}H_{22}(OH)COOH | 4-5 | Castor oil. |
-----------------------------------------------------------

This acid combines with two atoms of bromine or iodine, and is converted
by nitrous acid into the isomeric ricinelaidic acid, which melts at
52 deg.-53 deg. C. Pure ricinoleic acid, obtained from castor oil, is optically
active, its rotation being [alpha]_{d} +6 deg. 25'.

_Hydrolysis or Saponification of Oils and Fats._--The decomposition of a
triglyceride, brought about by caustic alkalies in the formation of
soap, though generally represented by the equation already given (pp. 6
and 7)--

C_{3}H_{5}(OR) + 3NaOH = C_{3}H_{5}(OH)_{3} + 3RONa,

is not by any means such a simple reaction.

In the first place, though in this equation no water appears, the
presence of the latter is found to be indispensable for saponification
to take place; in fact, the water must be regarded as actually
decomposing the oil or fat, caustic soda or potash merely acting as a
catalytic agent. Further, since in the glycerides there are three acid
radicles to be separated from glycerol, their saponification can be
supposed to take place in three successive stages, which are the
converse of the formation of mono- and diglycerides in the synthesis of
triglycerides from fatty acids and glycerine. Thus, the above equation
may be regarded as a summary of the following three:--

_ _
| OR | OH
(i.) C_{3}H_{5} | OR + NaOH = C_{3}H_{5} | OR + RONa
|_OR |_OR
_ _
| OH | OH
(ii.) C_{3}H_{5} | OR + NaOH = C_{3}H_{5} | OR + RONa
|_OR |_OH
_ _
| OH | 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,