THE COLORIMETRIC ESTIMATION OF SMALL AMOUNTS OF CHROMIUM, WITH SPECIAL 
REFERENCE TO THE ANALYSIS OF ROCKS AND ORES. 
By W. F. HlLLEBRAND. 
Introduction. 
In the analysis of a number of highly titaniferous magnetites con- 
taining chromium, phosphorus, and vanadium, the satisfactory separa- 
tion of all these bodies in a form lit for separate determinations became 
a serious problem. The method of T. Fischer ] — digestion of the precipi- 
tated lead salts with a strong solution of potassium carbonate — appears 
to offer the long-needed satisfactory quantitative separation of arsenic, 
phosphorus, chromium, tungsten, and molybdenum from vanadium, the 
normal lead meta-vanadate remaining quite unattacked, according to 
the author, while the other lead salts are wholly decomposed, but the 
applicability of this method to the separation of the minute amounts 
often found in rocks and ores has not been tested. The time required 
is considerable, hence it was desirable to devise a more rapid way for 
determining both chromium and vanadium without resorting to this 
separation. That this object has been measurably achieved, with cer- 
tain limitations as to vanadium, the work thus far done seems to indi- 
cate. The present paper will deal only with the rapid estimation of 
chromium either in absence or presence of any or all of the elements 
above mentioned. 
In view of the high coloring power of the chromates, it is surprising 
that so little use has been made of this property as the basis for a 
quantitative method for the estimation of chromium. A search through 
some of the more important text books has revealed no reference to 
such a method, although L. de Koningh 2 has successfully applied it in 
the analysis of articles of food. Yet the results attainable by colori- 
metric comparisons of dilute alkaline solutions of unknown strength 
with those of a known standard leave little to be desired in point of 
quantitative accuracy. 
'Inaugural Dissertation, Rostock, 1894. 
2 Nederl. Tydsch. voor Pharmacie, Cheinio, en Toxicologic, 1889, p. 257. 
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