88 PROCEEDINGS OP THE AMERICAN ACADEMY 



VII. 



THE DETERMINATION OF CHROMIUM IN CHROME 



IRON ORE. 



By Leonard P. Kinnicutt and George W. Patterson. 



Presented January 9, 1889. 



The complete decomposition of chrome iron ore, and the determination 

 of the amount of chromium, is one of the difficult problems of quanti- 

 tative analysis. Of the very many methods that have from time to 

 time been published, one given last year by Donath,* using barium 

 dioxide as the oxidizing and fusing agent, seemed the most expeditious 

 and simple. 



The method as given by him was as follows. One part of the very 

 finely divided mineral was mixed with five times its weight of barium 

 dioxide, and heated for one half-hour in a porcelain crucible over one 

 Bunsen lamp. The semifused yellowish green mass thus obtained 

 was treated with dilute hydrochloric acid. After a few hours, all the 

 chromium was found in solution as the chromate of barium. The 

 barium was precipitated with sulphuric acid, and the filtrate from 

 the barium sulphate neutralized with sodium carbonate, and a few 

 drops of an alkaline solution of permanganate of potassium added to 

 oxidize any chromium that might have been reduced. The excess of 

 permanganate was then removed by the very careful addition of fer- 

 rous sulphate, and the amount of chromium determined volumetrically. 



Donath, however, did not publish any results to show the accuracy 

 of the method, and it was on this account that we were led to repeat 

 his work. 



A few experiments were sufficient to satisfy us that the perfect de- 

 composition of chrome iron ore from Pennsylvania could not be 

 accomplished in the manner described by Donath. A number of 

 fusions of the very finely powdered and sifted mineral with five or 

 even ten times its weight of barium dioxide were made, and in every 

 case the residue contained a greater or less amount of the black unde- 

 composed mineral. Also we were unable to obtain any porcelain cru- 

 cibles in which more than one fusion could be safely accomplished ; 

 while if the fusion was made in platinum crucibles, we obtained, as 



* Dingler's Polytechnisches Journal, vol. cclxiii. p. 245. 



