202 PROCEEDINGS OF THE AMERICAN ACADEMY 



of potash is a chromate of chromic oxide, having the formula CraOs 

 CrOs. Scliweitzer expressed his conception of the reaction by the 

 formula 



4 (KO 2 CrOa) + 2 NO^ = 2 (KO CrOg) + 2 (KO NO5) + 6 (CrO^) ; 

 we shall write it, in accordance with the results of our analyses, 

 2 (KO 2 CrOg) + NO2 = KO NO5 + KO CrO^ + CrA CrOg. 



3. The same partial reduction of the chromic acid in bichromate of 

 potash, which in the reaction just described is effected by nitric oxide, 

 may be accomplished by alcohol with the aid of light. The precipitate 

 so produced has been analyzed by Vogel,* who assigns to it the com- 

 position which would be expressed by the formula CraOa CrOa, though, 

 for reasons hereafter to be considered, he seems to prefer the formula 

 Cr02. The precipitate thus obtained by alcoholf is identical in color 

 and texture with that produced by nitric oxide, or by the double re- 

 action between a neutral salt of chromic oxide and monochromate of 

 potash. It is unnecessary in this connection to refer to the well-known 

 reduction of aqueous chromic acid by sulphurous acid, by certain or- 

 ganic acids, by alcohol, and by paper ; light and heat facilitate the re- 

 duction, and the brown chromate of chromic oxide is often produced 

 when the reduction is but partial. } 



4. Again, the chromate of chromic oxide may be obtained by the oxi- 

 dation of the hydrate of chromic oxide. When pure hydrated chromic 

 oxide is treated with chlorine water, the oxide is converted into the 

 brown chromate of chromic oxide, provided that the quantity of chlo- 

 rine water be not sufficient to effect the solution of the chromate of 

 chromic oxide formed in the chlorhydric acid which results from the 

 reaction. Of course, the chromate of chromic oxide cannot be pre- 



* Jour. pr. Ch., LXXVII. 482, (1859,) and Dingler's Polyt. J., CLIII. 391. 



t We desire to correct a serious misprint in Vogel's note, as given in the Journal 

 fiir praktische Chemie (LXXVII. 482), and thence transferred into Kopp & 

 Will's Jahrcsbericht fiir 1859, p. 171. In the second line of the Article, " Ammo- 

 niak " should be " Alkohol.'' We trust this correction may save others the trouble 

 we took before it occun-ed to us that the error was a typographical one, in endeav- 

 oring to verify or account for tlie marvellous statement that bichromate of potash 

 was reduced by ammonia. The word is correctly printed in the abridgment of the 

 same article given in Dingler's Journal, CLIII. 391 



t Gmeliu's Handbook (Cavendish Soc. Ed.), IV. 119. 



