SOUNDS THAT BURN

Evening Star, Issue 19855, 2 May 1928, Page 14

SOUNDS THAT BURN

MISSING LINK IN SCIENCE A missing link between tho . vibrations of sound avid heat seems to have been supplied by Professor 11. W. Wood, of John Hopkins University, who describes, his interesting experiments in an article in the ‘Scientific American’ (New. York, March). A sounding body vibrates as a whole, whereas heat is duo to molecular jnotion; yet Professor Wood shows that, by making the sound vibrations rapid enough, tho sensation and many of the effects of ordinary heat may be . produced. Writes Dr Wood; — “ A shallow glass dish filled with oil stands on a table close ,to a coil of wire, the terminals of which lead down through tho surface of the fluid. Supported over tho centre of the dish is a small tube of glass, the bottom of which dips into the oil. The upper end of tho tube is drawn out into a long thread of glass, the size of a horsehair. “ The thread looks harmless enough, but it is shaken by invisible vibrations at tho rate of 300,000. a second. If we hold the end of it lightly between the thumb and finger, wo feel nothing of this tumult, but if wc squeeze it it burns like a red-hot wire, and we find a deep groove in tho skin, with white seared edges. “If the end of the thread is pressed against a pine chip the wood smokes and emits sparks, the thread rapidly burning its way through the chip, leaving a hole with charred and blackened edges. If a plate of glass is substituted for the chip tho thread eventually bores its way through this, throwing out tho displaced glass in tho form of a fine white powder. These aro a few of the many remarkable effects obtained with high-frequency sound vibrations in a series of experiments in collaboration with Mr Alfred L. Loomis. “Tho classical theory of heat attributes what wo speak, of as temperature to an unorganised vibration of atoms. The interesting question presents itself as to whether, some of tho effects of heat can bo imitated by mechanical vibrations of sufficiently Higher frequency than 15,000. or 20,000 per second, and the amplitude or intensity is very small. “A plate of quartz, cut from a clear and perfect crystal in the proper direction, has the curious property of expanding and contracting under the influence of a periodic electrical field. A quartz plato about one-third of an inch thick has a natural frequeiey of vibration of about 300,000 per second, and if wo tune the electrical oscillator to this same frequency resonance occurs, and the amplitude of tho vibration of the quartz plate becomes very groat. “ Tho apparatus employed in the present work was built in tho research laboratory of the General Electric Company at Schenectady. “ We employed quartz plates varying in thickness from seven to fourteen millimeters, with which wo obtained waves with frequencies ranging from 100,000 to 700,000 cycles per second.

“ Immersion o[ the pinto in oil is necessary, for a potential of 50,000 volts, oscillating 300,000 times a second, is applied to the electrodes. If the plate were in air it would lly in pieces as a result of the vibration. Even in tho oil bath plates are broken to pieces if the voltage is raised much above 50,000. “ Sound naves of such high frequency do not escape from the nil hath into the air, but are reflected back from the surface of tho fluid, which is raised up in a mound 2ii? or 3in in height by the pressure of the radiation reflected back by tho surface, tho top of the mound spitting oil drops, which are sometimes projected to a height of a foot or more. “If a beaker of water is lowered into the oil, the waves pass up into tho water, the surface of which is at once pushed up into a mound, while countless clanging air bubbles appear in the fluid. “ If we pour a little mercury into tho beaker clouds of fine particles of mercury are projected up into the water, which soon becomes as black as ink. Emulsions can bo formed in this way with melted paraffin and water, molten sulfur and oil, or fusible alloy of low melting point and water. “If a shallow' layer of a liquid lighter than w r ater, such as benzol, is pub into a. _ beaker and subjected to the vibration, . the benzol is driven into the air in the \V>nn of a cloud or mist of very fine iycrticles, the beaker filling rapidly •ith a white smoke. “A glass tube two or three feet in length and an _ inch in diameter is coated on the inside with a film of heavy oil, and the lower end dipped into the bath of vibrating oil ; the film immediately gathers itself together in a beautiful system of equidistant rings, which lino the tube from top to bottom. These rings show the position of the nodes of the stationary waves formed by the interference of the high-frequency vibrations which are running up and down the tube. “ A glass tube, closed at the bottom and drawn at tho top to a slender rod of glass, is mounted over the oil bath, with its lower end dippiing below tho surface. A small hall of red wax is stuck to the top of tho rod. As soon as the oscillator is started the wax melts at its surface of contact with the rod, and the hall slides down, leaving a scries of red rings on tho rod about oue-sixteenth of an inch apart. “The energy thrown iuto the rod is much greater than when a solid rod is merely dipped into the oil, and it was with a collector of this form that the powerful heating effects described in the opening paragraph were obtained. The rod may ho drawn out in a flame, forming a thread several feet in length. These threads invariably snap into fragments when the oscillator is operated with its full pow'er, and burn turought the skin when squeezed between tho finger and thumb. “These curious heating effects were first noticed when taking the temperature of the oil fountain with a thermometer. Though the instrument registered only two degrees above room temperature, the tube became so hot at the point at which it was held between the thumb and finger that it had to bo released. The heating, of course, is duo to the rapid pounding of the transverse vibrations. “The maximum heating effects arc I obtained with a small flat-bottomed conical flask, drawn down at tho top to a rod about .5 millimeters (oncfiftioth of an inch) in diameter. A dry pine chip pressed against the top of tho rod smokes and emits an occasional spark, while the rod rapidly perforates the wood, forming a nolo with charred edges, “If a glass rod is cemented with sealing wax to the centre of a circular glass disk dusted with lycopodium a beautiful system of concentric circular rings forms' on tho plate as soon as the lower end of the rod is clipped in the vibrating oil. If the rod is cemented to the disk at a short distance from the centre tho complicated pattern reproduced in tho figure is formed.’’ The effect of tho vibrations on a block of ice, immersed in a beaker of ice water, with smaller fragments of ice to check the heating, is reported by Professor Wood to bo very remarkable. After a short exposure to the waves,] if tho ice is removed from the beaker aiid squeezed in tho hand, the block crumbles into a mass of small fragments. Tho heating has taken place throughout tho entire mass of . ice, and melting apparently occurs at the faces of the component crystals. _ Tho same effect was not obtained with “ pond ice,” perhaps due' to the fact that in this case wo are dealing with a single crystal. Ho goes on: One of tho most spectacular effects

is obtained witli the vibrations when <a glass tube is closed at one end and drawn down to a diameter of about 7 millimeters near the other. Tho tube is clamped to the rack and pinion stand and the rounded bottom lowered into the mound of vibrating oil. The constricted portion is tho seat of very intense vibrations, and heats rapidly. If now wo apply a little oil with a medicine-dropper to tho outside of the tube, above the constricted portion, a very surprising thing happens. The oil spreads over the surface and is thrown out in numerous jets of spray, resembling smoko, and a dense cloud gathers about the tube. “ With a collector of ibis type the amplitude of the vibration frequently becomes so great that the tube is fractured in a curious manner, small irregular pieces of glass breaking away from the constricted part. In the case of particles exceeding a certain size, suspended in water—coal-dust, for example—flocculation occurs the moment the liquid is traversed by the waves, the particles rushing together to form clusters which presently gather into a single irregular mass just under the surface. This phenomenon was photographed with a cinematograph, and by studying tho individual pictures the process of flocculation can be followed, ft is planned to take pictures with a high-speed machine, so that slow motion pictures can ho projected, and the motion of the particles watched at leisure. "Small burns made by pressing the skin against the end of the glass rod appear to differ somewhat in the way in which they heal from burns made by mere contact with a hot point, and it seems probable that the high-fre-quency vibration has sonic tissue-de-stroying power. •‘We found many interesting biological effects of the vibrations. Red blood corpuscles arc destroyed. Undiluted blood is * lakcd ’ by the vibrations. Small unicellular organisms are killed and the cells torn open. Distinct evidence was obtained also that the red corpuscles could be destroyed within the body of a living animal ia mouse), and small fish and frogs arc quickly killed by the vibrations. ‘‘A wide field of investigation in biology appears to be opened up hr these experiments. It seems quite possible that results of importance can be obtained along the linos initiated by Professor Loeh, who punctured embryos with fine needle-points, and then studied their subsequent abnormal growth.”