Topics in.
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Chemical Instrumentation feature Edited by 5.
Z. LEWIN, New York University, New York, N.Y. 1 0 0 0 3 . chemical applications as welding (which depends on ultrasonic removal of oxide coatings from metals), nor t o such highly specialized techniques as sonic cardiography and encephalography.
These articles, most of which are to be contributed by guest authws, are intended to serve the readers of this JOURNALby calling attention to new developments i n the theoy, design, w auailabiliby of chemical laboratory instmmentation, or by presenting useful insights and explanations of topics that are of practical importance to those who use, or teach the use of, modern instrumentation and insbummtal techniques.
P r o d u c t i o n of S o n i c W a v e s
Audible frequencies are conveniently produred by mechanical devices sueh as tuning forks, or electrumeehanical loudspeakers, but these cannot give high enaugh poxer a t high frequencies. UItmsonic whistles and sirens are nsefrd in G a l e n W. E w i n g , Deportment o f Chemistry, Seton Hall University, some applications. Rut by far. the most widelv used sources are based on pieeoSouth Orange, New Jersey 07079 electric crvstala and mnenetostrictive devices. Applicittiuna in chemistry and related Comptwsionnl waves represent one Piezoelectric eryrtsla inehde not only fields are generally in four categories: mechanism of propagatiug energy throngh quartz, hut also llochelle salt, hsrium ( I ) physical elIectii per sr, inch~dingd t r a solids, liquids, and gsses. This form of t,itanate, lead zirconate, ammonium disorm cleaning of small objects, disintewave motion shares many of the properhydrogen phosphate (ADP), and lithium gvation of semisolid entities, sueh as blood ties and mathemstienl treatments which sulfate. For laboratory apparatus quartz, cells and bacteria, and eohgulrtt,ion or we cwtomarily associate with electrohsrium bitannte and lead airconate are clomping of powders or particles in susmagnetic i.adi:tti~n_ Thus sonic1 radiamost commonly utilized. Rochelle salt pension; (2) physical properties as tools tion is charaatwizod by a. velocity v , is more s t n ~ n g l ypiezoelectric, but is soft, in chemical analysis, pmticrderly sonic which is dependent on the medium of easily broken, and melts a t ahout 75°C. attenuation as s measwe of stwponded propagation, h y a freq~leneyf , whieh is The usefulwx of Rochelle salt, ADP, solids in a slurry, and the velocity of sonic independent of the medinm, and by a and lithium sulfate is also limited by their waves as determined by the nature of the wavelengt,h A, which is t h e quotient of the soh~bility in water. Barium titanate is medium; (3) flowmeters, thmngh applicafilnt two parameters, fabricated its 8, polycrystalline ceramic, tion of t h e Doppler effect; and (4) morex = v/j and has much t o recommend it, hut its or-less specific chemical effects readting eleqtrieal nmnerties decreahe slowly with . . The velocity innges between 104 and f m m lacaliaed heating 1 , ~ cavitation. age. 10' em/see; (,he lower values are found in Tnhle 1 is indicative of e w ~ w applicat Whatever piezoelectric crystals is chosen gsses, the intermediate in liqnida, and t h e tions. I n this review we will give no is coated with metal foil or eqltivalent high values ill 8olids (eompnre this with consideration t o the well-established field electrodes on opposite faces. B n ac po101* cm/sec, t h e velocity of light. in uaeuo). of ultrasonic cleaning, nor t o such nontent,ial applied across these electrodes The wavelengths may range from abont will c m a e t h e cryst,al t o vihrate. The 10-4 t o 111* cm, whieh corresponds t o T a b l e 1. Applications of Sonic a n d vibratim will be most intense (for a given electromsgnetic wavelengths from t h e Ultrasonic E a u i ~ m e n t : Summorv o f excitation) when the dimensions of the infrared thnnlgh t h e mie~~owaveand Entries in current Buyers' ~ u i d k s crystal permit a. mechanics1 resonanre, hut radio regions, 1TP ha (1 he = 1 cycle/iec), forced vibrations of wefnl intensity can corresponding to the "short-wave" radio Number of Entries be produced at notrl.esanant frequenrie?, Anal. Ind. region. essential if the frequency is t o he rranned. Cateeolv Chem.* Science6 R8s.S Sonic waves can he shsorbed, scattered, hlagnetostriction is a dimensional roflerted, refracted, and diffracted, and Generators 15 11 38 change produced in a hat. of nickel and intet.femu;e can be observed, just as in Analyaer8, so~lnd . . . 17 33 of some other metals and alloys by the optics. The freqlwtcies w e too low t o Analyzers, ldtraimposition of a. magnetic field. This is produce nsefd interaction with malecolar , . . 12 14 sound accomplished a t high freqnerrcies by mr... ... Analysis equipment 7 ~ntationalor vibrational levels, hut sonic rounding t h e bar with a solewid fed by an Cleaners 25 28 41 energy e m be transferred t o molecdes !I 12 ... Disint,egrators oscillator. The "bar" takes the form of 2nd large pnl.ticles as translational energy, Probes 6 19 28 a thin walled t h o or a h!mdle of wires, t o thus prudocing heat. Therefore chemical Surgical knives .. . 3 3 rzduee eddy-eilrrent nud hysteresis losses. effects of sound and ultrasmnld mnst he ... 3 ... Cardiographs hlctgnet,
