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 remained the same from early in the 14th century to the present day. It can boast of having satisfied all military requirements for five and a half centuries and is even now very far from being superseded.

Excellence in the Explosive was attained in the case of gunpowder by grinding the materials to fine powder and thoroughly incorporating them. Thus each particle of combustible had its necessary oxygen close at hand and when the combustion was started at some one point by a spark it rushed through the mass with a speed sufficient to cause the explosion. But some eighty years ago chemists found that it was possible to get a yet more perfect intermingling. They discovered substances in which the combustible and the oxygen are present in one and the same molecule. Like the lion and the lamb, of which the prophet speaks, they lie down together and it is not until the molecule is shattered by heat or shock or some other like agency that they rush together into combustion. As might be expected such a combustion 19