SAPONIFIABLE OILS, FATS AND WAXES

183

If ifc is desired to determine insoluble and soluble acids the solution which
has just been used for the determination of saponification number may be
used for this purpose. For detailed directions refer to other works on this
subject.1
Reichert Number and Reichert-Meissl Number.—There is no
sharp line of division between the fatty acids volatile with steam
and those not volatile and it is not possible to effect more than a
very approximate separation by a method of distillation unless
this is continued for a very long time. On the other hand
fairly constant proportions of acids may be distilled if the method
is rigidly standardized. In this way figures may be obtained
that have a value in identifying certain oils and fats. The
determination is made chiefly in the examination of butter and
its substitutes. Pure butter contains volatile acids to the extent
of nearly 10 per cent of the total fatty acids.
The saturated acids to and including capric acid are the only
ones of the series that may be distilled without decomposition.
They are therefore known as "volatile" acids while the higher
acids (above lauric) decompose when distilled and are therefore
called '"non-volatile." Lauric acid distills with steam but is
slightly decomposed. Although the volatile acids boil at tem-
peratures higher than 100° they can be distilled with steam.
The method proposed by Reichert and modified by Meissl has
been extensively adopted. It should be understood that neither
method gives the correct per cent of volatile acids but simply the
proportion that will be distilled under certain stated conditions.
The Reichert Number is the number of cubic centimeters of tenth-
normal base required to titrate the adds obtained from 2.5 gm of oil
or fat by Reichert's distillation process. The Reichert-Meinsl
number is the same as the Reichert number except that 5 gm of
oil or fat is used. The Reichert-Meissl number is not exactly
double the Reichert number.
The Reichert-Meissl number of most oils, fats and waxee in
less than 1 and the determination will be of little service in
identifying these oils. The following oils are exceptional in
this respect.
i LEWKOWITSCH, "Chemical Technology and Analysis of Oils, Fats and
Waxes;" Assoc. Off. Agri. Chemists, "Methods of Analysis;" MAHIN,
'' Quantitative Analysis.''