An inexpensive, indigenous and a simple electronic instrument based on voltage follower, currentto-voltage converter, zero crossing detector and a phase detector has been developed for measurement of a.c. conductivity. Real and imaginary parts of complex impedance are determined for a given sample as a function of frequency and the given sample is represented by a pure electronic model.

The effects of N,N-dimethylformamide and dimethyl sulfoxide on the temperature of adiabatic compressibility minimum (Tβ) and sound velocity maximum (Tu) of water have been studied. The structural contributions to the shift in Tβ and Tu, [ΔTβ str.]exp. and [ΔTu str.]exp., have been found to be negative for both solutes. Both [ΔTβ str.]exp. and [ΔTu str.]exp. are higher for dimethyl sulfoxide than N,N-dimethylformamide indicating that the sulfinyl group (Remark: Graphics omitted.) is more efficient in structure disruption than the formylimino group (Remark: Graphics omitted.). The results have been explained in the light of hydrogen bonding equilibria by the solutes.

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The effect of acetonitrile on the temperature of the adiabatic compressibility minimum (t.a.c.m.) and temperature of the sound velocity maximum (t.s.v.m.) of water has been studied. The structural contribution to the shift in t.a.c.m. and t.s.v.m., (ATg,str.)exp, and (ATU,str,)exp., has been found to be positive at low concentrations, becoming maximum around A ' , 2 0.0 18 and thereafter decreasing to become negative around A ' , 1.0.045. This behaviour is explained in terms of the effects of added acetonitrile on the structure of water.