16 H. C. COOKE 
Strength of Concentration of 
Ferric Solution Silver in Solution 
0.0000 formula wt. per liter o.o211 formula wt. AgSO, per liter 
0.0067 . 02324 
. 0134 . 02404 
.0267 . 02404 
.O401 .02476 
.0535 .02470 
.062 .02508 
.124 .02657 
. 248 .03012 
5 BID .02908 
. 496 .02864 
.620 03123 
enrichment, as the concentration of ferric salt in earth waters prob- 
ably never exceeds 0.05 F. 
The cause of this behavior may be as follows: silver sulphate 
lonizes primarily into the ions Ag and AgSO,, secondarily into the 
ions 2Ag and SO,. The concentration of the silver ions is abso- 
[Ag}* [SO], 
Ag.So, 
addition of a large concentration of sulphate ions, as by the addi- 
tion of ferric sulphate, must correspondingly decrease the con- 
centration of the silver ion present. Since, however, the concen- 
tration of the silver in the solution increases, much of the silver 
must be present in some non-ionized form. The recent work of 
Harkins' would make it seem probable that the silver is present 
as part of the complex ion AgSO,, the solubility of which would 
of course not be affected by the presence of the SO, ion. 
lutely limited by the equation =a constant. The 
EQUILIBRIUM BETWEEN FERRIC, FERROUS, AND SILVER SULPHATES 
The reaction Fe,(SO,),+-2Ag = 2FeSO,+Ag,SO, has already been 
studied by Stokes, and the fact noted that it is an equilibrium 
reaction, which proceeds to the right with rising temperature. In 
ore deposits where secondary enrichment is going on, the ferric 
sulphate formed in the upper parts of the oxidized zone must be 
* Harkins, Jour. Am. Chem. Soc., XXXIII (1911), 1836. 
2 Stokes, loc. cit. 
