vogel_practical_ochem_3.pdf

10] THEORY OF GENERAL TECHNIQUE 21
temperature at which the solution just becomes homogeneous is taken
as the critical solution temperature. The same result is obtained by
observing the temperature at which the second phase appears. The water
content may then be deduced with the aid of the following table, and
checked, if desired, by a determination of the density (Section XI,2).
PUKIVY OF CH3OFI (%) C.S.T. a4o
100-0
99-80
99-65
99-50
99-35
99-05
98-G9
98-41
98-01
97-48
97-13
36-55°
37-90 !
38-95
40-05 |
41-00 i
43-00 j
45-00
46-25
48-05
50-15
51-10 j
0-79578
0-79634
0-79676
0-79718
0-79760
0-79845
0-79947
0-80026
0-80140
0-80292
0-80390
For ethyl alcohol, two volumes of dic?/cZohexyl * are mixed with one
volume of the alcohol, a thermometer is introduced, and the mixture
heated until it becomes clear. The solution is then slowly cooled, with
constant stirring, and the temperature is determined at which the opalescent
solution suddenly becomes turbid so that the immersed portion of
the mercury thread of the thermometer is no longer clearly visible. This
is the C.S.T. The water content may then be evaluated by reference to
the following table.
I
PURITY OF C2H6OH (%)
, 100-0 '
1 99-9
99 • 8
| 99-7
99-6
| 99-5
99-0
| 98-5
1
C.S.T.
23-4°
25-4
27-3
29-2
31-0
32-8
41-0
48-0
d 20 *
«4o
1 0-78934
0-78966
i 0-78997
0-79028
, 0-79059
1 0-79089
| 0-79243
1 0-79346
THEORY OF MELTING AND FREEZING
1,10. Melting point and vapour pressure. The melting point of a
crystalline solid is the temperature at which the solid begins to change
into liquid under a pressure of one atmosphere. For pure substances,
the change from the solid to the liquid state is quite sharp (within 0-5°),
hence the temperature is valuable for purposes of identification. Moreover,
the melting point is considerably influenced by the presence of other
* This may be prepared by the catalytic reduction of pure diphenyl (see Section 111,150).