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which are readily soluble in water. After the reaction, the purified material is washed with water until the washings are colorless.

Muraour believes the sulfite process for the purification of TNT to be an American invention. At any rate, the story of its discovery presents an interesting example of the consequences of working rightly with a wrong hypothesis. The nitro group in the m-position in and y-TNT is ortko, or ortho and para, to two other nitro groups, and accordingly is active chemically. It is replaced by an amino group by the action of alcoholic ammonia both in the hot and in the cold, and undergoes similar reactions with hydrazine and with phenylhydrazine. It was hoped that it would be reduced more readily than the unactivated nitro groups of a- or symmetrical TNT, and that the reduction products could be washed away with warm water. Sodium polysulfide was tried and did indeed raise the melting point, but the treated material contained finely divided sulfur from which it could not easily be freed, and the polysulfide was judged to be unsuitable.

+ NaNOj rby diluting with water. The organic solvents are recovered by distillation, and the residues, dark brown liquids known as "TNT oil/' are used in the manufacture of non-freezing dynamite. The best process of purification is that in which the crude TNT is agitated with a warm solution of sodium sulfite. A 5 per cent solution is used, as much by weight of the solution as there is of the crude TNT. The sulfite leaves the a-TNT (and any TNB, TNX, and 2,4-dinitrotoluene) unaffected, but reacts rapidly and and

In seeking for another reducing agent, the chemist bethought himself of sodium sulfite, which, however, does not act in this case as a reducing agent, and succeeded perfectly in removing the and y-TNT.

The reaction consists in the replacement of the nitro by a sodium sulfonate group: j^y

The soluble sulfonates in the deep red solution, if they are thrown into the sewer, represent a loss of about 4 per cent of all the toluene—a serious loss in time of war—as well as a loss of many pounds of nitro group nitrogen. The sulfonic acid group in these substances, like the nitro group which it replaced, is ortho, or ortho and para, to two nitro groups, and is active and still capable of undergoing the same reactions as the original nitro $roup. They may be converted into a useful explosive by reaction with methylamine and the subsequent nitration of the resulting di-nitrotolylmethylamines, both of which yield 2,4,6-trinitrotolyl-3-methylnitramine or m-methyltetryl.

m-Methyltetryl, pale yellow, almost white, crystals from alcohol, m.p. 102°, was prepared in 1884 by van Romburgh by the nitration of dimethyi-m-toluidine, and its structure was demonstrated fully in 1902 by Blanksma, who prepared it by the synthesis indicated on the next page.

and y-TNT lose their active nitro group by the action of aqueous alkali and yield salts of dinitro-m-cresol. The mixed dinitro-m-cresols which result may be nitrated to trinitro-m-cresol, a valuable explosive. Their salts, like the picrates, are primary explosives and sources of danger. and y-TNT react with lead oxide in alcohol to form lead dinitrocresolates, while a-TNT under the same conditions remains unaffected.

In plant-scale manufacture, TNT is generally prepared by a

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