TNT: Trinitrotoluenes and Mono and Dinitrotoluenes

THE MANUFACTURE OF TNT 43
nitrating* acids. Thus, the TNT in solution in the
spent acid is reclaimed, so the percentage dissolved does
not matter.
Even after this separation of the spent acid, there
still remains a considerable amount of acid in the TNT.
In order to obtain a marketable product, this acid must
all be washed out. To perform this operation, the
TNT is blown from the separating pan or, if the separation
was made in the nitrator, from the nitrator to the
washing tanks. The washing is accomplished by means
of hot water (85 to 90° C.) Seven or eight changes of
water are necessary for the complete removal of the
acid.
The washing of TNT was originally for the sole purpose
of removing the acid and rendering the TNT neutral
to litmus. This process has been extended and
elaborated upon, until to-day, in a modern plant, the
primary steps in the actual purification of the TNT are
carried out in the washing kettle. Various chemicals
have been tried in solution in the wash water. The
one great success in this line is sodium sulphite.
Besides acting as a neutralizing agent to the acid, the
sodium sulphite liquor exerts a solvent action on the
lower nitration products of toluene, and thus serves to
remove some of these impurities from the symmetrical
trinitrotoluene. The usual manner of using the
sodium sulphite wash is to give first about four washes
with hot water, then two washes with sodium sulphite
liquor, which contains 20 kilograms sodium sulphite
per 1000 liters water. This chemical wash is followed
by a slightly acidified water wash, and then with two
more pure water washes. Various other chemicals,
such as sodium carbonate, sodium bicarbonate, etc.,