on Mr. Hutchins’s Experiments. 323 
ever, is not the whole contraction which it fufters ; for it ap- 
pears, by an extract which Mr. iiutchins was fo good as to 
give me from a meteorological journal, kept by him at Albany 
Fort, that his thermometer once iunk to 490° below nothing, 
though it appeared, by a fpirit thermometer, that the cold 
fcarcely exceeded the point of freezing quicklilver. There are 
two experiments alfo of Profeflor braun, in which the ther- 
mometer funk to 544 0 and 5 5 6 0 below nothing, which is the 
greateff defeent he ever obferved without the ball being cracked. 
It is not indeed known how cold his mixtures were ; but from 
Mr. Hutchins’s, there is great realon to think that they could 
not be many degrees below — 40°. It fo, the contraction which 
quicklilver buffers in freezing is fometimes not much lets than its 
expanlion by 500° or 5io°ofheat, that is almoft r kdof its w hole 
bulk, and in all probability is never much more than that. 
It is very likely, however, that the contraction which quick - 
filver buffers in freezing is no very determinate quantity ; for a 
confiderable difference may frequently be obferved in the 
fpeciffc gravity of the fame piece of metal, caff different 
times over, and almoff all caff metals become heavier by 
hammering; and it is likely that the fame thing may ob- 
tain in quicklilver, which is only a metal which melts 
with a much lels degree of heat than the reff. I do not 
know, indeed, how much this variation can amount to ; but, 
on caftinp- the fame piece of tin three times over, I found its 
O * 
denfity to vary from 7,252 to 7,294, though I have great rea- 
l'on to think that no hollows were left in it, and that only a 
fmall part of this difference could proceed from the error of 
the experiment, ff his variation ot dculit\ is as much as is 
produced in quicklilver by an alteration of 66° of heat ; and it 
is not unlikely, that the defeent of a thermometer, on account 
of the contra&ion of the quicklilver in its ball by freezing, 
may 
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