of cracked ice are added during the course of five minutes.
The dimethylaminobenzaldehyde generally separates gradually
in fifteen to twenty minutes, but in some cases does not.
If the precipitate does not form, the solution is placed
in a refrigerator for a few hours or overnight. The mixture is
filtered with suction and washed at least ten times with 300 cc.
of water. The precipitate is sucked as dry as possible for fifteen
to thirty minutes.

The slightly moist aldehyde is distilled under diminished
pressure from an oil bath, by means of a 1-l. Claisen flask.
A small amount of water comes over first, then the thermometer
rises rapidly to the boiling point of the aldehyde (180'0/22 mm.).
In changing receivers between the water fraction and the aldehyde,
care should be taken to keep the side-arm of the distilling
flask warm; otherwise, on starting the distillation again,
the aldehyde will solidify in the side-arm and cause trouble.
It is advisable not to collect the very last portion of the distillate
with the main portion, as the former is frequently quite red.
This is best added to crude material from another run. The main
distillate is dissolved in 100 cc. of alcohol in a 2-l. beaker,
then 1000 cc. of water are gradually added with vigorous mechanical
stirring to prevent lumping. The aldehyde separates, and is
filtered with suction. The product, when dry, weighs 125-130 g.
(56-59 per cent of the theoretical amount), and melts at 73'0.

The aldehyde prepared in this way is in the form of small
granular crystals, which vary in different runs from a flesh color
to a lemon yellow. For practically all purposes, this slightly
colored product is entirely satisfactory and is essentially pure,