(4) Castor oil possesses a very constant iodine degree —
from 84-0 to 847, and is distinguished from all other oils and
fats by this figure, by the points of fusion and solidification
of its. fatty acids (13° and 3° C. respectively), by the saponifi-
cation test and by its ready solubility in alcohol and acetic
acid.
(5) In' twenty samples of olive oil, collected fi:om various
sources, the absorption of iodine varied only within 3 degrees.
The addition of about 5 per cent, of a drying oil, or 15 per
cent' of cottonseed, sesamd, arachis, or rape-seed, may be
established with certainty.
(6) Animal fats, as is well known, are liable to alteration in
respect to their consistency and proportion of oleic acid, owing
to variety, age, and food of the animal whence derived. In
the case of butter-fat the absorption of iodine varies between
the limits of 26 and 35.
(7) 'When the nature of two fats in a mixture is known
their proportion may be determined approximately by the
formula : —

100 (I— k)

m—n

■Where x ^ the percentage of one fat.
y =1 „ „ the other.
I =: iodine degree of the mixture.
m= „ „ „ fat X.
«= « „ .. „ y.
(8) The age of a fat, so long as great alterations have not
taken place, does not affect its iodine absorption. If, how-
ever, an oil has become rancid and contains free acid, .the
iodine degree suffers considerable depression.
PART VI.
MATERIALS USED IN THE MANUFACTURE OF
RAIL WA Y GREASE.
