HOW THE GIANT DESTROYS

Pukekohe & Waiuku Times, Volume 6, Issue 274, 11 May 1917, Page 2 (Supplement)

HOW THE GIANT DESTROYS

FACTS ABOUT EXPLOSIVES.

At Gettysburg a sharpshooter built himself a little wall between immense boulders in the devil's den. He was found dead behind the wall with uo wound upon his body. In the battlefields of Europe many men d'o without wound. Natural attitudes show they died instantly. The only theory which fits the facts is (says C. H. C'landy in the "Scientific American") that they die from what kills the worker in compressed air—the dread caisson disease or "the bends."

Bubbles froth to tho top of an uncorked champagne Ik>ul<\ In a soda siphon are no risible bubbles, but many are in liquid which squirts from it. Sudden release of pressure draws gas from a liquid.

It is supposed that tremendous pressure from violent explosion and its sudden release causes bubbles of air to form in the blood of the men who die without a wound. In "the lands'' these are allowed to escape slowly (and painfully) while pressure is gradually reduced. Tho man lives. If pressure is suddenly reduced tho bubbles are large enough to stop the heart beating. The man dies. On the battlefield there is nothing to soften the sudden increase and decrease of pressure. A man died at Gettysburg in a situation between huge rocks which might easily have allowed tho puny shells of '63 to create sufficient pressure to make him kin to his dead soldier brother of 1916. Wo read so much of shells and explosions and detonations and shrapnel and forty-two centimetro guns and "high" explosives that we pas;* them by as commonplaces—dread, perhaps, and fearful, but still, a matter of course in war. Yet—what is an explosion?

WHAT AN EXPLOSION IS

Is is Icommonly supposed that explosion is l>ut a rapid burning of a chemical compound. Sudden combustion may bo explosion, but not all explosions are merely rapid combustion. Many ignite and burn harmlessly which, hit with a hummer, will tear anything to piece* in tfia immediate vicinity. Gunpowder—which explodes by rapid combustion, is no longer even the prototype of explosive. So wonderful when first discovered, it s now a back number, out of date, a very pigmy, compared to somo of Hs "high"' relatives. Even its rate of burning ia no more a marvel. How fast a compound will "explode"' is important. AH explosives require confinement to be effective, just as a blow requires something solid to land upon to do damage. The most vicious uppercut wiH not hurt a chin in front of which there is a pillow. Similarly gunpowder, which, ineffective as it is, may yet be terribly destructive when fet off in confinement, will go up in a harmless puff of smoke if ignited in a littlo pile on the ground. But a piece of dynamite on the ground will blow a hole in the earth. From this has come the absurd belief that dynamite explodes only downwards. Any explosive acts with equal forco in all directions. Unconfined, slow-burning gunpowder can push the air away fast enough to make room for its bulk of released gas, while dynamite changes from a solid to a gas so quickly that the inertia of the air is «11 the confinement it needs. Support a stick of dynamite on the under side of a plank resting on two logs and this will be shattered as fully as if rested on the ground with dynamito on top. Capping a charge of dynamite on an exposed surface with a handful of mud is a custom which some miners have found effective. They say, "It holds down tho force." And when the dynamite has been slowed up in the factory by the admixture of some inert substance, even so modest a confinement as a handful of mud gives just the added inertia needed by the confining air to make the rending force most effective. Tho same thing can lie observed if a heavy metal weight or stone is placed over a charge of gunpowder on tho ground—there will bo no doubt of the hole blown in the earth under such circumstances.

THE MERCURY FIEND

Not all explosives are burning compounds or mixtures. There is the peculiar and not thoroughly understood phenomenon of detonation. The most common detonator is fulminate of mercury. This small confined fiend from the Hades of Explosia is not used to do damage itself—for it has no great power to move weight or rend at a distance. With one or two exceptions, it is tho mosit vicious of all the •compounds wh'ch go off at a blow. Its use 14 to fire tho explosive which does the damage. In its own field it is supreme. —not only in setting the larger giant to his task, but in telling him how he shall do U. It makes much difference to some explosives whether they are fired with a fulminate, which shocks them into action, or whether heat alono inspires them to work. Thus 15 grains of fulminate of mercury will start King Guncotton doing damage much more effectively than 70 times as much nitroglycerine. Tho force of a detonator is enormous —but effective for but a short distance. Gunpowder will explode, and propagate its explosion at a rate of from two to three metres a second up to an outside limit of 300 metres a second under the most favourable conditions. The fulminates have a minimum propagation of about- 8000 metres a second. A metro is something over three feet. A sixty-mile-an-hour express train goes 89 feet a second. Imagine feet a second and you will know why a very minute quantity of fulminate of mercury going off in your hand will carry a finger with it and yet not burn your coat.

Tho wnole power of any explosion, whether it bo a burning or a detonation —which is a sudden flying of certain chemicals into ga.s all at once everywhere throughout tho mass regardless of heat—is caused by Nature's total refusal to permit two bodies to occupy tho same place at the same time. Gunpowder occupies a hole drilled !in a rock deep enough to accommodate a pint. A fuse explodes it. During the time it takes that pint of gunpowder to change to a gas it grows, so that there are 110 pints of gas occupying the hole —or trying to. If tho hole is strong enough they might—but it isn't. They pu.sh the ny-k apart and make room for thomselves. If it was a pint of good dynamite there would bo :\ volume of pints of gas trying to occupy that pint hole. And if it was blasting gelatine, pints! Hut the matter is not wholly otic or

two things in the same mjku-o at the same time, but how long the two are given to adjust themselves to the fart - which that they can't occupy the same space at the same time! Here we com.* again t.i the rate of explosion.

Tho explosive tester calls it the relativi kineti" energy. He express it in kilogram metres j>er second. One does not need to know the scientific meanin:' of the term to understand its significance. Gunpowder is rat \\ :is h.iv-

ing a kinetic energy of 458". Picric acid, which is one of the giante of the explosive family, owns *c having a kinoti- energy of nearly 3.000,000. The last twenty years has seen a vast development of the "art" of making explosives. In the American Civil War wo knew gunpowder. In th's war we have smokeless powder, guncotton. dynamite, '"high" explosvcs together. Modern war is so terrible because of man's ability to make sukstances which can kill at enormous distances, and 1 which can wreck and ruin with the. mere power of their resistless sweep. the shock of their passing. But a few yanrs ago, if a picco of exploding shell didn't actually hit a man. it wan harmless. The crater thrown up by Grant's gunpowder mine at Petersburg—a giant in it -a div—would bo an ant-hole to the crater of one modern European shell. ini much have wo progressed (!) 'n "«J wan!