on Mr. h u r c n i.ns's Experiments. 30 '$ 
the freezing mixture, funk to 450° below nothing, though the 
cold of the mixture was never more than - 46 ; fo that the 
quickfilver was contraftcd not lefs than 404° by the a&ion of 
freezing. 
If a glafs of water, with a thermometer in It, is expofed to 
the cold, the thermometer will remain perfe&ly flationary from 
the time the water begins to freeze till it is intirely congealed, 
and will then begin to fink again. In like manner, if a ther- 
mometer is dipped into melted tin or lead, it will remain per- 
fectly flationary, as I know by experience, from the time the 
metal begins to harden round the edges of the pot till it is all 
become folid, when it will again begin to defcend ; and there 
was no reafon to doubt that the fame thing would obtain in 
quickfilver. 
From what has been juft faid it was concluded, that if this 
apparatus was put into a freezing mixture of a fufficient cold- 
nefs, the thermometer would immediately fmk till the quick - 
filver in the cylinder began to freeze, and would then continue 
Fationary, fuppofing the mixture Fill to keep cold enough, till 
it was intirely congealed. This Fationary height of the ther- 
mometer is the point at which mercury freezes, though in or- 
der to make the experiment convincing, it was neceffary to 
continue the procefs till fo much of the quickfilver in the cy- 
linder was frozen as to put the £i<F out of doubt. 
If the experiment had been tried with no further precautions, 
I apprehended that conliderable difficulties would have occurred, 
from want of knowing whether the cold of the mixture was 
fufficiently great, and when a fufficient quantity of the quick- 
filver was frozen ; for, in the firF place, there would be no 
judging when a fufficient quantity was frozen without taking 
out the apparatus now and then to examine it, which could not 
S f 2 be 
