SONIC STUDIES OP LIQUIDS. I 759The rate of vaporization and condensation is affected to a remarkable degree by the state of dryness. Ammonium chloride which has been dried for ten days at 60°in a high vacuum appears to be completely dissociated in the vapor state. Urbana, Illinois

No abstract

Ultrasonic velocity has been measured at 30°C in the four chlorinated methanes: methyl chloride, methylene chloride, chloroform, and carbon tetrachloride, at pressures from 1.5 cm Hg to more than one atmos in the case of methyl chloride, and with the others to the vapor pressures available up to 28°C and at frequencies from 0.2 to 2 Mc sec l . Dispersion of the velocity has been found in each case, the relaxation frequency/pressure ratios, correcting for departure from the ideal gas law, at 30° being in CHaC!, CHCla, and CC!. respectively 1. 13, 27.3, and 23.3 Mc sec l atmos-I . In CH2C!2 two relaxations have been found with respective frequency/pressure ratios after similar corrections of 2.27 and 105 Mc seC I atmos-I . 6

The steady state of motion of a fluid between two infinite plane parallel boundaries is found for the case in which one of the boundaries is given a prescribed periodic motion normal to its surface, the other boundary being infinitely rigid or being assigned a coefficient of reflection. The excess pressure at any point in the fluid is found, being of particular interest at the boundary of the source where it has a term in phase with the velocity of the source and one in phase with its displacement. These terms pass through cyclical values as the distance between the source and reflector is increased, the first passing through sharp maxima, the second changing rapidly from negative to positive values at reflector distances of an integral number of half wavelengths in the fluid. Application is made to the case where the source is the surface of a piezoelectric plate maintained in forced vibration. The equivalent electric network of the plate and coupled fluid column is found to be the same as that for the plate alone, with modified resistance and capacity coefficients, making possible consideration of the theory of the acoustic resonator interferometer in conjunction with driving and measuring circuits.