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property of boiling at a certain degree of heat, which 
is by no means to be obferved in other metals. The 
degree of heat, in which mercury begins to boil, is 
not at 600 of Fahrenheit’s fcale, as is generally ima- 
gined; but at lead: at 709 of the fame fcale, which 
correfponds with 414 of our author’s, whofe cypher 
is at the heat of boiling water. 
Both the boiling and freezing of mercury have this 
in common ; that when it begins to boil, it rifes with 
rapidity; and defcends rapidly, when it begins to 
freeze. If, therefore, the mean term of the con- 
gealation of mercury is fixed at 650 below the cypher, 
and the term of its boiling at 414 above the cypher; 
its greated contradion to its greated dilatation, will 
be 1064 degrees of our author’s thermometer, and 
1237 of Fahrenheit’s; as 212 is the point of boil- 
ing water in this lad, and 32 the freezing one; which 
correfponds with iyo, under the term of boiling wa- 
ter, in our author’s. Hence every one will fee the 
great alteration of fpecific gravity in frozen and boiling 
mercury, as, between one and the other, the tenth 
part of the volume is ledened. 
_ B nr ay be afked, why the mixture of fnow and 
niturous acid does not run into a folid mafs, and form 
itfelf into ice, but remain of a foft confidence, al- 
though actually much colder, than what is required 
to freeze aquafortis? We have already mentioned, 
that aquafortis freezes at 204 of our author’s thermo- 
meter, which correfponds with 34 below the cypher 
of Fahrenheit’s. The frigorific mafs, in a degree 
of cold far below this, remained foft like a pultice. 
The caufe of this extraordinary phenomenon feems 
to be no other than a continuation of the folution of 
2 , 2 the 
