VOLUMETRIC ESTIMATION OF VANADIUM IN PRESENCE OF SMALL AMOUNTS OF 
CHROMIUM, WITH SPECIAL REFERENCE TO THE ANALYSIS OF ROCKS AND ORES. 
By W. F. HlLLEBRAND. 
Outline and Limitations of^ the Method. 
When chromium and vanadium occur together and the former has 
been estimated colorimetrically as detailed in the preceding paper, the 
vauadium can in many instances be at once estimated without sepa- 
rating from the chromium by the well-known method of titration with 
potassium permanganate in sulphuric acid solution after reduction by 
sulphurous acid and expulsion of all excess of the latter. 
The application of the method is subject to one limitation — the chro- 
mium must not be present above a certain moderate amount. This 
limitation is due to the considerable amount of permanganate required 
to produce a clear transition tint when titrating in a hot solution, as is 
necessary with vanadium. In a cold solution of chromic sulphate 
much less permanganate is needed to produce the peculiar blackish 
tint without a shade of green, which affords a sure indication of 
excess of permanganate, but in a hot and especially a boiling solution 
the oxidation of the chromium ' itself takes place so rapidly that a 
very large excess of the reagent may be added before a pronounced 
end-reaction is obtained. Nevertheless, as will be shown, quite satis- 
factory determinations of as little as 1 or 2 milligrams of vanadium 
pentoxide can be made in presence of as much as 30 milligrams of 
chromic oxide. 
Inasmuch as chromium is almost never a prominent constituent of 
the clays, coals, iron ores, and rocks in which vanadium has been thus 
far reported, the method promises to be of great advantage in rock 
and ore analysis, where these elements probably frequently occur 
together, generally with phosphorus and sometimes arsenic. It is not 
directly applicable in presence of molybdenum, and arsenic must first 
be removed by hydrogen sulphide if present. 
'Storer, through Gmelin-Kraut, Vol. II, pt, 2, p. 290. 
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