ent. on the oil.

In this method, it is very frequently most difficult to obtain a
distinct separation of ether and aqueous soap solution--an intermediate
layer of emulsion remaining even after prolonged standing, and various
expedients have been recommended to overcome this, such as addition of
alcohol (when petroleum ether is used), glycerine, more ether, water, or
caustic potash solution, or by rotatory agitation.

A better plan is to proceed as in the method above described as far as
dissolving the resulting soap in 200 c.c. water, and then boil for
twenty or thirty minutes. Slightly cool and acidify with dilute
sulphuric acid (1 to 3), boil until the fatty acids are clear, wash with
hot water free from mineral acid, and dry by filtering through a hot
water funnel.

Two grammes of the fatty acids are now dissolved in neutral alcohol
saturated with some solvent, preferably a light fraction of benzoline, a
quantity of the solvent added to take up the unsaponifiable matter, and
the whole boiled under a reflux condenser. After cooling, the liquid is
titrated with N/2 aqueous KOH solution, using phenol-phthalein as
indicator, this figure giving the amount of the total fatty acids
present. The whole is then poured into a separating funnel, when
separation immediately takes place. The alcoholic layer is withdrawn,
the benzoline washed with warm water (about 32 deg. C.) followed by neutral
alcohol (previously saturated with the solvent), and transferred to a
tared flask, which is attached to a condenser, and the benzoline
distilled off. The last traces of solvent remaining in the flask are
removed by gently warming in the water-oven, and the flask cooled and
weighed, thus giving the amount of unsaponifiable matter.

_Constitution of the Unsaponifiable Matter._--Unsaponifiable matter may
consist of cholesterol, phytosterol, solid alcohols (cetyl and ceryl
alcohols), or hydrocarbons (mineral oil). Cholesterol is frequently
found in animal fats, and phytosterol is a very similar substance
present in vegetable fats. Solid alcohols occur naturally in sperm oil,
but hydrocarbons, which may be generally recognised by the fluorescence
or bloom they give to the oil, are not natural constituents of animal or
vegetable oils and fats.

The presence of cholesterol and phytosterol may be detected by
dissolving a small portion of the unsaponifiable matter in acetic
anhydride, and adding a drop of the solution to one drop of 50 per ce