38 CONTRIBUTIONS TO CHEMISTRY AND MINERALOGY. [bull. 167. 
As with colorimetric methods in general this one gives better results 
with small than with large percentages of chromium, yet it can be 
applied in the latter cases with very fairly satisfactory results by 
making a larger number of consecutive comparisons with the same 
solution. 
Outline of Method. 
The chromium is brought into a measured volume of solution as 
monochromate rendered alkaline by sodium carbonate, and the whole 
or a portion of this solution is then compared with a definite amount of 
a somewhat stronger standard, likewise made alkaline with sodium 
carbonate. The latter is diluted with water till both seem to be exactly 
alike in color, when a simple calculation gives the amount of chromium 
sought. The actual comparison takes little time, and any number of 
repetitions can be made if desired in order to secure greater accuracy 
from the mean of a large number of observations. The preparation of 
the solution to be tested offers nothing novel, but certain precautions 
have to be observed therein as well as in the color comparisons which 
will be touched upon later. 
Testing of Method by Comparison of Standard Solutions. 
Two standard solutions were prepared by dissolving 0.25525 and 
0.5105 gram potassium chromate in 1 liter of water made alkaline by 
a little sodium carbonate, each cubic centimeter then corresponding 
respectively to 0.1 and 0.2 milligram chromic oxide, in which latter 
form chromium is usually reported in rocks and ores. Definite amounts 
of one of the standards were then diluted with varying amounts of 
water in a tall, square glass vessel with exactly parallel sides. Into an 
exact duplicate of this vessel 5 cubic centimeters or more of the 
standard were introduced from a burette and diluted with water from 
another burette till exact agreement seemed to be reached on looking 
through the glasses horizontally. 
In the following tables are recorded all observations without regard 
to the sequence in which they were made. No greater pains were 
taken to get exact agreement of color than are ordinarily observed in 
our routine titanium estimations, which are carried out in a precisely 
similar manner, so that the results may be taken to represent every- 
day work without extreme precautions. In only two cases can the 
observations be considered really bad, viz, the third comparison of No. 
6 and the first of No. 1G. 
