172 Prof. G. Wiedemann on the Magnetic 



If ferric hydrate be dissolved in a not too dilute solution of 

 ferric chloride (in which latter, according to the experiments 

 to be subsequently mentioned, the ferric chloride continues 

 without dissociation almost unaltered), the magnetism of the 

 solution is composed directly of that of the ferric chloride and 

 that of the colloid solution of ferric oxide, as well as that of 

 the water. 



Such a solution contained 0*177 gram of iron in the ferric 

 chloride, 0*020 gram of iron in the colloid solution of the 

 oxide. Its observed magnetism was equal to 30*07, while the 

 magnetism of an equal volume of a solution of ferric chloride, 

 which contained 0*394 gram of iron, was 68*31, and that of a 

 solution of colloid ferric oxide, which contained 0*204 gram 

 of iron, was 7*56. According to this the magnetism of the 

 ferric-chloride solution containing the oxide is calculated at 



^^x 7-56 4-^(^x68*3 = 0*74 + 30*68 = 31*42, which is 

 0*204 0*394 



not far from the value found. From the diminution of the 

 magnetism of a dissolved ferric salt, especially the salts of the 

 organic acids, it can in other cases be proved that a greater 

 or smaller portion of it is decomposed into colloid ferric oxide 

 and acid by dissolving (see further on). 



If to a solution of sal ammoniac in ammonia freshly precipi- 

 tated chromic hydrate be added, the latter dissolves, producing 

 a deep-cl ark-red solution. Its magnetism, obtained in the 

 round glass vessel, was as stated in the following Table, in 

 which Gr denotes the weight of chromium in 10 cubic centims. 

 of the solution, M the magnetism of the solution after de- 

 ducting those of the vessel and the water or of the sal-ammo- 

 niac solution, a the atomic magnetism : — 



Gr. M. ct. 



Chromic oxide in sal ammoniac 0*482 155 35*1 



Ferric nitrate 0*473 453 100 



The magnetism of the chromium in this solution is there- 

 fore but little inferior to (about 0*9 of) that of the chromium 

 in the chromic salts (4*9). 



When chromic oxide is dissolved in potash solution, it 

 retains exactly the same magnetism as in its combinations 

 with acids. Thus the magnetism of 20*42 grms. of a solution 

 of chromic nitrate in the round glass, after deducting the 

 magnetism of the glass, was equal to 44*3 ; that of 19*25 

 grms. of potash lye was, in like manner, equal to — 6*6 ; that 

 of the chromium in a mixture of 4*72 grms. of salt-solution 

 and 13*27 grms. of potash lye was equal to 11*1, while the 

 calculation of the magnetism of the chromium in the solution 

 as it corresponds to the magnetism of the salts gives the 



