Solutions of nitrous acid in dilute (0.1 M HC1) or more concentrated (~5 M HC104) acid exhibit a contribution to the ultraviolet absorbance that is quadratic in [HN02]. In dilute acid this excess absorbance is attributed to N203 formed through equilibrium 1, 2HN02 = N203 + H20. From the measured spectrum of eN2o3Ai vs. wavelength (245-260 nm) and by comparison with eN2o3 obtained in pulse radiolysis by Grátzel et al., A, is determined as (3.03 ± 0.23) X 10™3 M™1, in agreement with the value calculated thermochemically. The coefficient of physical solubility of N203 in water is computed as 0.70 ± 0.05 M atm™1. The extinction quadratic in [HNOJ is independent of acid concentration in dilute acid but increases strongly in more concentrated acid, suggesting a possible second absorbing species of stoichiometry HN203+.

1) Hunt, D. F.; Shabanowltz. J.; Harvey, T. M.; Coates, M. Anal. Chem. 1985, 5 7 , 525-537. McMuttrey, K. D.; Wildman, N. J.; Tai, H. Bull. Environ. Toxicol. 1983, 31 ~ 734-737. van Graas, 0.; de Leeuw, J. W.; Schenck, P. A. in Advances h Organic Geochemistry 1979; Douglas, A. G., Maxwell, J. R., Eds.; Pergamon: London. 1980 DD 485-494. van de W n t I D.; Brown, S. c.; philp, R. P.; Simonett, B. R. T. GWchlm. C o s m h l m . Acta W80, 4 4 , 999-1013. van de Meent, D.; de Leeuw, J. W.; Schenck, P. A. J. Anal. Appl. fvrol. 1980. 2 . 249-263. Schenck, P.' A.; de Leeuw, J. W.; Viets, T. C.; Haverkamp, J. I n Petroleom, Geochemkf?y and Exploration of Europe; Brooks, J., Ed.; Blackweil Scientlfic: 1983; pp 267-274. van der Kaaden. A.; Boon, J. J.; de Leeuw, J. W.; de Lange, F.; Schuyi, P. J. W.; Schulten, H. R.; Bahr, U. Anal. Chem. 1884, 56, SaizJimenez, C.; de Leeuw, J. W. Org. Geochem. 1984, 6 , SaizJimenez, C.; de Leeuw, J. W. Org. Geochem. 1984, 6 , Nlp. M.; de Leeuw. J. W.; Schenck, P. A.; Meuzeiaar, H. L. C.; Stout, S. A.; Given, P. H.; Boon, J. A method for the determlnatlon of hydrogen peroxide In the amblent atmosphere is described, using bnplnger or dlffuslon scrubber collectlon of H,02 wlth aqueous-phase analysis by an enzyme-catalyzed fluorescence technique. Interference from ozone at amblent levels Is removed by gas-phase reactlon wtth excess nltrlc oxlde. The lmplnger and dMuslon scrubber collectlon technlques glve equlvalenl results for atmospherlc gas-phase H202 wtth h l t s of detectkn of 0.1 ppbv for approximately 60-mln and 10-mln sampllng times, respectlvely . The development of techniques for measuring gaseous and aqueous HzOz and other hydroperoxy compounds has been the focus of substantial research effort following the recog-Permanent address: Practical Engineering College of Beer-Sheva, P.O. Box 45, Beer-Sheva, Israel.nition that HzOz could rapidly oxidize dissolved S(1V) compounds to sulfuric acid throughout the normal pH range of rain, cloud, and fog waters (pH 2-7) (1,2). The high solubility of HzOz in water (Henry's law constant -lo5 M atm-') leads to significant aqueous concentration (1-100 MM) in, e.g., cloud water, even a t low parts-per-billion by volume gaseous HzOz concentrations in air entering clouds (3-5). Several methods for determining aqueous-phase HzOz in atmospheric samples have been developed or improved recently based on luminol chemiluminescence (61, (p-hydroxypheny1)acetic acid (POH-PAA) dimer fluorescence (5, 7-9), scopoletin fluorescence quenching (lo), and peroxyoxalate chemiluminescence (I 1).Measurements of gas-phase hydrogen peroxide have been attempted by collection of the peroxide in aqueous solution using impingers or condensation collection devices (12).However, these efforts have been shown to give unreliable resulta due to the in situ formation of hydrogen peroxide from low-solubility constituents of ambient air and/or compressed air during collection (13-15). It has been suggested that this

Formation constants have been determined for the mixed-metal complexes between indium(III) and uranium(VI) with malic, citric, and tartaric acids. In the cases of malic and tartaric acids the equilibrium can be written as U022 + + In3 + + 2HaL = U02InL2~+ 6H+. The logarithms of the equilibrium constants are -7.62 for the malate system and -7.14 for the tartrate.In the case of citric acid the equilibrium is U022+ + In3+ + 2H,L = U02InL23_ + 8H + where two of the protons come from the hydroxy groups. The logarithm of the constant is -11.58. Infrared measurements on trilaurylamine extracts of the mixed-metal complexes have been made and are discussed. The dimerization constant for the formation of (uranyl citrate)2 was determined poten tiometrically and found to agree with the literature values. However, arguments are presented for the necessity of recalculating the values presented in the literature for the equilibrium U022+ + H8L = U02L~+ 3H+. The logarithms of the recalculated values are -7.40 for malate, -6.30 for citrate, and -6.85 for tartrate.

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Publication costs assisted by the Practical Engineering CollegeVapor pressure osmometric measurements on benzene solutions of n-hexanoic, n-nonanoic, and n-dodecanoic acids were performed at 31°. The osmometric data in the concentration range 0.5-9.0 X 10-2 M were interpreted in terms of dimer and trimer equilibria and oligomerization constants were calculated. The aggregation tendency increases with increasing chain length and the same trend was observed in the calculated activity coefficients. Enthalpies of aggregation, estimated from the heats of dilution and the distribution of the oligomers, were found to be -7.6 to -9.2 kJ per mole monomer units for the dimer and from -9.2 to -10.9 kJ per mole of monomer units for the trimer, for the three acid studied. The heats of dilution for concentrations up to 0.04 M were the same for the three acids studied and the differences in the free energy were attributed to an entropy contribution. The activity of the solute, calculated from osmometric measurements, was combined with the integral heat of dilution data to calculate the entropy change for the aggregation process.