The shapes and terminal velocities of bubbles rising in viscous liquids have been determined. For Morton numbers (M) greater than 4 × 10−3 the drag coefficient and dimensionless bubble shape are functions only of Reynolds number (R). Shape regimes and terminal rise velocities have been correlated. The flow field around a rising bubble was visualized through the hydrogen bubble tracer technique. For M > 4 × 10−3 and R < 110 the bubbles trailed closed, laminar toroidal wakes. For R > 110 the wake was open and unsteady. Streamlines for the flow were obtained by raising a ciné camera at the same speed as the bubble and filming the H2 tracer bubbles. Results are presented for R < 150 and 7·4 × 10−4 < M < 850.

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The ~dothermic ~ea~ion of AI + with O 2 is studied using a guided ion-beam apparatus. The reaction cross section IS measured as a function of kinetic energy from 0 to 20 eV. The threshold energy for the reaction, Eo, is determined from an empirical model to be 3.64 ± 0.04 eV. Phase s~~ calculations of the cross section performed with Eo as the only adjustable parameter yield a similar result, Eo = 3.60 ± 0.02 eV, and predict the absolute magnitude of the reaction cross sectio~ wi~ experime~tal error. We conservatively quote the threshold energy as 3.62 ± 0.12 e V which IS ~omewhat higher than the thermodynamic threshold calculated using literature thermochemistry, 3.40 ± 0.16eV. This may indicate that a slight barrier to the reaction exists or that AIO+ is produced in an excited state, or that the literature thermochemistry needs revision.Our results suggestDg (AIO+);;;.1.50 ± 0.12 eV and I.P. (AIO) <9.75 ± O.13eV.

hydrated with water molecules, and combined with hydroxyl ions in the form hydroxo-complexes (Hahne and Kroontje, 1973; Long and Angino, 1977;Stumm and Morgan, 1981). At high metal concentration and high pH, polynuclear hydrocomplexes are expected to be present (Olin, 1961). A detailed description of the speciation of lead has been discussed previously (Esalah et al., 2000). The speciations of cadmium and zinc are similar to that of lead (Long and Angino, 1977). Experimental MeasurementsDi-(n-octyl) phosphinic acid was synthesized by the peroxide catalyzed reaction between 1 -octene and hypophosphorus acid by Peppard et al.'s modification (Peppard et al., 1965) to the procedure described by Williams and Hamilton (1 952). The acid was purified and then converted to its sodium salt.The experimental precipitation procedure is described in detail elsewhere (Esalah et al., 2000). Briefly stated, all solutions were prepared with distilled water, and the pH of the solution was adjusted with HNO, before adding the precipitating agent. The temperature was maintained a t 22 f 1 "C. The feed solution (35 mL) containing the metal ions, calcium, and nitrate or chloride was treated with an aqueous solution (5 mL) of the precipitating agent. The samples were shaken in tightly closed jars. After the equilibrium was reached (less than 5 min), a white precipitate was separated using Fisher brand fast flow filter papers from the clear aqueous phase. The equilibrium pH was measured using R Metrohm 691 pH Meter (Q Metrohm, Herisau, Switzerland), and the metal content of the filtrate was determined by atomic absorption spectrometry using a Thermo Jarrel Ash model SH 11 (Thermo Jarrell Ash, Waltham, MA) surface beam atomic absorption spectrophotometer. The wavelengths were 283.3 nm, 228.8 nm, 213.9 nm, and 422.7 nm for lead, cadmium, zinc, and calcium, respectively. For concentrations below 1 p.p.m., the metal content was measured by an Inductively Coupled Plasma using a Thermo Jarrel Ash Trace Scan (Thermo Jarrell Ash, Waltham, MA) axial torch sequential ICP. The wavelengths used for lead, cadmium, and zinc were 220.3 nm, 214.4 nm, and 21 3.8 nm, respectively. The sensitivity of the inductively coupled plasma instrument is at least 10 times higher than that of the atomic absorption spectrophotometer. The concentration of the precipitating agent in the aqueous phase was measured by a Dohrmann DC-183 Total Organic Carbon Analyzer (Dohrmann, Santa Clara, CA), with a Dohrmann DC-85 NDlR Detector module. The same procedure was used to study the mixture of the three metals.For the measurements of the solubility products of the precipitates of cadmium and zinc phosphinates, the procedure used was similar to the one described elsewhere (Esalah et al., 2000) for lead phosphinate. Basically, the precipitates were washed with distilled water and left to equilibrate in distilled water a t 22 f 1°C. The metal content of the liquid phase was then determined as described above.