Behaviour of Chemical Compounds. 277 



If the molecular magnetism of the salts is equal to yu-g, the 

 magnetism ijUq of the oxides is : — 



Manganous oxide fjLo = 0-?>\[i.s 



Nickclous oxide ,, 0'47 



Didymic oxide ,, 0*52 



Cupric oxide ,, 0"21 



Ferric oxide ,, 0"13 



Ferric oxide with alumina * „ 0*55 



Chromic oxide „ 0*35 



The same after strong incandescence „ 0*39 



The same with alumina * „ 0*56 



Therefore the molecular magnetism of the burnt oxides is 

 much less than that of the corresponding salts and hydrates ; 

 it varies also according to the manner of exhibition and treat- 

 ment of the oxides. From the behaviour of the mixtures of 

 ferric and chromic oxides Avith alumina it follows that when 

 the coagulation of individual particles of the magnetic oxides 

 is prevented by the presence of an indifferent substance, their 

 magnetism turns out greater. This may arise from the en- 

 hancement of the molecular forces that hold the magnetic 

 atoms of metal in their relative position and prevent their 

 rotation, occasioned by the condensation with the heating, 

 being considerable ; and in that case, with a finer division, 

 the demagnetizing mutual action of the parts lying side by 

 side is as much weakened as the macrnetizino- action of those 

 situated one behind another. Since in certain cases the former 

 is greater than the latter, this distribution may effect an in- 

 crease of magnetism. Whether moreover the diminutions of 

 magnetism here observed are to be attributed only to the con- 

 siderable alterations of density, or are connected with an actual 

 change in the atom-grouping, cannot at present be decided. 



12. The Hydrates of the Superoxides of manganese, cobalt, 

 and nickel have only a very feeble magnetism ; it is different 

 with the magnetism of the so-called superoxide of chromium, 

 Cr02. The round glass vessel was filled first with a solution 

 of chromic sulphate, and then with one of bichromate of potass, 

 and each time the magnetism determined ; in the second case 

 it was nearly equal to that of water, therefore negative. After- 

 wards the glass was partly filled with the first, and then filled up 

 to the mark with the second solution, and the magnetism again 



* The ferric and cliroinic oxides were, for these experiments, precipi- 

 tated jointly with the alumina from a mixed solution of ammonia-alum 

 and ferric chloride or chromic nitrate, and the mixture afterwards heated 

 to incandescence. 



