the Congelation oj $luickjilver. \ 
the fe gentlemen aie explicable in the following manner. When 
tiie air becomes fufficiently cold to freeze quickfilvcr, that me- 
mufl; be (landing about — 39 0 , or, in the common way of 
marking the boiling point, fomewherc between - 40° and 
— 50 , in the tube of a thermometer expofed to it. As the 
fmall thread of mercury in the tube mufl be more eafily affected 
by the cold, it will probably congeal before any other part, and 
fhek faff about the abovementioned degrees. The rem hide*- 
of the mercury will then go 011 to freeze, and as i iffero i nch 
a great contraction in becoming folid, muff leave a confide e 
vacuity in the bulb of any common thermometer. Confe- 
quently, when the cold, from whatever caufe, comes to be lefs 
than is required for keeping the metal in a folid ffate, the fmall 
thread that was frozen in the tube immediately melts, and 
finks down into the vacuity of the bulb, where the whole mafs 
remains, till by its gradual liquefaction it expands again into 
the tube, and becomes ajuff meafure of the temperature. This 
agrees exaCtly with what M. tornsten obferved. In the even- 
ing of the the quickfilver congealed 111 Ins thermometer, 
and part of it ffuck in the tube at - 54 0 , but fubfided into the 
vacuity left in the bulb, as foon as it was expofed to heat. 
When the inftrument had been kept in the warm room till the 
quick hi \ er ie»afcended into the tube, it froze and adhered again 
in the open an, and the lame phenomena were repeated. If 
M. TORNSTEN be exaCt in faying it always became faff at - 54°, 
the circumffance is cuiious, and may have depended upon lorn© 
particular ffate or the tube in that part, or upon the flrff (hoot- 
ing of the mercury after it had been cooled to a certain degree 
below its freezing-point. But when the thermometer was ear- 
ned back into the open air before any of the quickfilver had 
1-ifen out of the bulb, the effect of the cold could not be to 
F f f 2 
lorce 
