The Handbook of Soap Manufacture | Page 5

or entirely to be explained by the
power which it has of emulsifying oily substances, of wetting and
penetrating into oily textures, and of lubricating texture and impurities
so that these may be removed easily. It is thought that all these
properties may be explained by taking into account the low cohesion of
the soap solutions, and their strong attraction or affinity to oily matter,
which together cause the low surface tension between soap solution and
oil.
CHAPTER II.
CONSTITUTION OF OILS AND FATS, AND THEIR
SAPONIFICATION.
Researches of Chevreul and Berthelot--Mixed Glycerides--Modern

Theories of Saponification--Hydrolysis accelerated by (1) Heat or
Electricity, (2) Ferments; Castor-seed Ferment, Steapsin, Emulsin, and
(3) Chemical Reagents; Sulphuric Acid, Twitchell's Reagent,
Hydrochloric Acid, Lime, Magnesia, Zinc Oxide, Soda and Potash.
The term oil is of very wide significance, being applied to substances
of vastly different natures, both organic and inorganic, but so far as
soap-making materials are concerned, it may be restricted almost
entirely to the products derived from animal and vegetable sources,
though many attempts have been made during the last few years to also
utilise mineral oils for the preparation of soap. Fats readily become oils
on heating beyond their melting points, and may be regarded as frozen
oils.
Although Scheele in 1779 discovered that in the preparation of lead
plaster glycerol is liberated, soap at that time was regarded as a mere
mechanical mixture, and the constitution of oils and fats was not
properly understood. It was Chevreul who showed that the manufacture
of soap involved a definite chemical decomposition of the oil or fat into
fatty acid and glycerol, the fatty acid combining with soda, potash, or
other base, to form the soap, and the glycerol remaining free. The
reactions with stearin and palmitin (of which tallow chiefly consists)
and with olein (found largely in olive and cotton-seed oils) are as
follows:--
CH{2}OOC{18}H{35} CH{2}OH | | CHOOC{18}H{35} + 3NaOH =
3NaOOC{18}H{35} + CHOH | | CH{2}OOC{18}H{35} CH{2}OH
stearin sodium sodium glycerol hydroxide stearate
CH{2}OOC{16}H{31} CH{2}OH | | CHOOC{16}H{31} + 3NaOH =
3NaOOC{16}H{31} + CHOH | | CH{2}OOC{16}H{31} CH{2}OH
palmitin sodium sodium glycerol hydroxide palmitate
CH{2}OOC{18}H{33} CH{2}OH | | CHOOC{18}H{33} + 3NaOH =
3NaOOC{18}H{33} + CHOH | | CH{2}OOC{18}H{33} CH{2}OH

olein sodium sodium glycerol hydroxide oleate
Berthelot subsequently confirmed Chevreul's investigations by directly
synthesising the fats from fatty acids and glycerol, the method he
adopted consisting in heating the fatty acids with glycerol in sealed
tubes. Thus, for example:--
3C{18}H{35}O{2}H + C{3}H{5}(OH){3} =
C{3}H{5}(C{18}H{35}O{2}){3} stearic acid glycerol tristearin
Since glycerol is a trihydric alcohol, i.e., contains three hydroxyl (OH)
groups, the hydrogen atoms of which are displaceable by acid radicles,
the above reaction may be supposed to take place in three stages. Thus,
we may have:--
(1) C{18}H{35}O{2}H + C{3}H{5}(OH){3} =
C{3}H{5}(OH){2}C{18}H{35}O{2} + H{2}O monostearin
(2) C{18}H{35}O{2}H + C{3}H{5}(OH){2}C{18}H{35}O{2} =
C{3}H{5}(OH)(C{18}H{35}O{2}){2} + H{2}O distearin
(3) C{18}H{35}O{2}H + C{3}H{5}(OH)(C{18}H{35}O{2}){2} =
C{3}H{5}(C{18}H{35}O{2}){3} + H{2}O tristearin
There are two possible forms of monoglyceride and diglyceride,
according to the relative position of the acid radicle, these being
termed alpha and beta respectively, and represented by the following
formulæ, where R denotes the acid radicle:--
Monoglyceride:--
CH{2}OR CH{2}OH | | (alpha) CHOH and (beta) CHOR | |
CH{2}OH CH{2}OH
Diglyceride:--
CH{2}OR CH{2}OR | | (alpha) CHOH and (beta) CHOR | | CH
{2}OR
CH{2}OH

According to the relative proportions of fatty acid and glycerol used,
and the temperature to which they were heated, Berthelot succeeded in
preparing mono-, di- and triglycerides of various fatty acids.
Practically all the oils and fats used in soap-making consist of mixtures
of these compounds of glycerol with fatty acids, which invariably occur
in nature in the form of triglycerides.
It was formerly considered that the three acid radicles in any naturally
occurring glyceride were identical, corresponding to the formula--
CH{2}OR | CHOR | CH{2}OR
where R denotes the acid radicle. Recent work, however, has shown the
existence of several so-called mixed glycerides, in which the hydroxyls
of the same molecule of glycerol are displaced by two or sometimes
three different acid radicles.
The first mixed glyceride to be discovered was oleodistearin,
C{3}H{5}(OC{18}H{35}O)(OC{18}H{35}O){2}, obtained by Heise
in 1896 Mkani fat. Hansen has since found that tallow contains
oleodipalmitin, from C{3}H{5}(OC{18}H{35}O)(OC{16}H{31}O),
stearodipalmitin, C{3}H{5}(OC{18}H{35}O)(OC{16}H{31}O),
oleopalmitostearin,
C{3}H{5}(OC{18}H{33}O)(OC{16}H{31}O)(OC{18}H{35}O) and
palmitodistearin, CH(OC{16}H{31}O)(OC{18}H{35}O){2}, the latter
of which has also been obtained by Kreis and Hafner from lard, while
Holde and Stange have shown that olive oil contains from 1 to 2 per
cent. of oleodidaturin,
C{3}H{5}(OC{18}H{33}O)(OC{17}H{33}O){2}, and Hehner and
Mitchell have obtained indications of mixed glycerides in linseed oil
(which they consider contains a compound of glycerol with two
radicles of linolenic acid and one radicle of oleic acid), also in cod-liver,
cod, whale and shark oils.
In some cases the fatty acids are combined with other bases than
glycerol. As examples may be cited beeswax, containing myricin or
myricyl palmitate, and