Sound absorption in a $0.02 M MgSO4$ solution and in a $0.02 M MgSO4‐0.6 M NaCl$ mixture at 25°C and pressures up to 307 arm

Sound absorption from 30 to 300 kHz in a $0.02 M MgSO4$ aqueous solution and in a $0.02 M MgSO4−0.6 M NaCl$ aqueous mixture were measured at pressures of 1 and 307 atm and 25°C with a 100‐liter titanium spherical resonator. Assuming a single relaxation process for both solutions, measured data were analyzed for the values of the maximum absorption per wavelength, (αλ)_m, and of the relaxation frequency, f_r. The f_r values are 149 kHz for the pure solution and 162 kHz for the mixture. Slight decreases of f_r values with pressure were shown in both solutions. (αλ)_m values decrease linearly with pressure according to the equation of $(αλ)m(P) + (αλ)m(o)(1‐aP)$⁠, where P is in atmg and a = 6.4 × 10⁻⁴/atmg for pure solution and 6.5 × 10⁻⁴/atmg for mixture. These pressure coefficients are nearly the same as that in the sound absorption‐equation for seawater for Schulkin and Marsh [J. Acoust. Soc. Am. 34, 864 (1962)] but 21% smaller than that measured in Lyman and Fleming seawater [Hsu and Fisher, J. Acoust. Soc. Am. Suppl. 1 69, S48(1981)] and 38% smaller than that in 0.5 M magnesium sulfate solution [Fisher and Simmons, J. Acoust. Soc. Am. 62, 558 (1977)]. [This research was supported by ONR, NSF and ARPA.]