Behaviour of Chemical Compounds. 285 



a portion of the hydrogen of the ammonium group, and con- 

 sequently the salts were composed similarly to the cobalt- 

 ammonium saltSj and therefore perhaps 



TT 



CuS04' + 2NH3= ^Cu, SO4, 

 H3 



XT 



CuS04 + 5NH3=CuS04 + ^CuSO, + 3NH3, 



H3 



represented their composition, is untenable. It is much more 

 probable that here also the ammonia^ similarly to water of 

 crystallization, attaches itself to the unaltered group of the 

 cupric salt. 



The peculiar violet compound obtained when freshly preci- 

 pitated chromic oxide is dissolved in ammonia, and the solu- 

 tion, mixed with excess of hydrochloric acid, slowly evapo- 

 rated to crystallization, is sometimes regarded as the salt of a 

 proper chromium base similar to the platinum bases, as tetra- 

 mine chromic chloride Cr (^113)4 CI3 + Hg 0. The magnetic 

 investigation of the solid salt gave the following results : — 



G. M. cc. 



Ammonio-chromic chloride ... 0*6492 61*8 42*4 

 Ferric chloride 0-1244 26'1 100, 



while the atomic magnetism of the chromium in the ordinary 

 chromic salts is equal to 41*9. Hence in ammonio-chromic 

 chloride the chromium exhibits the same deportment as in the 

 chromic salts. Here, too, we cannot assume that the atom- 

 group containing the chromium is essentially other than in 

 the latter ; and we are compelled to attribute to the ammonia 

 a similar part as to the water of hydrates — precisely as in the 

 ammoniacal nickel- and copper-salts. The formula of the salt 

 should accordingly be written: — Org Cle, 8NH3, 2H2 0. 



18. Dissociation. — It is known that a number of ferric salts in 

 their solutions undergo dissociation, at a lower or higher tem- 

 perature, into colloid ferric oxide and acid. We have already 

 (p. 172) mentioned that by the determination of the magne- 

 tism of these salts their partial dissociation can be quantita- 

 tively verified. If m^ is the magnetism of unit weight of iron 

 in the solid salts or in those present in a very acid solution 

 and not dissociated, mi the magnetism of unit weight of iron 

 in the colloid solution of ferric oxide, m the magnetism of unit 

 weight of iron in the solution of a partially dissociated salt in 

 which the quantity of the ferric oxide combined with the acid 



