20 H. C. COOKE 
chloride solution of less strength the solubility of the silver chloride 
must be less than its solubility in pure water; the solubility curve 
will consequently be as shown in Fig. 1, which was obtained as 
follows: silver in chloride solutions exists in two forms, as silver 
ion and as part of some non-ionized molecule or some complex 
ion. The concentration of the silver ion in solution is inversely 
proportional to that of the chloride ion according to the equation 
CagXCoa=k, a constant. Hence addition of sodium chloride to 
silver chloride solution will very rapidly reduce the concentration 
of silver ion to a very small quantity (see Fig. 1). Silver in the 
non-ionic form may be present as molecular silver chloride, but the 
amount of this is so small as to be negligible; it may also be present 
in combination with sodium chloride, forming compounds of com- 
position as yet undetermined, but which may be supposed, from 
analogy with the corresponding cyanide compounds, to have the 
formulae NaAgCl, or Na,AgCl,. The silver would then enter 
into solution as part of the complex negative ion AgCl, or AgCl;’ 
whose solubility would not be affected by the presence of chloride 
ion. -The table shows that the amount of AgCl in solution as com- 
plex ion attains 0.0018 gm. per liter only when the amount of 
sodium chloride present is 34.3 gm. per liter, and that thereafter 
. the concentration of complex ion increases proportionally much 
faster than does the concentration of the soldium chloride; hence 
it is probable that in sodium chloride solutions of strength less than 
34.3 gm. per liter the concentration of complex ion, and therefore 
that of silver, will never be more than proportional to the amount 
of sodium chloride present, but usually less. The curve showing 
the total silver in solution will consequently be of the form shown 
rig 1 Oikep 30 
From these experiments, therefore, it is concluded that only 
when the amount of sodium chloride in ground-waters exceeds 
34.3 gm. per liter may such waters be solvents superior to those 
in which chlorides are absent. Such concentrations occur rarely 
in nature. 
An accurate determination of the strength of the sodium chloride 
solution which contains the minimum amount of silver chloride 
will be of value as rendering possible the determination of the 
