A Manual of the Chemistry of the Carbon Compounds

THE CARBON COMPOUNDS. 45
fatty acids, the lower members are miscible with water in all proportions,
whilst those following next dissolve only in certain proportions,
and the highest are insoluble in water. All hydrocarbons are
either very sparingly soluble, or quite insoluble in water; by replacing
ia them a part of the hydrogen by hydroxyl or oxygen, compounds
are formed which are more soluble, generally in proportion to the
more oxygen they contain. Thus butyl C4H,0 is almost insoluble in
water, butyl alcohol C4H9(OH)2 readily soluble, and butylene alcohol
C4H,,(OH) mixes with water in all proportions. Succinic acid C4HBO4
is more soluble than butyric acid" Tr " - J —"' -"" r ' " n !4H8O2, and malic acid C4H006 " is
very deliquescent.
PEAOTIONAL DISTILLATION.
This is an operation often made use of in the preparation of pure
carbon-compounds to isolate the different constituents contained in
a mixture of volatile bodies. On subjecting a mixture of two
liquids to distillation, at the beginning a large proportion of the more
volatile body comes over; but the boiling-point rises continually, and
more and more of the vapoxir of the less volatile compound mixes with
that of the more volatile. It is only when the difference between the
boiling-points of the two bodies is very considerable that it is possible
to effect an almost complete separation Toy one distillation. In this
case, when the operation is carried on very slowly, the more volatile
body distils at a nearly constant temperature; and as soon as all of it
has passed over, the thermometer rises rapidly to the boiling-point of
the less volatile compound. But in most cases it is impossible even
to approach a separation by only one distillation. By collecting separately
the portions distilling between certain intervals of temperature,
say between each 5°, or 10°, the first wiH consist chiefly of the lower
boiling body, and the last of the less volatile substance; whilst the
composition of the greatest portion boiling between these two approaches
more or leas to that of the original mixture.
The following example shows well how very imperfectly even bodies
whose boiling-points are not close together are separated by one
distillation. A mixture of 100 grams of ethyl alcohol (boiling-point
78 4°) and 1.00 grams of amyl alcohol (boiling-point 132°) was distilled
from a long-necked flask, and the distillate collected in 7 fractions,
the composition of which was found by optical analysis:—
Boiling-point....
Woiglitor fraction . . .
Pot cost, ot Ethyl Alcohol
Poi-cont. of AinylAlcoliol
80°~90° 0O 6 -W0" ioo»-no° noM*o» 129MS0" i3o»-m« 131MS2"
47
88'1
w-o
100-0
45
8S 18
100
29
01-5
386
IOO-O
M
58-1
470
100-0
18
18*
Sl-8
100-0
ii
05-5
100O
30
0-2
9U 3
100-0