The Elk Mountain pilot., 1881-07-21
THURSDAY, JULY II, 1881.
TO REGULATE CHLORZDZZ-
ING ROASTING OF ORE.


The main points which have to be
considered at chloridizing roasting
are: The time of roasting, the tenn
perature, the amount of salt and the
loss of silver. The first thing neces-
sary to know, is the amount of silver
contained in the ore-for this pur-
pose reliable average sample must be
taken, including the salt if already
mixed; this sample to be No. I. 1t
must be taken either while it is
charged in the furnace, or at the bat
terry over ten or fifteen minutes while
it drops from the sieves. The roast
ing should be carried on at moder-
ate heat. After three or four hours,
when the ore assumes a woody condi-
tion, other samples are taken from
different parts of the furnace, mixed
together, and the assay sample there
from marked No. 2. One hour later
athird sample is taken, No. 3; half
an hour after this No. 4, and before
the discharge or duringthe discharge,
No. 5. The temperature of the last
hour should be a moderate light red
heat. In case there is a double or
treble hearth furnace, one sample
more should be taken from the hearth
next to the finishing hearth, just be-
fore moving the charge over to the
finishing hearth, but as there are three
charges on three hearths, the samples
have to be taken of one charge as it
progresses from one hearth to the
other.
While the next charge is treated in
the same way, but higher heat ap-
piled, the samples already taken must
be assayed. In order to find the pro-
gress of chlorination, the assay of No.
Lis not needed, it serves only to as
certain the loss of silver during the
roasting. One assay OF No. I, how
ever, would not be sufficient, because
the weight Of the ore changes. For
instance, the iron sulphuret (pyrites)
loses its sulphur, which is replaced by
the lighter oxygen, and weighs then
s. per cent. less, but in taking up chic
rine,. in place of the oxygen, it gets
much heavier than it was when sui
phuret, gaining IS per cent, but {:
great deal of the chloride Of iron vol
atilizes. For this reason two assays
of No. I are weighed out, one to be
assayed in the usual way, to find out
the amount Of silver per ton, and the
other half ounce is subjected to roast
ing under the muff1e, in a roasting
cup for one hour and half or two,
at about the same heat as in the fur.
mace, then weighed out and noted
how many grains were lost or gained,
IS compared with the original 24c
grains.
The other samples are assayed tc
ascertain how much of the silver was
chlorid,zed. If, then, all the assay
samples showed a progress in chlori.
nation, so that No. S was the highest,
but still not satisfactory, it indicate.
that either the time was too short, O,
the heat too low, or perhaps moi
enough salt !; these assays show also
the relative loss OF silver.
While these assays were made, the
next charge as before mentioned, was
to be conducted at somewhat in.
creased heat, and samples taken as
before. If now, for instance, the las,
two samples should show the same
percentage of chlorination, it were
evident tina, the roasting was carried
on too long. In case the chlorina-
tion were still too low, and the last
one the highest. then the roasting
should be tried one hour longer
eventually more heat or more salt, but
always controlled by assays. Such
investigation may take two or three
days, or more.
To ascertain the loss Of silver, an
average sample is taken when the
roasting is finished, and for an assay,
weigh out, not half an ounce, but Sc
many grains as there were found after
roasting Of No. I under the muffle,
and this weight considered as half an
ounce If then, for instance, the frs,
assay Of No. should give 50 ounces
per ton, and that of the roasted ore