadium in such ores to be in a lower condition of oxidation (V 2 3 ). 
Lindemann's 3 contrary conclusion with regard to certain iron ores, 
because the vanadium was extracted as V 2 5 by sodium-carbonate 
fusion without niter, is not valid, since this would probably be the 
case even if it existed in the ore as V 2 3 . 
XIX. FERROUS IRON. 
COMPARISON OF SEALED-TUBE AND HYDROFLUORIC- ACID METHODS — 
COMPARATIVE WORTHLESSNESS OF THE FORMER IN ROCK ANALYSIS. 
No point in rock analysis has been the cause of greater solicitude to 
the chemist, and especially to the mineralogist and petrographer, than 
the determination of iron in ferrous condition. The sealed-tube or 
Mitscherlich method with sulphuric acid, for a long time the only 
available one, is in theory perfect, since complete exclusion of oxygen 
is easily attainable. Its chief hitherto recognized defect lies in the 
inability to always secure complete decomposition of the iron -bearing 
minerals, and even to ascertain, oftentimes, whether or not the decom- 
1 Hillebrand and Ransome: Am. Jour. Sci., 4th series, Vol. X, p. 120, 1900. 
2 Pogg. Ann., Vol. CXX, p. 20, 18G3. 
3 Dissertation, Jena. 1878, through Zeitsch. fur anal. Chernie, Vol. XVIII, p. 99, 1879. 
