The Handbook of Soap Manufacture | Page 9

| OH (iii.) C{3}H{5} | OR + NaOH = C{3}H{5}
| OH + RONa |OH |OH
Geitel and Lewkowitsch, who have studied this question from the
physical and chemical point of view respectively, are of opinion that
when an oil or fat is saponified, these three reactions do actually occur
side by side, the soap-pan containing at the same time unsaponified
triglyceride, diglyceride, monoglyceride, glycerol and soap.
This theory is not accepted, however, by all investigators. Balbiano and
Marcusson doubt the validity of Lewkowitsch's conclusions, and Fanto,
experimenting on the saponification of olive oil with caustic potash, is
unable to detect the intermediate formation of any mono- or diglyceride,
and concludes that in homogeneous solution the saponification is
practically quadrimolecular. Kreeman, on the other hand, from
physico-chemical data, supports the view of Geitel and Lewkowitsch
that saponification is bimolecular, and though the evidence seems to
favour this theory, the matter cannot be regarded as yet definitely
settled.
Hydrolysis can be brought about by water alone, if sufficient time is
allowed, but as the process is extremely slow, it is customary in
practice to accelerate the reaction by the use of various methods, which
include (i.) the application of heat or electricity, (ii.) action of enzymes,
and (iii.) treatment with chemicals; the accelerating effect of the two
latter methods is due to their emulsifying power.
The most usual method adopted in the manufacture of soap is to
hydrolyse the fat or oil by caustic soda or potash, the fatty acids

liberated at the same time combining with the catalyst, i.e., soda or
potash, to form soap. Hitherto the other processes of hydrolysis have
been employed chiefly for the preparation of material for candles, for
which purpose complete separation of the glycerol in the first
hydrolysis is not essential, since the fatty matter is usually subjected to
a second treatment with sulphuric acid to increase the proportion of
solid fatty acids. The colour of the resulting fatty acids is also of no
importance, as they are always subjected to distillation.
During the last few years, however, there has been a growing attempt
to first separate the glycerol from the fatty acids, and then convert the
latter into soap by treatment with the carbonates of soda or potash,
which are of course considerably cheaper than the caustic alkalies, but
cannot be used in the actual saponification of a neutral fat. The two
processes chiefly used for this purpose are those in which the reaction
is brought about by enzymes or by Twitchell's reagent.
I. Application of Heat or Electricity.--Up to temperatures of 150° C. the
effect of water on oils and fats is very slight, but by passing
superheated steam through fatty matter heated to 200°-300° C. the
neutral glycerides are completely decomposed into glycerol and fatty
acids according to the equation--
C{3}H{5}(OR){3} + 3H.OH = C{3}H{5}(OH){3} + 3ROH.
The fatty acids and glycerol formed distil over with the excess of steam,
and by arranging a series of condensers, the former, which condense
first, are obtained almost alone in the earlier ones, and an aqueous
solution of glycerine in the later ones. This method of preparation of
fatty acids is extensively used in France for the production of stearine
for candle-manufacture, but the resulting product is liable to be dark
coloured, and to yield a dark soap. To expose the acids to heat for a
minimum of time, and so prevent discoloration, Mannig has patented
(Germ. Pat. 160,111) a process whereby steam under a pressure of 8 to
10 atmospheres is projected against a baffle plate mounted in a closed
vessel, where it mixes with the fat or oil in the form of a spray, the rate
of hydrolysis being thereby, it is claimed, much increased.

Simpson (Fr. Pat. 364,587) has attempted to accelerate further the
decomposition by subjecting oils or fats to the simultaneous action of
heat and electricity. Superheated steam is passed into the oil, in which
are immersed the two electrodes connected with a dynamo or battery,
the temperature not being allowed to exceed 270° C.
II. Action of Enzymes.--It was discovered by Muntz in 1871 (Annales
de Chemie, xxii.) that during germination of castor seeds a quantity of
fatty acid was developed in the seeds, which he suggested might be due
to the decomposition of the oil by the embryo acting as a ferment.
Schutzenberger in 1876 showed that when castor seeds are steeped in
water, fatty acids and glycerol are liberated, and attributed this to the
hydrolytic action of an enzyme present in the seeds. No evidence of the
existence of such a ferment was adduced, however, till 1890, when
Green (Roy. Soc. Proc., 48, 370) definitely proved the presence in the
seeds of a ferment capable of splitting up the oil into fatty acid and
glycerol.
The first experimenters