The silver thus obtained is
perfectly pure. If the amount of copper present is only small, it can
usually be removed by fusing the precipitated powder with a little
niter and borax.
In this way a spent silver bath was found to contain per liter
1st experiment 1.5706 grms.
2d " 1.5694 "
------
Mean 1.5700 "
The presence of silver could not be qualitatively ascertained in the
residual liquor.
Although sheet zinc, or zinc and iron sheets, serve so well for the
precipitation of silver, they cannot be employed for the recovery of
gold. The latter separates out in such a case very incompletely and as
a firmly adhering lustrous film in the zinc. On the other hand, finely
divided zinc, the so-called zinc dust, is an excellent substance to
employ for precipitating gold quantitatively and in the form of powder
from spent cyanide liquors. When zinc dust is added to a spent gold
bath and the liquid periodically stirred or shaken, all the gold is
precipitated in two or three days. The amount of zinc to be added
naturally depends on the quantity of gold present.
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