xed fatty and rosin acids, and the
rosin content, a fairly good idea of the constitution of the soap may be
deduced.

The titre, iodine number, and saponification equivalent are determined
in exactly the same manner as described under Fats and Oils.

The presence of rosin may be detected by the Liebermann-Storch reaction,
which consists in dissolving a small quantity of the fatty acids in
acetic anhydride, and adding to a few drops of this solution 1 drop of
50 per cent. sulphuric acid. A violet coloration is produced with rosin
acids. The amount of rosin may be estimated by the method devised by
Twitchell (_Journ. Soc. Chem. Ind._, 1891, 804) which is carried out
thus:--

Two grammes of the mixed fatty and rosin acids are dissolved in 20 c.c.
absolute alcohol, and dry hydrochloric acid gas passed through until no
more is absorbed, the flask being kept cool by means of cold water to
prevent the rosin acids being acted upon. The flask, after
disconnecting, is allowed to stand one hour to ensure complete
combination, when its contents are transferred to a Philips' beaker,
well washed out with water so that the volume is increased about five
times, and boiled until the acid solution is clear, a fragment of
granulated zinc being added to prevent bumping. The heat is removed, and
the liquid allowed to cool, when it is poured into a separator, and the
beaker thoroughly rinsed out with ether. After shaking, the acid liquor
is withdrawn, and the ethereal layer washed with water until free from
acid. Fifty c.c. neutral alcohol are added, and the solution titrated
with N/1 KOH or NaOH solution, the percentage of rosin being calculated
from its combining weight. Twitchell suggests 346 as the combining
weight of rosin, but 330 is a closer approximation.

The method may be also carried out gravimetrically, in which case
petroleum ether, boiling at 74 deg. C. is used for washing out the beaker
into the separator. The acid liquor is run off, and the petroleum ether
layer washed first with water and then with a solution of 1/2 gramme KOH
and 5 c.c. alcohol in 50 c.c. water, and agitated. The rosin is thus
saponified and separated. The resinate solution is withdrawn, acidified,
and the resin acids collected, dried and weighed.

_Halphen's Reaction._--This is a special test to determine the presence
or absence of cotton-seed oil fatty acids in mixtures. Equal parts of
the fatty acids, amyl alcohol, and a 1 per cent. solution of sulp