The electric dipole moments of cis-and trans-azobenzene, two cis-and three trans-azopyridines, and of five azoquinolines have been calculated from measurements of the dielectric constants, specific volumes, and refractive indices of their solutions in pure benzene a t 25.00'. Of the azoquinolines, only the 6,6'-isomer showed any change in its dipole moment after exposure to ultraviolet light. The conformations of the various molecules in solution are discussed.THE electric dipole moments of azobenzene and of the azopyridines have been measured previously. That reported for 4,4'-azopyridine (2.0 D) seems exceptionally high, and merits further investigation, but in any case the results have only been employed in discussing cis-trans isomerism. Equally interesting are the conformations of these molecules, as it is unlikely that either the cis-or the trans-forms are planar in solution. The dipole moments of five azoquinolines have also been measured. Only with the 6,6'isomer did irradiation with ultraviolet (u.v.) light change the dipole moment, indicating a very small conversion of the stable trans-into the less stable cis-form. The U.V. spectra of the compounds in pure ethanol were measured and agreed with published results.3 EXPERIMENTAL AND RESULTSPreparation and Purification of the Azo-compounds.-The dipole moment of each compound Azobenzene. Purified nitrobenzene in methanol was reduced by refluxing with sodiumThe mixture was neutralised, filtered, most of the It was then filtered off, washed The into the cis-isomer by irradiation in glacial acetic acid A Hanovia mercury vapour lamp, placed 25 cm. from the Most of the residual trans-isomer was precipitated with water and filtered The remaining azobenzene was extracted with cold chloroform, washed rapidly with was measured immediately it had been purified.hydroxide and powdered zinc for 12 hr. methanol distilled off, and the compound allowed to crystallise. well with water, and warmed with dilute hydrochloric acid to remove occluded zinc salts. trans-azobenzene was washed, dried, and recrystallised from ethanol to constant m. p. (69"). solution with U.V. light for 6 hr. solution, was used. off. trans-Azobenzene was converted

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The ability of three crystalline proteins (bovine p-globulin, pepsin and insulin) to stabilize the dispersion of air in water has been studied in two ways : in part 1, by passing air continuously through a protein solution and observing the foam formed and, in part 2, by measuring the average life of individual bubbles formed under the surface of protein solutions and under spread protein monolayers. The effects of changing the protein concentration, pH and ionic strength of the solutions were studied and the results correlated with previous observations on the mechanical properties of films of the same proteins.An attempt is made to explain the observations in terms of three successive processes in the formation of protein films : adsorption, surface denaturation and finally coagulation. It is concluded that only surface-denatured protein is effective in stabilizing the air bubbles.Four general methods are available for investigating the ability of a substance (i) Dynamic method-by studying the rate at which a foam is produced or (ii) Static method-by measuring the rate at which liquid drains from a foam. (iii) SingZe bubble method-by studying the life-time of individual bubbles blown under the surface of the solution.(iv) Size-distribution method4 method which follows the change in surface area of the foam with time is probably the most fundamental but is the most tedious in practice.to stabilize the dispersion of air in liquid as a foam : the stationary volume of foam formed under standard conditions.

The electric permittivities of 17 pyrroles have been measured in benzene and 1.4-dioxan solutions at one radio and two microwave frequencies. Their dielectric relaxation is discussed in terms of the size and possible internal rotations of the solute molecules. One conclusion drawn, that internal rotation in 2-acylpyrroles is negligible, is supported by n.m.r. evidence. Their electric dipole moments in benzene solutions at 25.0 "C are analysed in terms of component moments and it is concluded that 2-acylpyrroles and similar molecules exist in a syn-conformation. In 1 ,rl-dioxan solutions the apparent increments in the electric dipole moments of pyrroles with a free N-H indicate the presence of hydrogen bonding to the solvent.

The electric dipole moments of three phenanthrolines, four bipyridyls, and 2,2'-biquinolyl have been calculated from measurements of the dielectric constants, specific volumes, and refractive indices of their solutions in pure benzene a t 25.00". They are discussed in terms of the dipole moments expected by the vector addition of the moments of two pyridine molecules and of the interaction between them.

The orientation polarisations and dipole moments of four cyclic organic sulphides , and the related sulphoxides and sulphones, have been calculated from measurements of the dielectric constants, specific volumes, and refractive indices of their solutions in benzene. The dipole moments are discussed in terms of the moment of the sulphur-oxygen link and the geometrical structure of the molecules. The dipole moments of five cyclic ethers have also been measured, and the carbon-oxygen bond moment evaluated and compared with that of non-cyclic ethers.THE electric dipole moments of several organic sulphides, sulphoxides, and sulphones are recorded in the literature but only in four cases have the moments of the sulphide and the corresponding sulphoxide and sulphone been measured. No cyclic sulphoxides or sulphones have been investigated.

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An empirical method is described by which the structures of certain organic molecules may be calculated from rotation spectra measurements when the experimental data alone are insufficient to give a unique solution. The structures of pyridine, pyrrole, furan and thiophen have been calculated and are discussed. The application of the method to a straight-chain molecule is also considered.