THE ELECTROLYTIC DISSOCIATION THEORY 387 



containing ammonia and water. The following series of 

 compounds containing trivalent cobalt were prepared, and 

 their constitution determined by chemical and physical methods : 



[co(NH 3 ) 6 ]"ci;",[Co(NH,)5Cl]"ci,",[co(NH 3 ),Cl 2 ]"ci',[co(NH 3 )3Cl 3 ]. 



As the formulae indicate, the first compound consists of a 

 trivalent complex ion consisting of 6 NH 3 groups associated 

 with one cobalt atom, and all the chlorine is ionised ; in the 

 second compound a chlorine atom has replaced a NH 3 group 

 in the positively charged complex and the remaining two 

 chlorine atoms are ionised. The chemical behaviour completely 

 bears out the different character of the halogen atoms in the 

 second compound ; thus only two-thirds of the chlorine can be 

 precipitated by silver nitrate. 



Werner 1 further showed that the place of the basic ammonia 

 in such compounds can be taken by neutral groups such as 

 water molecules ; thus the following series of cobalt compounds 

 are known : 



[CoCNH 3 )J-Cl 3 ^ 



. . . upto[Co(H.,0) 6 T"ci/" 



In this case the positive ion remains trivalent, as the substituent 

 is neutral. A further instructive example is the green hexa- 

 hydrate of. chromium chloride, which, according to Werner, has 



the formula Cr A, ^ O'+2H 2 0; and, in fact, the substance 



in question can lose two molecules of water without any 

 alteration in its characteristic properties. 



Werner's results have been confirmed by many other 

 investigators, so that if the presence of free ions in solution 

 be granted, there can be no doubt that at least in some cases 

 they are associated with solvent molecules. 



Werner further expressed the view that the cause of electro- 

 lytic dissociation is to be found in the association of the metallic 

 constituent of the salt with water molecules, and was thus able 

 to bring the electrolytic dissociation theory into line with the 

 old hydrate theory. He writes in 1893 : 2 "The first condition 

 for the electrolytic dissociation of a salt is the capacity of its 



1 Loc. cit. p. 132. 3 Zeit. anorg. Client. 1893, 3, 294. 



