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378 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

The residue left after the solvent - alcohol (in the earlier crystallization method)
or xylene (from the washing technique) - has been distilled off, is a semi-solid

substance consisting of α− trinitrotoluene, its isomers, dinitrotoluenes and other

nitro compounds, all of them found as impurities in TNT.

The mixture, known as “TNT oil”, generally melts within a wide temperature

range, for example from room temperature up to 60°C. It may be used as a com-

ponent of ammonium nitrate explosives for the mining industry.
The “exudation process” is a modified purification by crystallization. At present

it is applied to purify grade III TNT and to recover impurities present in TNT

for use as “TNT oil” in the preparation of explosive compositions. The process

may be carried out in two ways.

In one of them TNT, scattered over sloped flat pans (Fig. 79, p. 351), is put

into a chamber heated to 60°C. After several hours the low-melting impurities

segregate as oil which collects in a special vessel placed below the pans.

Another method consists in melting TNT in tilting kettles (converters) heated

by steam or hot water which are then left at rest at room temperature or slightly

higher (e.g. 30°C) for slow crystallization. Under such conditions large crystals

of TNT are formed immersed in an oily mixture of other nitro compounds. The

latter is removed by breaking the solidified substance and inclining the kettle so

as to enable the oil to run out.

The oily product has been used as an ingredient of coal mining explosives as

so-called “liquid TNT”. This material also comprised the liquid mixture of nitro

compounds forming the residue after distillation of alcohol (or any other solvent)

used for crystallization of TNT.

In an earlier Russian method (Belenkii [8]) crude, granulated TNT was washed

with hot water in wooden tanks lined with sheet lead, and equipped with an air

bubbler.

For a batch of 1000 kg of TNT 1000 l. of water were used at a time. The water

was brought to boiling by direct heating with steam (1-2 hr). After boiling for 5 min

heating and air mixing were stopped, and the TNT allowed to settle at the bottom.

After 10-15 min the water was separated by decantation. This operation was repeat-

ed 6-8 times with new portions of fresh water, until the acidity of the TNT fell

to 0.02% (calculated on H 2 SO 4 ). The whole washing process took about 7 hr.

The use of lead-lined tanks for the first two washings, and a wooden tank for the

next ones proved advantageous,

Norell [26] invented a continuous method of crystallization of TNT from nitric

acid. A diagram is given in Fig. 92, according to the A. B. Bofors patent.

The crystallizing vats (1).-(5) are provided with heating jackets (3) and

stirrer (4). The vats communicate through the overflow (7) and pipes (6). The
last crystallizer has an outlet (8) provided with a screw type conveyer to remove
a semi-solid mixture of crystals of TNT plus mother liquor.
The first vat is provided with pre-crystallizer (9) and a stirrer (10). The molten TNT
(II) and solvent (12) (i.e. nitric acid) is introduced to the pie-crystallizer in which TNT