[ 6 73 ] 
grees more in the open air. The teftimony of fo 
many philofophers, each of whom had refpedively 
made the experiment, will, no doubt, be fufficient 
to prove the truth of it. But in order to remove all 
doubt about it, it muft be remarked, that diftilled 
cjuicklilver only was made ufe of in every experi- 
ment ; nay, in fome, the quick hi ver was revivified 
from fublimation. There can therefore be no fufpi- 
cion, that what they ufed was impure, or mixed with 
any heterogeneous matter. This appears to have 
happened to Mr. De Lille de la Croyere, when he 
fays, that in Siberia he found the quicklilver con- 
gealed in the barometer : and even his papers, which 
are in the academy, fhew that he made a miftake in 
his remarks j for, according to them, the mercury 
became folid as foon as it fell to about ipy or aoo 
degrees : but the mercury, which is pure, does not 
congeal at that degree j for otherwife it would not be 
very extraordinary with us to fee it take a folid form, 
becaufe it is not rare to find the cold at this degree 
here. We may believe, that the quicklilver ufed by 
Mr. De la Croyere was impure, and therefore might 
fooner become an amalgama than pure mercury. 
Now there are two things we cannot reafon upon 
with any certainty : As to the hardnefs of the quick- 
filver congealed, it appeared to have had, in fome 
elfays, lefs hardnefs than lead, and in others more : 
alfo we cannot be very lure of the degree of cold, by 
which the mercury is confolidated. The greateft 
part of the experiments agree in this, that the quick- 
silver becomes folid, when it falls in the thermo- 
meter to yoo degrees, more or lefs. Neverthelefs, 
they do not fo fufficiently agree as to deduce any 
thing certain about it. 
Although 
