BOOK hammer alfo in the freezing mixture, fo as to acquire the fame
XI
■ degree of cold as the frozen quickfilver. Another portion of
quickfilver being congeled by the fame prbcefs as before, I took
out the hammer,, and ftruck the folid mafs of quickfilver as hard
as I could 5 it refilled the .ftroke, and yielded a dead found like
lead} I ftruck it again, and made a fmall dent j a third, time,
and made a larger dent, until it gradually extended and flattened
under the hammer, feparated like an amalgama- of the confiftence
of cheefe, and foon liquefied.
To me the congelation of quickfilver was a matter of mere
curiofity ; but the dodtor’s experiments, tended not only to prove
its abfblute congelation, but likewife to, afcertain exaitly the
freezing point, and to ftiew, contrary to- the opinion of feveral
philofophers, that the purity or impurity of the mercury did not
in any wife affeit the fuccefs of the experiment.
As the fubjedt is in itfelf extremely curious, and rendered ftill
more interefting by the very able treatife puhlifhed by Dr. Blag-
den, Secretary of the Royal Society, in the Philofophical Tranf-
aftions, on the Hiftory of the Congelation of Quickfilver, I
fhall here infert a fummary account of the experiments and ob-
fervations communicated by Dr. Guthrie himfelf. I fhall only
add, that I myfelf was witnefs to moft of the experiments mentioned
in the following account.
“ Mr. Jofeph Adam Braun, Profeffor of the Imperial Academy
of Sciences of St.Peterfburg, difcovered, in December 1759, that
mercury might be rendered folid by means of artificial cold y and
fince
C O N G E L A T I O N OF Q U I C K S I L V E R .
■fince that time it has been congeled in feyere winters by the cold
of the atmofphere in the northern countries of both the old and
new continent.”
This congelation of mercury by the natural cold, renders the
knowledge of its freezing point'a'matter of great importance to
the natural hiftory of the earth as well as of man, as by determining
the degree of cold neceffary to effeft this; phamomenon, we
fhall be able to form an eftimate of the real degree of cold
obtaining in the countries near the poles, and confequently of
the power inherent in living animals to refift it. Until lately
our ideas on this fubject were confufed and erroneous. The experiments
and obfervations of the moft able naturalifts in different
parts of Europe and America were only of partial ufe to natural
hiftory and phyfics, by giving a place to mercury amongft the
malleable metals, and by demonftrating that there is nothing ef-
fentially fluid in its nature, but that it is a metal- which melts
with a lefs degree of heat than the others.
But ftill the philofopher was not informed what reliance he
could place on the mercurial thermometer towards determining
the cold of climates, as the motions of the quickfilver appeared
by thofe very experiments extremely irregular in the lower
parts of the fcale, falling many degrees in an inftant, and after it
had defcended below a certain point finking fuddenly into the
the bulb, and thereby indicating (if any conclufion could be
drawn from its defcent) that the animals of the northern countries
could refift the aftion of cold fome hundred degrees below, the
freezing
.