54 CONTRIBUTIONS TO CHEMISTRY AND MINERALOGY. [bull. 167. 
ized with nitric acid and boiled for a few moments, the filtrate being 
added to the main one. 
Mercurous nitrate was now added to the alkaline solution in some 
quantity so as to obtain a precipitate of considerable bulk containing 
chromium, vanadium, molybdenum, tungsten, phosphorus, and arsenic, 
should all happen to be in the rock, and also an excess of mercurous 
carbonate to take up 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 precipitate, 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 filtering, 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 phosphorus or arsenic. The residue is fused with a very little 
sodium carbonate, leached with water, and the solution, if colored 
yellow, filtered into a graduated flask of 25 cubic centimeters or more 
capacity. The chromium is then estimated accurately in a few minutes 
by comparing with a standard alkaline solution of potassium monochro- 
mate (p. 37). 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 in a small pressure bottle. 1 If the color of the precipitate 
indicates absence of arseuic, the filter with its contents is carefully 
ignited in porcelain and the delicate sulphuric acid test for molyb- 
denum is applied. 
The filtrate, in bulk from 25 to 100 cubic centimeters, is boiled in a 
current of carbon dioxide to expel hydrogen sulphide, and titrated at a 
temperature of 70-80° 0. with a very dilute solution of permanganate 
representing about one milligram of V 2 5 per cubic centimeter as cal- 
culated from the iron strength of the permanganate, one molecule of 
V 2 5 being indicated for each one of Fe 2 :s . One or two checks are 
always to be made by reducing again in a current of sulphur dioxide gas, 
boiling this out in a current of carbon dioxide again, aud repeating the 
titration. 
As shown in a previous paper (p. 45), the presence of even thirty times 
as much 0r 2 O 3 as V 2 5 does not prevent a satisfactory determination of 
the vanadium if the precautions therein given are observed, provided 
there is present not less than one half to 1 milligram of V 2 5 in absolute 
aiftmnt. In absence of chromium less than half a milligram can be read- 
ily estimated. The phosphoric acid almost invariably present does not 
affect the result. 
1 From a sulphuric solution the separation of molybdenum by hydrogen sulphide is much more 
rapid and satisfactory than from a hydrochloric solution. 
