uspended with its bulb completely immersed in the oil. With anise and
fennel, the oil is cooled down with constant stirring until it just
starts crystallising, when the stirring is interrupted, and the maximum
temperature to which the mercury rises noted. This is the solidifying
point.

In the case of otto of rose, the otto is continually stirred, and the
point at which the first crystal is observed is usually regarded as the
congealing point.

_Melting Point._--This is best determined by melting some of the solid
oil, or crystals, and sucking a small quantity up into a capillary tube,
which is then attached by a rubber band to the bulb of the thermometer,
immersed in a suitable bath (water, glycerine, oil, etc.) and the
temperature of the bath gradually raised until the substance in the tube
is sufficiently melted to rise to the surface, the temperature at which
this takes place being the melting point.

The melting point of otto of rose is usually taken in a similar tube to
the setting point, and is considered to be the point at which the last
crystal disappears.

_Iodine Absorption._--In the authors' opinion, this is of some value in
conjunction with other data in judging of the purity of otto of rose. It
is determined by Huebl's process as described under Fats and Oils, except
that only 0.1 to 0.2 gramme is taken, and instead of 10 c.c. of
chloroform, 10 c.c. of pure alcohol are added. The rest of the process
is identical.

SOAP.

In the analysis of soap, it is a matter of considerable importance that
all the determinations should be made on a uniform and average sample of
the soap, otherwise very misleading and unreliable figures are obtained.
Soap very rapidly loses its moisture on the surface, while the interior
of the bar or cake may be comparatively moist, and the best way is to
carefully remove the outer edges and take the portions for analysis from
the centre. In the case of a household or unmilled toilet soap, it is
imperative that the quantities for analysis should all be weighed out as
quickly after each other as possible.

_Fatty Acids._--Five grammes of the soap are rapidly weighed into a
small beaker, distilled water added, and the beaker heated on the water
bath until the soap is dissolved.

A slight excess of mineral acid is now added, and the whole heated until
the separated fatty acids are perfectly clear, when they are collected
on a tared filter paper, well washed with hot water and dr