The gunpowder period of warfare was actively initiated at the battle of Cressy, in which, as a contemporary historian says, “The English guns made noise like thunder and caused much loss in men and horses.”  Smokeless powder as invented by Paul Vieille was adopted by the French Government in 1887.  This, then, might be called the beginning of the guncotton or nitrocellulose period—­or, perhaps in deference to the caveman’s club, the second cellulose period of human warfare.  Better, doubtless, to call it the “high explosive period,” for various other nitro-compounds besides guncotton are being used.

The important thing to note is that all the explosives from gunpowder down contain nitrogen as the essential element.  It is customary to call nitrogen “an inert element” because it was hard to get it into combination with other elements.  It might, on the other hand, be looked upon as an active element because it acts so energetically in getting out of its compounds.  We can dodge the question by saying that nitrogen is a most unreliable and unsociable element.  Like Kipling’s cat it walks by its wild lone.

It is not so bad as Argon the Lazy and the other celibate gases of that family, where each individual atom goes off by itself and absolutely refuses to unite even temporarily with any other atom.  The nitrogen atoms will pair off with each other and stick together, but they are reluctant to associate with other elements and when they do the combination is likely to break up any moment.  You all know people like that, good enough when by themselves but sure to break up any club, church or society they get into.  Now, the value of nitrogen in warfare is due to the fact that all the atoms desert in a body on the field of battle.  Millions of them may be lying packed in a gun cartridge, as quiet as you please, but let a little disturbance start in the neighborhood—­say a grain of mercury fulminate flares up—­and all the nitrogen atoms get to trembling so violently that they cannot be restrained.  The shock spreads rapidly through the whole mass.  The hydrogen and carbon atoms catch up the oxygen and in an instant they are off on a stampede, crowding in every direction to find an exit, and getting more heated up all the time.  The only movable side is the cannon ball in front, so they all pound against that and give it such a shove that it goes ten miles before it stops.  The external bombardment by the cannon ball is, therefore, preceded by an internal bombardment on the cannon ball by the molecules of the hot gases, whose speed is about as great as the speed of the projectile that they propel.

[Illustration:  (C) Underwood & Underwood

THE HAND GRENADES WHICH THESE WOMEN ARE BORING will contain potential chemical energy capable of causing a vast amount of destruction when released.  During the war the American Government placed orders for 68,000,000 such grenades as are here shown.]

[Illustration:  (C) International Film Service, Inc.