also cooled to 0'0, are run in during five minutes. The mixture
is treated with 500 g. more of cracked ice, and a cold solution
(0'0) of 290 g. of technical sodium nitrite dissolved in 600 cc.
of water are allowed to run in slowly (twenty to thirty minutes)
from a dropping funnel, the end of which is drawn to a small tip,
and reaches nearly to the bottom of the flask. During this addition,
the stirrer is operated rather vigorously, and the temperature is
kept as near 0'0 as possible by the frequent addition of cracked ice
(about 1 kg).

In the meantime, a sodium sulfite solution is prepared by dissolving
890 g. of sodium hydroxide, of about 90 per cent purity, in about 1 l.
of water and then diluting to 6 l. A few drops of phenolphthalein
solution are added and sulfur dioxide passed in, first until an acid
reaction is indicated and then for two or three minutes longer.
During the addition of the sulfur dioxide, the solution is cooled
with running water. On account of the strong alkaline solution,
the original color produced by the phenolphthalein is very faint,
but this slowly increases until it becomes deep just before the acid
point is reached. It is best to remove a small sample of the liquid
from time to time, dilute with three or four volumes of water
and add a drop more of phenolphthalein.

The sodium sulfite solution is placed in a 12-l. flask and cooled
to about 5'0. Approximately 500 g. of cracked ice are added, and then,
with mechanical stirring, the diazonium salt solution is run in as
rapidly as possible. The mixture becomes a bright orange-red. The
flask is now warmed to about 20'0 on a steam bath, until the solid
sodium sulfite, which has separated while cooling, redissolves.
The total amount of liquid is now about 10 l. One-half of this