hillebrand.] DISTRIBUTION OF VANADIUM AND MOLYBDENUM. 53 
It was not until the greater part of the above tests had been finished 
that any careful attempt was made to identify molybdenum as well as 
vanadium. From the evidence gathered during the latter part of the 
work it would seem that molybdenum, when it does occur, is a much 
less important constituent quantitatively than vanadium, and that 
unlike the latter it accompanies the more acid rocks. Molybdenite is 
a well-known accessory constituent of some granites, etc., but in the 
above instances its amount was extremely small and no hint was 
obtained as to its state of combination. 
Chemical Method Employed. 
In conclusion it is proper to outline the method by which the fore- 
going tests were carried out, and to indicate the precautions that must 
be observed in order to insure good results. 
Quite a number of workers have busied themselves with the problem 
of vanadium estimation in ores and rocks, particularly magnetites and 
other iron ores, and the methods used have been often diverse in parts 
if not altogether. There is nothing absolutely novel in the following 
except that chromium and vanadium when together need not be sepa- 
rated, but are determined, the former colorimetrically, the latter volu- 
metrically, in the same solution as detailed elsewhere (p. 44). 
Five grams of the rock are thoroughly fused over the blast with 
20 of sodium carbonate and 3 of sodium nitrate. After extracting 
with water and reducing manganese with alcohol it is probably quite 
unnecessary, if the fusion has been thorough, to remelt the residue as 
above, though for magnetites and other ores containing larger amounts 
of vanadium than any of these rocks, this may be necessary, as Edo 
Claassen has shown. 1 The aqueous extract is next nearly neutralized 
by nitric acid, the amount to be used having been conveniently ascer- 
tained by a blank test with exactly 20 grams of sodium carbonate, etc., 
and the solution is evaporated to approximate dryness. Care should 
be taken to avoid overrunning neutrality because of the reducing 
action of the nitrous acid set free from the nitrite, but when chromium 
is present it has been my experience that some of this will invariably 
be retained by the precipitated silica and alumina, though only in one 
case have I observed a retention of vanadium, it being theu large. The 
use of ammonium nitrate instead of nitric acid for converting the 
sodium carbonate into nitrate did not seem to lessen the amount of 
chromium retained by the silica and alumina. 
As a precautionary measure, therefore, and always when chromium 
was to be estimated also, the silica and alumina precipitate was evapo- 
rated with hydrotiuoric and sulphuric acids, the residue fused with a 
little sodium carbonate and the aqueous extract again nearly neutral- 
1 Am. Cheni. Jour., Vol. VIII, p. 437. 
