Now, what is the fearsome stuff with which such bombs are loaded? A new chemical compound? Not at all. What they contain is simply the mixture of two of the most harmless things in the world--oxide of iron (which is simply iron rust) and powdered aluminum. When these two innocent substances are mixed together the result is a compound truly infernal in its potentialities for mischief. It is not an explosive but if set on fire it burns with an intensity that is positively appalling. Nothing will put it out; no quantity of water has any effect upon the raging flames it engenders. This is the material used for loading incendiary bombs. It is ignited in such projectiles by a mercury-fulminate cap that sets off a fuse containing powdered magnesium--the stuff photographers employ for flashlights. THIN SHELLS OF STEEL. These bombs are thin shells of steel or iron--mere containers for the mixture before described. They are so contrived that the fuse is instantly ignited when they strike. Whereupon the shell is melted by the heat generated within it and a flood of fiercely burning metal is scattered in all directions. All of this seems rather extraordinary, and it is worth explaining. Oxygen has an affinity for iron, readily combining with the latter--which is the reason why iron is liable to rust. This rust is a chemical compound of iron and oxygen; in other words, oxide of iron. But oxygen has a much greater affinity for aluminum. And so, when the two metals are powdered and mixed together and heat is applied the oxygen flies out of the iron rust and combines with the aluminum. The process is started in the bomb by the burning magnesium. And then the oxygen passes out of the iron and into the aluminum so rapidly that an enormously high temperature is developed. It runs up to 3500 or 4000 degrees Fahrenheit--which means, of course, a tremendous combustion. The mixture of aluminum and iron burns like so much tinder--though such a way of putting it is absurdly feeble. The present war has been conspicuously marked by reversions to ancient methods of fighting. In this line the incendiary bomb offers an excellent illustration. It is in effect merely an adaptation of an idea utilized by the Saracens--we should call them Turks nowadays--in their warfare with the Crusaders of the Middle Ages. DREAD INSTRUMENT OF WAR. The instrument of war most dreaded by the Crusaders, as they found it in the hands of the Turks, was the incendiary bomb--a projectile that flew through the air "like a fiery dragon" as they described it, and set fire to whatever it touched. Sometimes it was provided with iron barbs, by which it clung to buildings.