ime) H.C. COOKE 
bath. As fast as the solution became colorless, more nitric acid 
was added, until further addition caused no change of color. The 
solution was then evaporated to dryness, the precipitate heated 
to a red heat, cooled, and weighed. ‘Trial of this method with a 
weighed amount of pure antimony trisulphide showed it accurate 
to 1 per cent. 
MAKING UP SOLUTIONS 
A ferric sulphate solution was made, containing 35 grams of 
Kalhbaum’s C.P. powdered ferric sulphate per liter. This gave a 
solution nearly F/20 (actually 0.0535 F. An F/1 solution=solu- 
tion containing 1 formula weight in grams per liter). The sulphuric 
acid solution used was roughly F/20. That used in the first series 
of experiments was 0.0635 F; that used in the second series, 
0.0502 F. These solutions will hereafter be mentioned simply 
as ‘ferric sulphate solution” and ‘‘decinormal sulphuric acid,” 
and in the tables will be designated as ‘‘F”’ and “‘A,”’ for brevity. 
A proportionality, such as A:F::1:3, indicates the proportions of 
acid and ferric solutions. The total volume of all solutions, unless 
otherwise stated, is 200 c.c. 
ACTION OF SOLUTIONS ON MINERALS. SERIES 1 
As may be seen from the tables, this series of tests included 
not only the silver minerals, but also those with which it is most 
closely associated, i.e., the sulphides of arsenic, antimony, and lead. 
Copper sulphide was not tested, since Vogt" had already proved its 
ready solubility in ferric solutions. The table also shows that 
both the dilute sulphuric acid and the dilute ferric sulphate solu- 
tions exert a powerful solvent action on all the minerals tested except 
argentite; that in each case the action is much more powerful 
when ferric sulphate is present; and that, except in the case of 
galena, an increase in the concentration of the ferric sulphate does 
not cause a corresponding increase in the solvent action. The 
absence of results in the case of the lump argentite is rather to be 
ascribed to the smallness of the surface exposed than to an actual 
absence of action. This will be shown in the table (Series 2). 
™ Vogt, Genesis of Ore Deposits (1896), p. 676, footnote. 
