The Chemistry of Powder and Explosives - Sciencemadness Dot Org

144 AROMATIC NITRO COMPOUNDS
which is theoretically possible and is indicated above for that
reason, there is not more than a trace. 23 During the trinitration a
small amount of the a-TNT is oxidized to trinitrobenzoic acid,
finally appearing in the finished product in the form of TNB,
which, however, does no harm if it is present in small amount. At
the same time some of the material is destructively oxidized and
nitrated by the strong mixed acid to form tetranitromethane,
which is driven off with the steam during the subsequent boiling
and causes annoyance by its lachrymatory properties and unpleasant
taste. The product of the trinitration is separated from
the spent acid while still molten, washed with boiling water until
free from acid, and grained—or, after less washing with hot
water, subjected to purification by means of sodium sulfite.
In this country the crude TNT, separated from the wash water,
is generally grained by running the liquid slowly onto the refrigerated
surface of an iron vessel which surface is continually
scraped by mechanical means. In France the material is allowed
to cool slowly under water in broad and shallow wooden tubs,
while it is stirred slowly with mechanically actuated wooden
paddles. The cooling is slow, for the only loss of heat is by radiation.
The French process yields larger and flatter crystals, flaky,
often several millimeters in length. The crystallized crude TNT
is of about the color of brown sugar and feels greasy to the touch.
It consists of crystals of practically pure a-TNT coated with an
oily (low-melting) mixture of /?- and y-TNT, 2,4-dinitrotoluene,
and possibly TNB and TNX. It is suitable for many uses as an
explosive, but not for high-explosive shells. The oily mixture of
impurities segregates in the shell, and sooner or later exudes
through the thread by which the fuze is attached. The exudate is
disagreeable but not particularly dangerous. The difficulty is that
exudation leaves cavities within the mass of the charge, perhaps
a central cavity under the booster which may cause the shell to
fail to explode. There is also the possibility that the shock of
setback across a cavity in the rear of the charge may cause the
shell to explode prematurely while it is still within the barrel of
the gun.
The impurities may be largely removed from the crude TNT,
23 3,5-Dinitrotoluene, in which both nitro groups are meta to the methyl,
is probably not formed during the dinitration, and S- and c-TNT, namely
3,4>E>- and 2,3,5-trinitrotoluene, are not found among the final products of
the nitration of toluene.