The Goldfield news. [volume] (Goldfield, Nev.) 1904-1911, 1909-06-12
Determination in Field.

of freely.
Determination in Field.
A chemical test for the presence OF
alunite is a very simple matter and can
easily be made in the field where water
that is free from sulphates ear be OBJ
tanned. The necessary apparatus in
cludes two or three pint tin cups Cor
tin cans may be used), a small mortar,
and a spoon, cartridge, or other meas
ure that will hold about a gram 10
grains) of the powdered rock. "a
O.44 calibre cartridge one inch long will
hold about half a gram of powdered
rock.) A few ounces of barium chlor-
Idle will also be needed.
When a test is to be made for the
presence of ~alunite a small piece of the
rock is first pounded up with a hammer
and then ground to a fine powder in
the mortar. About a gram of the pow
der is measured out into a tin cup
which is nearly filed with water. The
water is then boiled for Is or 90 min
utes and allowed to stand until all the
powder has settled. The clear water,
which contains in solution whatever
gypsum was present, is then gently
poured into another cup or can "A'
without removing any more of the pow
der than absolutely necessary. The
undissolved powder is then dried in the
cup and heated to a dull red, after
which it is allowed to cool and again
boiled with water as before, in order
to dissolve the ~decomposed %alunite.
After the remaining powder has settled
the clear water is then gently poured
off into another cub 3D."
A small portion of the barium chlor-
ide is now dissolved in a little water,
which should give a clear solution or
be only very slightly clouded. The
water in both the cups 'A' and OBJ
is heated nearly to boiling and some of
the barium chloride solution added to
each. If either solution becomes cloudy
it is proof of the presence Of sulphates.
If "a" is clouded and ''B" remains
clear, the rock contains gypsum but
no a~lunite, while if OBJ is clouded
and "A' remains clear, alunite lis
present without gypsum.
In the arid regions of the West and
Southwest the waters frequently con
tain sulphates, and this, it is feared,
may prove the chief source of trouble
in the application of the method. In
any ease it is always we'll to test the
water before going to the trouble of
preparing the rock powder. Take a
little of the water in a cup and add "a
few grains of the barium chloride; if
more than a very slight milkiness is
produced this water cannot be used
in the determination, since the sui
pilates in it would prevent the detec-
ton of those in the rock.
When suitable water can be procured
any prospector can easily and quickly
apply these tests after a little prac-
tice. Thus he may know positively
whether or not alunite is present, ami
if it is he may prepare to sink deeper
with a reasonable expectation of find
ING gold also. A rough estimate of the
amount of ~alunite present may be made
from the quantity of precipitate thai
clouds the water in OBJ when the
barium chloride solution is added. In
making these tests it should be remem-
bered that alunite is insoluble in either
hot or cold water, and that it is decom-
posed and made soluble only when 1T
is distinctly heated to a dull red. Care
must be taken, however, not to heat
the powder to a bright red, as this
would drive off some of the sulphur
trioxide which is easily recognized by
it's pungent odor. When this happens
a fresh sample should be taken and
another test made.