hillebkand.j DISTRIBUTION OF VANADIUM AND MOLYBDENUM. 55 
In case the volume of permanganate used is so small as to make 
doubtful the presence of vanadium, it is necessary to apply a qualitative 
test which is best made as follows : The solution is evaporated and heated 
to expel excess of sulphuric acid, the residue is taken up with 2 or 
3 cubic centimeters of water and a drop or two of dilute nitric acid, 
and a couple of drops of hydrogen peroxide are added. A characteristic 
brownish tint indicates vanadium. Unless the greater part of the free 
sulphuric acid has been removed the appearance of this color is some- 
times not immediate and pronounced, hence the above precaution. 
The above is a surer test to appl v than the following : Reduce the bulk 
to about 10 cubic centimeters, add ammonia in excess and introduce 
hydrogen sulphide to saturation. The beautiful cherry-red color of 
vanadium in ammonium sulphide solution is much more intense than 
that caused by hydrogen peroxide in acid solution, but the action of 
ammonia is to precipitate part or all of the vanadium with the chromium 
or aluminum that may be present or with the manganese used in titrat- 
ing, and ammonium sulphide is unable to extract the vanadium wholly 
from these combinations. Usually, however, the solution will show 
some coloration, and addition of an acid precipitates brown vanadium 
sulphide, which can be collected, ignited, and further tested if desired. 
Summary of Results. 
Vanadium occurs in quite appreciable amounts in the more basic 
igneous and metamorphic rocks, up to 0.08 per cent or more of V^O y , 
but seems to be absent or nearly so from the highly siliceous ones. 
The limited evidence thus far obtained points to the heavy ferric- 
aluminous silicates as its source — the biotites, pyroxenes, amphiboles. 
As opportunities offer further evidence will be accumulated and it is 
hoped that other chemists will lend their aid. 
Limestones and sandstones appear to contain very small amounts of 
vanadium, as shown by analyses of a composite sample of each, aggre- 
gating over 700 different occurrences. 
From the few tests of molybdenum it appears as if this element were 
confined to the more siliceous rocks. It is present in no observed case 
in amount sufficient for quantitative measurement when operating on 
5 grams of material. 
Note. — Since the above was written a few tests have been made on 
minerals of which powdered samples were at hand. A phlogopite from 
Burgess, Canada, gave 0.007 per cent V 2 3 . Mica from Laurel Hill, 
Georgia, gave 0.020 per cent V 2 3 . Protovermiculite from Magnet 
Cove, Arkansas, gave 0.04 per cent V 2 3 . Ilallite from Chester 
County, Pennsylvania, gave 0.01 per cent V 2 3 . Jeffersonite from 
Franklin Furnace, New Jersey, gave none, and a nonferruginous amphi 
bole from St. Lawrence County, New York, gave a faint trace. 
