692
was lately thrown upon the fubjeft, by a courfe of experiments made at the defire ofthe Royal Society , by Mr. Hutchins, Governor of Hudfon’s Bay, who received excel-lent inftruflions from Mr. Cavendilh, and Dr. Black, profeffor of chymiftry in the uni-verfity of Edinburgh. Thefe directions, and an apparatus made in London , enabledthe Governor to perceive, that the fudden arid confiderable delcent which takes place inthe lower parts of the thermometer, when expofed to great cold, happens from the con-traction of the metal in its frozen (late, and does not atfeCt the regularity and juftnefs ofits contraction whilft it remains fluid. This great point was principally ascertained bymeans of a fpirit thermometer, which was found not to freeze as loon as the mercury,and thereby indicated the degree of cold produced by his frigorific mixture, whenthe mercurial thermometer ceafed to meafure it on account of its contraction on becom-ing folid.
“ To prove that the defcent of the mercury in the thermometer was derived fromthis new-difcovered principle, namely, the contraction of the metal in freezing, and 10try whether pure mercury required a greater degree of cold to freeze it than adulteratedmercury, 1 made thefe experiments with various forts of mercury:
“ 1. 1 procured from Winterberger, a famous chymift of St. Peterfburgh, the pureftmercury known to chymifts, viz.' revivified from calomel by filings of iron. 2. FromDr. Pallas, native mercury, collected in a mine where no other metal is found but alittle iron. 3. Common barometer mercury, furnilhed by Morgan, an Englifh opticianat Peterfburgh, as he received it from England for filling his inftruments. 4. Sixdrachms-of common mercury, which I adulterated by diflolving in it a quarter of a grainof 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 purpole of thefe experi-ments ; alfo one with highly rectified fpirits of wine, diftilled by Winterberger,
“ Adjtiining is a drawing of the apparatus I employed in thefe experiments, whichwas fuggefted to me by my learned friend Dr. Black ; it differs from that employed byMr. Hutchins in being more fimple, and confequently the mercury was more eafily ex-amined during the procefs of congelation.
“ December the 22d, 1784. In a calm clear evening, Reaumur’s thermometer at17 degrees below o, after expofing the apparatus on a table in my court-yard (where Imade my experiments) for two hours, to acquire the temperature of the atmofphere, Ipoured a little of the purified mercury, No. 1, into the glafs tube, and having inferteda thermometer filled with the famepurifie'd mercury, fo that its bulb was covered withthe mercury in the tube, I placed them in the water-glafs, filled with the freezing mix-ture, and in fix minutes tranfported them into a fecond, with fimilar contents ; the mer-cury in four minutes more became folid, and when I drew out the thermometer, withthe frozen mercury fufrounding its bulb in the form of a folid cylinder, it flood at 32Idegrees below o. Perceiving, however, a little fluid mercury ftill remaining in the tube, Ire-placed the thermometer with the mercury adhering to its bulb, and in a few minutesthe mercury rofe about half a degree; drawing it up a fecond time, I found the mer-cury melted, and the bulb quite free. From this experiment it proves, that the freez-ing point of pure mercury is at 32 \ degrees below o on this thermometer; for as thereremained a little mercury ftill fluid in the tube, there feems to have been only pro-duced fufficient cold to freeze it, and as on its rifing half a degree the mercury becamefluid, the point of congelation is accurately determined.”
“ Second experiment.—On the 9th January, 1785, between fix and half part feven.in the evening, I made the following experiments in prefence of Mr. Epinus, Mr. Coxe,
8 . and