with
ammonia in excess, where it separates into a lower aqueous layer of
ammonium sulphate solution and an oil, consisting of crude pyridine.
This is purified by fractionation in iron stills and distillation over
caustic soda. Most of it is used for denaturing spirit of wine in
Germany, for which purpose it is required to contain 90% of bases
boiling up to 140 deg. C. (see ALCOHOL).

[Illustration: FIG. 4.--Benzol Still (elevation).]

_Working up of the Middle-Oil Fraction (Carbolic Oil
Fraction)._--Owing to its great percentage of naphthalene (about 40%)
this fraction is solid or semi-solid at ordinary temperatures. Its
specific gravity is about 1.2; its colour may vary from light yellow
to dark brown or black. In the latter case it must be re-distilled
before further treatment. On cooling down, about four-fifths of the
naphthalene crystallizes out on standing from three to ten days. The
crystals are freed from the mother oils by draining and cold or hot
pressing; they are then washed at 100 deg. C. with concentrated
sulphuric acid, afterwards with water and re-distilled or sublimed.
About 10,000 tons of naphthalene are used annually in Germany, mostly
for the manufacture of many azo-colours and of synthetic indigo.

The oils drained from the crude naphthalene are re-distilled and
worked for carbolic acid and its isomers. For this purpose the oil is
washed with a solution of caustic soda, of specific gravity 1.1; the
solution thus obtained is treated with sulphuric acid or with carbon
dioxide, and the crude phenols now separated are fractionated in a
similar manner as is done in the case of crude benzol. The pure phenol
crystallizes out and is again distilled in iron stills with a silver
head and cooling worm; the remaining oils, consisting mainly of
cresols, are sold as "liquid carbolic acid" or under other names.

Most of the oil which passes as the "creosote-oil fraction" is sold in
the crude state for the purpose of pickling timber. It is at the
ordinary temperature a semi-solid mixture of about 20% crystallized
hydrocarbons (chiefly naphthalene), and 80% of a dark brown, nauseous
smelling oil, of 1.04 spec. grav., and boiling between 200 deg. and
300 deg. C. The liquid portion contains phenols, bases, and a great
number of hydrocarbons. Sometimes it is redistilled, when most of the
naphthalene passes over in the first fraction, between 180