hillebkand.] VOLUMETRIC ESTIMATION OF VANADIUM. 45 
TESTING THE METHOD. 
A solution of sodium vanadate was prepared by fusing 0.037 gram 
of pure vanadium peutoxide with sodium carbonate and diluting to 1 
liter. Each cubic centimeter contained 0.000937 gram vanadium pen- 
toxide. Of this, sufficient amounts were mixed with varying volumes 
of a standard solution of potassium chromate. After in some cases 
determining chromium colorimetrically, sulphuric acid was added, sul- 
phur dioxide gas [ introduced for a few moments, and the excess of the 
latter expelled by boiling in a rapid current of carbon dioxide, without 
which its complete expulsion is difficult. When cooled to from 70°-80° 
O. the titration was made with very dilute solution of permanganate 
corresponding to about 1 milligram vanadium peutoxide to the cubic 
centimeter as calculated from its equivalent in iron. By repeating the 
reduction and boiling, any number of check tests can be rapidly made 
in the same solution. The solutions ranged in bulk from 50 to 200 
cubic centimeters according to the amounts of chromium added. 
With the larger chromium contents the differences in the quantity of 
permanganate used, according as titration was effected at practically 
boiling temperature or a somewhat reduced one, were very apparent. 
In oue case, at nearly boiliug heat, 10 milligrams of chromic oxide 
were largely oxidized to chromium trioxide, as shown by the change of 
color from dark green to yellow. Even at 70°-80° with this amount of 
chromium the results for vanadium will be too high unless the precau- 
tion is taken to ascertain the needed correction by adding permanga- 
nate to an equal bulk of hot chromic sulphate solution containing 
approximately the same amount of chromium. When this is done, 
however, the results are satisfactory even when as much as 30 milli- 
grams of chromic oxide are present and only 1 or 2 milligrams of 
vanadium peutoxide. 
The following tables contain the results of a considerable number of 
tests, those in Table II being tabulated separately in order to show the 
degree of accuracy attainable with a large excess of chromium by 
applying the correction above mentioned and also the amount of this 
correction. 
'The direct use of a solution of sulphur dioxide or of an alkaline sulphite is inadmissible unless 
these have been freshly prepared, since after a lapse of time they contain other oxidizable bodies 
than sulphurous acid or a sulphite. The sulphur dioxide is best obtained as wanted by beating a 
flask containing a solution of sulphur dioxide, or of a sulphite to which sulphuric acid has been added 
