SECONDARY ENRICHMENT OF SILVER ORES 9 
METHOD OF PROCEDURE 
The mineral to be tested was first powdered. In the prelimi- 
nary experiments natural minerals were used, and only that por- 
tion which would pass through a 40-mesh sieve was used. It was 
thought, however, that the unequal sizing of the mass of mineral 
so obtained might affect the results materially. Therefore in the 
later experiments with chemically pure materials, only the fraction 
that passed an 80-mesh and was held by a 1oo-mesh sieve was 
used. Of this material a certain amount, usually 1.0000 gm., was 
weighed out, washed into a flask, and covered with 200 c.c. of the 
solution whose action was to be tested. The corked flask was then 
set away in the dark room at room temperature. After standing for 
a period of from one to three months, during which time the flask 
was shaken almost daily, the contents were analyzed. In some 
cases the analysis was of the liquid contents, after the solid residue 
had been removed by filtration; in others, where such analysis 
would prove difficult, it was thought sufficient to determine the 
materials in solution qualitatively, and the loss of weight of the 
solid residue. The latter was done by filtering into a weighed 
Gooch crucible, drying at 120° C., and weighing. This procedure 
was always adopted when the minerals used were the double sul- 
phides pyrargyrite and polybasite. 
Where stibnite was the sulphide acted upon, the procedure dif- 
fered, in that the solutions themselves were analyzed. This was done 
because of the ease of the analysis and for the greater accuracy 
thereby obtainable. In the absence of ferric sulphate the solutions 
were repeatedly evaporated to dryness in the presence of nitric 
acid. The resulting precipitate was then heated to a dull-red heat, 
whereby it was converted into the oxide Sb,O,, then cooled, and 
weighed. Where ferric sulphate was present, hydrogen sulphide 
was passed in until there was no further precipitate. The solution 
was then filtered, the filtrate being repeatedly passed through the 
filter until clear, after which the precipitate was dried and washed 
with carbon disulphide to remove excess of sulphur. The anti- 
mony trisulphide remaining on the filter was redissolved in con- 
centrated hydrochloric acid, the resulting solution mixed with 
concentrated nitric acid, and cautiously evaporated on a water 
