SECONDARY PRECIPITATION OF GOLD 263 
nous chloride solution was made up and 38 mg. of gold in the form 
of chloride was added. Very dilute potassium hydroxide solution 
was added in small amounts, with repeated shaking until the 
solution was almost neutral to litmus. Precipitation occurred at 
once. The precipitate was allowed to settle for 24 hours, then 
all but 100 c.c. was decanted by means of a slow siphon. The 
remaining solution was filtered and added to the decanted portion. 
A 50¢c.c. portion was tested for gold by the phenyl hydrazine 
test’ in a Nessler tube, with blank for comparison. As this showed 
no gold, 5ooc.c. of the solution was concentrated to 100 c.c. and 
the test was repeated. This again gave negative results. The 
test used readily detects concentrations of less than one part per 
million, consequently the second test showed the gold remaining 
in the original solution to be less than two parts in ten million. 
Since the precipitation is so complete we are forced to the con- 
clusion that these reactions can take place in solutions of extreme 
dilution—such solutions as would be formed in the leaching of 
gold from a manganiferous lode. 
The fact that in certain cases mine waters actually show 
alkaline reaction is well established. Emmons? has shown that 
at Ducktown, Tenn., the waters show decreasing acidity with 
depth. This was for water in an abandoned shaft. For circulating 
waters the change is probably greater. It is doubtless due to 
interaction with the constituent minerals of the surrounding 
rocks. 
The following list gives the more common gangue and rock- 
forming minerals showing alkaline reaction to litmus or phenol- 
phthalein :3 
™ The phenyl hydrazine test mentioned has been described by Pozzi Escot, Ann. 
de Ch. Anal. (1907), XII, go-g1. It consists in adding to the solution to be tested, 
a few drops of formic acid, then a few drops of saturated phenyl hydrazine hydro- 
chloride. The presence of gold is shown by a purple tint which may be used in the 
colormetric estimation of small amounts of gold. This method as tested by the writer 
gave strong tint in a 5oc.c. Nessler tube to solutions containing nine parts of gold 
in ten million of water. The advantage over the oxalic acid test is that the reaction 
is almost instantaneous and no heating is necessary. 
2W. H. Emmons, U.S. Geol. Survey Bull. No. 470, p. 172. 
3Kenngott, Neues Jahrbuch (1867), p. 302; F. Cornu, Tschermak Mitteilung, 
XXIV, 417-32, a XXV, 480. 
