309 
SOME NOTES ON THE ESTIMATION OF CHROMIUM AS CHROMIC 
OXIDE. 
BY 
Wma. M. BLANCHARD AND PAULINE NORRIS. 
Schirm (Chem.-Ztg., 33, S77) states that chromium can be determined 
gravimetrically by precipitation from a chromic salt by ammonium nitrite 
solution and igniting the precipitate with the filter in a Rose crucible. 
Schoeller and Schrauth (Chem.-Ztg., 33, 1257) state that accurate grayvi- 
metric determinations of chromium may be made by precipitation from a 
boiling, dilute solution of the chromic salt by the addition of one ce. of 
aniline and boiling for five minutes. The precipitate is filtered, washed, and 
ignited. 
Hanus and Lukas (8th. Intern. Congr. Appl. Chem., I, 209-12) state that 
chromic hydroxide can be precipitated quantitatively from neutral or alka- 
line solutions containing chromates by hydrazine hydrate and some of its 
derivatives. 
Rothaug (Z. anorg. Chem., 84, 165-89) states that a long series of estima- 
tions made by precipitating chromium hydroxide by means of ammonium 
hydroxide, ammonium sulphide, the iodide-iodate method, and by hydroxyl- 
amine, gave results running high from 0.17% to 1.60%, the error being due 
to the formation of chromic chromate during the ignition. 
These statements are interesting compared with the assertions of Fres- 
enius (Quant. Chem. Analysis, 6th. Ger. Edition, Cohn’s Eng. Translation, 
page 281) that when chromium is precipitated in glass vessels, the results 
are high owing to contamination with silica; if the precipitation is carried 
out in porcelain vessels, the results are much more satisfactory, and if 
platinum vessels are used, the results are quite accurate. 
With a view to verifying the statements of Fresenius or those of Roth- 
aug, the following experiments were made: The purest obtainable potas- 
sium dichromate was carefully recrystallized and the chromium estimated 
by evaporating to dryness solutions to which were added ethyl alcohol and 
hydrochloric acid, redissolving, and precipitating the chromium from boiling 
dilute solutions with ammonium hydroxide. After washing, the precipitate 
was ignited with the filter, heated over a Meeker burner and afterwards 
with blast lamp, cooled and weighed, 0.1500 gram of the dichromate was 
taken each time; this quantity should give 0.0775 gram chromic oxide. 
Five determinations in beakers of the best American glass gave 
0.0791, 0.0797, 0.0791, 0.0794, 0.0795. 
Five determinations with precipitation in a large porcelain casserole gaye 
0.0794, 0.0790, 0.0796, 0.0798, 0.0794. 
Five determinations with precipitation in a large platinum dish gave 
0.0798, 0.0797, 0.0791, 0.0792. 0.0794. 
Three determinations with glass beakers, the precipitate being dissolved 
and reprecipitate, gave 0.0796, 0.0790, 0.0789. 
