Arizona weekly citizen., 1895-12-21
FIRE ASSAYS.
The Chief Chemist at the Denver
Branch Mint Discusses the
Subject.

Subject.
H. Van F. Furuan, chief chemist at
the United States mint in this city. who
is known in ecientific circles as one or
the best as>ayers in the country, write
as follows in answer to query trop
The News as to the general accuracy OF
the fire method:
"As there is q popular Impressio
amongst many miners and others that
the fire assay (the usual method) for
gold and silver gives results which are
not only too low, but TIA. the method
frequently gives but small proportion
Of the precious metal contents of our
ores, the writer, at the request OF The
News. has consented to give a few re-
marks on the subject.
Every mining community, and es-
pecially Cripple Greek, at the present
time is inundated with process men, who
claim that they, bv their own particular
pet process, can save far more than the
assay value of the ore, 'as the fire assay
10 no good Practical chemists and
metallurglste, of course, pay no atten-
ton to such statements as the discus
eIon is an old one and the accuracy of
@ fire assay for gold and silver has
en- SO frequently tested and demon
rated that q discussion at this time
ould seem futile. Whilst there is SOM
oason for the belief that the fire asssy
% not return the full precious metal
ltents of the ore, the truth remains
at it gives results which, considered
/ = )m a commercial standpoint, are most
excellent, and SO near the actual con-
tents in these metals that the writer
doubts if any greater degree of accuracy
is attained in the valuation of CONNER
cial products than that which is the re-
suit of the present Colorado practice fof
the assay and valuation Of ores.
"Under the English system for the
purchase Of base metals "copper" and lead)
the practice prevails OF making an aesay
as the Cornish copper assay, which Is
to represent the percentage of
base metal which will be obtained in
the actual smelling operation. Such a
system does not prevail in the United
States, and as regards the assay for the
precious metals the results obtained are
supposed to actually represent the
amount OF gold and silver in the ore. as
nearly as possible by commercial meth
DDS. the inevitable losses in smelling be-
ing allowed for by proper deductions
from the price paid for the ore.
"Whilst losses Of the precious metals
do occur In the fire assay, when the
assay il properly conducted these losses
are quite small and not nearly as great
as many suppose. In a recent series of
experiments conducted by the writer
the total actual loss of silver in crucible
assays vas 25S per cent. This was the
average Of large number OF expert
ments on a variety OF material, the
charges being made up so as to represent
nearly every variety OF ore likely TO be
encounter d. The loss Of gold was but
0.3 per cent. In another series OF ex-
per;ments by the scorifcation method
the silver loss was "a per cent and the
gold loss was 0.6 per cent. These assays
ore all run In the ordinary manner
{ ch as would prevail in good CONNER
eial work. Recently the writer exsmin-
ed three samples Of Cripple Creek ore
with tie following results: By crucible
assaye: No. !, 800 and 80 ounces gold
per ton; No. 2, 90 ounces gold per ton;
No. 8, 22.5 ounces gold per ton. By
sc.rification assay: No. l, 39.5 and 800
ounces gold per ton; No. ?. 80 and S,S
ounces gold per ton; No. 3, 21.S and % 0
ounces gold per ton. Before making
these assays the samples were divided
and half of each was sent to an eminent
eastern chemist who determined the
gold contents by chemical analysis with
the following results: No. ], 800 ounces;
No. 2, sS ounces; No. 3, 22.O ounces
gold Per ton.
"As the chemical analysis should have
given all the gold present the results
show that the fire assay may be relied
upon. This ore was a high grade tel
luride, which is populsrly supposed to
he about the most difficu ore to assay
and obtain correct results by the fire
methods. The slightly higher results
obtained by tie fire method will be
readily understood by practical assay
ers."-Rocky Mountain News.