A MAGNETOSTRICTION OSCILLATOR PRODUCING INTENSE AUDIBLE SOUND AND SOME EFFECTS OBTAINED



A MAGNETOSTRICTION OSCILLATOR PRODUCING INTENSE AUDIBLE SOUND AND SOME EFFECTS OBTAINED

THESIS

Presented to the Faculty of the Graduate School of The University of Texas in Partial Fulfillment of the Requirements

For the Degree of DOCTOR OF PHILOSOPHY

By

Samuel Newton Gaines, S* E», M. A. (Fort Worth, Texas)

Austin* Texas June* 1931

’ IS AN ORIGINAL NANUET ?T IT NAY NOT 7'” COPIX THE AUIHOxi'S PERMISSION

A MAGNETOSTRICTION OSCILLATOR PRODUCING INTENSE AUDIBLE SOUND AND SOME EFFECTS OBTAINED

Approv/d r

Approved;

THIS IS AN ORIGINAL MANUSCRIPT IT MAY NOT BE COPIED UTYOUT THE AUTHOR’S PERMISSION

' Deah/ of £he G/adiJate School

PREFACE

The phenomenon of magnetostriction, which may be defined as the lengthening or shortening of magnetic material upon magnetization, has been known for almost ninety years, and as early as 1847 James P. Joule made a careful and dependable set of magnetostrictive measurements. This deformation is exeedingly small, the change in length amounting to an increase of 18 parts in a million in the case of cast cobalt when magnetized to saturation, and to a decrease of 35 parts in a million in the case of nickel. Since it was considered a second-order effect, it was given little attention until about five years ago, when apparatus was developed in the Bell Telephone Laboratories to measure with great exactness the change in length of magnetic alloys and was applied to the very practical purpose of determining the proper proportion of nickel for the now commercially important substance, permalloy.

This work at the Bell Telephone Laboratories made use not only of the direct magnetostrictive effect but also of the inverse magnetostrictive effect, which certainly is not insignificant in size to quote McKeehan,

tt No one would be likely to classify as secondary the fact that the magnetization of nickel in a moderate magnetic field can temporarily be reduced to one-tenth of its normal value by tension well within its elastic limit. M

Since 1926 there has appeared a flood of articles on researches concerned with magnetostriction, showing an increasing interest on the part of physicists in this once neglected phenomenon.

The author wishes to acknowledge with thanks the assistance of Dr. s. Leroy Brown under whose direction the research was undertaken, who suggested the particular field, and who throughout the work gave most helpful suggestions. Dr. C. P. Boner lent important advice in connection with the assembly and operation of the apparatus. Dr. F. L. Whitney, of the department cff geology, very kindly made the microphotographs of eroded nickel. And Mr. Louis H. Gruber, mechanician of the department of physics, constructed the special nickel tubes and other parts.

CONTENTS

Preface - - iii Contents - - v introduction - - 6 Description of Apparatus - 8 Nickel Tubes Ruptured by Magnetostrictive Vibration 12 Loudness of Sound Produced IS Mound or Fountain of Water Produced above Vibrator 17 How the Reciprocating End-Plate Acts as a pump 21 Erosion of Metal by Water 24 Mechanical Production of Colloidal Carbon SO Emulsion of oil in Water 31 Colloid Produced from seed 32 Frogs and Minnows unhurt by Sound, Larvae Killed 34 Bacteria Killed by Audible sound. Law of Survival 35 Biological Research Not Complicated by Temperature 36 Heating Effects of the intense Sound 37 Tactual Illusions 39 Bubbles Responsive to Sound 40 •Atomization* of Liquids 43 The Reaction of Radiation Pressure 45 A Nickel Tube Vibrating in Two unrelated Modes 47 A Mode of Vibration Half the Frequency of Fundamental 48 Tall Striations in Kundt Tube 49 Striation Wall One Particle Thick 50 Growth of Seedlings Affected 51 Longitudinal Striations Produced in a Kundt Tube 54 summary 57 Bibliography 59

INTRODUCTION

The use of a rod or tube of magnetic material (nickel, iron. Nichrome, Monel metal, stainless steel, etc.) to stabilize an oscillating electric circuit, was first proposed by G. W. Pierce\ and such rods were employed by him in the production of standards of frequency in the range from 1,000 cycles per second to about 100,000 cycles and in the measurement of the 2 velocity of sound in solids. Other investigators have used such rods for various purposes, but so far as the writer knows there have been no investigations at great amplitudes of vibration#

Quartz crystals, actuated by intense electrostatic fields through the pieze-electric effect, have been employed by Langevin, Boyle, Wood and Loomis, Richards and Loomis, Hubbard, and 3 others to produce within liquids very strong, ultrasonic vibrations, some effects of which they have noted# Intense audible sound, however, has never been produced by use of

resonant crystals, because crystals thick enough to give audible sound at resonance would require extremely high voltages to make them oscillate strongly; Wood and Loomis found it necessary to use as much as 50,000 volts between opposite faces of quartz crystals a few millimeters thick to produce intense vibrations of frequencies ten to twenty times that of the highest audible sounds.

In the present investigation the object has been to increase the power input of magnetostrictive nickel tubes to the limit as set by the mechanical properties of nickel, and then to discover and investigate properties of the intense audible sound produced by the longitudinal vibration. This research in the sonic range has followed somewhat the work done by the above mentioned experimenters in the supersonic range, but has produced some results and effects that so far have never been reported.

G. W,: "Magnetostriction Oscillators,” Proc. American Academy of Arts and sciences, April, 1928; reprinted Proc, Institute of Radio Engineers, Jan, 1929,

2 Black, K. C.: ”A Dynamic study of Magnetostriction,” Proc. American Academy of Arts and sciences, April, 1928#

Lang, E. H., and Myers, J. A.: "Static and Motional Impedance of a Magnetostriction Resonator,” Proc. Institute of Radio Engineers, October, 1929, pp 1687-1705#

a Boyle, R. W,, "Ultrasonics,” Science Progress, 1928-29, pp 75-105,

Wood, R. W., and Loomis, A. L., “The Physical and Biological Effects of High-frequency Sound Waves of Great Intensity,” Philosophical Magazine, Vol. 4, 1927, pp. 417-436#

Richards, w. T., and Loomis, A. L#» "Chemical Effects of Highfrequency Sound Waves,” Journal of American Chemical Society, Dec. 1927, pp. 3086-3100#

Harvey, E. N.» and Loomis, A. L.» "High-frequency Sound Waves of Small Intensity and their Biological Effects,” Nature, April

1928, pp. 622-624. Harvey, E. N., and Loomis, A. L., "Destruction of Luminous Bacteria by High-frequency Sound Waves," Journal of Bacteriology. 1929, Volume 17, p. 373.

Schmidt, F. 0., Johnson, G. h., and Olson, A. R., "Oxidations Promoted by Ultrasonic Radiation," Journal of the American Chemical Society, Feb., 1929, pp. 370-375.

Schmidt, F. 0., "Ultrasonic Micro-manipulation", Protoplasma, Aug., 1929, pp. 332.

Richards, W. T., "Chemical Effects of High-frequency Sound Waves* Study of Emulsifying Action." journal of the American Chemical Society, June, 1929, pp. 1724-1729.

Abello, T. P., "Absorption of Ultrasonic Waves by Various Gases," Physical Review, June, 1928, pp. 1083-1091.

Chambers, Leslie, and Harvey, E. N., "The Histological Effects of Supersonic Waves of High Intensity upon the fish Lebistes reticulatus and the larva of the frog Rana sylvatica." Journ. Morph, and Physiol., in press.

DESCRIPTION OF THE APPARATUS

The apparatus for producing the intense sound and introducing it under water was developed in the high-frequency physical laboratory of the University of Texas.

Two, 250-watt, UV-204A radiotrons, operating in parallel at plate voltages as high as 2,000, were employed. Fig. Al. Parasitic oscillation between radiotrons was prevented by means of the resistances, and Rg, of 18 ohms each. The 2.5-ampere hot wire ammeter, was protected from injury in case of breakdown of the large oil-immersed variable condenser, Cl, by means of two condensers, Cg, each of which was rated at 1,740 volts and had a capacity of one microfarad. By-pass condensers, C 4, were similar to condensers, Cg. Grid condenser, Cg, was of 0.002 microfarad capacity, and grid leak resistance, Rs, included 8,600 ohms.

The solenoids, and Lg, Figs. Al and A 2, were wound on bakelite spools, each 3.5 centimeters inside between ends and with a hole about 2.2 centimeters in diameter, large enough to give the 3/4-inch nickel tube ample room. The insulating power of these spools was of much importance, as the nickel tube and water in contact with it had to be touched occasionally with the fingers of the operator during operation. The experimenter stood upon an insulating platform to further insure his safety.

The solenoids were wound with No. 22 B. and S., enameled, cotton-covered copper wire; and, after being wound, each coil was dipped into insulating compound until saturated and then baked, this treatment being found necessary in order to prevent breakdowns between layers during operation and to make the

coils more or less waterproof. The D.C. resistance of was 7 ohms and that of Lg was 3 ohms. The solenoids were fastened to a baseboard of bakelite.

The vibrator was a pure nickel tube, unannealed, 3/4 inch (1.83 centimeter) outside diameter, 26.4 centimeters long, with walls of No. 20 Stub’s gauge. It was found that the unannealed, cold-drawn material gave stronger oscillation than the annealed. One end of the tube was closed with a flat plate of nickel of the same diameter as the tube, the two being welded together. The half of the tube opposite to the end closed by the nickel plate contained a narrow, longitudinal slit to diminish electrical eddy currents in the metal. The slit did not eliminate eddy currents, the heating effect of which was still so great as to prevent a tube from being operated air-cooled for longer than one minute at a time. Beyond this period, with temperature somewhere in the neighborhood of the melting point of solder, it was observed that nickel tubes cease to give maximum response in magnetostrictive oscillation.

With the tube above described, simple solutions were obtained to the problems of operating nickel tubes continuously for hours at a time and of introducing the sound into water from beneath the surface,- problems that had to be successfully met before bacteria, seed, or other biological material could be effectively exposed to the sound. The two coils, Ln and L« t were located over the same half of the tube, that containing the slit (lower half, Fig. AS), while the upper part extended into the vessel of water, a flexible water-tight connection being made between the orifice of the vessel and the center of the

nickel tube, a bottle of convenient size, the bottom removed, was inverted and used as water vessel. Immediately beneath the end-plate, the tube was pierced by two tiny holes which permitted four for five drops of water per second to trickle through the tube and cool the lower half, encircled by the coils. The slit had to be closed to prevent moisture from getting into the coils; a waxed paper, lemonade "straw" reinforced by rubber cement served this purpose satisfactorily.

It was discovered that the coils, when located as above described, on the one half of the tube, proved just as effective in energizing the tube as when on opposite sides of the middle as used by experimenters hitherto. It was also found that no reversal of connections of a coil was necessary. Explanation of these two facts is to be found in the theory of magnetostriction oscillation as given very simply by in his article on "Magnetostriction Oscillators." Referring to the usual arrangement, with plate coil on the right side of the middle of the nickel tube and the grid coil on the left side of the middle, he says,

"Any small fortuitous change of current through the plate coil L-» changes the magnetization of the rod and causes it to be deformed (lengthened or shortened)• This deformation is propogated along the rod to its left-hand end and exists temporarily as a deformation within the coil Lg. The deformation changes the state of magnetization and consequently induces an electromotive force in Lg* This acts on the grid and produces an amplified current change in the plate circuit and in The oscillating currents in the system thus build up to a large amplitude with a frequency determined by the frequency of longitudinal vibration of the rod*"

There being a node at the middle of the tube, the waves in opposite halves are at all times mirror reflections of each other; consequently, the inverse magnetostriction effect, upon which

the action of the grid coil depends, acts at the same time that it would have, had the grid coil been situated an equal distance on the other side of the center of the ttibe. And this inverse magnetostriction effect, a transient change in the permeability of the magnetic material due to stresses incident to the passage of the wave, is independent of the actual direction of movement of this disturbance.

In order to obtain maximum amplitude of vibration, it was necessary to establish, with a D.C. electromagnet, a fairly strong polarizing field in the half of the nickel tube within the coils. The polarizing magnetic circuit is indicated in Fig. Al. In Fig. AS, this auxilliary magnetic circuit will be seen to include the iron standard of the support, the clamp supporting the vessel of water, the lower half of the nickel tube, the iron core of a magnetizing coil, the iron foot of the standard, and iron scale weights wherever necessary to fill in. This magnetizing field was maintained by 110-volt, direct current, the winding totaling several thousand turns of No. 22 copper wire.

In making connections it was essential that the magnetomotive force due to the D.C. component of the current in the plate coil aid the polarizing field. It was also essential, as pointed out by Pierce, that the grid coil be connected in opposite sense to that of familiar oscillator circuits.

cit.



Fig. Al.



Fig. A2.

NICKEL TUBES RUPTURED BY MAGNETOSTRICTIVE VIBRATION

The apparatus above described proved more than sufficient to produce maximum practicable amplitude of vibration in nickel tubes, as all of the tubes were eventually broken, the cause being evidently fatigue of the metal. The crack in each case was circumferential and near the middle of the tube, this being the location of the node of the fundamental mode of longitudinal vibration. Typical fatigue cracks in nickel tubes are shown in Fig. 81, only the middle portions of the tubes being included in the photograph. The crack in the tube to the left developed after 13 hours of vibration with half of the tube under water. The fine crack in the tube to the right, seen just starting from the top of the slit, is the result of 20 minutes* vibration in air; subsequent operation of the tube caused the crack to spread circumferentially almost completely around the tube. The time of beginning of a fatigue crack was always indicated by a very material lessening in the maximum intensity of vibration ©btainable.

At the node of motion, the material has been stressed a great number of times in compression and tension, the stresses being no small fractions of the elastic limits of the nickel; internal friction occurs causing change in crystalline structure and loss of molecular strength.

Measurements of the amplitude of vibration of the 26*4 centimeter nickel tube were made with an ocular micrometer as shown in Fig. 82, and resulted in o>Ql millimeter when the upper half of the tube was in water, and three times this, o*o3 millimeter, when the whole tube was in air. The latter vibration was easily visible to the unaided eye.

The value of the maximum instantaneous tension, T m » at the center, when the tube is vibrating, may be calculated. A rod or tube vibrating longitudinally in its fundamental mode has a sinusoidal distribution of tension; consequently.

tv — A m



where T a is the average tension. Now

T a -

♦

where e is the elongation of the half of the tube, i.e., the amplitude of vibration, L is the half-length, and Y is Young’s modulus.

Young’s modulus for nickel is 32 x 10$ pounds per square 5 inch , and the length of the tube between the node of motion and the end of the tube is 13.2 centimeters; consequently, the value of the maximum instantaneous tension at the middle of the vibrating tube is,

£ T m =—X *—*99s *32 X , I2 L = 11,400 lb./in. 2 *3 x lo*2

The condition of tension at the middle of the rod alternates, of course, with a condition of compression whose maximum value must be about equal to the maximum value of the tension.

A Under the heading, "Fatigue of Materials”, M. Merriman states that experiments made by Woehler on wrought iron and by Baushinger and others on the fatigue of steel have resulted in the following laws:

of Chemistry and Physics, 1930, Chemical Rubber Pub. Co. sMerriman, M., of Materials,” 1910, John Wiley and Sons, Inc., N.Y.» pp* 353-358, p. 381.

*l. The rupture of a bar may be caused by repeated applications of a unit-stress less than the ultimate strength of the material.

tt 2. The greater the range of stress, the less is the unit-stress required to produce rupture after an enormous number of applications.

H 3. When the unit-stress in a bar varies from 0 up to the elastic limit, an enormous number of applications is required to cause rupture.

”4. a range of stress from tension into compression and back again, produces rupture with a less number of applications than the same range of stress of one kind only.

H 5. When the range of stress in tension is equal to that in compression, the unit-stress that produces rupture after an enormous number of applications is a little greater than one-half the elastic limit.

"The term ‘enormous number* means about 40 millions, that being the number used by Woehler to cause rupture under the conditions stated. - - - »

And later, on page 382, Merriman says,

"The indications are that any stress, however small, will produce fatigue when it is repeated a number of times in a material that has a crystalline structure.”

The elastic limit of nickel is not given in any of the available collections of physical data, but the "Handbook of 7 Chemistry and Physics” gives 61,000 pounds per square inch as the breaking point of nickel# The breaking stress for drawn iron is given as 96,000 pounds per square inch, the elastic limit as 29,000 being but three-tenths of the breaking stress. Mild steels have elastic limits five-tenths to six-tenths as great as their breaking strengths. Now three-tenths of 61,000 pounds per square inch is 18,500, and five-tenths is 30,500, so that it is probable that the elastic limit of the unannealed, cold-drawn nickel tubing used lies in the neighborhood of 24,000 pounds per square inch.

The calculated maximum instantaneous unit stress, 11,400 pounds per square inch at the node of a nickel tube vibrating in air is, therefore, about half the elastic limit, hence, according to the fifth law quoted above, should produce rupture after about 40 million vibrations, about 75 minutes of oscillation at 8900 cycles per second.

The time required to break an 8900-cycle tube vibrating in air varied from 15 minutes to about 90 minutes. It is evident, then, that with the amplitude of vibration obtained in air and the high frequency of vibration of the 26.4-centimeter tube, such a tube should be expected to develop a fatigue crack after a period of time of the order of magnitude observed.

Hickel tubes operating with the upper half surrounded by water often lasted 13 hours or more before a crack appeared.

The author suggests that this new device for quickly fatiguing nickel should prove of value to investigators interested in the mechanical properties of this important metal. X-ray analysis of the crystal structure in the vicinity of the fracture should prove interesting.

7 Loc. cit.



Fig. B1



Fig. B2

LOUDNESS OF SOUND PRODUCED

The sound produced by a tube vibrating in open air was of sufficient intensity to cause pain to the unprotected ears of a person remaining for a few minutes within ten feet of the apparatus. The use, however, of small pads of cotton batting upon the ears was found sufficient to enable the investigator to work all day in comfort while exposed to the radiation.

When a nickel tube was operated in air, no difference in loudness was noticeable after removing the disk from the end of the tube; neither did extending the slit the full length of the tube have any apparent effect upon the intensity of the sound generated. The D.C. polarizing field did, however, very noticeably increase the intensity of the sound produced by a tube.

MOUND OR FOUNTAIN OF WATER PRODUCED ABOVE THE END-PLATE OF VIBRATOR

A mound or fountain somewhat similar to that described 8 by Wood and Loomis in their work with ultrasonic vibration, was raised above the surface of the water directly over the closed end of the nickel tube. Fig. Cl is taken from the article by Wood and Loomis; Fig. 02 is from an article by 9 Hopwood showing "Mound of oil produced by pressure of sound radiation (n = 400,000)". Fig. 03 shows the mound of water produced above the vibrating nickel tube when there was 6.5 centimeters of water above the end-plate of the tube. Figs. C 4, C 5, 06, 07, and 08 show the mound or fountain when there was but 1 centimeter of water above the end-plate of the tube. The heights of the fountain were often four or five centimeters; the height of the fountain or mountain reported by Wood and Loomis was as much as 7 centimeters.

Fig. C 9 shows a stream of large drops of water and mist produced when there were but 2 millimeters of water above the end-plate of the vibrating tube. Some of the water drops were thrown 40 centimeters above the liquid surface#

The pictures suggest that in the case at least of a vibrating nickel rod the mound raised is due in part to water moving upward in a vertical column. That such a vertical current does exist was proven by stretching a membrane about a centimeter beneath the surface of the water and a couple of centimeters above the end of the tube. When the latter was vibrated, the membrane was observed to bulge as tho struck by a vertical column of moving water. As the membrane was found to be of ap-

proximately the same density as the water, the bulging of the membrane could hardly be ascribed to radiation pressure resulting from partial reflection of the sound at the membrane, nor did it seem probable that the sound had been so strongly absorbed by the membrane as to result in radiation pressure upon the membrane. The surface of the water above the membrane suffered little or no disturbance.

The following mathematical consideration shows that the energy density of a sound within the liquid of sufficient intensity to produce a mound 4.2 centimeters high would have to be of an order of magnitude that hardly seems probable, namely, 3.5 x 10 times the energy density produced in air by the human voice.

Sacia and Black 10 , of the Bell Telephone Laboratories, have found that 2 micro-watts per square centimeter at the "transmitter* (Just in front of the mouth) is an average value for vowels in ordinary speech. Now the velocity of sound in air at 20®C. is approximately 344 meters per second. Hence we may calculate the energy density, U, in air Just in front of the mouth of the speaker,

z watt 2 y in" 6 - U - cm? 2 x 10~ b joule *OOO5B erg 34400 2®*_ 3T4W cm J cm? sec*

Turning now to the nickel rod vibrating about one centimeter below the surface of water and producing a fountain or mound 4.2 centimeters high above the surface of the water, let

us assume that the fountain is raised by the pressure of radiation normally incident at the water-air boundary and totally reflected at this boundary. Then, since the pressure, p, would be ecgual to twice the energy density,

p = 2UI or.

U, -J2_ - _ g x 980 dyne „ 2 060 erg 1 ~ 2 cm? cm?

Hence,

U 1 2060 erg per cm. « 3.5 x 10 6 U *OOO5B erg per cm?

A simple test was next devised that seems to the writer to be decisive and to indicate that no appreciable mound due to radiation pressure was present on the surface of the water# The upper part of the tube was introduced into a trough having glass sides, as shown in Figs. CIO and Cll. , The water above l the end-plate of the vibrating tube was about 8 centimeters deep. By use of a narrow shingle, the water in the trough was given a motion of about half a foot per second from right to left past the end of the tube. The bump was observed to shift to the left, as shown in Fig CIO. The water was next made to move from left to right over the end of the tube, and the mound moved to the right, as shown in Fig. Cll. As is clearly indicated in the latter photograph, there was no appreciable indication of a mound above the end of the vibrator, and it will be noticed in each photograph that the stream of very tiny bubbles, which indicates the location of the column of moving water, unmistakably points toward the mound. When the speed of the water was increased to several feet per sec-

ond, the mound failed to appear on the surface of the water, and the stream of tiny bubbles was seen to bend downward indicating that the column of moving water was joining in the general circulation within the trough*

The author reasons that sound, because of its high velocity in water, would not be appreciably changed from its vertical course by the comparatively slow, horizontal motion of the water, therefore, that the mound, if it had been due to radiation pressure, would have remained practically stationary above the end-plate of the tube*

In view of the above, the author believes he has proved beyond doubt that the mound or fountain of water produced by his apparatus is not due appreciably to radiation pressure but to a colutai of water moving vertically upward from the reciprocating end-plate of the nickel tube. And the author suggests that some experimenter possessing a crystal oscillator try the experiment of giving sideways motion to the oil above the crystal, noting whether or not the mound is decidedly shifted in the direction of the motion. In the event the mound of oil is due partly to a vertical convection current and partly to radiation pressure, two mounds should appear when the oil is moving sideways, and quantitative measurements of the two effects could be obtained*

sLoc. cit.

F. L., "Experiments with High-frequency Sound Waves", Journal of scientific Instruments, Feb, 1929, p. 34.

Sada., c. F e , and Black, C. J.» Bell System Technical Journal, July, 1926, p. 393.



Fig. Cl



Fig. C2 Fig. 13. Mound of oil produced by pressure of sound radiation (n = 400,000)



Fig. C3



Fig. C4



Fig. C5



Fig. C6



Fig. C7



Fig. C8



Fig. C9



Fig. C10



Fig. C11

HOW THE RECIPROCATING END-PLATE ACTS AS A PUMP

The existence of a column of water moving upward from the reciprocating end-plate of the nickel tube requires that something equivalent to valve action be present, since such action is essential to the operation of a reciprocating pump*

Valve action in the present case doubtless results from the presence of cavitation at the end of the tube. When the mound begins to appear on the surface of the water, cavitation is invariably observed upon the end-plate and a clattering noise suggesting water-hammer is always heard. The cavitation is in the form of a white, hazy, fairly symmetrical pattern,- as shown in Fig. Dl, which was obtained by photographing the vibrator from above with a watch crystal covering its end so that the surface of the water was freed from disturbance. The hazy lines of the pattern converge at the central white bubble* Fig. D 2 is a magnified side view of this bubble. Cavitation is to be expected because the acceleration of the vibrating tube is very great. The acceleration, y», of the end-plate is given by the formula,

yH « 4ir 2 n 2 A cos 2TTnt

where n is the frequency* A the amplitude* and t the time The maximum value of this acceleration is.

Y”

At 8900 cycles per second and the measured amplitude under water of *Ol millimeter* the maximum acceleration becomes

Y« = 39>48 x x <OOl cm* ~ 3*13 x 10 6 cm * « 31*3 sec? sec?

This is about one-tenth of the acceleration of the bullet of an army rifle while the bullet is moving under the influence of

the powder gas in the gun barrel.

The water fails to follow the reciprocating end-plate, the force of inertia being greater than that of adhesion between water and nickel, and cavitation results. The discontinuity is presumably a vacuum containing some water vapor and a little air, and is, of course, a transient of very short duration. The presence of some air, presumably derived from that dissolved in the water, is indicated by the fine mist of air bubbles in the column of moving water, which mist is clearly shown in Figs. CIO and Cll and in Fig. C 3.

The fact that the cavitation does not appear over the whole of the plate might be explained by assuming that the plate does not move as a whole but divides up into nodes and loops of motion like a Chladni platej some observations to be given later, however, seem to oppose this assumption.

At each vibration, when the plate recedes from the water, the water at the circumference has time to rush in a short way toward the center of the plate to partially fill the cavitation. When the plate returns, the cavity probably disappears, only to reappear again the next half cycle. The thin ring of water that started toward the center of the plate continues to shrink of its own inertia until it is near the central bubble, when it spurts upward giving rise to the vertically moving column of water. The motion of the shrinking ring of water would resemble somewhat part of the progress of the splash of a drop of mercury upon a smooth glass plate as illustrated in Fig* D 3, taken from page 23 of Prof. A. M. Worthington’s booklet, "The Splash of a

Drop•”

The theory given above seems to explain in a fairly satisfactory manner the valve action that must necessarily exist in order that the reciprocating end of the tube may act as a pump#

-Worthington, A. "The Splash of a Drop»», Society for Promoting Christian Knowledge, London, 1895*



Fig. D1



Fig. D2



Fig. D3

EROSION OF METAL BY WATER

It was discovered that if a layer of solder covered the end-plate of the nickel tube vibrating in magnetostriction water, a dark gray pattern developed upon the surface of the soft metal within a few minutes. The pattern was somewhat rose-shaped. When a round disk of steel was soldered upon the end of the nickel tube,- a gray, rose- or star-shaped pattern developed on its surface. In all subsequent investigation,the nickel end-plate alone was used, after having been polished.

The effect was first attributed to oxidation. Tests, however, of the eroded and non-eroded areas of nickel, using poten-12a tiometer and calomel cell , showed that there was no higher degree of oxidation of the eroded surface than of the polished surface adjacent to it. Subsequently, the author was able to recover some of the finely divided nickel that had come from the eroded areas. It was still in the bright, metallic state.

A careful photographic study of the phenomenon of cavitation and the attendant erosion was then conducted, all the photographs being taken of the erosion of a nickel end-plate that had been welded upon the end of the nickel tube and then polished.

Aftdr taking the photographs, I ran across reference to a phenomenon of erosion, the reference being in that delightful little book by sir William Bragg , ”The World of Sound”, pages 133-135. The phenomenon was described as a harmful actioh upon propeller blades of fast ships due to cavitation of water in the wake of the screw propeller followed by collapse of the cavity. There being no cushion of air to break the force of

the blow, the latter is very intense and sharp. ”The effect,” says Bragg, «Is well known to naval engineers, because it often has a destructive effect upon ship propellers; the blows are as violent as if they had been struck by hammers.”

In the search for literature on the subject, I was very kindly aided by letters from Mr. Stanley S. Cook of the Parsons Steam Turbine Company, Ltd., of England, and Mr. A. R. Marron, shop superintendent of the Norfolk Navy Yard, Portsmouth, Va., both of whom I hereby heartily thank. The literature on the 13 subject is small. Lord Rayleigh , in 1894, gives the following account of previous consideration of the subject:

"When reading 0. Reynold’s description of the sounds emitted by water in a kettle as it comes to a boil and his explanation as to the partial or complete collapse of bubbles as they rise through cooler water, I proposed to myself a further consideration of the problem thus presented; but I had not gone far when I learned from sir C. Parsons that he also was interested in the same question in connection with cavitation by screw-propellers and that at his instigation Mr. S. Cook, on the basis of an investigation by Besant, had calculated the pressure developed when the collapse is suddenly arrested by impact against a rigid, concentric obstruction. During the collapse, the fluid is regarded as incompressible. "In the present note, I have given a simpler derivation of Besant’s results and have extended the calculation to find the pressure in the interior of the fluid during the collapse. It appears that before the cavity is closed these pressures may rise very high in the fluid near the inner boundary. "As formulated by Besant, the problem is »an infinite mass of homogeneous incompressible fluid acted upon by no forces is at rest, and a spherical portion of the fluid is suddenly annihilated; it is required to find the instantaneous alteration of pressure at any point of the mass and the time in which the cavity will be filled up, the pressure at an infinite distance being supposed to remain constant. 1w

Then follows a solution of the problem as proposed; and upon the assumption that the radius of the original boundary is twenty times the radius of the final boundary and that the pressure at an infinite distance is one atmosphere, it was found that the instantaneous alteration of pressure would be 10,300 atmospheres, equal to 68 tons per square inch*

In 1915, a committee was formed by the Board of Invention and Research of the English navy, for the investigation of the different "possible causes of corrosion or erosion". The investigations of this committee occupied 18 months, and re- 14 suited in 1919 in a paper by Sir Charles A. Parsons and Stanley S. Cook, published in the journal, "Engineering", giving the results of the investigation and a description of the apparatus developed. The paper reads, in part:

*The corrosion or erosion of propellers has for many years engaged the attention of engineers and builders, and the capricious character of the action has rendered it difficult to assign an adequate and satisfactory cause to account for the observed results. - -

“The possible causes of corrosion or erosion considered may be stated under five headings:

"(1) The nature of the surface of the metal and the state of the original stress on this surface

"(2) Stresses in the blades under working conditions

*(3) Infringement of water at high velocity on the surface of the blades

*(4) Cavitation

*(5) Water-hammer produced by the closing up of vortex cavities.*

Each of these possible causes was made in turn the subject of investigation, and the conclusion was reached that the effect was due to a combination of the last two possible causes. The paper is very concisely reviewed in the "Journal of the American society of Naval Engineers* l , for August, 1920, and, 15 as quoted to me in a letter by Mr. A. R. Marron, the review is as follows:

tt lt will be recalled that at last year’s meeting of the Institution of Naval Architects a paper was presented by Sir Charles A* Parsons and Mr. Stanley s. Cook entitled “Investigations into the Causes of Corrosion or Erosion of Propellers l *, an abstract of this paper being given in (•Shipbuilding and Shipping Record* of April 17, 1919. The theory was advanced that rapid and deep erosion of propeller blades and the denting of bosses might be due to the waterhammer effect produced ty the closing up of vortex cavities. That the blow produced toy the rapid collapse of a vortex cavity is sufficient to produce a destructive effect on a metal was clearly sir Charles Parsons at the conversazione of the Royal society at Burlington House, when he exhibited the apparatus which was employed by the sub-committee of the Board of Invention and Research to investigate the subject of propeller erosion. A hollow cone is fitted at its apex, with a die cap through which is a hole of the same diameter as the end of the cone, a thin metal plate being placed between the cap and the cone. The cone is placed in water in a tall tank and after being filled with water it is thrust quickly downward on to a block of rubber at the bottom. This momentarily forms a cavity at the apex of the cone, which closes with a perceptible metallic click and with sufficient force to puncture the metal plate. The plate is 0.03 inch thick, piercing of which indicates a pressure of 140 tons per square inch. It is difficult to see how the effect of these collapsing vortices on propeller blades can be resisted. •

The photographic record of the results of the work done by me on this phenomenon of erosion as exhibited upon a polished plate of nickel welded to the end of the nickel vibrator. Is attached herewith#

Explanations of the photographs are as follows:

Figo El: Nickel plate on end of the tube, immersed in water vibrating# The erosion pattern and central crater, which have been produced by previous vibration, are to be seen clearly#

Fig. E 2: Same as El, except that the tube is now vibrating. It will be noticed that the erosion pattern is no longer visible, being covered by the similar cavitation pattern. The central bubble of this pattern is dimly to be seen. Wherever there was a point of the star of the erosion pattern the cavitation pattern has extended out to the edge of the disk. It was observed that the longer the tube was vibrated the closer the points of the eroded area approached the edge of the disk. In connection with this photograph, reference should be again made to Fig. Dl, which is a view from directly above the endplate of the vibrating immersed nickel tube. The white cavitation pattern and central white bubble are clearly shown. Reference should also be made to Fig. D 2, an enlarged view of the

central misty cavitation bubble, directly beneath which the pit forms.

Fig. S 3: The polished ends of two tubes, after three minutes’ vibration each under water.

Fig. E 4: The same two end-plates after 30 minutes’ vibration under water.

Fig. E 5: The end of a similar tube after two hours 1 vibration under water.

Fig. E 6: This photograph shows the result of a study to determine whether the star shape of the patterns was due to vibration of the disk in the manner of a Chladni plate. The welded nickel plates on the ends of the tubes vary in thickness progressively from 2 millimeters in the case of "a" to 10 millimeters in the case of w d“. Unfortunately, end-plate *a w cracked partly loose from the tube soon after the vibration under water was started, and so its markings are of no significance in this connection. It seems reasonable that if the star-shaped patterns owe their shape to the existence of a Chladni disk type of vibration of the end-plate, then the thicker the disk the less pronounced should be this pattern. Such was not the case in the results of the test, for *b* with plate 4 millimeters thick has less pronounced pattern than plate «c» 6 millimeters thick, and plate H d* 10 millimeters thick. Each was vibrated under water for 45 minutes. The external diameter of each tube was 3/4 inch (19.2 millimeters) and the thickness of the wall .7 millimeter. The above observations seem to indicate that the peculiar rose or star-like shape of the erosion patterns cannot be explained as due to a Chladni disk vibration of the end-plate.

The central craters of the erosion patterns are well shown in Figs. E 4, E 5, and EG. The craters shown in Fig. E 6 are about 0.5 millimeter deep; but in disks that have been vibrated several hours under water the central crater has attained depths approaching 1 millimeter* Interesting characteristics common to these craters are the irregular perimeter and undercut wall.

Fig. E 7: Microphotograph of a portion of a pattern on an endplate with marking very similar to in Fig. SB* The magnification is forty diameters, the curved edge of the disk is to be seen in the upper right-hand corner. The dark portion is the part of the previously polished surface that still is unaffected. The eroded portion reminds one of the surface of the moon when viewed through a good telescope; the roughness of the moon is, I believe, partly ascribed to the impacts of many meteorites.

Fig* SB: Another magnified view of the eroded surface of the end-plate shown in Fig* E 7 • 5

Fig* 39: Microphotograph, magnification 20 diameters, of the

bottom of a pyrex glass flask after two hours* exposure to the vibration while immersed in water at a distance 2 millimeters above the end-plate of a nickel tube. It was observed that throughout this time cavitation bubbles connected the endplate and flask. It seems certain that this whitening and scarring of the surface of the glass is due to the same phenomenon as the erosion of the nickel, i.e., cavitation of the water followed by water hammer*

Fig* E 10: Microphotograph (magnification 50 diameters) of the bright, very fine, metallic nickel powder eroded from the polished surface of the end-plate of a nickel tube vibrated under water. This powder is to be found floating upon the surface of the water a few hours after the vibration* A borax bead test confirms nickel*

The discovery that metals may be eroded under water by magnetostriction vibration and the investigation that has followed, as outlined above, lead the author to make the following claims of contribution to knowledge of the important effect of erosion of metal by water:

(1) That the apparatus developed (Fig* A 2) is simple and the tests readily made upon plates of any metal that may be soldered to the end-plate of the nickel tube; consequently the apparatus should be of practical value in research and in routine testing in laboratories devoted to the testing of materials for ships, especially in comparative studies of erosion of different metals proposed for propellers;

(2) That the erosion of glass (Fig* E 9) is new, as is also the formation of a comparatively deep pit in metal at the center of a fairly symmetrical erosion pattern (Figs* El, E 3, E 4, E 5, and E 7);

(S) That the recovery of the bright, finely divided, metallic nickel and the results of the potentiometric tests of bright and eroded surfaces, confirm the conclusions of other investigators that the action is purely mechanical*

X S . *The Electromotive Force of Nickel and the ?io eCt of s cclu aed Hydrogen”, Am. Chem. Journ* V01.xL1»N0.3,1909. Bragg, w. H.,*The World of Sound”, Bell and Sons, London, 1927.

y— , Lord, «On the Pressure Developed in a Liquid during the Collapse of a Spherical Cavity>” Phil. Mag. Vol. 38, 1894.

14 Parsons, sir Charles a., and Cook, Stanley S.,"lnvestigation into Causes of Corrosion or Erosion of Propellers," Engineering, 1919, p. 515»

communication to the author•



Fig. E1



Fig. E2



Fig. E3



Fig. E4



Fig. E5



Fig. E6



Fig. E7



Fig. E8



Fig. E9



Fig. E10

MECHANICAL PRODUCTION OF COLLOIDAL CARBON

Soot from a smokey acetylene flame was deposited upon the sides of a carefully cleaned, upper half of a nickel tube, and the tube was vibrated under distilled water. This was repeated a number of times,vsing carbon tetrachloride, benzene, methyl alcohol, acetone, transformer oil, and two samples af Nujol. The black suspensions that resulted were passed through filter paper of fairly fine texture, except for one sample of the Nujol. The sols of carbon were caught in labeled test tubes, as shown in Fig. Fl. Each, upon test, strongly exhibited the Faraday-Tyndall effect. Evidently the soot had been sheared between vibrating rod and water into particles of colloidal size.

The dispersions of carbon in water and in acetone proved to be fairly permanent, as shown in Fig. F 2, which photograph was taken after the colloids tad remained quiet for one month.

Except for the fact that the mechanical motion used was translation rather than rotation, the phenomenon is similar to that used in the*colloid mill» which during the past ten years has come into commercial use*

W* T. reported in 1929 the production of an extremely thin dispersion of glass in water, using intense sound of supersonic frequency*

17 Richards, W. T.» “Chemical Effects of High Frequency Sound Waves, a Study of Emulsifying Action** Journ. Am. Chern. Soc. June, 1929, pp 1724-1729.



Fig . Fl



Fig. F2

EMULSION OF OIL IN WATER

10 It has been reported by Wood and Loomis , working with ultra-sonic sound, that, if two non-miscible liquids such as oil and water were exposed to the radiation in the same vessel, an emulsion or colloidal solution is formed.

This effect has been obtained satisfactorily by the author, using the intense audible sound produced by magnetostriction oscillation. The photograph on the right in Fig. F 3 shows a beaker containing oil floating on water. This was exposed to the radiation for one minute by dipping the beaker into the fountain of water above the vibrating tube until within 2 millimeters from the end-plate.

The result is shown on the left. (The gray spots on the photographs, which resultedfrom an accident to the negative, must be eliminated from consideration.) It will be noticed that the water is now very cloudy with colloidal oil. The farther edge of the bottom of the beaker has disappeared from view, and the boundary line between the two liquids has become dim*



Fig. F3



Fig. F4

COLLOID PRODUCED FROM SEED

While testing the effect of strong vibration upon seed, it was observed that a colloid formed in water above the seed exposed to the intense audible sound* Fig. F 4 is a photograph by transmitted light showing this effect. The control is on the left and has been treated like that on the right except for a 35-minute exposure to the intense sound. The seeds were clean. The exposure was made by lowering the flask into the water above the vibrating tube until about 2 millimeters from the end-plate of the tube. Temperature was carefully controlled by surrounding both flasks with ice water during the period of exposure. Tests with thermometer showed that the temperatures of the water in the two flasks never exceeded 13°C. during the irradiation, and were never more than 5£ a apart*

The suspended substance was probably partly protein as was indicated by the disagreeable odor developed when the liquid was exposed to air for a couple of days*

FATIGUE OF GLASS

An effect of strong supersonic sound reported by Wood and Loomis is its tendency to cause glass exposed to it to crack as shown in Fig. Gl t taken from their article. A curious tendency of the glass that has cracked away to leave rounded or oval openings seems to be indicated in the figure.

A similar effect was obtained with the intense audible sound produced by magnetostrictive vibration. Fig. G 2 shows a flask used for about five hours in exposing bacteria to the sound. At the right is a pyrex beaker that has been subjected to the sound. Fragments of glass in each case were perserved t their round or oval character is apparent.

21 Loc. cit.



Fig. G1



Fig. G2

FROGS AND MINNOWS UNHURT BY SOUND, LARVAE OF MAY FLY KILLED

Frogs and minnows put into water with the vibrating rod were not killed, even after exposures totaling thirty minutes. If the tube was started oscillating when a minnow was directly over it, the fish darted away; but the minnows acted normally anywhere else in the vessel, and often struck at food particles during the irradiation*

A minnow was put into a test tube containing water, and the tube held in water for one minute close to and directly above the oscillating rod* Though visibly tired by the treatment, the fish rapidly recovered afterwards and suffered no ill effects*

The larvae (nymphs) of the May fly, however, when put into test tube and similarly treated, were killed, only five seconds being required*

THE BACTERICIDAL EFFECTS OF HIGH FREQUENCY SOUND WAVES*

Reprinted from The Journal of Infectious Diseases, Vol. 47, No. 6, Dec., 1930, pp. 485-489

O. B. WILLIAMS AND NEWTON GAINES AUSTIN, TEXAS The biologic effects of supersonic waves have received attention from a number of investigators, following the pioneer work of Wood and Loomis. 1 Few of these studies, however, have dealt with the effects on bacteria, and no studies appear to have been made on the effect of high intensity waves of sonic frequency. The purpose in this paper is to present some of the results that have been obtained in a study of the lethal effects of such waves on bacteria. APPARATUS The apparatus for producing the intense sound and introducing it under water was developed in the high-frequency physical laboratory of the University of Texas. Two 250-watt, UV-204A radiotrons, operating in parallel at about 2,000 volts on the plates, were employed (chart 1). Parasitic oscillation between radiotrons was prevented by means of the resistances, R x and R 2, of 18 ohms each. The 2.5 ampere hot wire ammeter, Ami, was protected from injury in case of breakdown of the large oil-immersed variable condenser, Ci, this protection being secured by means of two condensers, C 2, each of which was rated at 1,740 volts and had a capacity of one microfarad. By-pass condensers, G, were similar to condensers, C 2. Grid condenser, Cs, was of 0.002 microfarad capacity, and grid leak resistance, Ra, included 8,600 ohms. The solenoids, Li and L 2, were wound on bakelite spools, each 3.5 cm. inside between ends and with a hole about 2.2 cm. in diameter. The wire used on the solenoids was B. and S. no. 22, enameled, cotton-covered copper; and, after being wound, each coil was dipped into insulating compound until saturated and then baked, this treatment being found necessary in order to prevent breakdowns between layers during operation and to make the coils more or less waterproof. The D.C. resistance of Li was 7 ohms and that of L 2 3 ohms. *From the Departments of Physics and Bacteriology of the University of Texas.

1. Wood, R. W., and Loomis, A. L.: Philosoph. Mag. 4:417, 1927.

2

O. B. Williams and N. Gaines

The vibrator was a pure nickel tube, cold-drawn, unannealed, three-fourths inch (1.83 cm.) in outside diameter, 26.4 cm. long, with walls of no. 20 Stub’s gage. When in operation, the tube vibrated longitudinally, at about 8,800 cycles per second, with a node of motion at the center.

The nickel tube was operated in a vertical position, the upper half surrounded by an inverted glass bottle of about 1 liter capacity, the bottom of which had been removed, A flexible, water-tight connection was made between the orifice of the vessel and the center of the nickel tube. The bottle was filled with water to a depth of several centimeters above the end of the vibrator. This end of the tube was closed with a flat plate of nickel of the same diameter as the tube and welded to it.

Just under this end-plate, the tube was pierced by two tiny holes that permitted 4 or 5 drops of water per second to trickle down through the tube cooling its lower half, which was encircled by the solenoids. The lower half of the

nickel tube contained a narrow, longitudinal slit to cut down electrical eddy currents in the metal. The slit was stopped with a cork strip extending from top to bottom so as to prevent moisture from getting into the coils.

In order to obtain maximum amplitude of vibration, it was necessary to establish, with a D.C. electromagnet, a fairly strong magnetic flux in the lower half of the nickel vibrator.

In making connections it was essential that the magnetomotive force due to the D.C. component of the current in the plate coil aid the auxiliary magnetic field mentioned in the preceding paragraph. It was also essential that the grid coil be connected in opposite sense to that of ordinary oscillator circuits. The electrical circuit was tuned to the natural frequency of the nickel rod.

With the powerful magnetostriction apparatus described, it was possible to introduce so much energy into the water that a fountain of water 4 cm. high was produced, even though water covered the end of the tube to a depth of 2 cm. The glass vessels containing the suspensions of bacteria to be exposed to this intense radiation were

High Frequency Sound Waves

3

immersed in this fountain and forced down into the water until within about 1 mm. of the end of the vibrating tube. When this glass container was a thin, flat-bottomed flask, a hump several millimeters high was observed on the surface of the liquid in the flask.

For the theory of magnetostriction oscillators, the reader is referred to an article by Pierce, 2 who produced the first oscillators of this type.

ORGANISMS EMPLOYED AND METHOD OF EXPOSURE

The organism employed in this work was a typical citrate-negative strain of Escherichia coli that had been originally isolated from the spleen of a cadaver at autopsy.

Cultures for exposure were grown in casein hydrolysate medium. The age of the culture ranged from twelve to twenty-eight hours at the time of exposure. No differences due to age have been observed. Dilution blanks were prepared from sterile fifteenth-molar phosphate buffer solution of pn 7 (colorimetric). Gauze-covered cotton plugs and plugged pipets were used in order to minimize the possibility of contamination.

Twenty to thirty cubic centimeters of a 1 : 100,000 dilution of the original culture was prepared in a 50 cc. pyrex Florence flask, and the initial concentration of cells determined by quantitative plating in standard nutrient agar. The suspension was then exposed to the radiation, and at suitable intervals of time samples were removed for plating. Five plates were made of each dilution at each interval of time and the results averaged. There was close agreement between plates of both the same and of different dilutions.

Preliminary tests indicated that an exposure of at least ten minutes was necessary in order to obtain significant and decisive results. In most of the experiments, platings were made at ten-minute intervals over a period of sixty minutes. These values were not, however, rigidly adhered to.

RESULTS

The accompanying table gives the results obtained in two experiments, and chart 2 shows those obtained in experiment 3 graphically. Since other experiments gave essentially the same results, they need not be included here.

It is apparent that there is essentially a straight line relationship between the time of exposure and the logarithm of the number of survivors. The slope of this line may vary with different experiments, but the values obtained in any one experiment lie on or very near a straight line.

2. Pierce, G. W.: Proc. Am. Acad. Arts & Sc. 63:1, 1928; reprinted Proc. Inst. Radio Engineers 17:42, 1929.

4

O. B. Williams and N. Gaines

lo determine possible effects of the magnetic field, a suspension in a pyrex tube was placed within the coils where the field was much more intense than was the case in any of the other experiments. An exposure of three minutes was sufficient to heat the tube to a point where it was comfortably warm to the hand. Accordingly, at intervals ranging between two and three minutes, the tube was removed and

cooled in tap water. The total exposure was thirty minutes. The initial count on the suspension was 11,300 per cubic centimeter and the count at the end of the test was 11,900. The lethal effect evidently was not due to the magnetic field.

Little is known as yet about the chemical effects of high frequency sonic -or supersonic waves. That effects on bacteria are not directly due to oxidation is indicated by the fact that tests for peroxide were

High Frequency Sound Waves

5

negative and by the fact that a suspension irradiated under very low oxygen tension (obtained by flushing out the vessel with hydrogen) showed an effect similar to that displayed by cultures irradiated in air.

In contrast with the experiments of Harvey and Loomis, 3 no difficulty due to heating has been encountered. The temperature of the water in which the flask was suspended did not in any experiment reach the optimum for growth of this organism. It was usually about 30 C. Heating of the cells cannot, therefore, be considered as a factor in the cause of death, since “hot spots” of sufficient intensity to exert lethal effects could not exist in the relatively cool medium.

In one experiment, owing to difficulty in tuning the circuit, the hump on the surface of the liquid in the flask was not manifest during the first fifty minutes of the experiment; it appeared almost coincident with the beginning of the final ten minute period of exposure. The counts of the initial concentration and for each of the first five sampling periods agree within 5 per cent of each other, while the count at the end of the last period showed a decrease of approximately 20 per cent. Other experiments in which the hump on the liquid surface was usually pronounced support the opinion that the amplitude of vibration markedly influences the results, the decrease being more rapid in the instances of powerful vibration. From this it would appear that the lethal effects are possibly due to the violent agitation, probably within the cell, produced by the high frequency waves. However, the possibility of comminution by the suspending medium cannot be excluded.

Mammalian blood corpuscles suspended in physiologic solution of sodium chloride and irradiated for ten minutes showed approximately 50 per cent lysis. This is in accord with the results of others who have used higher frequencies than was the case in this work.

SUMMARY

It has been possible to kill cells of Escherichia coli by exposure in liquid to high frequency audible sound waves of about 8,800 cycles per second. The lethal effects are probably due to a violent agitation set up within the cell by these waves. Lytic action on red blood corpuscles has been observed.

3. Harvey, E. N., and Loomis, A. L.: J. Bact. 17:373, 1929,



Chart 1. —Oscillator circuit.



Chart 2.—Death of bacteria.

Survivors per Cc. Time of Exposure, Exper. 3 Exper. 4 Min. 13 Hour Culture 27.5 Hour Culture 0 6,200 7,900 10 5,900 6,300 20 4,400 4,800 30 4,100 3,700 40 3,300 3,200 50 2,800 2,700 60 2,400 2,500

Lethal Effects of High Frequency Sound Waves on Escherichia Coli

BACTERIA KILLED BY AUDIBLE SOUND, LAW OF SURVIVAL DISCOVERED

Bacteria (Escherichia coll) in buffer solution in a small flask were irradiated directly above the end-plate of the nickel tube which 'was vibrating under water, as shown in Fig* Al. Samples were taken at the beginning and every ten minutes for an hour. This particular piece of work was done jointly with Dr. 0. B. Williams, Associate Professor of Bacteriology at the University of Texas. We were aided by his student, Mr. Nathan C. Carpenter. The results of this part of the work have been published in full in the Journal of Infectious Diseases, Vol. 47, No. 6, Dec., 1930, pp. 485-489,- reprint of which article is being bound herewith* A semilogarithmic plot of the survivors per cubic centimeter appears in Chart 2 of the reprint, data for which are given just above the chart. The nickel tube used for the irradiation of the bacteria had a frequency of 8700 cycles per second; the current in the plate and grid coils was one ampere*

It will be noticed in Chart 2 that the data fall very nearly upon the straight line. The number of survivors obeys the logarithmic law.

-.017t N - 6800 e

where N is the number of survivors per cubic centimeter* e is the base of natural logarithms, and t is the.time in minutes.

BIOLOGICAL RESEARCH AT SONIC FREQUENCIES IS NOT COMPLICATED BY TEMPERATURE EFFECTS.

The best temperature for growth (optimum temperature) of the bacteria used in the above test is 37°C., and the temperature of the buffer solution containing these organisms never reached this value during the irradiations. It was found that the heating effect due to viscosity of the water was, at sonic frequencies, so small as to be negligible. When water containing ice was used in the vessel surrounding the rod, it was determined by thermometer that the water within the flask never became more than Centigrade warmer than the water in the vessel on the same level as the flask, even after 40 minutes of continuous exposure to the sound.

The fact that the temperature can be readily controlled if the sound used is within the audible range is a fact of importance to further research in the biological effects of 18 sound. Wood and Loomis have pointed out that the kinematic coefficient of viscosity increases with the square of the frequency. They found that at frequencies from 300,000 to 400,000 cycles per second the heating of liquids is very pronounced. Water in a test tube surrounded by ice water, suffered a rise in temperature as great as one degree every three seconds.

— —— xo Lac. cit.

HEATING EFFECTS OF THE INTENSE SOUND

When a finger was placed under water near the end of the vibrating rod but not necessarily in contact with it, a burning sensation was felt that could not be endured. When the tube was vibrated in air at maximum intensity and was firmly held between the fingers near one end, the sensation of pain produced was not endurable; that this burning sensation was really due to increase of temperature of the flesh was proved by touching the fingers immediately to one*s cheek, when a decidedly higher temperature of the flesh was detected.

A cork firmly fastened in the end of a nickel tube and vibrated either in air or under water, quickly became so hot at its center, due to the degeneration of sound energy into heat within the viscous cork, that the gases of dry distillation blew out a vent hole in about 25 seconds, the production of gas practically ceased after one minute of treatment. The cork was then removed from the nickel tube and cut With razor blade to reveal the axial section.

In order to obtain an estimate of the temperature produced within the cork, a capillary glass tube containing mercury was introduced into the center of a cork, which was then firmly fastened to the end of the tube and vibrated. After the vibration the capillary was removed and examined; the presence of tiny drops of condensed mercury in the glass tube above the original drop indicated that the temperature within the cork had been in the neighborhood of the boiling point of mercury, 357°C., or higher.

Fig* Hl shows axial sections of six charred corks; the

cinders that remain within the corks are clearly indicated. The *irradiation* of the cork in each case lasted for only one minute, and the vent hole appeared in from 25 to 30 seconds after the first sound was introduced.

In Fig* H 2 are also shown some corks into which the intense audible sound has entered. At the left in this illustration is shown the method of fastening the cork into the end of a nickel tube; and on the right, with white card above it, is shown the cork used in obtaining an estimate of temperature, with capillary tube containing mercury, thrust into its center.

These experiments in which corks have been successfully charred through the degeneration of audible sound energy into heat are the first successful attempts in which striking heating effects have been obtained with sound of audible frequency. The phenomenon happens to be the reverse of that of the anipp tube,- being the direct conversion of the energy of audible sound into heat energy, in direct contrast to the direct conversion of heat energy into audible sound.



Fig. H1



Fig. H2

TACTUAL ILLUSIONS

The following phenomena, while not heating effects, were closely associated with the above• A nickel tube,, held lightly between the fingers near one end and made to vibrate while the circuit was being tuned, seemed to become very smooth, as though covered by a film of oil* And, when the point of maximum intensity of vibration was being passed through, the tube seemed to swell between the fingers. Test with calipers, however, showed no such enlargement was actually taking place. The phenomenon of apparent swelling proved very useful in tuning the circuit to the point of maximum vibration of the rod.

BUBBLES RESPONSIVE TO SOUND

When a nickel rod is vibrating under water, bubbles of certain sizes ranging from about one millimeter in diameter downward, are to be seen within the water or against the sides of the vessel, dancing or darting about in a very erratic manner, the motion of the single bubble suggested strongly the movement of a molecule as pictured in the kinetic theory of gases, of particular interest is the fact that these bubbles, which I am calling ’’resonant* for lack of a better name, are translucent, the air-liquid surface being strongly disturbed causing them to look white; and interesting also is the fact that, seemingly, only bubbles of certain sizes are thus erratic in their movements and translucent.

bubbles are often attracted one to the other, doubtless due to the Bernoulli effect, and here and there two such bubbles will be seen to join themselves together producing a single bubble that posseses neither the cloudy surface nor the erratic movements of its parents.

The photography of a ’’resonant* bubble proved to be difficult, but by lowering a watch glass into the water until it was within a millimeter of the end of the vibrating end-plate and using a dark field illumination, a fairly good picture was obtained after a number of trials. This is the irregular lightning-like trace in Fig. jl. Inspection will reveal, in addition to the general erratic character of the path, a series of minute irregularities.

The translucent surface of a ’’resonant 11 bubble must be due to ripples of some sort, perhaps to a ripple or ripple group that runs round and round such circumference that the moving ripple gets an impulse each time a wave-front passes the bubble.

As a rough check upon the reasonableness of the above theory, an equation will be derived connecting the diameter, D, of a *resonant M bubble with the number, n, of successive ripples contained in the great circle of the bubble,- U denoting the velocity of a ripple, and f denoting the frequency of the sound.

We shall assume for the sake of simplicity that U is independent of D and equal to the velocity of a ripple on the level surface of water, about 30 centimeters per second. A frequency of 8900 cycles per second will be used. Evidently,

MD « U n T

Solving for D,

n _ nu D w

To determine the smallest size of resonant bubble, i.e., the bubble for which a ripple maltes one complete circuit between the arrival of successive wave fronts of the sound* let n — 1 ; then

D - nU = — .0107 millimeter. 11l

It was observed that bubbles barely visible to the naked eye were often H resonant“; and so, there seems to be a degree of reasonableness to the above theory.

The following phenomenon, observed several times, indicates that the surface of a ’’resonant* bubble possesses something akin to circular motion. When a translucent bubble that had

happenedto attach itself to the side of the water vessel chanced to capture a short bristle from foreign solid material in the water,- the bristle would whirl around, sometimes clockwise sometimes counter-clockwise.

A rapid, orbital motion of a *resonant w bubble about some point on the surface of the vibrating rod or of the sideof the glass vessel was often observed* the bubble remaining in contact with the surface of the solid.

The whirling of particles suspended in liquid exposed to sound has been observed by Harvey, Harvey, and 20 and Schmidt has observed rotary and orbital motions of particles in a suspended drop of liquid exposed to sound of about 750,000 cycles per second frequency♦

T 9 Loc. oit.

20 , LOC • cit •



Fig. J1

"ATOMIZATION” OF LIQUIDS, A POSSIBLE EXPLANATION

’//hen the nickel tube was inverted and a drop of water or oil suspended from its closed end and the tube vibrated but with circuit not tuned for exact resonance with the vibrator, it was found that the surface of the drop had become translucent, the whitened appearance being due to the disturbed condition of the surface, Fig. £2. When, now, the tuning condenser, Cl, Fig. Al, was varied so that the circuit approached resonance with the rod,- the vigor of oscillation increased and the cloudy drop ejected a fine spray from its tip, as shown in Fig. K 3. If, however, instead of merely approaching resonance, the circuit was suddenly tuned to the point of maximum response of the rod, the cloudy drop ejected extremely fine drops of liquid from all parts of its surface, as is fairly well shown in Fig. K 4 (In Fig. K 4, a cork fixed in the open end of the tube is serving instead of end-plate.)

Very similar ’’atomization 1 ’ phenomena have been observed 22 23 by Wood and Loomis and by Harvey, Harvey, and Loomis , using supersonic vibration.

In the present research, a file-like pattern was observed upon the surface of the vibrating drop, and it occurs to the author that the ’’atomization”is probably due in part to this ripple pattern becoming so pronounced as to break into the fine spray. A similar phenomenon occurs when the edge of a 24 bowl containing water is strongly bowed • It is also probable that cavitation within the drop aids in the formation of spray.

If such a ripple pattern occurs at the interface of liquids when exposed to sound, it may offer mechanism for the emulsification observed at such boundaries.

22 Loc. cit.

cit.

24 Bragg, Sir William H., ”The World of Sound I *, p. 88.



Fig. K1 Fig. K2





Fig. K3



Fig. K4

THE REACTION OF RADIATION PRESSURE

When the lower end of a vertical vibrating rod was dipped into water and then raised, a much larger drop of water rem&lned attached to it than when it was not oscillating* If the vibration was made more intense, the drop could be seen to flatten out against the end of the rod* This flattening suggested strongly that the liquid was being pressed up against the oscillator*

The phenomenon of the flattening out of a drop is clearly shown in Figs. Kl and K2* In Fig* Kl, the rod is stationary and a drop of ordinary size is suspended from its end. In Fig* KB, the rod is vibrating, and it will be noticed that the shape of the drop has changed decidedly, that the drop seems to be pushed up against the vibrator*

The drop of liquid, since it was moving with the rod, was doubtless radiating intense sound, and it seems reasonable that it was the back pressure of sound radiation which flattened out the drop and which enables a vibrating rod to retain a larger drop of liquid than when at rest*

The only other possible explanation for the flattening out of the drop seems to be that an increase in surface tension took place during vibration* To test this possibility, the rod was assembled in the apparatus in the usual with closed end inside a vessel of water, as shown in Fig* K 5; and the platinum ring of a Du Nouy tensiometer was lowered into the three millimeters of water above the end-plate of the tube* The surface tension was measured with the tube at rest and then with it vibrating with sufficient intensity to raise a

Ficj.

smooth mound of water 2 millimeters high above its end* No difference in surface tension could be detected.

We seem forced to the conclusion, then, that the phenomenon under consideration is, indeed, due to the reaction of radiation pressure upon the hanging drop* If this explanation is correct, this is the first time that the reaction of radiation pressure A upon the radiator has been demonstrated*



A NICKEL TUBE VIBRATING IN TWO UNRELATED. MODES AT ONCE

A nickel tube vibrating in air, when actuated by currents of nearly the natural frequency of the tube, was often observed to emit beats, which were doubtless due to the tube’s vibrating at the frequency of the circuit and at its own natural frequency at the same time. By carefully varying the capacity, C-p operator could reduce the number of beats as low as four or five per second before the tube and circuit pulled Into step with each other.

A MODE OF VIBRATION HALF THE FREQUENCY OF THE FUNDAMENTAL

When a vibrator was operating in air at full amplitude of vibration and especially after the nickel had warmed up a little, the tube often gave, in addition to the fundamental* a lower note which proved to be of just half the frequency of the fundamental. Several tubes of different lengths and diameters were thus investigated, and each time the lower note was just half the fundamental frequency, Measurement of the frequencies was made by the beat method, a carefully calibrated audio-frequency oscillator being used.

The phenomenon occurred even when the tube was clamped lightly at the center*

TALL STRIATIONS IN KUNDT TUBE

A glass Kundt tube of one inch internal diameter was excited by a very strongly vibrating nickel tube, three-fourths inch in diameter, and the distance from vibrator to reflecting disk was carefully adjusted. Tall cork dust striations, some extending three-fourths of the way across the tube, were obtained. These persisted as long as the sound was continued.

STRIATION WALL ONE PARTICLE THICK

A Kundt tube of 1-3/4 inches internal diameter was excited by a nickel tube, grains of rice l * being employed instead of cork dust. The sound was sufficient to raise striation walls consisting of grains of the rice, the walls being several grains high. The walls were everywhere but one grain 25 thick, as demanded by Koenig’s striation theory.

25 Koenig, W», H Hydrodynamisch-akustische unterzuchungen, M Wied* Ann* XLII, 1891, pp. 353 and 549*

RATE OF GROWTH OF SEEDLINGS AFFECTED BY SOUND

Indications have been obtained of the following:

(1) That the exposure of radish or turnip seed to very intense audible sound (8900 cycles per second) may affect the rate of growth of the seedlings produced;

(2) That, for some reasons as yet undetermined, the effect may be an acceleration of growth or a retardation, or no decided effect at all;

(3) That a given batch of irradiated seed showing an acceleration or a retardation on the first planting will, upon subsequent plantings, usually repeat the effect exhibited by the first planting;

(4) That the acceleration or retardation, expressed in weight of the live plant, may be as much as 25%.

The indications listed above are derived from the set of tabulated results bound herewith*

About 500 seed were introduced into a 25-c.c* flask and covered with about 15 c.c* of water* The flask was then exposed to the intense sound in the same manner as were the bacteria* as illustrated in Fig* Al. the bottom of the flask being maintained about 2 millimeters from the end-plate of the tube vibrating under water. This irradiation lasted for 35 to 40 minutes*

The 500 seed of the control were placed in a similar bottle and surrounded by the same conditions as the irradiated seed except for the exposure to sound* Temperature was carefully controlled by surrounding both flasks with ice water during the time of exposure to sound* Fig* F 4 is a picture by transmitted light of the two flasks at the end of an irradiation of the one on the right. The formation of a colloid in the water above the irradiated seed has already been discussed*



Immediately aftdr exposure, the batches of seed were separated from the water. The first planting was then made, and the remaining seed were preserved in dry filter paper for subsequent plantings.

The serial numbers used on the sheet of tabulated results may be explained by an example. *Radish irradiation number 3, planting number 4», abbreviated "R 34 refers to the third batch of radish seed exposed to the sound and to the fourth planting of these seed.

Six to ten days after planting, the seedlings produced were "harvested.* The part of each plant below where the root hairs begin was removed, the length of the stem (hypocotyl) was measured, and the weights of the average plant first live then dried, were obtained.

Fig. 81 shows planting R 52 shortly before it was "harvested*. The control seed had been planted in quadrants numbers 1 and 3, 50 seed to the quadrant. The irradiated seed had been planted in quadrants 2 and 4, 50 seed to each quadrant. Figs. S 2 and S 3 show the appearance of the quadrants of planting RBl as the seed began to sprout. Fig. 82 is a photograph taken 51 hours after planting, Fig. S 3 was taken 69 hours after planting.

Fig. 84 shows the appearance of R 63 "eliminated because of low %*s of germination.* Fig. 85 shows R 73, "eliminated because irradiated quadrants differed, widely. *

The results seem to indicate that there were at work at least two different effects of sound upon the seed during irradiation, one operating to accelerate the growth and the other

to retard it. Alteration of the endosperm by the sound energy so as to make this food more available to the germ and also the partial breaking up of the seed covering (as suggested by the formation of a colloid above the irradiated seed) may have operated to accelerate growth. Such possible effects as bruising or overheating of the germ may account for the retardation of growth.

Presumably, both effect or effects tending to accelerate growth and effects tending to retard it were always present in the same seed; and, if they were of about equal magnitude, the net result was neither acceleration nor retardation.

Fig. S 6 shows two quadrants of planting R42> a typical case of retardation of growth. Fig. S 7 shows two quadrants / of R 91 t a case typical of accelerated growth of seedlings.



Fig. S1



Fig. S2



Fig. S3



Fig. S4



Fig. S5



Fig. S6



Fig. S 7

Weic/ht of H fSeedLeaves %> /Icce/eraf/o/i Co/c/us/od Strut! NOS. Uo/ft of Seef&* Fating zo /Fermination nypoco Con- Irra- % — T Con-, 5rm- troi diated ' Control rroldiateol Cm, Cm. r L/' 0/* Irra, irnt- ' Conrro/ d/fted «■»?. am. v e. Urie-o/ 70 Zr/rd Oan - Trtra - ControTtro! dialed Zrna. Tiypooo^y/ Uye j] ried Radish / / 7/75/30 84 84 /00%> S.tt5.?Z t/4%> 395 J2t4 /£/% .00635. 00653 708% (4% 2!% 8% IRdidi 2 / 7/22/30 66 62 94 6.22 6,54 /057a ,1689 106% G 1 2 2 7/30 72 6! 85 6.09 S.93 97% .1143 J473 92. -3 -8 J Radish 3 / 7/26/30 68 77 H5 581 6.15 104 J3?2- ,1694 /2Z t 00732-.O09O! 72.4 22 24 3 2 £6 60 107 6, OB 5:40 c / .1861.1608 86 .00414,00837 92 -H -14 -8 3 3 7/30 66 7Z 708 6.5-7 7.00 707 J777.H70 tzz , 00796.0/000 !2(> 7 22 2b 3 4 8// 72 90 6.88 7J6 104 .1813 .7957 708 ,oo83o. oo873 70S 8 y 3 £ 8/? 605 84 139 5,/4 5,27 103 ,182.7 .1863 702 .00781.00803 103 3 ■ 2 3) Turnip / / 8/9/30 65.5 44.6 68 4.44 2J2 48 ,0617.0442. 72 -52 -78 Turnip 2 / 8/H/30 38.7 88.7 /oo .053i .0524 W ,0034 ,00248 703 -1 3 ] 2 2 8//3 87 42 /06 .0556.0507 9/ .0017?. OO2Z? 81 -9 ~/8 f 2 3 8/23 85 60 7/ J03* .08-48 92 ,00432.00440 /02- -8 2 J Radish 4 / 8/9/30 57549.3 86 £74 3708 88 .2)35.7477 69 ,00962,0068? 72 -!2 -31 - 28 4 2 8/Z2/ 74 58 78 7548 J08C 70 .00725.0 0622 86 -30 - /4 । 4 3 8/74 822 78,5 76 ,/683 99 .00812.00777 -/ -4 J /ladish 5 / 8////30 44.1 50.0 U3 .1048 ,/OS8 /O/ / 5~ 2 8/3 £3 43 ?/ ,/633 J350 83 .00887.00787 8? - / 7 -// 3 8/20 36 sr /4s £30 +.16 85 .2425.1728 79 .0/075.0/6/3 93 -2/-7 1 5" 8/23 467213 4/ 5.5/ 5.4/ 96 .3035.254) ,01388 86 -4 -70 ~/4 J UM £ 1 8/7/30 8/25 24 2/ 86 452 453 7/7 .2745.3230 //8 ,01391 ,0/636 H7 17 /8 / 7 6 2 78 40 222 3/3 5.02 97 .1508.211$ 740 ,00827.01043 /zc -3 40 2b 1 6 3 % 6 # r* • t Radish 7 I 8/25/30 8/26 56 58 50 43 704 86 5.30 0.36 6.42 6.0? 70/ 95 .2115.2045 I 7 ,oo?24.oo?/1 /oo / ~3 0 7 Z 7 3 7/2 6.5T4 6 33 / -3 7 j/ 7ft /+7 77 * Radish 8 / 8/26/30 68 73 707 £51 650 /OO ,2046.2340 109 0 9 8 2 8/29 6! 56 92 6.576.05 92 97 .00444,0(092 HO -8 -3 /O 8 3 9/4 54 50 93 6.78 7.32 708 .0OS'5/f .00462 82 8 ~/2 8 * 7/4 68 58 & .oo468.OOS/3 /09 9 Radish 9 / 33 36 109 6.18 6.43 /OO ,2/75.2720 125 ,00/87.0/232 127 0 25 27 4 2 9/4 56 55 98 J?33-2200 //4 .00S83,00696 H9 74 /9 9 3 50.50. A /oo .7678 .2020 H9 ,0043? .00443 HZ 79 72

LONGITUDINAL STRIATIONS PRODUCED IN A KUNDT TUBE

When a strongly vibrating nickel tube was introduced into a glass Kundt tube of considerably larger diameter than the vibrator, it was found possible to produce striations of cork dust running parallel to the axis of the Kundt tube rather than across it, also to produce striations that formed scallops running the length of the tube. These scallops were probably a combination of the longitudinal striations and the ordinary transverse type.

In all the photographs shown,- Ll, L 2, etc., the internal diameter of the glass tube used is 1-3/4 inches. In each case the reflector consisted of a brass disk slightly smaller in diameter than the internal diameter of the glass tube.

This brass disk had a small hole in its center; and, because of the possibility that the striations might in some manner be affected by this hole, test was made with the latter stopped up flush with the surface of the disk. The production of longitudinal striations was not affected*

Fig. Ll striations of the ordinary type perpendicular to the axis of the tube,- i.e., perpendicular to the 26 direction of propogation of the sound, which Koenig proved must be the case for the striations to be stable. The reflector is to be seen at the tight in the figure.

The striations in Fig. L 2 resemble those in Ll» but exhibit a tendency toward the longitudinal type*

The mixed type of striation, forming scallops along the

length of the tube, has been photographed from the side of the tube, instead of the top, to give a better idea of these really beautiful striations. The end of the vibrating nickel tube is shown to the left, and it will be noticed that it does not point straight along the axis of the glass tube.

The longitudinal type of striation is illustrated in Figs. L 4 and L 5. In order to obtain these it was found necessary that the axis of the vibrator made a considerable angle with the axis of the glass tube. Notice that even in these two photographs, the tendency to form scallops, curving first to one side of the glass tube then to the other, is still to be seen.

Now, according to Koenig’s theory, the striation must form at right angles to the direction of propagation of the sound. It would seem, then, that at least part of the sound waves within the tube in all but Fig. Ll must be moving at right angles to the axis of the glass tube, probably forming standing waves between opposite walls of the tube.

As to the manner in which sound of such direction could be produced, let us consider a wave front that starts from the end-plate of the nickel tube, Fig. L 6, and is reflected from one wall to the other until it strikes the brass disk; here it will be regularly reflected and make a. zigzag return, the return path being symmetrical with the other, the axis of the glass tube being axis of symmetry. The wave reflected at the brass disk will cross the oncoming wave at places a, b, c, d, etc. If paths b-m-a-n, etc. are a whole number of wavelengths, the motion of the air particles at a, b. c, d, etc.

will be at right angles to the axis of the Kundt tube,- the motion, of the air particles at the particular instant shown in Fig. L 6 being toward the reader at places a, c, etc. and away from the reader at b, d, etc. The directions of the resultant sound at the places under consideration would be, of course, only approximately at right angles to the axis of the Kundt tube, because the vector of the returning reflected sound is weaker than that of the oncoming original sound because of losses due to absorption, diffraction, etc.

The theory just given is strongly supported by two facts. First, if longitudinal striations are to be found in a tube at all, there will always be striations of this type next to the reflector,- Figs. L 2, L 4, and L 5. Second, as mentioned in a preceding paragraph, scallops running lengthwise of the tube curve first to one side of the KUndt tube then to the other, suggesting that the resultant motion of air particles has opposite direction at adjacent scallops. The bowing of the longitudinal striation is probably due to variation of the phase of the reflected wave, which would result in a slight difference in the direction of motion of the air particles located to the left or right of each of the points a, b, c, etc.

26 L00. cit.



Fig. L1



Fig. L2



Fig. L3



Fig. L4



Fig. L5



Fig. L6

SUMMARY

(1) Apparatus has been developed capable of pushing the magnetostriction oscillation of nickel, the most magnetostrictive element, to the limits set by its mechanical strength;.

(2) The sound produced has been introduced under water from beneath the surface;

(3) The above mentioned devices have made possible the production at sonic frequencies not only of phenomena hitherto obtainable only with piezo-electric crystals vibrating at supersonic frequencies but also of new phenomena, some of which probably open the door to new fields of investigation.

The interiors of corks are charred to cinder by the sound. A mound or fountain 5 centimeters high forms on the surface of water when the rod vibrates beneath the surface; it is proved that this phenomenon is due to pumping action of the reciprocating rod and not due to radiation pressure.

Erosion of metals by cavitation and resultant waterhammer effect has been obtained and a photographic investigation made of the erosion patterns produced; practical application cf the technique employed is suggested*

Theories designed to explain "resonant 1 * bubbles and the "atomization* of liquids have been developed.

Carbon deposited on the sides of the nickel vibrator goes into colloidal solution when the tube is vibrated under water.

The reaction of radiation pressure upon the radiator itself is demonstrated experimentally for the first time.

Larvae are killed immediately by the sound; bacteria are killed, dying off in accordance with simple logarithmic law.

The irradiation of seed by the intense sound changes the rate of growth of the seedlings produced*

Striations in a Kundt tube that are parallel to its axis are produced, and an explanatory theory developed.

BIBLIOGRAPHY

Abella, T. P.: “Absorption of Ultrasonic Waves by Various Gases,” Physical Review, June, 1928, pp. 1083-1091.

Black, K. C.: “A Dynamic Study of Magnetostriction,” Proc. American Academy of Arts and sciences, April, 1928.

Boyle, R. W.: "Ultrasonics,” Science Progress, 1928-29, pp. 75 - 105.

Bragg, W. H.: ”The World of Sound”, G. Bell and Sons, Ltd., London, p. 88.

Chambers, Leslie, and Harvey, E. N., ”The Histrological Effects of Supersonic Waves of High Intensity upon the fish Lebistes reticulatus and the larva of the frog Rana sylvatica,” Journ. Morph, and Physiol., in press.

Harvey, E. N., and Loomis, A. L., "High-frequency Sound Waves of Small Intensity and their Biological Effects”, Nature, April 21, 1928, pp. 622-624.

Harvey, E. N., Harvey, E. 8., and Loomis, A. L., ’’Further Observations on the Effect of High Frequency Sound Waves on Living Matter,” Biological Bulletin, Dec., 1928, pp. 459-469.

Harvey, E. N., and Loomis, A. 1., “Destruction of Luminous Bacteria by High-frequency Sound Waves,” Journal of Bacteriology, 1929, Vol. 17, p. 373.

Koenig, W.: “Hydrodynamisch-akustische Untersuchungen,“ Wied. Ann. XLII. 1891, pp. 353, 549.

Handbook of Chemistry and Physics, 1930, Chemical Rubber pub. Co.

Hopwood, F. L., ’’Experiments with High-frequency Sound Waves”, Journal of scientific Instruments, Feb. 1929, p. 34.

Lange, E. H., and Myers, J. a.: ’’Static and Motional Impedance of a Magnetostriction Resonator,” Proc. Institute of Radio Engineers, October, 1929, pp. 1687-1705.

Mckeehan, L. W.: ”Magnetostriction”, Journal of Franklin Institute, 1926, p. 737.

Merriman, M., ”Mechanics of Materials,” 1910, John Wiley and Sons, Inc., N.Y., pp. 353-358, p. 381.

Pierce, G. W.: "Magnetostriction Oscillators,” Proc. Am. Acad, of Arts and Sciences, April, 1928; reprinted Proc. Inst, of Radio Engineers, Jan., 1929.

Rayleigh, Lord: “On the Pressure Developed in a Liquid during the Collapse of a Spherical Cavity,” Phil. Mag. Vol. 38, 1894.

Richards, W. T., and Loomis, A. L. : ”Chemical Effects of Highfrequency Sound Waves,” Journal of American Chemical society, Dec., 1927, pp. 3086-3100.

Richards, W. T.: “Chemical Effects of High-frequency Sound Waves, Study of Emulsifying Action,” Journ. of Amer. Chem. Society, June, 1929, pp. 1724-1729.

Sada. 0. F., and Black, C. F., Bell System Technical Journal, July, 1926, p. 393.

Schmidt, F. 0., Johnson, C. H.• and Olson, A. R.: “Oxidations Promoted by Ultrasonic Radiation,” Journal of the American Chemical Society, Feb., 1929, pp. 370-375.

Schmidt, F. 0.: ’’Ultrasonic Micro-manipulation,” Protoplasma, Aug., 1929, p. 332.

Wood, R. W., and Loomis, A. L., “The Physical and Biological Effects of High-frequency Sound Waves of Great Intensity,’* Philosophical Magazine, Vol. 4, 1927, pp. 417-436.

Schoch, E. P., “The Electromotive Force of Nickel and the Effect Of Occluded Hydrogen,” Am. Chem. Journ. Vol. XLI, No. 3, 1909.