Hillebeand.] VANADIUM (cHROMIUM) AND MOLYBDENUM. 83 
as above, though for some magnetites and other ores containing Larger 
amounts of vanadium than the generality of rocks, this may be neces- 
sary, as Edo Claassen has shown. 1 The aqueous extract isnexl nearly 
neutralized by nitric acid, the amount to be used having been conven- 
iently ascertained 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 pro- 
duced during fusion, but when chromium is present it has been my 
experience that some of this Avill invariably be retained by the pre- 
cipitated silica and alumina, though only in one ease have I observed 
a retention of vanadium, it being then large. The use of ammonium 
nitrate instead of nitric acid for converting the sodium carbonate into 
nitrate does not seem to lessen the amount of chromium retained by 
the silica and alumina. 
As a precautionary measure, therefore, and always when chromium 
is to be estimated also, the silica and alumina precipitate should be 
evaporated with hydrofluoric and sulphuric acids, the residue fused 
with a little sodium carbonate and the aqueous extract again nearly 
neutralized with nitric acid and boiled for a few moments, the nitrate 
being added to the main one. 
Mercurous nitrate is now added to the cold alkaline solution in some 
quantity, so as to obtain a precipitate of considerable bulk, containing, 
besides mercurous carbonate, chromium, vanadium, molybdenum, tung- 
sten, phosphorus, and arsenic, should all happen to be in the rock. 
The mercurous carbonate serves to counteract any acidity resulting 
from the decomposition of the mercurous nitrate. Precipitating in a 
slightly alkaline instead of a neutral solution, renders the addition of 
precipitated mercuric oxide unnecessary for correcting this acidity. 
If the alkalinity, as shown by the formation of an unduly large pre- 
cipitate, should have been too great, it may be reduced by careful 
addition of nitric acid until an added drop of mercurous nitrate no 
longer produces a cloud. 
After heating and tiltering, the precipitate is ignited in a platinum 
crucible, after drying and removing from the paper to obviate any 
chance of loss of molybdenum and of injury to the crucible by reduc- 
tion of arsenic. The residue is fused with a very little sodium car- 
bonate, leached with water, and the solution, if colored yellow, filtered 
into a graduated flask of 25 or more cubic centimeters capacity. The 
chromium is then estimated accurately in a few minutes by comparing 
with a standard alkaline solution of potassium monochromate (p. *<>). 
Then, or earlier in absence of chromium, sulphuric acid is added in 
slight excess and molybdenum and arsenic, together with occasional 
traces of platinum, are precipitated by hydrogen sulphide, preferably 
Am. Chem. Jour., Vol. VIII, p. 437, 1880. 
