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COXE’S TRAVELS IN™ RUSSIAs 691
Having inferted a tube containing quickfilver ina mixture of fnow and [pirit of nitre,
he took it out in ten minutes, placed it in a fecond mixture, and in five minutes the
quickfilver was congealed. The tube being broken, the quickfilver appeared in a folid
mafs like a ball of filver, and being ftruck with a hammer was flattened into twice Its ex-
-tenfion before it liquified.
But the hammer being much warmer than the frozen quickfilver, melted the parts
which it touched, feeming to have the fame effect upon the mercury as a warm iron
upon wax; I defired, therefore, Dr. Guthrie to place the hammer alfo in the freezing
mixture, fo as to acquire the fame degree of cold as the frozen quickfilver. Another
portion of quickfilver being congealed by the fame procefs, I took out the hammer, and
{truck. the folid mafs of quickfilver; it refifted the ftroke, and yielded a dead found like
lead; I ftruck it again, and made a fmall dent, a third time, and made a larger dent,
until it gradually extended and flattened under the hammer, feparated like an amalgama
ef the confiftence of cheefe, and foon liquefied.
To me the congelation of quickfilver was a matter of mere curiofity; yet the do¢tor’s
experiments tended not only to prove its abfolute congelation, but likewife to afcertain
the freezing point; and fhew that the purity or impurity of the mercury did not affect
the fuccefs of the experiment.
As the fubje&t is extremely curious, and rendered ftill more interefting by the able
treatife publifhed by Sir Charles Blagden, in the Philofophical Tranfa€tions, | fhall infert a
fummary account of the experiments and obfervations communicated by Dr. Guthrie,
and fhall only add that I was witnefs to moft of the experiments. ;
“ Mr. Jofeph Adam Braun, Profeffor of the Imperial Academy of Sciences of St.
Peterfburgh, difcovered, in December 1759, that mercury might be rendered folid by
means of artificial cold, and it has been fince congealed in fevere 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 neceflary to effect this phenomenon,
we fhall be able to eftimate the real degree of cold in the countries near the poles, and
confequently the power inherent in living animals to refift it. Until lately our ideas on
this fubje& were confufed and erroneous.. The experiments and obferyations of the
moft able naturaliftsin Europe and America were only of partial ufe to natural hiftory
and phyfics, by placing mercury amongtft the malleable metals, and by demonftrating
that there is nothing eflentially fluid in its nature, but that it is a metal which melts with
a lefs degree of heat than the others. :
“© Still 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
zppeared by thofe very experiments extremely isregular in the lower parts of the icale,
falling many degrees in an inftant, and after defcending below a certain point, finking
fuddenly into the balb, and thereby feeming to indicate that the animals of the northern
countries could refift the aGtion of cold fome hundred degrees below the freezing point.
of water. This fuppofition ftaggered the faith of many philofophers, and made them
anxious that the matter fhould be more fully inveftigated. Accordingly the Royal So-
ciety of London defired its members refiding in cold countries, to turn their’ attention
towards determining the point of congelation of mercury, and remark the defcent of
the mercury in the thermometer during the procefs from the freezing point of water to
that of mercury, in order to form a jufter notion of its real contraction. But new light
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