the Congelation of Vitriolic Acid, 279 
vitriolic acid, in a mixture of fait, fnow, and water ; and foon 
afterwards, while the acid was yet fluid, I immerfed in it a 
thermometer, the mercury of which quickly funk from 50° 
to 29°. While I was moving the thermometer in the fluid, in 
order to make it acquire the exa£t temperature, I law the mer- 
cury fuddenly rife, and upon looking at the acid, I obferved 
numberlefs finall cryfhals floating in it, which had been fud- 
denly formed. The degree to which the mercury then rofe was 
46° j. Another time, while the acid was freezing, the thermo- 
meter placed in it flood at 45 0 . 
From the above obfervations, the following inferences may 
be drawn. 
1 ft, That the vitriolic acid has a point of eafiefl freezing ; 
that is, there is a certain ftreugth or denfity, at which this acid 
freezes with conliderably lels cold than at any other ftrength, 
greater or lefs ; and that this denfity is nearly to that of water as 
1 780 is to 1000. 
2dly, That the greater or lefs difpofltion of congelation of 
the vitriolic acid, which is free from the fmoking quality that 
is peculiar to the acid obtained by diftilling martial vitriol, does 
not depend on any other quality or circumftance than its 
ftrength or denfity. 
^dly, That the freezing and thawing degree of the moft 
congelable acid is about 45 0 of Fahrenheit’s fcale. It is, 
however, to be obferved, that this degree is inferred from the 
temperature indicated by the thermometers immerfed in the 
freezing and thawing acids ; but that I never effected the con- 
gelation of the fluid acid, without expofmg it to a greater cold, 
namely, either that of melting fnow, or of the external air in 
frofty weather. 
S f 2 
Like 
