OF ARTS AND SCIENCES. 341 



having stood in the cold during twenty-four hours ; at the end of this 

 time, bits of paper were introduced in order to destroy this color, after 

 effecting which, the solution was tested : it contained no inconsiderable 

 amount of chromic acid. 



The foregoing experiments were all repeated, with almost absolutely 

 identical results, with solutions prepared by dissolving chemically pure 

 hydrated sesquioxide of chromium in dilute sulphuric acid. The for- 

 mation of chromic acid in the cold may have been a little less rapid 

 in this case than in the experiments with chrome alum ; the mixture 

 containing peroxide of lead, however, afforded an abundance of it 

 when tested after having stood two hours, and still more at the end of 

 twenty-four hours. That containing peroxide of manganese also gave 

 a fine reaction of chromic acid after standing twenty-four hours. The 

 trial with acidulated permanganate of potash was not tested until the 

 purple color of the solution had disappeared ; this was found to have 

 occurred after the expiration of forty-eight hours ; the solution was 

 then yellow, and afforded the reaction of chromic acid. 



Sesquioxide of chromium, dissolved in dilute nitric acid, is also con- 

 verted into chromic acid when the solution is boiled with peroxide of lead, 

 with peroxide of manganese, or with a solution of permanganate of pot- 

 ash acidified with dilute nitric acid ; minium produced the same result, 

 though somewhat more slowly. This action is much less rapid in the 

 cold ; the sample tested with permanganate of potash contained chromic 

 acid after having stood during twenty-four hours ; the solution to which 

 peroxide of lead had been added assumed a decided yellow color, and 

 afforded the reaction of chromic acid after standing three or four days ; 

 but the portion which had been mixed with black oxide of manganese 

 gave rto^ indication of chromic acid when examined at the end of the 

 fifth day. 



When dilute chlorhydric acid is used, instead of the sulphuric or 

 nitric acids of the preceding experiments, similar results are obtained ; 

 at least with peroxide of manganese and with solution of chameleon 

 mineral, both in the cold and when heated. "With peroxide of lead, 

 however, the results are less satisfactory. I have not been able to 

 obtain any decisive indication of the formation of chromic acid in this 

 experiment, but at the same time am not sure that minute traces of 

 it may not have been present. The conversion of the peroxide into 

 chloride of lead apparently interferes with the production of chromic 

 acid. 



