as can be judged by the melting point. For reagent purposes it
is desirable to remove the color completely, particularly since
the product obtained as just described has a tendency to take
on a reddish tinge on exposure to light. Further purification can
be accomplished by dissolving the aldehyde (it dissolves slowly)
in dilute hydrochloric acid (1 part of concentrated acid, sp. gr.
1.19, to 6 parts of water), 125 g. of aldehyde requiring 700 cc.
of the acid. The solution is placed in a jar and diluted with
half its volume of water, and dilute sodium hydroxide solution
(15-20 per cent) is added slowly with mechanical stirring.
At the beginning, the aldehyde comes down slightly colored.
After about 10 to 30 g. are precipitated, however, the product
appears white; this point can be readily seen. The first precipitate
is filtered off and added to the next run of crude material,
or fractionally precipitated again from hydrochloric acid.
The rest of the aldehyde is now precipitated by means of more sodium
hydroxide solution, and comes down almost white. At the very end of
the neutralization, particularly if the original product was quite yellow,
the last 4 to 5 g. of aldehyde should be precipitated separately,
as they are inclined to be slightly colored. If too much alkali is
added towards the end of the neutralization, a brown color appears,
but the addition of a little hydrochloric acid will destroy this color.
The main portion of the precipitate is filtered and dried; it weighs
95-100 g., m. p. 73'0. The succeeding runs yield 115-128 g.
of finished product, on account of the extra crude material obtained
from the distillation and reprecipitation of the previous run. 2. Notes

The aldehyde that is obtained without reprecipitation
gradually takes on a pinkish tinge on exposure to light.
After the reprecipitation, however, this characteristic disappears.