OF ARTS AND SCIENCES. 219 



resents would contain, and it is, moreover, questionable if the protoxide 

 of manganese could exist in contact with chromic acid. The subse- 

 quent observations of Fairrie* explain these difficulties. He mixed 

 the solutions of chloride of manganese and chromate of potash, and so 

 obtained a precipitate whose composition by analysis was 3 (MnaOs 

 CrOs) -\- CrgOs -f- 6 HO. Fairrie's criticism on the analyses of War- 

 ington and Bensch, that they overlooked the chromic oxide formed by 

 the reaction, is no doubt just. He also remarks, that the precipitate 

 appeared to be formed by the action of seven equivalents of chromate 

 of potash on six equivalents of chloride of manganese, but offers no 

 explanation of the reaction. The decomposition is explained by the 

 formula, 



7 (KO CrOs) + 6 (MnCl) = 3 MnoOs CrOs) + CrA + 6 (K CI) 

 + KO 2 C]03. 



Six equivalents of the protoxide of manganese are oxidized into three 

 equivalents of sesquioxide of manganese, at the expense of the three 

 atoms of oxygen which two equivalents of chromic acid give up in 

 changing into one equivalent of chromic oxide ; pi'obably the chromic 

 oxide so formed enters into combination with the chromate of manga- 

 nese, rendering it basic. Chloride of potassium and bichromate of pot- 

 ash remain in the filtrate.f 



* Jour. Chem. Soc, IV. 300 (1852). 



t We do not wish to leave the subject of the metallic chromates without noticing 

 the remarkable analyses published by Malaguti and Sarzeau (Ann. de Ch. et de 

 Phys., [3.] IX. 431, 1843) of the chromates of copper, zinc, cadmium, and nickel. 

 The figures of these analyses correspond exactly with the following singular for- 

 mulae : — 



(CuO)4 CrOs + 5 HO, (CdO) (Cr03)2 + 8 HO, 



(ZnO)4 CrOs + 5 HO, (NiO)4 CrOs + 6 HO. 



All these precipitates were washed with boiling water till no color came from 

 them, and it is clear that these chromates, like those which we have studied, may 

 be deprived of the greater part of their chromic acid, if not the whole, by prolonged 

 washing ; hence the basic character of the substances analyzed. The marvel is, that 

 the analyses corresponded so exactly with such peculiar formulae ; it is hardly con- 

 ceivable that the publication of many analyses of each of these substances should 

 not show the existence of a series of compounds, which conform to no definite for- 

 multe. 



