depression of freezing-point can be found from the
equations :
rise in boiling-point ___
, depression of freezing-point __
an ^ _c
where m is the true molecular weight of the dissolved substance. If, on the contrary, the pressure is i times too large, as is the case with electrolytes, then the rise in boiling-point and the depression of freezing-point become equally exceptional and lead to results for the molecular weight which are i times too small.
The value found for m being evidently inversely pro- portional to the number of particles of matter in solution, we are again led to the equation
l s * 1 as 1 + (n — 1) X
N v '
and thus we have new methods of determining x — by means of the boiling-point and the freezing-point.
As the value of x is independent of the method by
tainingw gram-molecules of substance dissolved in g grams of solvent, have been given.
We know that *—/- = m* and that A = b'- (A being the rise
in the boiling-point).
And Arrh6nius has shown that —
p = /&S=-BTS. Now, substituting the values of - of the two first equations in this last, we get
P = J s-J- B T S = ", B TS. /M B ;
N.B. — p denotes the osmotic pressure ; m is the molecular weight (gaseous) of the solvent; t is the boiling-point of the solvent in absolute degrees.
For cryoecopic phenomena analogous relations can be established.
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