The absorption and velocity of sound in binary mixtures of water with alcohols, glycols, and glycol ethers have been measured at frequencies in the range of 5-25 megacycles, using the optical diffraction method originally developed by Debye, Sears, Lucas, and Biquard. However, the method of absorption measurement has been improved by utilization of a high gain, secondary multiplier-type photo-tube viewing the first-order diffraction spectrum, the change in intensity of this spectrum being an index of the sound absorption in the liquid. This method has proved more rapid and precise than other diffraction techniques described in the literature. Ultrasonic absorption peaks at intermediate concentrations have been found in mixtures containing acetone, ethanol, propanol, isopropanol, and tertiary butanol and in the monoethyl and monobutyl glycol ethers. In both series, the magnitude of the peaks increases as one progresses from the ethyl to the butyl derivative, and there is a simultaneous shift of the peak toward higher water concentration. No absorption peaks were found in mixtures containing methanol, glycol, monomethyl glycol ether, or dioxane. Velocity peaks at intermediate concentrations have been found in all of the mixtures listed. Mixtures of tertiary butanol and methanol show neither absorption nor velocity peaks.The observed absorptions are considerably greater than would be expected from classical theory. Consequently, the experimental data appear to require a new, or at least modified, theoretical approach. The problem is discussed briefly in the light of modern theories of molecular association, liquid crystal formation, etc.

The problem of examining opaque surfaces in the electron microscope is discussed and it is s?own tha~ n(;me of the methods heretofore described is completely satisfactory for the examinaon of .o,rgamc surfaces. Tw? new methods, a low. pressure po.lystyrene-silica technique and a s!lver-s!l~ca double e~aporatlOn method, a~e described and It IS demonstrated that they allow o~sen:atlOn of o!,gamc fis well as metallurgical surfaces. Electron micrographs of fiber surfaces, blOlog;lcal material, pamt films, ores, and metals are included to illustrate the utility of these techmques.

After a brief review of various applications of ultrasonic techniques, considerable attention is paid to the established methods employed for making sound waves visible. I t is shown that these methods are primarily modifications of the technique of "schlieren photography" originally developed by Foucault and used frequently for photographing phenomena (e.g., air flow analysis) in which refractive index gradients are set up. The advantages and disadvantages of the various techniques are discussed in some detail and it is shown that a technique employed by Willard is particularly well adapted to the visualization of ultrasonic waves. A modification of this method is discussed, the experimental apparatus is described and typical photographs of ultrasonic wave patterns are shown. In particular, the close analogy existing between light waves and ultrasonic waves with respect to the wave phenomena of refraction, diffraction, and interference is demonstrated in a number of photographs.

The application of ultrasonic methods to the determination of the elastic constants of solids is considered in some detail. It is shown that a rotating plate technique in which ultrasonic transmission is plotted as a function of the angle of incidence of the waves allows determination of the velocities of dilatation and shear waves in the plate. From these data, Poisson's ratio and the mechanical moduli may be determined. Details of an apparatus for making such measurements are given. The elastic constants of several metals have been measured with this equipment and the values obtained are shown to be in agreement with previous published data. In addition, measurements of a number of thermoplastic and thermosetting resins have been made successfully. It has been found that in the case of Melmac Resin 26–8B there is no variation in the elastic constants as a function of cure time.

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