NATURE OF EXPLOSIVES

Otago Witness, Issue 3495, 1 March 1921, Page 37

NATURE OF EXPLOSIVES

LECTURE BY PROFESSOR INGLIS. An interesting lecture on the subject of explosives was given by Professor Inglis at ttie University liuiidmgs on uie 23rd, under the auspices of the Workers’ Educational Association. The lecture was illustrated by many experiments, with the assistance oi an array ot chemicals, gas containers, and other apparatus, and one could not but wonder at the marvels of Nature which permitted the lecturer to handle without anxiety, substances which in certain combinations and conditions would have brought the whole building down like a house oi cards. An explosion was defined by the lecturer as a very rapid reaction between two substances, and a resulting increase in volume which gave a shock to the air that was transmitted through it in the form of a wave. If the air did not give way quick enough, the apparatus had to and would be broken. It was possible, however, to get a vigorous explosion where the substances were no more bulky, but where they were exploded by heat. Every explosive, he explained, consisted of two parts; oneburned and the other enabled it to burn. It was possible to make substances, which in themselves were perfectly harmless, explode in a dangerous way. The whole point was to get. the right conditions. These points the professor proceeded to illustrate by carrying out a series of experiments with a mixture of hydrogen and air, varying the proportions so as to obtain results varying from a startling bang to a shrill-toned pop. Sometimes there was no sound, only a bright flash of flame. This explosive flame, ho explained, passed through a mixture very rapidly, but at a definite rate. As a sample of a detonator (a very rapid explosive) the professor put into a small glass tube a pinch of a substance, found in on© of the laboratories, and known to be an explosive of some kind. Suspending the tube behind a screen, he applied heat. there was a deafening report, and all that was left of the glass was a small square in the grip of the stand. Another interesting experiment was per formed with a mixture, of chlorine and hydrogen, so sensitive that- it only required a bright light to make it explode. The gas was contained in thin glass bulbs, one of which the professor had blown to bits in the daytime by holding it in the sunlight. With the light of a burning magnesium wire he set off another to such good effect, that the glass completely disappeared in one loud burst. Tincture of iodine and ammonia, he explained, also gave an extremely dangerous explosive in the dry state When spread out in that, condition, a fly walking over it was sufficient to set it. off, and it had even been exploded by the vibration of a violin. Of this ter-

rifying substance tho professor manufactured a small sample, which exploded in a series of crackles, causing a dense smoke of purple vapour. These explosives, he explained, were all useless for commercial purposes, which required an explosive that would explode when wanted, and yet burn quite safely. Of the explosives in practical use he first touched upon gunpowder, which he said consisted of sait-petre—the function of which wag to supply the oxygen—sulphur, and charcoal. The salt-petre, reacting with the others produced solid particles, which were the smoke that yas seen in an explosion. To have a smokeless powder there must be no solids, only gaseous vapour. Such substances had been known for a long time, but they were very dangerous. Nitro-glveerine—glycerine and nitric acid, which was obtained from saltpetre—could be exploded with a slight shock. A great advance was made when scientists found a kind of earth which would soak up the nitro-glycerina and made a safe explosive, called dynamite. Another explosive made was guncotton, in which cotton was treated with nitric acid, and which required a mild explosion to set it off. In all these, the lecturer explained, the chemical changes took place very rapidly, and the greatest advance in the making of smokeless powders was the discovery of a blend of nitro-glycerine and guncotton, ■which gave a vigorous explosion that did not take place too rapidly. Blasting gelignite was explained to consist of 83 per cent, of nitro-glycerine and 7 per cent, of guncotton. The professor also explained the constituents of modern high explosives, such as lyddite, picric acid, and T.N.T. (toluene treated with nitric acid), and described amonal (ammonium nitrate and aluminium powder) as a safe and very valuable explosive for ordinary use, because it required special conditions for its explosion In conclusion he mentioned the novel use of explosives in planting fruit trees, pointing out that while in the ordinary way growth was confined to the small area broken with the spade, the use of an explosive had been found to shatter th© subsoil. with the result that the growth of the tree benefited. Certain area? in France, which, it was thought, had been ruined by the shelling, had been found to have benefited in this way. The professor was accorded a hearty vote of thanks for his lecture.