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692 COXE’s TRAVELS IN RUSSIA.
was lately thrown upon the fubje@t, bya courfe of experiments made at the defire of
the Royal Society, by Mr. Hutchins, Governor of Hudfon’s Bay, who received excel-
lent inftruCtions from Mr. Cavendith, and Dr. Black, profeffor of chymiftry in the uni-
verfity of Edinburgh. Thefe direGions, and an apparatus made in London, enabled
the Governor to perceive, that the fudden and confiderable defeent which takes place in
the lower parts of the thermometer, when expofed to great cold, happens from the con-
traction of the metal in its frozen ftate, and does not affect the regularity and juftnefs of
its contraction whilft it remains fluid. This great point was principally afcertained by
means of a {pirit thermometer, which was found not to freeze as foon as the mercury,
and thereby indicated the degree of cold produced by his frigorific mixture, when
the mercurial thermometer SSaee to meafure it on account of its contraction on becom-
ing folid.
“é To prove that the ofeede of the mercury in the thermometer was derived from
this new-difcovered principle, namely, the contraction of the metal in freezing, and to
try whether pure mercury required a greater degree of cold to freeze it than adulterated
mercury, | made thefe experiments with various forts of mercury:
“<1, I procured from Winterberger, a famous chymitt of St. Peterfburgh, the pureft
mercury known to chymifts, viz. revivified from calomel by filings of iron. 2. From
Dr. Pallas, native mercury, colleéted in a mine where no other metal is found but a
little iron. 3. Common barometer mercury, furnifhed by Morgan, an Englifh optician
at Peterfburgh, as he received it from England for filling his inftruments. 4. Six
drachms of common mercury, which I adulterated by diffolving in it a quarter of a grain
of tin foil.
«I procured alfo fome thermometers made with great care and accuracy by Morgan,
filled with the fame purified mercury, No. 1. for the exprefs purpofe of thefe experi-
ments; alfo one with highly reCtified fpirits of wine, diftilled by Winterberger.
** Adjoining is a drawing of the apparatus I employed in thefe experiments, which
was fuggefted to me by my learned friend Dr. Black ; it differs from that employed by
Mr. Hutchins in being more fimple, and confequently the mercury was more eafily ex-
amined during the procefs of congelation.
«* December the 22d, 1784. Ina calm clear evening, Reaumur’s thermometer at
17 degrees below o, after expofing the apparatus on a table in my court-yard (where I
made my experiments) for two hours, to acquire the temperature of the atmofphere, E
poured.a little of the purified mercury, No. 1, 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 mix-
ture, and in fix minutes tran{ported them into a fecond, with fimilar contents ; the mer-
cury in four minutes more became folid, and when I drew out the thermometer, with
the frozen mercury furrounding its Ballon in the form of a folid cylinder, i itf{tood at 322
degrees belowo. Perceiving, however, a little fluid mercury till remaining in the tube, I
re-placed the thermometer with the mercury adhering to its bulb, and in a few minutes
the mercury rofe about half a degree; drawing it up a fecond time, I found the mer:
cury melted, and the bulb quite free. rom this experiment it proves, that the freez-
ing point of pure mercury is at 32} degrees below o on this thermometer ;_ for as there
Peed a little mercury ftill fluid in the tube, there feems to have Mee only pro-
duced fufficient cold to freeze it, and as on its rnifing half a degree the mercury became
fluid, the point of congelation i is accurately determined.”
« Second experiment.—On the gth January, 1785, between fix and half paft feven
in the evening, I made the following a. in vrefence of Mr. Epinus, Mr. Goxe,
and
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