344 PROCEEDINGS OF TUE AMERICAN ACADEMY 



oxide of hydrogen, perchromic acid is formed ; this imparts a beautiful, 

 though exceedingly evanescent, blue color to the solution. The per- 

 chromic acid is soluble in ether, which removes it from its solution in 

 water without injuring its color, which indeed disappears far less rap- 

 idly from the ethereal than from the aqueous solution. 



The details of the process to be followed in applying this test may 

 be found in Barreswil's Memoir upon Perchromic Acid.* 



I have obtained satisfactory results by operating as follows. A so- 

 lution of impure pei'oxide of hydrogen is prepared by triturating per- 

 oxide of barium with water in a porcelain mortar, and pouring the 

 thin paste obtained by small portions into a quantity of common chlor- 

 hydric acid, which has previously been diluted with four or five parts 

 of water, the latter being agitated meanwhile with a glass rod. The 

 solution thus obtained may be kept for a considerable time without 

 undergoing change. I have not, for that matter, noticed any decom- 

 position in those with which I have operated. 



A piece of peroxide of bai'ium as large as a pea is more than suffi- 

 cient to prepare 150 cubic centimetres of the solution. In testing, 

 some six or eight cubic centimetres of the solution of peroxide of hy- 

 drogen are to be placed in a narrow test-tube, and covered with a 

 layer of ether about half a centimetre in thickness. The solution sus- 

 pected to contain chromic acid is now to be poured little by little into 

 the solution of peroxide of hydrogen, the tube which contains the 

 latter being closed with the thumb, and gently inverted after each ad- 

 dition, so that the ether may dissolve the perchromic acid as fast as it 

 forms. All violent agitation of the mixture is to be avoided, since it 

 tends to hasten the destruction of the blue color. The result of the 

 test can hardly be deemed satisfactory, unless a blue ethereal solution 

 is obtained, for many of the salts of chromium impart a bluish-purple 

 color to their aqueous solutions. Since this color is persistent, how- 

 ever, it cannot be confounded in any case with the fugitive blue of 

 perchromic acid, although it might at times conceal the latter so long 

 as it remained dissolved in the water ; for the rest, it is absolutely in- 

 soluble in ether. 



One or two experiments regarding the delicacy of the reaction may 

 be mentioned in this connection. A solution containing one part of 



* Ann. Ch. et Phys. (3), XX. 364. 



