OF ARTS AND SCIENCES. 345 



noi'mal cliromate of potash in 20,000 parts of water afforded a per- 

 fectly distinct blue ethereal solution of perchromic acid, when tested 

 with peroxide of hydrogen as above described. A solution of one 

 part chromate of potash in 30,000 parts of water also gave a distinct 

 reaction, though the blue color was less deep than in the preceding ex- 

 periment. With 40,000 parts of water the reaction was faint, though 

 still discernible ; as much so, perhaps, as the yellow of the aqueous so- 

 lution of the chromate. 



I have also detected, by means of this test, the presence of chromic 

 acid in the aqueous solution of a bead, of ordinary size, obtained by 

 fusing sesquioxide of chromium with borax in a loop of platinum wire 

 in the oxidizing flame of the blowpipe. Plattner * had already sup- 

 posed that the yellowish color, which compounds of chromium impart 

 to borax in the oxidizing flame, was due to formation of chromic acid. 

 It is doubtful, however, whether the fact has been previously experi- 

 mentally proved. 



Several experiments have also been made in order to ascertain 

 whether the presence of peroxide of iron would interfere with the 

 oxidation of the sesquioxide of chromium. "Weighed portions of pro- 

 tosulphate of iron were boiled with nitric acid in order to oxidize the 

 iron, and mixed with weighed portions of clirome alum ; the solutions 

 were then treated with a slight excess of caustic ammonia, and boiled. 

 After washing the precipitates formed, they were subjected to the 

 action of oxidizing agents. 



I have operated upon mixtures composed of: — 



No. 1. 



* ProBirkunst mit dem Loethrohre, von Plattner, (Leipzig, 1853,) S. 144. 

 VOL. IV. 44 



