The results reported by Kurtze and Tamm for sound absorption in MgSO4HCl solutions and the results reported by Eigen, Kurtze, and Tamm for sound absorption in H2SO4 solutions are discussed. The puzzle is that the HSO4 ion‐pairing effects seem to be radically different from those exhibited by NaSO4 and other salts. H2SO4 exhibits significant sound absorption and displays a different concentration dependence below 0.1M than most salts exhibiting sound absorption. When NaCl is added to MgSO4 solutions, the reduction in absorption can be calculated from the equation given by Kurtze and Tamm: A/A0 = [MgSO4/([MgSO4] + f[NaCl]), where A0 is the absorption in pure MgSO4 aqueous solution, A is the absorption when NaCl is added, and the brackets denote concentration of the salt within the bracket. For NaClMgSO4 mixtures Kurtze and Tamm found f = 0.21. For HClMgSO4 mixtures f was not independent of the ratios of salt concentrations. These puzzles are discussed in the framework of the differential sound‐absorption technique suggested by Fisher to measure ion pairing of unsymmetrical electrolytes. [Research supported by the National Science Foundation.]

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