340 PROCEEDINGS OF THE AMERICAN ACADEMY 



that oxide of chromium is immediately changed to chromic acid when 

 treated with a solution of hypochlorous acid ; and of Carney,* who 

 has found that chromic acid is produced when a galvanic current is 

 caused to flow through a dilute solution of caustic alkali in which ses- 

 quioxide of chi'omium, even that which has been ignited, is suspended. 



For my own part, I have observed that sesquioxide of chromium 

 may be converted into chromic acid in the wet way by the agency of 

 several substances besides those already mentioned, and that the pres- 

 ence of free alkali, so far from being necessary, as has been implied by 

 previous observers, with the exception perhaps of Frommherz, is not 

 by any means essential in most instances to the success of the opera- 

 tion, oxidation occurring very readily in several cases in strongly acid 

 solutions. 



A dilute solution of chrome alum — which by experiment was as- 

 certained to contain no chromic acid — was acidulated with sulphuric 

 acid, a little peroxide of lead was added, and the whole boiled ; on- 

 filtering, the solution was found to be of a yellow color, and readily 

 afforded the reaction of chromic acid when tested with dilute solution 

 of peroxide of hydrogen, viz. a magnificent blue coloration due to the 

 formation of perchromic acid. 



A solution of permanganate of potash, acidulated with dilute sul- 

 phuric acid, being substituted for the peroxide of lead in the preceding 

 experiment, produced a similar result. Peroxide of manganese also 

 replaces perfectly the peroxide of lead in this experiment. 



It is not even necessary that these mixtures should be heated. 

 Dilute solution of chrome alum, acidulated with sulphuric acid, and 

 mixed with a small portion of peroxide of lead, having been allowed 

 to stand in the cold, was found to contain traces of chromic acid at the 

 end of half an hour ; after standing eighteen hours, a considerable 

 quantity of chromic acid had formed. 



A similar solution, in which peroxide of manganese was used instead 

 of the peroxide of lead, gave a fine reaction of chromic acid at the end 

 of eighteen hours. 



A quantity of solution of permanganate of potash, acidulated with 

 dilute sulphuric acid, having been added to a dilute solution of chrome 

 alum, also acidulated with sulphuric acid, retained its purple color after 



* Proceedings of Boston Society of Natural History, VI. 409. 



