376 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVESThe yield of TNT is as high as 97-99% of theory.
If an unfractionated mixture of the mononitrotoluene isomers is used (i.e.the product of straight nitration of toluene), TNT with a melting point of 78.7°C
results. If the starting material is free from m- nitrotoluene, e.g. if pure o- nitroto-
luene is used, TNT with a melting point of 80.6°C is produced.
TABLE 86Nitrators Composition of nitrating mixtures, % Temperature
Nos. HNO 3 H 2 SO 4 H 2 O °C1-3 0.9 89.2 9.9 65
4-6 3.0 90.1 6.9 75
7-9 7.9 87.8 4.3 80
10-12 7.5 89.8 2.7 85
13-15 7.5 91.4 1.1 90
16-18 7.7 91.8 0.5 90PURIFICATION OF TNT
In the purification of TNT the following impurities have to be removed:
(1) traces of nitric and sulphuric acids;
(2) unsymmetrical isomers;
(3) products of incomplete nitration;
(4) by-products (tetranitromethane, trinitrobenzene, nitrobenzoic acids, nitro-
cresols, etc.).
The aim of final purification is to remove all those products which are present
TNT and which are more reactive than TNT itself (isomers, nitrocresols, nitro-
benzoic acids etc.) or which can easily give oily exudation products (isomers, lower
nitrated substances).
The oily exudation product (TNT-oil) is very undesirable for the following
reasons :
(a) Exudation produces porosity of the TNT charge and reduces its density.
This reduces its explosive effect. In artillery shells it can produce a dislocation
of the charge on firing, compression of the air included in the cavities, and pre-
matured explosion.
(b) The oily products can penetrate into the threaded parts of the shell and
form “fire channels” through which the ignition of propellant can ignite the charge.
(c) The oily products can penetrate into the detonating gaine if the charge
of the gaine is unprotected by a metal envelope (e.g. former English gaines made
up of TNT in a silk bag). The oily products reduce the detonating powers of the
gaine.
The first purification step is thorough washing of the TNT with hot water, in
washing tanks or by emulsification.