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382 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

together to form a unit. It is divided into sections by vertical walls, each section

consisting of two parts: a larger one for mixing the TNT with water (mixers),

and a smaller one for separating both phases (separators).

The vertical walls are provided with holes to allow both molten TNT and water

to flow through. Each segment is also provided with horizontal perforated iron

plates. The mixers are equipped with stirrers, rotating at high speed, which can

direct the contents of the unit upwards or downwards.

FIG. 96. Continuous washing of TNT (British method [6]).

It can be seen from the diagram that the molten TNT to be washed flows in

counter-current against a stream of hot water. In the mixers, emulsification of

the TNT in water takes place. The emulsion then passes through an overflow at

the top or at the bottom of the mixer (depending on the direction given by the

stirrer) to the separator, where the TNT collects at the bottom and flows to the

adjacent mixer by an outlet near the bottom. Water rises to the top of the separator

and passes in counter-current through an overflow to another mixer. By direct

steam heating a temperature 80-100°C is maintained in the trough. The cover

of the latter is provided with vent ducts for escaping vapours.

For 1000 kg of TNT about 2500 1. of water is used. The output amounts to 1.5

tons of TNT per hour. After washing the acidity of TNT falls to 0.1-0.2% of H 2 SO 4

The sulphitation of TNT is carried out in a unit illustrated in Fig. 97.

The granulated, crude TNT is washed with hot water in a wooden vat A, equipped

with a stirrer rotating at a speed of 75 r.p.m., and with a sheet metal lid connected

to a ventilating pipe. The mixture in the vat is heated by steam introduced through

a silicon-iron pipe. The acidity of the TNT falls after washing to below 0.1% of

H 2 SO 4. The number of washing operations depends on the initial acidity.
The molten, deacidified TNT is drained off to a crystallizer, placed below.
The crystallizer consists of a wooden cylindrical vessel, 0.9 m high and 2.8 m in

diameter, equipped with a wooden stirrer.

For crystallization the molten TNT is run from vessel A into a crystallizer
filled with water, heated to 90-100°C. The ratio of water to the TNT should be

1:1 by volume. The content of the crystallizer is allowed to cool. At about 75°C

the TNT begins to crystallize. After the temperature has fallen to 50°C (in about

4 hr from the time the crystallizer was loaded) sodium sulphite solution is added
and the mixture is allowed to react for half an hour at a temperature of 40-45°C.

The concentration of Na 2 SO 3 in the crystallizer is 34%. The weight of the Na 2 SO 3