BOOK quickfilver froze on Mr. Hutchins’s thermometers, graduated ac-
XI. i cording to the feale of Fahrenheit, was 40; and a thermometer
adjufted in the manner recommended by the Committee of the
Royal Society, freezes in 38 T, or in whole numbers 39 below
freezing point, or 3] o f Reaumur, which anfwers to the con-
clufion drawn by Dr. Guthrie from his experiments, eilimating
the point of mercurial congelation at 32 of Reaumur, or 40 below
O of Fahrenheit.
As the degree of artificial cold requifite to congele quickfilver
had been greatly mifconceived and exaggerated, a fimilar mifcon-
ception alfo prevailed with refpe£t to the degree of natural cold
neceffary to the fuccefs of the experiment.
Profeffoi' Braun eftimated, that the degree of natural cold
ought not to be lefs than 190 of De Lille, or 17 below O of
Fahrenheit, and that opinion was generally adopted by the na-
turalifts of Ruffia, as when the mercury in the thermometer
flood above that point, they conceived it needlefs to attempt
the experiment.
Dr. Guthrie, however, in the courfe of his experiments fuf-
ficiently proves, that the congelation fucceeded in a cold not
exceeding O 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 congele quickfilver.
Mr. Walker congeled quickfilver by means of a mixture of,
equal parts, of vitriolic- acid and Itrong fuming nitrous acid with
fnow,
fnow, the temperature of the atmofphere being only at 30, or
2 degrees below freezing point.
The fame ingenious gentleman has alfo ihewn, that it may be
even frozen in fummer, in the hottefl climates, by a particular
combination of the frigorific mixtures, without the ufe of ice *.
I fhall clofe this chapter with leveral curious experiments
made in Siberia by Dr. Pallas, for the purpofe of affcertaining the
difference of the heat in animals during their torpid and natural
Hates.
Dr. Pallas having made an inciiion into the abdomen of a
hedge-hog during its torpid Hate, and placed Fahrenheit’s thermometer
in its belly, the mercury rofe only to 39}; and the animal
gave no more figns of feeling, than if it had been actually
dead, as well whilll he was making the inciiion, as when he was
fewing up the wound, although the animal was immediately
afterwards put into a warm room, gradually recovered from its
lethargy, and walked about the chamber with as much infenfi-
bility as if no operation had been performed.
The doftor kept this hedge-hog in his houfe from December
to the end of March; and although the heat of the apartment in
which it lay was feldom under 60 degrees, yet it eat no food;
and was never out of its torpid Hate, except once or twice, when
it was placed behind the Hove, in a heat from 77 to 80. Roufed
* W a lk e r 's Experiments on the P ro - periments on the Congelation o f Q u ic k -
<Ju£tion o f Artificial Cold , P h il.T ran .v o l. filver in England, Philof. Tranfa&ions
Ixxviti. p. 3.95.— A lfo W a lk e r ’s E x - for 1789, vol. lx x ix . part 1 1 . p. 199.