Experiments on freezing Mixtures . 261 
really congealed, the frozen part of the acid muft have been 
much weaker than the reft, if not mere water. Accordingly, 
during the melting of the undecanted part, the frozen particles 
fwam at top. Mr. M c Nab added fnow to a little of the de- 
canted liquor, but it did not diflblve, and no increafe of cold 
was produced. 
19. From thefe experiments it appears, that fpirit of nitre is 
fubjeft to two kinds of congelation, which we may call the 
aqueous and fpirituous ; as in the flrft it is chiefly, if not in- 
tirely, the watery part which freezes, and in the latter the 
fpirit itfelf. Accordingly, when the fpirit is cooled to the point 
of aqueous congelation, it has no tendency to diflblve fnow and 
produce cold thereby, but on the contrary is difpofed to part 
with its own water ; whereas its tendency to diflblve fnow and 
produce cold, is by no means deftroyed by being cooled to the 
point of fpirituous congelation, or even by being actually con- 
gealed, When the acid is exceflively dilute, the point of 
aqueous congelation muft neceflarily be very little below that 
of freezing water ; when the ftrength is ,21, it is at — 1 7 0 , 
and at the ftrength of ,243, it feems, from Art. 16. to be at 
— 44°J. Spirit of nitre, of the foregoing degrees of ftrength, 
is liable only to the aqueous congelation, and it is only in 
greater ftrength s that the fpirituous congelation can take place. 
This feems to be performed with the leaft degree of cold, when 
the ftrength is ,411,. in which cafe the freezing point is at 
— i°|, When the acid is either ftrongeror weaker, it requires ^ 
a greater degree of cold ; and in both cafes the frozen part- 
feems to approach nearer to the ftrength of ,41 1 than the un^- 
frozen part; it certainly does fo, when the ftrength is greater 
than ,411, and there is little doubt but what it does fo in the 
other, cafe. At the ftrength of ,54 the point of fpirituous- 
congelations 
