The electric strength and molecular structure of liquids

Further measurements of the electric strength of liquids are used to support the theory of a breakdown criterion, suggested in an earlier paper, in which conduction electrons in the liquid excite molecular vibrations associated with individual groups within the molecules. It has been demonstrated that collision cross-sections could be assigned to these groups and the breakdown strength derived. This criterion is used to relate the breakdown strengths of a series of alkyl benzenes recently measured by Sharbaugh, Crowe and Cox and a cross-section for the benzene ring is determined. The additive effect of the various group cross-sections is found as before, but it is necessary to consider dipole effects as well as liquid structure in order to explain the increased cross-section values for the alkyl groups. The general correctness of the concept is further demonstrated by measurements of the strength of a series of dimethyl siloxanes. It is assumed that cross-sections are to be associated with the oxygen sites and also with the methyl groups. The value of the methyl cross-section determined in this case is identical with that found from the previous measurements on the alkanes. Lastly, the presence of a puckered ring structure as well as steric hindrance is suggested as the cause of the strength of cyclohexane calculated from alkane measurements being different from the measured value.