SAPONIFIABLE OILS, FATS AND WAXES

195

serious. The problems ,of the analyst are now increased many
fold by the large development of the industry of hydrogenation
of liquid oils.
It has been seen that the most important difference between oils
and fats lies in the larger proportion of olein in the former and of
stearin and palmitin in the latter. Olein differs from stearin
only in that it contains one unsaturated double bond in each
oleic acid residue; the problem of saturating this group by the
insertion of hydrogen, thus forming stearin, is one that has occu-
pied the attention of chemists for many years. At the present
time the hydrogenation of the cheaper liquid oils (e.g., cottonseed,
corn and peanut) to form edible fats is an industry that has at-
tained large proportions. While this process changes liquid
oils to solid fats, it will also make a corresponding change in any
analytical constants or tests that depend upon the degree of
unsaturation, as well as in the physical properties of the oil.
Linolin, linolenin and glycerides of still less saturated acids will
be changed to stearin. Consequently the halogen absorption
number, drying properties, specific gravity, refractive index and
temperature reactions will be materially altered, as will also the
odor and the general appearance and consistency. It has been
stated that fish oils probably owe their characteristic odor to
glycerides containing highly unsaturated acids, while the some-
what similar odor of linseed oil is due to glycerides of linolic and
linolenic acids. It is interesting to note that these odors are
entirely lost through hydrogenation and that the fats so produced
are no longer recognizable by tests depending upon unsaturation.
Many special tests for other oils, such as the Halphen reaction
for cottonseed oil and the Renard test for sesame oil, fail in the
hydrogenated product.
From one standpoint it might appear that the determination
of what oils originally formed the raw materials for the " hard-
ened^77 product is not a necessary one for the analyst to solve,
since the properties of the finished product are, after all, the ones
that have the chief practical interest for us. Yet it may some-
times happen that the identity of the original oil or the proof
that a hydrogenating process has been employed may have a
legal or other significance; the development of a series of suitable
tests is therefore very desirable.