290 Dr. Blagden’s Experiments on 
its freezing point ; namely, the folution of one part of the 
fait in five of water, whofe freezing point proved 27°!, and 
which cooled to 1 6° before the cryflals of ice fhot. I11 two other 
inftances it funk fully nine degrees below its freezing point. 
And, as already has been mentioned, the folutions of this 
fait are remarkably tranfparent. 
In trying the greatefl: cold to be obtained by mixing Ro- 
chelle fait with fnow, I could get the thermometer no lower 
* 
than 2 4 0 . 
Glauber’s fait likewife was fubje£fed to the experiments, 
but its utmoft effect in producing cold with fnow appearing to 
be only two degrees, this was too fmall a fcale for fettling any 
thing as to the ratio. A folution of it in water, in the pro- 
portion of 1 15, cooled readily to 31 0 ; but the fait was depo- 
fited in great quantities, and often fo faff, as to flop the cool- 
ing of the bottom of the liquor entirely, though the veffel 
was immerfed in a ftrong frigorific mixture. This pheno- 
menon has been obferved before ; but does not take place, to 
the fame degree, in the folutions of any other fait with which 
I am acquainted, though I evidently perceived fomething of 
it in the flrong folutions both of nitre and of fal ammoniac. 
It is exa&ly the converfe of the cold produced by diffolving 
falts in water ; for as there fome heat is abforbed, and becomes 
latent, by the change of the fait from a folid to a fluid {fate, fo 
here fome heat is evolved as the fait aflumes the folid cryflal- 
line form. The effect is fo much more manifefl with Glau- 
ber’s fait only, I imagine, becaufe the formation of the cry- 
ftals proceeds fo rapidly ; whence the quantity of heat gene- 
rated equals or exceeds the cold communicated by the freezing 
mixture. Some odd appearances are produced by this fudden 
flop 
