n the soap pan, had the bulk been used without examination. After
observing the appearance, colour, and odour of the sample, noting any
characteristic feature, the following physical and chemical data should
be determined.

_Specific Gravity at 15 deg. C._ This may be taken by means of a Westphal
balance, or by using a picnometer of either the ordinary gravity bottle
shape, with perforated stopper, or the Sprengel U-tube. The picnometer
should be calibrated with distilled water at 15 deg. C. The specific gravity
of solid fats may be taken at an elevated temperature, preferably that
of a boiling water bath.

_Free acidity_ is estimated by weighing out from 2 to 5 grammes of the
fat or oil, dissolving in neutral alcohol (purified methylated spirit)
with gentle heat, and titrating with a standard aqueous or alcoholic
solution of caustic soda or potash, using phenol-phthalein as indicator.

The contents of the flask are well shaken after each addition of alkali,
and the reaction is complete when the slight excess of alkali causes a
permanent pink coloration with the indicator. The standard alkali may be
N/2, N/5, or N/10.

It is usual to calculate the result in terms of oleic acid (1 c.c. N/10
alkali = 0.0282 gramme oleic acid), and express in percentage on the fat
or oil.

_Example._--1.8976 grammes were taken, and required 5.2 c.c. of N/10 KOH
solution for neutralisation.

5.2 x 0.0282 x 100
------------------ = 7.72 per cent. free fatty acids,
1.8976 expressed as oleic acid.

The free acidity is sometimes expressed as _acid value_, which is the
amount of KOH in milligrammes necessary to neutralise the free acid in 1
gramme of fat or oil.

In the above example:--

5.2 x 5.61
---------- = 15.3 acid value.
1.8976

The _saponification equivalent_ is determined by weighing 2-4 grammes of
fat or oil into a wide-necked flask (about 250 c.c. capacity), adding 30
c.c. neutral alcohol, and warming under a reflux condenser on a steam or
water-bath. When boiling, the flask is disconnected, 50 c.c. of an
approximately semi-normal alcoholic potash solution carefully added from
a burette, together with a few drops of phenol-phthalein solution, and
the boiling under a reflux condenser continued, with frequent agitation,
until saponification is complete (usually from 30-60 minutes) which is
indicated by the absence of fatty globules. The exce