��OUTLINES OF PHYSICAL CHEMISTRY
��100 grams of solvent, then the molecular depression c
will be - m, where m is the molecular weight of the dis-
V solved substance.
The value of c is independent of the nature of the substance dissolved, and varies only with the solvent employed.
For any given solvent, there are two methods of ascer- taining the value of c.
(1) We may determine the depression caused by the solution of a certain weight of a substance of known molecular weight in a certain amount of the solvent, and calculate c from the equation
c = -M
P
or (2) We may find c from varit Hoffs formula : l
C = : .
��in which t is the freezing point (in absolute degrees), and \ is the latent heat of fusion of one gram of the solvent.
The following table gives the values of c (experimental and calculated by varCt Hoff's formula) and of t and A.
�� �c
�C
�T
� �—
�experi-
�calcu-
�abso-
�A
� �mental
�lated
�lute
! Water .
�o
�79*4 calories (small)
�Acetic acid .
�Phenol .
�Formic acid .
� �Ethylene bromide
� �Benzene
�Naphthalene
�Nitro-benzene
i
��1 In his calculations varCt Hoff denotes by p the weight of substance dissolved in (100 — p) grams of solvent or 100 grams of solution. For dilute solutions the difference between this and BaoulVs system is very small.
�� �
