hillebrand.] COLORIMETRIC ESTIMATION OF CHROMIUM. 43 
The outcome was somewhat of a surprise, for it was scarcely to be 
expected that the long and laborious gravimetric separations should 
have resulted so well as they are shown to have done. It should be 
mentioned that for the gravimetric tests but 1 or 2 grams at most 
were used, which accounts for the reported absence of chromium in two 
instances, this report being based on the lack of color in the aqueous 
extract of the alkaline fusion after removal of manganese. 
No experiments have been made with high percentages, but the 
tables give with certainty the degree of accuracy even then attainable. 
Whether the chromic oxide to be estimated is 0.1 per cent or 100 per 
cent, the percentage result is the same, provided the dilution is alike 
in each case. For instance, if 99.5 per cent is found in a total solution 
of 100 cubic centimeters containing 0.01 gram chromic oxide, the same 
percentage holds if the total volume were 10 liters holding 1 gram 
chromic oxide. 
It is probably inadvisable to increase the strength of the standard 
much above that of No. 5 above, containing 0.2 milligram chromic 
oxide in form of potassium chromate to the cubic centimeter. 
No tests have been made with other alkaline solutions than sodium 
carbonate, in order to ascertain if there is a difference in the color 
intensities for like dilution, nor is it probably important to do so. 
