12$ Dr, Blagden’s Experiments on the 
middle of the water, was two or three degrees above 32 0 . To 
try how far this depended on the foulnefs of the water, I col- 
•le&ed fome of the muddy fediment which had been depofited 
from the New -River water, and added it to the pump-water, 
which had before born to be cooled to 24 0 or 25 0 , fo as to 
render it turbid ; when it congealed, in the fame manner as 
the New- River water had done, before the thermometer in the 
middle of it came to the freezing point. It muft not however 
be imagined, that water thus made turbid is incapable of being 
cooled below 32 0 , without freezing : I have fince repeated the 
experiments, with more caution in conducting them, and re- 
duced it two or three degrees below the point of congelation. 
But hill they have all confirmed the general fa£t, that fubf ances 
which lefifen the tranfparency of water, render it at the 
fame time much more difficult to be cooled below the freezing 
point, and difpofe it to fhoot into ice more readily, after it 
has pafied that point, than pure water would do. It feems to 
be of little confequence what the fubffance is that renders the 
water turbid : fmall particles of any kind floating through 
it, I believe, have this effeCt, which does not take place, or at 
leaf! to the fame degree, when the extraneous fubffance has 
fublided to the bottom. 
It is this circumffance, I fuppofe, which gave rife to the 
opinion, that boiled water freezes fooner than unboiled : for if 
the water contain calcareous earth, held in folution by 'means 
of fixed air, as is the cafe with moff kinds of fpring-water, 
this will be precipitated by the boiling, and will fenfibly trou- 
ble the tranfparency of the water; which, if expofed to the 
cold in that fate, will be liable to freeze fooner than the lame 
kind of water unboiled and tranfparent *. 
* See Fhi'.of >phical Tranfa&ions, Vol. LXV. p. 124. 
The 
