The results of previous and recent extended dielectric investigations on pure hexagonal ice crystals and on mixed-crystals containing hydrofluoric acid are summarized. Measurements of the d.c. conductivity were performed using electrodes of different nature. Quantitative electrolysis experiments demonstrate the ionic character of the electrical conductivity. The theory of the dynamic behaviour of dielectrics is applied to ice assuming that polarization changes only occur at lattice imperfections of two types : orientational defects (i.e. vacant and doubly occupied hydrogen bonds) and ionized states (i.e. H3O+ and OH-). For both cases the possible proton jumps are computed statistically. The theory gives the correct dispersion behaviour and shows that the static dielectric constant of pure ice (-100) is due to proton jumps at molecules adjacent to doubly occupied bonds. The theory is extended to mixedcrystals with HF. It can be concluded that at medium high HF concentrations the predominant dispersion mechanism takes place by proton transfer at H3O+ ions, whereas at the highest concentrations the vacant bond mechanism prevails. Finally, it is shown that the present theory of lattice imperfections in ice is consistent with all known structural and physical facts, inchding the zero-point energy. RESULTS OF DIELECTRIC INVESTIGATIONSThe dielectric properties of pure ice crystals are of great interest and have been studied repeatedly since 1924.1 The most reliable results were obtained in 1952 on polycrystalline ice2 and with single crystals an anisotropy of the dielectric constant of about 15 % was determined.3 Two features of the dielectric properties are astonishing : (i) Ice shows an ordinary Debye dispersion with an extremely low dispersion frequency (cod = 2 x 104 c/sec at -10" C) compared with that of the liquid (od -1011 c/sec) and of other polar substances. The temperature dependence of the relaxation time is given by The values 2.3 B = 5.3 x 10-16 sec and E, = 13-2 kcal/mole, which corresponds to 0.575 eV, have been verified in the present investigation.(ii) The static permittivity of ice is about 100 and is thus even higher than that of liquid water. The measurements of the real and imaginary part of the dielectric constant E' and E" fit the semicircles of the Cole plot E"(E') well except for very low frequencies where deviations occur even under the conditions of highest purity. For low temperature measurements the data give the appearance of fitting the Cole plot better, because the measurements have not been extended to sufficiently low frequencies. In this case the static permittivity obtained by extrapolation of the Cole plot is too large due to the d.c. conductivity q.(2)The imaginary part E" of the Debye dispersion should vanish at low frequencies since it is proportional to the frequency. Actually the deviations are such that E" diverges as 1/0. This behaviour might be interpreted as due to a frequencyr d = B exp (EJkT).(1)€; (go) = E i true + 2CJ'O7/EO.

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