278 Prof. G. Wiedemann on the Magnetic 



determined. Calculated for the atom of the chromium con- 

 tained in the chromic-sulphate solution^ it was found nearly 

 equal to the atomic magnetism of chromium in the ordinary 

 chromic salts. Thus the magnetism of the total chromium 



(1) in the solution of chromic sulphate 54*2 



(2) in the mixture 23*1 



The weights of chromic oxide in the two were as 23'62 : 11'30 

 ==1:0*47, the magnetisms as 1 : 0*43. Therefore the mag- 

 netism of the chromium oxide was not essentially changed 

 with the precipitation. Accordingly the so-called superoxide 

 of chromium is a saline combination of chromic acid with 

 chromic oxide, as, indeed, it is also well known that by 

 washing it with water it can be more and more decomposed 

 into those two constituents. 



13. Magnetism of the precipitated Metallic Sulphides. — 

 "While magnetic pyrites exhibits strong magnetism, in the 

 precipitated sulphides of the metals this is very little. For 

 the investigation the solutions of the salts of the magnetic 

 metals, in weighed quantities, in the glass vessel of the tor- 

 sion-apparatus, were precipitated by a solution of sulphide of 

 ammonium. It was then found that if, as above, yu-^ is the 

 molecular magnetism of the dissolved salt, that of 



Sulphide of manganese iJb^-=^0'21 fig 

 „ iron . . 0*05 



„ cobalt . . 0-04 



„ nickel . . 0-04 



These considerable differences cannot also be referred to an 

 alteration of density ; much rather may it be safely assumed 

 that the magnetic atom-group in the sulphides of the metals is 

 another than that in the oxygen and haloid salts and in the 

 hydrates. 



14. Ferric and Ferrous Oxalate of Potass. — By the deter- 

 mination of the molecular magnetism of these two salts, of 

 which the former (contrary to the rest of the ferric salts) is 

 green, while the latter is yellow, it can be forthwith demon- 

 strated that ferric oxalate of potassium possesses the molecular 

 magnetism of the peroxide salts, and the ferrous oxalate that 

 of the rest of the salts of the protoxides. Accordingly an 

 assumption of Haidinger's (Pogg. Ann. vol. xciv. p. 246, 

 1855), that the former salt, optically regarded, contained fer- 

 rous carbonate, cannot be maintained. 



15. Modifications of the Salts of Chromic Oxide. — When a 

 violet solution of chrome-alum is heated till it assumes a green 

 colour, after the cooling its magnetism remains the same as 



