is poured into another 12-l. flask, and both halves are warmed
on the steam bath to 60-70'0, until the color becomes quite dark
(thirty to sixty minutes). Sufficient hydrochloric acid (300-400 cc.)
is now added to each flask to make the solutions acid to litmus.
The heating is continued and the color gradually becomes lighter until,
after four to six hours, the solutions have become nearly colorless;
they may be heated overnight, if desired.

To the hot solutions are now added about one-third of their volume
of concentrated hydrochloric acid (2 l. to each portion) and the
mixtures cooled, first in running water, then in a freezing mixture,
to 0'0. The phenylhydrazine hydrochloride precipitates in the form
of slightly yellowish or pinkish crystals which may be filtered
off and dried.

The free base is liberated by adding to the phenylhydrazine
hydrochloride 1 l. of a 25 per cent solution of sodium hydroxide.
The phenylhydrazine separates and is taken up with benzene
(two 300-cc. portions). The combined extractions are well dried
with 200 g. of solid sodium hydroxide, poured off, and distilled.
Most of the benzene may be distilled under ordinary pressure,
and the remainder, and any low-boiling impurities,
under diminished pressure. The pure phenylhydrazine boils
at 137-138'0/18 mm., and is obtained as a pale-yellow liquid.
It can be crystallized on cooling in an ice bath; the crystals
melt at 230. The crude phenylhydrazine from two lots of aniline
(744 g.) is best distilled at one time and gives 695-725 g.
of pure product (80-84 per cent of the theoretical amount).