212 PROCEEDINGS OF THE AMERICAN ACADEMY 



prepared this oxide, as he supposed, by igniting the nitrate of chromic 

 oxide, observed the external properties of the substance, but did not 

 analyze it, and made use of it only as an aid in establishing the con- 

 tents of oxygen in chromic acid. In this essay he states the forrauljB 

 of the oxides of chromium as CrOs, Cr04, and CrOe, the last being the 

 acid. In a subsequent paper, * in speaking of the oxides of chromium, 

 he lays special stress upon the close relation between manganese and 

 chromium, and on the isomorphism of the sesquioxides of aluminum, 

 chromium, manganese, and iron. He now writes the formula of chromic 

 oxide as Cr^Oa, and in all probability the peroxide of manganese 

 (MnO^) was in his mind an argument for the oxide CrOa, though he 

 does not mention it in the paper referred to. Finally, in 1829, Berze- 

 liusf rejects the conclusions arrived at by Maus, and gives the follow- 

 ing reasons for his continued belief in the existence of the oxide CrOj. 

 The first reason urged is the analogy between the sulphur acids and 

 the oxides of chromium ; this comparison is based merely on the iso- 

 morphism of chromic and sulphuric acids. In the light of the better 

 knowledge both of the sulphur acids and of the oxides of chromium 

 which thirty years have given us, and with the cleai'er notions of chem- 

 ical classification which now prevail, we can find in the existence of 

 sulphurous acid no argument for the existence of an oxide of chromium 

 containing two atoms of oxygen. Secondly, Berzelius gives his own 

 idea of the reaction consequent upon mixing chromate of potash with 

 sesquichloride of chromium, which he thinks is not correctly described 

 by Maus ; according to Berzelius, the decomposition between these two 

 salts does not take place at once, but the mixed solution first becomes 

 dark yellow, soon changes to brown, a brown precipitate separates, and 

 the liquid remains brown ; hence he infers the formation of two com- 

 pounds of chromium and oxygen, one soluble and represented by the 

 formula CraOj, the other the insoluble CrOj. We have accurately 

 described in the first sentences of this paper the phenomena presented 

 on mixing a solution of sesquichloride of chromium with a solution of 

 chromate of potash, and have subsequently given the formula which 

 represents the reaction. There is no reason to suppose that any such 

 compound as CrjOj remains in solution ; when the brown precipitate 

 first formed has completely subsided, the color of the filtrate is that of 

 bichromate of potash. Lastly, Berzelius accounts for the fact that the 



* Pogg. Ann., VII. 415 (1826). t In his Jahresbericht, VIII. 123. 



