Bisbee daily review., 1915-11-14
TESTING WORKING CYANIDE
SOLUTIONS.

According to Edward H. Croghan
in the April issue Of the Journal of the
Chemical Metallurgical and Mining
Society of South Africa, great divers
ity Of results may be obtained in test
ing working cyanide solutions, and
suitable uniform procedure which
should be adopted on the Rand is high
ly desirable.
In working solutions with zinc pre-
cipitation in vogue solutions contain
ing both free cyanide and cyanide ex-
listing as double zinc cyanide, there
are I'm titrating with silver nitrate in
the presence Of potassium iodide az
Indicator, two end points that can be
observed. % the first appearance Of
a distinct opalescence or permanent
Gocculent whiush precipitate; (2l fol
lowing on l1) the appearance of a dis
. tinct permanent yellowish tint The
first point is premumed to approx
mately give the figures for free cy-
anide content, and the second de.
pending chiefly on whether there is
. present OF not sufficient free alkaH
and the dilution, the whole or a part of
the total cyanide. Subsequent refer
ences to the above two finishing points
viii be briefly termed the white and
yellow points respectively
There does not seem to be uni
formity in the matter of testing It is
ia consequence interesting TO note
that, supposing a test We're made on a
strong solution to the yellow point,
and 012E ken found the more cor
rect result for free ken, if the Ultra
ton had been conducted to the white
point, might only be O.06Fs. On slime
solutions the same result could occur
OO15l ken according to the yellow
point might not be on the white more
than O.OOSGl free ken, and possibly
less.
In the course of testing some work
ing solutions for free cyanide, it was
noted that the percentage of so-called
free cyanide according 10 the white
J or yellow points previously referred
to, and continuing the determination
for protective alkali on the same solu
ton which had been titrated by silver
nitrate with potassium iodide as indi
Gator.
The tests made, resulted i'm the fol
| lowing conclusions for ken: Q) Tn.
| white point results of both method.
! are much lower than those Of their re
/ spective yellow (2) The yellow poinl
data Of the ordinary method are ,
/ good deal higher than those of the vel
/ low under the special process-in fact
the former almost correspond to The
total cyanide found, particularly o
l the ordinary method fan Interestingly
I between those of the white and vel
low of the special procedure, with tw,
/ minor exceptions From the analyst.
il is indicated that neither the whit,
nor the yellow point data of the spe
cial method can lay claim to being 70
closer agreement with those of tn,
white point of the ordinary procedure
| Regarding protective alkali the fol
lowing is deducted CD Comparing III,
/ protective alkali results obtained b.
/ the ordinary method on solution
which had been titrated for free cy
anide. that is. to the point with thos'
of the special method, on the veal
cyanide solutions the agreement OF
the whole is close, but on the stronge
the former tends to be higher e.
The protective alkali figures found an
der the ordinary method on the solu
tons titrated 10 the yellow point viii
silver nitrate, are on the average dis
tinctly lower than those secured on thl
white point Of the ordinary, and seem