The dissolution profiles for a 1 cm sodium chloride cube, which was considered to represent a standard non‐distintegrating substrate, were obtained in seven kinds of dissolution apparatus. The results were used to assess experimental reproducibility and apparatus variables and to examine the adherence of the kinetics of the dissolution process to theoretical rate laws.

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The extension of the concept of isokinetic conditions into the dimension of pressure is discussed. The use of the enthalpy and entropy of activation at constant pressure and of the energy and entropy of activation at constant volume to characterize activated processes is discussed, and it is concluded that neither set can be rigorously justified as easier to understand, but that the constantvolume parameters are probably to be preferred most of the time. The effect of pressure up to 3 kbar on the rate of the acid-catalyzed hydrolysis of methyl acetate and ethylene oxide in acetone+ water mixtures has been measured. The constant-volume parameters of activation for the acidcatalyzed hydrolysis of methyl acetate vary with solvent in a less complicated way than the constantpressure parameters, the minima in the constant-pressure parameters not being present in the constant-volume parameters. The existence of the minima in the constant-pressure parameters is ascribed mainly to the large change of thermal expansivity when an organic liquid is added to water.The effect of solvent on the rate of hydrolysis of methyl acetate is dependent on the pressure, and reverses sign at about 2 kbar. The implications of this observation in the determination of reaction mechanisms is discussed.

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The catalytic effects of lanthanum ion on the rate of hydrolysis of p-nitrophenyl hydrogen methylphosphonate in aqileous solution at pH >7.0 are reported. Increases in rate by a factor of about 3.6 x lo4 have been observed. No such catalysis was found for diesters of methylphosphonic acid.