The third kind of high explosives uses as its base toluol.  This is not so familiar to us as glycerin, cotton or carbolic acid.  It is one of the coal tar products, an inflammable liquid, resembling benzene.  When treated with nitric acid in the usual way it takes up like the others three nitro groups and so becomes tri-nitro-toluol.  Realizing that people could not be expected to use such a mouthful of a word, the chemists have suggested various pretty nicknames, trotyl, tritol, trinol, tolite and trilit, but the public, with the wilfulness it always shows in the matter of names, persists in calling it TNT, as though it were an author like G.B.S., or G.K.C, or F.P.A.  TNT is the latest of these high explosives and in some ways the best of them.  Picric acid has the bad habit of attacking the metals with which it rests in contact forming sensitive picrates that are easily set off, but TNT is inert toward metals and keeps well.  TNT melts far below the boiling point of water so can be readily liquefied and poured into shells.  It is insensitive to ordinary shocks.  A rifle bullet can be fired through a case of it without setting it off, and if lighted with a match it burns quietly.  The amazing thing about these modern explosives, the organic nitrates, is the way they will stand banging about and burning, yet the terrific violence with which they blow up when shaken by an explosive wave of a particular velocity like that of a fulminating cap.  Like picric acid, TNT stains the skin yellow and causes soreness and sometimes serious cases of poisoning among the employees, mostly girls, in the munition factories.  On the other hand, the girls working with cordite get to using it as chewing gum; a harmful habit, not because of any danger of being blown up by it, but because nitroglycerin is a heart stimulant and they do not need that.

[Illustration:  The Genealogical Tree of Nitric Acid From W.Q.  Whitman’s “The Story of Nitrates in the War,” General Science Quarterly]

TNT is by no means smokeless.  The German shells that exploded with a cloud of black smoke and which British soldiers called “Black Marias,” “coal-boxes” or “Jack Johnsons” were loaded with it.  But it is an advantage to have a shell show where it strikes, although a disadvantage to have it show where it starts.

It is these high explosives that have revolutionized warfare.  As soon as the first German shell packed with these new nitrates burst inside the Gruson cupola at Liege and tore out its steel and concrete by the roots the world knew that the day of the fixed fortress was gone.  The armies deserted their expensively prepared fortifications and took to the trenches.  The British troops in France found their weapons futile and sent across the Channel the cry of “Send us high explosives or we perish!” The home Government was slow to heed the appeal, but no progress was made against the Germans until the Allies had the means to blast them out of their entrenchments by shells loaded with five hundred pounds of TNT.