Juniata sentinel and Republican. [volume] (Mifflintown, Juniata County, Pa.) 1873-1955, 1877-02-07

SCIENTIFIC.

The English Mint.-The Spectre
scope is now largely employed Al the
mint.in London, for testing the fine
ness of the gold and silver. In the re-
port by Mr.. Roberts. the chemist of the
mint. a diagram Is given showing the
comparative results of spectroscoplC
assaying and the ordinary parting as
say. This diagram consists of curve
the cOordinares of which are furnished
by the indications of the micrometel
in the eye piece of the spectrcscope, to-
gether with the known composition Ol
several alloys. The chief point noted
with regard TO this curve is that there
is a much greater change in the micro
meter readings for corresponding
change of composition in the alloy IN
the less pure than In the finer alloys.
Thus the difference between an alloy
containing 916.7 parts gold in the 1000
aud that containing 916.6, is shown by
(rOughly speaking from an inspection
of the drawlngl thirty divisions of the
micrometer scale, whereas the differ
ence between 1868 and 9l6.2 is shown
by about 200 divisions. This latter
fact may serve to show how infinitely
more susceptible the spectroscopic me-
thod is than that IN common use, when
one ten-thousandtb part of alloy is
marked by so very considerable a
change in the scale. 1t does not, how
ever, appear that any great practical
advance has been made in this novel
application of the spectroscope, al
though on one occasion this instru-
ment was used In testing the recently
made trial plate of pure gold. 1t was
found that Its spectrum, when compar-
ed with the solar spectrum showed alb
s0lutely no lines except those due to
gold. The result of Mr.. Roberts's long
labors was thus approved by the most
delicate of all possible tests. How long
these labors were may be seen by a ref
erence to the report of the preceding
year, in which it Is stated that over
1000 ASSAYS were made in the prepara-
ton of the two gold plates, the standard
carats or 9l6.66 parts in the 1000)
and that absolutely pure. The neces-
sity for these plates arises from the I'M
possibility OF obtaining absolutely ac-
curate results from the usual process
of chemical analysis. 1t has. there
fore, long been the practice in the an
nual testing of the coinage to check
the result by assaying, side by side
with the alloy under examination,
pieces of metal of known fineness. The
test plates III use since 1929 were found
not To be of their reputed standard,
that for gold being actually 9l6.3 in
stead of 916.6. 1t was, therefore, de-
termined 30 prepare new plates, and
this was done, with minute and elabor-
ate care, as detailed in the report for
1878. To still fnrther check the accur-
acy of the result, plates of absolutely
pure gold and silver were also prepar-
ed, and 1t was this new pure gold that
was examined by tine spectroscope.
These plates having been formally
tested and approved in 1878, the an
nual trial of the gold and silver coin
age was effected by their aid in 1874.
The natural result of this elevation of
the standard was that the Trial of the
Pyx' showed an apparent falling off in
the fineness OF the coins. However
the greatest variation from standard
was only four -thOusandth parts
(.0004) or one fifth of the legal "reme-
dy" of two thousandths (.002) allowed
as limit for variation.