Measurements are reported of the diffusion constant D(T) for xenon gas, in the form of the radioisotope 133Xe, through liquid n-octane, n-decane, and n-tetradecane, in the range 10–40 °C. The values range from D (10.0 °C, Xe→n-C14H30)=1.32×10−5 cm2/s to D (40.0 °C, Xe→n-C8H18)=6.02×10−5 cm2/s. A new experimental method is used in which D is obtained by monitoring the decrease in concentration as gas diffuses into the liquid in an effectively one-dimensional geometry. As expected, the results do not agree with the Stokes–Einstein law. They do follow the usual correlation Dηp=AT, with p=0.708 and A=9.80×10−8, where η is the liquid viscosity in centipoises and T is in K. Application to these results of the rough-hard-sphere theory of diffusion is discussed. A quantitative analysis cannot be made until molecular dynamics results for smooth-hard-sphere diffusion are available.

Measurements of the Ostwald solubility as a function of temperature L(T) are reported for 133Xe gas in liquid n-alkanes. All the alkanes from n-C5H12 through n-C20H42 were investigated and the temperatures ranged from 10.0 to 50.0 °C. The experimental method is recently developed and has some unique aspects. From the temperature dependent results the chemical potential Δμ20(T), the enthalpy ΔH̄20, and the entropy ΔS̄20 of solution were determined. Values for Δμ20(T) ranged from 2546 cal/mol for n-C7H16 at 50.0 °C to 1811 cal/mol for n-C14H30 at 10.0 °C. The range of ΔH̄20 was from −2818 cal/mol for n-C5H12 to −2117 cal/mol for n-C20H42, and the corresponding range in ΔS̄20 was −16.90 to −13.58 cal/mol K. A Barclay–Butler plot of the thermodynamic functions and a plot of the dependence of solubility on the Hildebrand solubility parameter for this system are displayed. All of the data obtained in this experiment may be given to better than 0.8% by the empirical relation Δμ20=−RT ln x2=−0.0637nT+2.575×10−2T2, in which x2 is the mole fraction of solute in the solvent at 1 atm partial pressure and T is the absolute temperature. Because the solute is an inert monatomic gas and the solvents are a single homologous series of nonpolar liquids, the results show some interesting simple physical interpretation.

. On the likelihood of decompression sickness during H2 biochemical decompression in pigs. J Appl Physiol 91: 2720 -2729, 2001.-A probabilistic model was used to predict decompression sickness (DCS) outcome in pigs during exposures to hyperbaric H 2 to quantify the effects of H2 biochemical decompression, a process in which metabolism of H 2 by intestinal microbes facilitates decompression. The data set included 109 exposures to 22-26 atm, ca. 88% H 2, 9% He, 2% O2, 1% N2, for 0.5-24 h. Single exponential kinetics described the tissue partial pressures (Ptis) of H2 and He at time t: Ptis ϭ ͐ (Pamb Ϫ Ptis) ⅐ Ϫ1 dt, where Pamb is ambient pressure and is a time constant. The probability of DCS [P(DCS)] was predicted from the risk function:Ϫr , where r ϭ ͐ (Ptis H 2 ϩ PtisHe Ϫ Thr Ϫ Pamb) ⅐ Pamb Ϫ1 dt, and Thr is a threshold parameter. Inclusion of a parameter (A) to estimate the effect of H2 metabolism on P(DCS): PtisH 2 ϭ ͐ (Pamb Ϫ A Ϫ Ptis H 2 ) ⅐ Ϫ1 dt, significantly improved the prediction of P(DCS). Thus lower P(DCS) was predicted by microbial H 2 metabolism during H2 biochemical decompression. probabilistic modeling; Sus scrofa; hydrogen diving; H2 metabolism; Methanobrevibacter smithii MODELING OF DECOMPRESSION SICKNESS (DCS) risk has been impeded by the inability to identify correlated physiological variables. Some studies have tried to find a correlation between DCS risk and variables such as body temperature, body weight, exercise, gender, adiposity, age, serum cholesterol, sensitivity to complement activation, Doppler bubble grades, and patent foramen ovale (4,12,16,23,28). However, where some studies have found a correlation, others refute those results (5,8,16). The only physiological variable that has been undisputedly correlated with DCS risk in rats is body weight (20). Because reliable physiological correlates are lacking, researchers have used a variety of models based solely on the physical history of the compression and decompression sequence to find variables that can predict the probability of DCS (26, 31-34).The DCS risk assessment used in this study builds on previously published models used in DCS research (26,31,33,34). The goal is to estimate the beneficial effects on DCS risk of the active removal of tissue H 2 by injecting H 2 -metabolizing microbes into the intestines of pigs during simulated H 2 dives and to suggest a physiological mechanism for the process called H 2 biochemical decompression (19). The metabolism of H 2 in the intestine is readily followed by measuring the release of CH 4 , the metabolic end product of the microbial metabolism (21)(1)The model presented here differs from earlier models of DCS (26,31,33,34) in that a parameter for the microbial metabolism of H 2 is included. In constructing this model, the microbial metabolism of H 2 was considered to have a direct physiological effect by influencing the gas kinetics. The measure of H 2 metabolism was based on either the total microbial activity injected into the animals (Inj), or as the CH 4 release rate (V CH 4 ) fr...

New measurements are reported of the Ostwald solubility L(T), as a function of temperature in the approximate range 10.0–50.0 °C, for 133Xe gas in 13 liquid organic solvents, viz., three cycloalkanes, six carboxylic acids, and four normal alkanals. From our data for each solute–solvent system we determine the mole-fraction solubility x2(T), and the following thermodynamic functions of solution: chemical potential Δμ0ρ2(T)=−RT ln L, enthalpy ΔH̄0ρ2, and entropy ΔS̄0ρ2, where Δμ0ρ2=ΔH̄0ρ2 −TΔS̄0ρ2S̄0ρ2, all based on the number density scale. New results are considered together with previous measurements of xenon solubility in liquid normal alkanes, alkanols, and perfluoroalkanes; in all, data and theory are treated for xenon solubility in 45 organic solvents from six homologous series. The average observed entropy of solvation of Xe is ΔS̄0ρ2=−4.1± 0.5 cal/mol K, remarkably independent of solvent. The results are analyzed with scaled-particle theory from which are obtained hard-core diameters a1, and cavity energies gcav and enthalpies hcav for all the solvents at 25 °C. Values of a1 range from 4.08 Å (for CH3OH) to 9.18 Å (n-C20H42), and gcav ranges from 2520 cal/mol (n-C6F14) to 9430 cal/mol (HCOOH). We discuss the application to solubility in these solvents of interaction site calculations; interaction potentials for the functional groups are available but difficult to apply to these solute–solvent systems. We also discuss the role of configurational entropy, as well as molecular dynamics approaches to calculation of free energies of solubility. Finally the results are examined empirically and values are given for the contribution to chemical potential, enthalpy, and entropy of solvation, of the six functional groups: CH2 (linear molecules), CH3, OH, COOH, CHO, and CH2 (cyclomolecules).

Measurements of the Ostwald solubility L(T) as a function of temperature in the range 10.0–50.0 °C are reported for 133Xe gas in 13 liquid normal alcohols: methanol through n-dodecanol, and n-tetradecanol. From the data for each solute–solvent system we find the mole fraction solubility x2(T), and calculate the following thermodynamic functions of solution: chemical potential Δμ○2(T) =−RT ln x2, enthalpy ΔH̄○2, and entropy ΔS̄○2, all based on the mole fraction scale. We also calculate directly from the Ostwald solubility the corresponding quantities based on the number density scale. These quantities are the chemical potential Δμ○ρ2(T) =−RT ln L, enthalpy ΔH○ρ2, and entropy ΔS○ρ2. The solute was chosen as an inert monatomic gas and the solvents were chosen in a polar homologous series in order to construct prototype solute–solvent systems. Solubility results and the associated thermodynamic functions are analyzed and compared with simple models.