346 PROCEEDINGS OF THE AMERICAN ACADEMY 



No. 4. 

 Grammes. 



10.00 FeOS03 + 7aq ^ 



0.25 KOSO3; Cr^Oa, 3 SO3+ 24aql 



No. 5. 

 20.00 FeOS03 + 7aq ] 



0.25 KOSO3; 0-2 03,3 SO3 + 24 aq! 



Portions of the precipitate produced by ammonia in each of these 

 solutions were dissolved in chlorhydric acid, and a part of this solution 

 was treated with an excess of cold potash lye of sp. gr. = 1.305 ; an 

 excess of caustic soda of sp. gr. = 1.07 being added to another por- 

 tion. After standing in the cold, out of contact with the air, during 

 eighteen hours, the alkaline mixtures were filtered, and the filtrates 

 thoroughly boiled. No precipitate of sesquioxide of chromium was 

 produced in any of them, nor did these filtrates afford any chromic 

 acid when boiled with peroxide of lead. 



Other portions of the moist original precipitates were dissolved in 

 chlorhydric acid, and these solutions treated with a slight excess of 

 dilute caustic soda. A small quantity of peroxide of lead was now 

 added to the mixture, and the whole thoroughly boiled during two or 

 thi*ee minutes. On filtering, yellow-colored solutions were obtained in 

 every instance, and on testing these with peroxide of hydrogen the 

 characteristic reaction of chromic acid was very distinct in each. 



The oxide of chromium in other portions of all of the original pre- 

 cipitates was also readily oxidized by boiling them with bromine in 

 presence of free alkali, as well as by dissolving them in concentrated 

 nitric acid, and boiling this solution with chlorate of potash. The 

 presence of chromium was, moreover, readily detected in Nos. 1 and 2 

 by boiling a mixture of precipitate and alkali with peroxide of man- 

 ganese, or with permanganate of potash ; but as these substances are 

 evidently less conveniently applied than the others which I have men- 

 tioned, no further experiments were made with them. 



It should perhaps be stated, that the experiments upon the precipi- 

 tate from mixture No. 5 were made upon portions of it weighing two 

 or three grammes, the entire weight of the moist precipitate being 

 something more than a hundred grammes. 



Among the various agents capable of oxidizing oxide of chromium 



