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COXE’S TRAVELS IN RUSSIA. 695
which ought to be carefully diftinguithe d from the contra€tion which takes place whilft
it preferves its fluidity ; therefore the ideas we have formed of the cold obtaining in the
habited countries near the poles, and the aftonifhing power of animals to refift it, muft
be erroneous *, as they have been taken from the extraordinary defcent of the mercury
in the thermometer, which we now know is derived from the contraétion of the mercury
when frozen, and not from fuch an extraordinary degree of cold, which if it had taken
place, muft have deftroyed the whole fyftem of organized bodies.
“¢ We cannot, according to our prefent knowledge of the fubjec, affert, that a much
greater degree of cold exifts than the point of the congelation of mercury ; no other
inftrument having been employed to afcertain it than the mercurial thermometer, which
is now proved of no authority below 32 degrees of Reaumur.
<¢ But it appears, that a thermometer filled with highly retified fpirits of wine pre-
ferves its fluidity in a cold of 32 degrees of Reaumur, or 47 of Fahrenheit, and pro-
bably in a greater, which may therefore be employed in northern climates with more
advantage than one filled with mercury.
“ The furprifing coincidence in the freezing of mercury congealed in Siberia by natural
cold, with that effected by means of artificial cold, merits attention, as they both fix the
freezing point of mercury at 32 of Reaumur ; profeflor Laxman, particularly in a late
paper to the Imperial Academy, declares, that he found common mercury conftantly
become folid at 210 of De Lifle (32:of Reaumur), and that in 1782, it continued fol! d
for two months together. Dr. Pallas alfo, in the third volume of his Travels, men-
tions the fame phasnomenon taking place about the fame part of the feale.”
In addition to Dr. Guthrie’s remarks, I fhall offer a few obfervations.
From a careful review of Mr. Hutchins’s experiments, and a comparifon of the ther-
mometers which he employed on that occafion, Mr. Cavendifh + concludes, that the
true point at which quickfilver froze on Mr. Hutchins’s thermometer, graduated accord-
ing to the fcale Fahrenheit, was 40; aud a thermometer adjufted i in the manner recom-
mended by the Committee of the Royal Society, freezes in 384, or, in whole numbers,
39 below freezing point, or 31; of Reaumur which anfwers to the conclufion drawn by
Dr. Guthrie from his experiments, eftimating the point of mercurial congelation at 32
of Reaumur, or 40 below o of Fahrenheit.
As the degree of artificial cold requifite to congeal quickfilyer was greatly mifcon-
ceived and exaggerated, a fimilar mifconception alfo prevailed with refpect to the degree
of natural cold neceflary to the fuccefs of the experiment.
Dr. Guthrie however proves, that the congelation fucceeded in a cold not exceeding
© of Fahrenheit; and fubfequent experiments made at Oxford by Mr. Walker fhew,
that a very fmall degree of natural cold is fufficient to obtain for the frigorific mixture
the degree of cold neceflary to congeal quickfilver. Mr. Walker froze quickfilver in
a mixture of equal parts of vitriolic acid and ee fuming nitrous acid with fnow, the
temperature of the atmofphere being only at 30, or 2 degrees below freezing point. He
has alfo fhewn, that it may be even frozen in ecimces in the hotteft climates: by a par-
ticular combination of the frigorific mixtures, without the ufe of ice f.
* Sir Charles Blagden ingenioufly infers, from a comparifon of natural cold, during a feries of years, at
Albany Fort, meafured by a {pirit thermometer, and of artificial cold produced by freezing mixtures, that
the extreme artificial cold. produced by {now and nitrous acid correfponds pretty cxactly with the extreme
of natural cold in the moft rigorous climates, which can be well inhabited ; and does not exceed 46° ofa
ftandard mercurial thermometer of Fahrenheit. Phil. Tranfac. vol. Ixxi p. 387,
+ Phil. Tranfac. vol. Ixxili, part 2. page 321.
{ Walker’s Experiments on the Production of Artificial Cold, Phil. Tranfac. vol. Ixxviii. p. 395.—Alfo
Walker’s Experiments on the Congelation of Rue in England, Phil. Tranfac, for 1789, vol. Ixxix.
art 2. p. 19
dips gaaes 7 I fhall
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