An investigation has been made of the changes in the apparent dielectric constant of three powdered sorbents, a silica gel, a mixed silica + ferric oxide gel and alumina, for both the adsorption and desorption of methyl alcohol, ethyl alcohol and water. Initial sorption isotherms were determined in order to calculate mean pore radii and surface areas. For each system investigated, both the isotherm and the capacity curve (the 1. M. THORP

The dielectric constant E (25"C, 1 Kc/s) of a chromatographic gel was determined after activation in V ~C U O at temperatures from 150 to 1015°C. The specific surface was evaluated from nitrogen sorption isotherms (-195°C). The total hydroxyl content, which may have included some intraglobular hydroxyl groups, in addition to " perturbed " and " free " surface hydroxyls, was determined by thermogravimetric analysis. For activation temperatures up to near the Tamman temperature (755°C) the composite polarization per gram of silica gel was a linear function of the total hydroxyl concentration, COH (mol g-'). Above this temperature, the polarization was independent of COH. These results can be explained on the basis of a polarization contribution from " perturbed " hydroxyl groups (where the hydroxyls can rotate from one hydrogen-bonded position to another), that from the isolated " free " surface hydroxyls remaining after activation above 755°C being negligible. Additional measurements of E were made on silica gel (activated at 664°C) at -85 and -195°C. The increase in E observed with decrease in temperature confirmed that part of the polarization of the system was contributed by surface hydroxyls constrained to rotate within cones about the Si-0 axes.

Sorption isotherms, reversible dielectric isotherms (over a frequency range from 2.5 Kc/sec to 1 Mcjsec) and corresponding reversible loss curves are reported for water, both adsorbed and desorbed, on a purified commercial silica gel and on two samples calcined at 610 and 810"C, respectively. The first linear, frequency-independent, region in each dielectric isotherm corresponded to water molecules adsorbed on surface silanol groups. Dispersion phenomena observed in the second region, up to 500 Kclsec, was attributed to Wagner-type dispersion due to the heterogeneous nature of the system and to the conductivity of the adsorbed film after monolayer completion.Differences in the dispersion phenomenon exhibited by the uncalcined and calcined gels could be explained on the basis of progressive reduction in the conductivity of the adsorbed f i l m on increasing the calcination temperature, partly due to progressive removal of ions still present on the surface of the uncalcined gel. At 1 Mc/sec, no dispersion is observed and then each dielectric isotherm consists of two linear regions, with the second (extending to near saturation) being of smaller slope than the first, and apparently characteristic of the dielectric behaviour of polar adsorbates on porous adsorbents.

Sorption and dielectric isotherms (100 Kc/sec-4 Mc/sec) have been determined using two commercial silica gels, B2 and C, a purified sample of B2, and a calcined (1000°C) sample of C. The first linear region in each dielectric isotherm corresponded to the adsorption of water molecules on silanol groups, one molecule of water being hydrogen-bonded to two silanol groups on gel B2. In the sorption hysteresis (capillary condensation) region, each commercial gel exhibited a dielectric hysteresis loop which changed in size with change in frequency. Neither the purified sample nor the calcined gel exhibited dielectric hysteresis. The pore structure of B2 was little aEected by purification, while that of the calcined gel was altered, but still evident. It was concluded that dielectric hysteresis was not related to pore size but was due to the solution of surface ionic impurities in capillary-condensed water. On removing impurities, and by working at 1 Mc/sec or above, reversible dielectric isotherms were obtained, consisting of two linear regions, the second being of smaller slope than the first.

The antibacterial activity of certain quinoxaline 1:4-dioxides has been described by McIlwain (1943), Wiedling (1945), Frisk (1946), and Iland (1948), and previous papers from this Laboratory described their action on Entamoeba hi8tolytica (Jones, Landquist & Stewart, 1953), and on viruses of the lymphogranuloma-psittacosis group (Hurst et al. 1953). We have found that quinoxaline 1:4dioxides show activity against Gram-negative bacteria, including Salmonella dublin and Salin. typhi, either in vitro or in infections in mice (Table 1). Similar observations have recently been published by Coulthard & Hale (1955). 2: 3-Dimethylquinoxaline 1: 4-dioxide (7218) proved to be one ofthe most effective agents against Salm. dublin infections in mice, being more active than aureomycin, but it had little activity in vitro. Similar results were obtained with E8cherichia coli and with Clo8tridium welchii, which was the most sensitive. It appeared, therefore, that an active metabolite was formed in vivo, and it was found that the blood and urine of sheep dosed with 7218 became active against Salm. dublin and Cl. welchii within an hour of dosing. Isolation of the metabolite from sheep's urine was attempted, the urine being treated with lead acetate until no further