facial cold; a glafs tube B, of about half an inch diameter, containing
a little mercury to be frozen, and in this tube is inferted a
thermometer A, fo that its bulb is buried in the mercury, but
no part of the item: the tube and thermometer thus arranged,
are placed in the above-mentioned water-glafs, containing the
freezing mixture.
December the 22d, 1784. In a calm clear evening, Reaumur’s
thermometer at 17 degrees below O, after having expofed the
apparatus on a table in my court-yard (where I niade my experiments)
for two hours, to acquire the temperature of the atmo-
fphere, I poured a little of the purified mercury, N ' i, into the
glafs tube, and having inferted a thermometer filled with the
fame purified mercury, fo that its bulb was covered with the
mercury in the tube, I placed them in the water-glafs, filled
with the freezing mixture, and in fix minutes tranfported them
into a fecond, with fimilar contents; the mercury in four minutes
more became folid, and when I drew out the thermometer, with
the frozen mercury furrounding its bulb in the form of a folid
cylinder, it flood at 32I degrees below O. Perceiving, however, a
little fluid mercury ilill remaining in the tube, I immediately replaced
the thermometer with the mercury adhering to its bulb,
and in a few minutes the mercury rofe about half a degree; when
drawing it up a fecond time, I found the mercury was melted,
and the bulb quite free from it. Now this experiment appeared
decifive, that the freezing point of pure^ mercury is at 32 i degrees
below O on this thermometer; for as there remained a
little
little mercury ilill fluid in the tube, there feems to have been CHAP.
only produced fufficient cold to freeze it, and as on its rifing half 1 .---- <
a degree the mercury became fluid, the point of congelation
feems to be accurately determined.
Second experiment.— On the 9th January, 178 5, between the
hours of fix and half pail feven in the evening, I made the following
experiments in prefence of Mr. Epinus, Mr. Coxe, and
other gentlemen; I inferted the O ' mercurial thermometer ufed in
the lafl experiment in a portion of the purified mercury, N° r,
and placed them in the cold mixture: the thermometer fell
flowly to 32 i, and was there flationary fome time, whilfl we
perceived the mercury in the tube freezing round the fides of it,
fo as to produce a coating like tin foil in the Leyden phial; and on
tranfporting it to a fecond glafs o f cold mixture, the thermometer
fell in five minutes to 36 degrees, where it remained flationary
during the time it continued in the mixture. What was very
remarkable in this experiment, the mercury in the thermometer
was ilill fluid, although its bulb was frozen into that contained
in the tube; for on reverfing the inflrument, the mercury ran
out of the bulb into the flem. Now, here is a proof that mercury
may be cooled 3 f degrees below its freezing point withQut
becoming folid.
Third experiment with native mercury.— It having been lately
aflerted, that a thermometer, filled with highly redtified fpirits
of wine, is better calculated to determine the freezing point of
mercury, than one filled with the fame metal, becaufe it refills
Vox.. III. K k congelation