342 PROCEEDINGS OF THE AMERICAN ACADEMY 



In concentrated sulphuric acid sesquioxide of chromium is evidently 

 slowly converted into chromic acid by the action of peroxide of lead, 

 even in the cold, since the solution becomes yellow after standing 

 eighteen or twenty-four hours. This action is very rapid if the mix- 

 ture be heated, a fine yellow solution being obtained at once. I have, 

 nevertheless, found it somewhat difficult to prove the presence of 

 chromic acid in this solution, since it appears to be decomposed when 

 diluted with water. ' 



With peroxide of manganese, a yellowish solution is also readily 

 obtained by boiling. In the cold, no reaction could be perceived at 

 the end of five days. 



"When a solution of sesquioxide of chromium in concentrated sul- 

 phuric acid is boiled with a small quantity of chlorate of potash, chro- 

 mic acid is formed. With very dilute sulphuric acid, this does not at 

 once occur ; but after boiling for some time, the acid becomes more 

 concentrated, and a portion of the chromium is then oxidized. Nitrate 

 of potash produces no similar result when used instead of the chlorate 

 in this experiment. 



When dissolved in concentrated nitric acid, sesquioxide of chromium 

 is slowly oxidized by peroxide of lead in the cold, abundant indications 

 of it having been obtained at the end of eighteen hours. The reaction 

 occurs at once if the acid be boiled. Minium also, when boiled with 

 solution of sesquioxide of chromium in concentrated nitric acid, rap- 

 idly converts it into chromic acid. With peroxide of manganese, no 

 chromic acid was obtained, either by boiling or after standing in the 

 cold during a week. When a solution of sesquioxide of chromium in 

 concentrated nitric acid is boiled with a small quantity of chlorate of 

 potash, the chromium is rapidly and completely converted into chromic 

 acid. With very dilute nitric acid this does not occur. Nitrate of 

 potash having been substituted for the chlorate in this experiment, no 

 chromic acid was formed. 



With concentrated chlorhydric acid and the above-mentioned oxi- 

 dizing agents, only negative results were obtained. As a general rule, 

 it is not easy to oxidize sesquioxide of chromium in the presence of 

 free chlorhydric acid, — a fact which accords with the well-known re- 

 ducing action exerted by this acid upon solutions of chromic acid or of 

 its salts.* 



* Vid. Rose, Handbuch der analytischen Chemie, I. 355 (Braunschweig, 1851). 



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