224 PROCEEDINGS OF THE AMERICAN ACADEMY 



that the formula MnOj is no argument for the formula CrOa , in the face 

 of the demonstration of the true character of the chroraate of chromium 

 heretofore given. On the contrary, the fact that the supposed brown 

 oxide of chromium is in reality composed of chromic oxide and chromic 

 acid, gives additional weight to the experimental evidence already 

 accumulated, that the peroxide of manganese is a compound of manga- 

 nic oxide and manganic acid. There is a striking similarity between 

 the methods of preparing chromate of chromium and manganate of 

 manganese, the more noticeable in view of the very different stabilities 

 and solubilities of the oxides of these two metals. Thus the action of 

 chlorine on chromic oxide gives rise to the formation of chromate of 

 chromium, while its action on the carbonate of manganous oxide pro- 

 duces the manganate of manganese.* Again, the gentle ignition of the 

 nitrate of manganous oxide produces a mixture of manganous oxide 

 with the higher oxides of manganese ; this mixture contains so much 

 manganate of manganese that the process has been patented as a meth- 

 od of obtaining a manganese oxide adapted to the preparation of chlo- 

 rine.! This result corresponds precisely with the result of igniting the 

 nitrate of chromic oxide. Again, the absorption of oxygen by heated 

 chromic oxide exposed to the air, observed by Kriiger, finds its exact 

 parallel in the absorption of oxygen by manganous oxide under the 

 same circumstances. A mixture of the higher oxides of manganese is 

 so obtained, and this process of ignition has been long known in the 

 arts as a means of " revivifying " black oxide of manganese, rendering 

 it available for the preparation of cldorine a second time, or through 

 an indefinite series of alternate reductions and oxidations. J 



* Gmelin's Handbook of Chemistry, IV. 207, Cavendish Soc. Ed. 

 t Berthicr, Ann. dc Chim. et de Phys., [2 ] XX. 187. Gatty, Eng. Patent Spe- 

 cifications, 22 Aug. 1857, No. 2230, p. 3. 



} Pfaff. Schweigger's Jour, fiir Ch. u. Phys., LIII. 122, (1828). 



Binks, C. Eng. Patent Specifications, 8 Feb. 1839, No. 7963, pp. 4, 8, and 9. 



Ebelmen. Ann. des Mines, [3.] XVII. 517 (1840). 



"Walters, G. S. Eng. Patent Specifications, 24 Mar. 1843, No. 9676. 



Balmain, W. H. " " " 31 Mar. 1855, No. 723, p. 4. 



Dunlop. " " " 22 Nov. 1855, No. 2637, p. 3. 



Barrow. " " " 26 Feb. 1856, No. 485, pp. 4, 9. 



Elliot. " " " 13 Oct. 1856, No. 2392, p. 4. 



Pattinson. " " " 21 Oct. 1856, No. 2475. 



Gossage. " " " 8 Nov. 1856, No. 2630, p. 7. 



Eeissig. Ann. der Ch. u. Pharm., CIII. 27 (1857). 



In several of these specifications the removal of alumina and sesquioxide of iron 



