Untitled

Otago Witness, Issue 2368, 20 July 1899, Page 54

SCIENCE NOTES.

— The increasing use of corundum in the arts -■- drawn attention to in a recent review in Nature. Apart from the gem form in which corundum, the crystallised Dxide of alumina, is found, the mineral is largely employed chiefly for abrasive purposes, mostly -in the form of corundum wheels, which are said to be twice as -effective and durable as emery wheels. Corundum wheels may be regarded as rotary files, the cutting points of which never grow dull. They are rapidly replacing files for cutting down- metal surfaces, and taking the place of grindstones for *uarpening tools. we are toi'd tnat, while a file is useless when at nas lost five per cent, of its weight, me corundum grains throughout wheel retain their cutting power so that can be worked until 90 per cent, of its weight is worn off. Thus, while it has

been estimated that to remove lib weight of iron with a file costs 2s 6d, the same amount of work can be done with an emery or corundum wheel in about one-eighth of tfr'e time and at one-seventh of the cost. Corundum is essentially an Indian mineral, although large deposits occur also in the United States, principally in North Carolina and Georgia ; there are also valuable deposits in British Ontario.

—It seems probable that in liquid air we have the most valuable caustic which has yet been discovered, and it is more than possible that its use may eventually supersede that oi the knife in certain very serious cases. Experiments on a small scale have been made in some of the American hospitals, and they are said to have been wonderfully successful. We do not hear, says the Globe, of anything of the kind being done in Britain, which is a pity, for the study of so powerful an erosive ought not to be neglected in a country where the death rate from cancer is increasing by leaps and bounds.

— The Government of Bombay has approved measures having for their object the prevention of the introduction of the disease known as the "Jigger,"' or, as it is sometimes written, " Chigger." The disease, it will be remembered, is produced by a pai'asite known' to science as Pulex penetrans. It usually attacks the feet, the female burrowing under the skin, where it gradually enlarges to the size of a pea. In the earlier stages detection is almost impossible, the minute black spot denoting the presence of the insect beng easily overlooked. Later on, as the enlargement, due to the development of numerous eggs, increases, a slight itching or pain is felt, "and the skin is se'en to be discoloured. When fully developed hte sac containing the egg ruptures, the eggs escape and develop into the mature insect. The sac can be wholly removed, but the operation is a difficult and delicate one. When the sac is ruptured a very serious inflammation, proceeding to disease of the bone, is sometimes set up. — Medical Press.

— Many lives are lost annually by accidental poisoning ; a mixture intended for outward application only is taken in mistake for the proper medicine, and death ensues. Now and then a well-known person is the victim, and then there conic' many suggestions as to the • best way of preventing such accidents in future. This was the case when Professor Tyndall was accidentally poisoned a few years ago ; and now that Dr A. K. H. Boyd has lost his life in the same lamentable way, many are asking how such fatalities can best be prevented. It is now the almost universal custom of the druggist to serve poisonous preparations in a fluted bottle of blue glass, so that a ministering hand can be warned, even in a dark room, where the red label cannot be seen, that caution is necessary. As most persons know, virulent poisons are not supplied at all to casual purchasers at chemists' shops ; but, unfortunately, some of the most dangerous compounds known are extensively used in the arts, and it is next to impossible to place any restriction, on their sale. A valuable suggestion has been recently made that all poisons should be put in bottles labelled not only with the name of the preparation, but also with its antidote — thus, " Silver nitrate — antidote, Common salt." This would, we think, be a most commendable practice j although it must be remembered that some poisons, common to certain trades, are so quick in their action that antidotes are useless unless they are actually at hand. — The tests of the new guns with which the Austrian artillery is to be armed are now approaching completion. Two kinds of guns will be introduced — a quick-firing one of seven centimetres calibre, and one of twelve centimetres for field use. Smokeless powder will be employed in the new weapons, one of the main features of which is the improved breech, which secures more rapid loading. — Telephotography has recently been applie'cl to a" novel purpose by Italian engineers in the Alps, south of Mont Blanc, where the frontier line between Prance and Italy lies among the mountains. The telephotographic camera produced a magnified picture of a distant object, and by means of such pictures the Italians have been able to study the details of French forts which they cannot approach near enough to photograph with an ordinary camera. — Tesla is reported to be making experiments with a new wireless telegraph, which will give a very high speed of signalling — namely, thousands of. words a minute. Its nature i»- not revealed, but he lias already invented ;i rotary make and break for charging and discharging a condenser 10,000 times a second by means of a stream of mercury striking a revolving metal disc carrying thin contact blades. With this device he ought to be able to produce very rapid sparks and signals in a wireless telegraph. — Four pieces of a meteorite which exploded and fell on the eastern slopes of Mount Zomba, British. Central Africa, on

January 25, have recently been added to the British Museum collection. The stones weigh respectively 14,17, 19, and 29 ounces. The Times states that when the meteorite fell an explosion was heard at Zomba, the reverberations lasting for a few minutes afterwards. The detonation was also heard at Chiromo, situated about 90 miles south of Zomba, and at Fort Johnston and beyond, a distance of about 70 miles in the opposite direction. Zomba was thus, roughly, the centre of the district over which the actual explosion of the meteorite took place. Ten fragments in all were found, the largest weighing 51b 12£oz. As far as at present known, the area over which the Zomba stones fell .represents about nine miles long by about three wide ; but, inasmuch as the fragments collected are only those which were seen to fall close to people or houses, it appears probable that a large number of may have reached the earth.

—It is announced from Berlin that the Engineering Committee of the Army has received a report on the recent experiments with liquid air for blasting purposes carried out in a foreign quarry. They are stated. to foreshadow a complete revolution in the application of explosives. The statement probably refers to experiments made at Ober-sievering-, but' it is not stated how the liquid air is produced cheaply. According to one report the liquid air is mixed with silicious marl to produce a deadly explosive, susceptible not to shock but to ignition. In the experiments one-fortieth of a litre of liquid air was mixed with silicious marl and placed in a crevice of rock 2ft deep. It was ignited by electricity, and blew up an immense mass of rock. The experts estimated that they would . have required 20 times as much dynamite, placed in a crevice 4^ft deep, to obtain a like result. Further experiments with -cannon showed that the new explosive exerts its enormous force without perceptibly generating heat, so that the gun remains quite cold. Combined with this advantage, it is calculated that the range of big guns will be considerably increased when the projectiles are discharged with the new explosive.