324 Jfefr 4 . cavendish’s Obfervaliom 
may vary as much in different trials, though the whole mafs 
of quickfilver is frozen and without any vacuities. 
The thermometer marked C was intended for trying how 
much the contraction of quickfilver is ; but the experiments 
made with it were not attended with fuccefs, as in the firfi: 
experiment it did not fink fo low as A had done, owing, mod 
likely, to the great cold of the weather which froze the quick- 
filver in .the tube ; and in the fecond experiment the ball 
broke. 
On the cold of the freezing mixtures . 
The cold produced by mixing fpirit of nitre with fiiow is 
owing, as was before laid, to the melting of the fiiow. Now, 
in all probability, there is a certain degree of cold in which the 
fpirit of nitre, fo far from diffolving lhow, will yield out part 
of its own water, and buffer that to freeze, as is the cafe with 
folutions of common fait ; fo that if the cold of the materials 
before mixing is equal to this, no additional cold can be pro- 
duced. If the cold of the materials is lefs, fome increafe of 
cold will be produced ; but the total cold will be lefs than in 
the former cafe, fince the additional cold cannot be generated 
without feme of the fnow being diffiolved, and thereby weaken- 
ing the acid, and making it lefs able todiffiolve more fnow ; but 
yet the lefs the cold of the materials is, the greater will be the 
additional cold produced. This is conformable to Mr. 
Hutchins’s experiments ; for in the fifth experiment, in 
which the cold of the materials was - 40°, the additional cold 
produced was only 5 0 . In the firfi: experiment, in which the 
cold of the materials was only -2^°, an addition of at leafi: 
1 9 0 of cold was obtained; and by mixing fome of the fame 
fpirit of nitre with fnow in this climate, when the heat of the 
materials 
