Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

412 CHOLIC ACID
slaughter-house and a small portion is used for isolating the most
important of the conjugated acids of the bile, namely, glycocholic add.
In a 750 c.c. separating funnel 250 c.c. of the bile are vigorously
shaken with 150 c.c. of ether ; then 25 c.c. of 4iV-sulphuric acid are
added, and the whole is at once shaken without interruption for
three minutes. After a rather long time-—usually by the next day-—
the glycocholic acid has separated in snow-white needles which form
a voluminous mass at the liquid interface. The crystals are collected
at the pump and washed with a little water and then with ether.
For purification they are dissolved in very little hot alcohol, and
water is added to the solution until turbidity appears.
Occasionally the glycocholic acid does not crystallise from the
acidified bile until several days have elapsed. Frequent shaking has
an accelerating effect. With summer bile the experiment often fails
because the components of such bile crystallise with more difficulty.
As far as experience goes, this has never been the case in winter.
Cholic Acid.-—Commercial potassium hydroxide (200 g.) is added
to fresh ox bile (2 1.) and the mixture is boiled under reflux for
eighteen hours. It is best to use a copper or iron flask, but a large
round-bottomed flask of Jena glass heated on a sand bath may also
be employed. After the alkaline liquid has cooled it is transferred to
a filter jar and made just acid to Congo paper by addition of hydrochloric
acid (1 part concentrated acid, 2 parts water) which is poured
in with constant stirring by means of a stout glass rod. The result
of the acidification is that the bile acids and the bile pigment (biliverdin)
are precipitated as a green resinous mass. At first this has the
consistency of dough, but after being left for twenty-four hours in the
salt solution it becomes harder, brittle, and crystalline. The hard
material is removed and broken up as far as possible with the fingers
under clean water in a basin. Then the crumbly mass is collected
at the pump and again washed well with water. The crude acids
must now be dried completely before further treatment. At least
eight days are necessary to accomplish this when the substance is
left exposed to the air in a thin layer on filter paper or wood. The
object is more rapidly achieved if the adherent water is removed
in a vacuum desiccator over concentrated sulphuric acid and solid
potassium hydroxide. Ultimately 100-110 g. of pale grey-green
substance, which can be powdered to a fine dust, are obtained.
In this condition it is transferred to a conical flask into which
absolute alcohol (a volume equivalent to two-thirds of the weight of