567 
1909 - 10 .] On the Precipitation of Soluble Chlorides. 
and thus we should get the solid appearing to associate in one solvent and 
not in another. 
(6) The solid may dissolve with the molecular weight corresponding to 
its simplest formula. 
(c) The undissociated solid may split up more or less completely into 
ions, as is generally the case when inorganic salts dissolve in water. 
(d) There may be complex formation between the “ simpler ions ” and 
the molecules, e.g. formation of complex ions. 
(e) In all these cases there almost certainly is some kind of combination 
with the molecules of the solvent. 
All these processes may take place simultaneously when solution occurs, 
just as a given chemical process may consist of a number of simultaneous 
reactions which are very difficult to detect. The different processes in- 
volved in solution may proceed to a different extent in different cases ; and 
moreover, in the case of any one salt and solvent, the different processes 
above mentioned may severally become more predominant at different 
concentrations, so that at different concentrations we may have very 
different chemical systems. 
Now the ionic theory, as applied to precipitation reactions such as we 
have been considering, treats of nothing more complex than the following 
equilibrium : — 
Solid salt undissociated salt in solution ions. 
There still remain complex formation and hydration to be taken into 
account. In dilute solution complex formation has been very fully studied 
by the application of the law of mass action to the ionic theory. In concen - 
trated solutions this fails us, so for the moment we wfill eliminate complex 
formation as much as possible by confining our attention to those salts which 
are known to undergo but little complex formation, i.e. the salts which give 
ions of greatest electro-affinity. We have then in solution the equilibria — 
Solid salt ^ nndissociated salt in solution ^ ions ^ hydrated ions, 
with possibly also 
undissociated salt ^ hydrated undissociated salt ; 
but, as Abegg* points out, the equilibrium which predominates in 
the case of those salts which give ions of strongest electro-affinity is 
probably — 
ions ~ ^ hydrated ions. 
VOL. xxx. 
* Z. fur anorg. Gh ., xxxix. 359, 1904. 
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