Results of an experimental investigation of the evolution of a nonlinear wave train on deep water are reported. The initial stage of evolution is found to be characterized by exponential growth of a modulational instability, as was first discovered by Benjamin ' Feir. At later stages of evolution it is found that the instability does not lead to wave-train disintegration or loss of coherence. Instead, the modulation periodically increases and decreases, and the wave train exhibits the Fermi–Pasta–Ulam recurrence phenomenon. Results of an earlier study of nonlinear wave packets by Yuen ' Lake, in which solutions of the nonlinear Schrödinger equation were shown to provide quantitatively correct descriptions of the properties of nonlinear wave packets, are applied to describe the experimentally observed wave-train phenomena. A comparison between the laboratory data and numerical solutions of the nonlinear Schrödinger equation for the long-time evolution of nonlinear wave trains is given.

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A simple relationship between the Benjamin–Feir instability associated with uniform solutions of the nonlinear Schrödinger equation and the long time evolution of the unstable solution is reported. The number of modes which actively participate in the energy sharing process associated with the instability is governed by the number of harmonics of the initial disturbance which lie within the unstable region as predicted by the Benjamin–Feir analysis. Generalization of this observation implies that equations which possess high wavenumber cutoffs in the instability characteristics should not thermalize in the conventional sense when undergoing such an instability, since active modes are confined to a finite range of wavenumbers.

Hydrolytic decomposition occurs during the fusion of a eutectic mixture of lithium chloride-potassium chloride containing traces of moisture if the fusion conditions are not controlled. The resultant contamination by hydroxyl ion greatly lowers the utility of this mixture as a fused salt solvent. The effectiveness of various procedures used for preparation of the fused salt solvent was followed by observation of the characteristic polarographic residual current using a platinum microelectrode. A preparative method is described which involves drying the mixture under moderate vacuum, fusion under anhydrous hydrogen chloride, and removal of the hydrogen chloride from the melt.