cooling of Water below its freezing Point. 145 
below its new freezing point ; and it has been already ob- 
ferved, that the addition of an acid always expelled much air from 
the water. It is not improbable, therefore, that if water 
could be thoroughly purged of air, it would readily bear to be 
cooled 18 degrees, or more, below its freezing point, without 
congelation ; though the deprivation of air, obtained by boil- 
ing it, is fuch only as will barely enable it to admit a cooling 
of j 2 degrees. 
Other fluids may bear to be cooled much more below their 
proper point of confolidation. This is evidently the cafe in 
what Mr. Cavendish calls * the fpirituous congelation of 
acids. Mr. M c Nab’s nitrous acid bore to be cooled from 30 
to near 40 degrees below its freezing point -j~ ; and Mr. Keir’s 
vitriolic acid at the ftrength of eafieff freezing continued fluid 
at 29 0 , though its heat became 46T when it began to congeal 
How low quickfilver may be cooled has not yet been afcer- 
tained, but probably many degrees below - 40°. 
So many of the above-mentioned fads were obferved in the 
year 1783, that I then ventured to remark, that “ inde- 
“ pendently of thefe circumftances, neither ftirring, agita- 
“ tion, a current* of frefh air on the furface, nor the con- 
“ tad of any extraneous body not colder, would [necefla- 
“ rily] caufe the water to fhoot into ice, notwithftanding the 
“ repeated aflertions of authors to the contrary **.” Similar ex- 
periments, made in the courfe of the fucceeding winters, have 
confirmed in general the former refults, and furnifhed the 
materials of the preceding flieets. I am very fenfible, that the 
* Philofophical Tranfa&ions, Vol. LXXVI. p.261. 
f Ibid. p. 252. 
J Ibid. Vol. LXXVII. p. 2 J 9 * 
** Ibid. Vol. LXXIII. p. 358. 
Vol. LXXVIII. 
U 
lubjed 
