8 H. C. COOKE 
in the processes, but this supposition should be confirmed by 
analyses of waters from horizons somewhat nearer the surface than 
those from which the above samples were taken. 
EXPERIMENTAL WORK 
The experimental work described in this paper deals with the 
following questions: 
a) Solvent effect of sulphuric acid and ferric sulphate on argen- 
tite and its associated sulphides; both natural and chemically pure 
artificial minerals being used. 
b) The solvent effect exerted on metallic silver by the various 
reagents that may occur in ground-waters, such as sulphates, 
chlorides, nascent chlorine, sulphuric and hydrochloric acids. 
c) Solvent effect of ferric sulphate solutions on silver chloride. 
d) Effect of the presence of ferric sulphate on the solubility of 
silver sulphate. 
e) The equilibrium in dilute solutions between ferric, ferrous, 
and silver sulphates and native silver. 
f) The substitution of silver for antimony or arsenic in the 
previously formed sulphides of these elements. 
g) The reaction of metallic silver with precipitated sulphur. 
As these experiments deal with somewhat widely different sub- 
jects, each series will be described and discussed separately. All of 
them were made under conditions approximating those which 
obtain in ground-waters. The temperatures were uniformly room 
temperatures, about 22°C. Pressures were atmospheric pressures. 
Concentrations of solutions were small, usually decinormal; these, 
although somewhat greater than those that obtain in ground-waters, 
may be confidently assumed to cause differences only in the speed, 
and not in the nature, of the reactions which take place. 
The paper also includes a discussion, based on the experimental 
work of Barlowt and Schierholz,? of the effect of chloride solutions 
on the solubility of silver chloride, and the precipitation of the 
silver from such solutions as sulphide. 
* Barlow, Jour. Am. Chem. Soc., XXVIII (1906), 1446. 
2 Schierholz, Szizungsberichte der Kaiserlichen Akademie der Wissenschaften zu 
Wien, tor, 2b (1890), 8. 
