Oxygen solubltltles in aqueous alcohol solutions were Investigated by Wlnkler's method at temperatures of 15, 25, and 37 O C . Methanol, ethanol, l-propand, I-butanol, and glycerol were employed at concentratlons up to 18 wt %. The relative solubllltks as compared to water decreased wlth decreadng temperature and with lncreaslna chaln length of the alcohols.For estimation of gas solubilities in mixed aqueous solutions of salts and organic substances, in particular for microbial culture media, an empiriil model has been shown to apply ( 1) which is based on "log additivity" of the individual saltlng-out effects:(1) ao/a is the ratio of the gas solubility in water to the one in a mixed solution. ao/a, is the individual ratio for an equally concentrated aqueous solution of component i alone. Instead of the Bunsen coefficients a (volume of gas, reduced to 0 O C and 101.3 kPa, per unit volume of solvent at a gas partial pressure of 101.3 kPa) any proportional solubility measure could be used.For salts and for some organic substances as well, the concentration dependencies can be described by the Sechenov equation:(2)Here c, is the concentration of substance i and K, is a slightly temperature-dependent constant that is specific to the substance and the gas. For small-chain alcohols eq 2 does not hold as even maxima and minima of gas solubility may be encountered with changing alcohol concentration. However, eq 1 stiil applies up to 10 wt % alcohol by introducing measured relative gas solubiliiies (a,/ao) for the particular alcohol concentrations (2). Unfortunately, literature data on oxygen solubilities in low-concentratiOn alcohol solutions are scarce and the available data disagree strongly (1). I t is the purpose of this paper to provide reliable solubility data in the low concentration range.log (ao/a) = c log (ao/a,) log (ao/a,) = K, c,
Experlmental SectionThe solutions were prepared from analytical-grade alcohols and distilled water. They were saturated with air in a short jacketed bubbling tower thermostat4 to f0.2 K. Prior to entering the bubbling tower the air passed through another thermostated saturation flask filled with the same solution. Thus, the concentrations as determined by refractometry hardly changed by stripping during the equilibration process. Samples of the saturated solutions were analyzed for their dissolved oxygen content by the Winkler titration method (3). Reproducibility was better than by 1 %. The measured oxygen concentrations, c (mg L-'), were converted to Bunsen coefficients by the following equation:(Y = 101.3c/{106p&(fb + f , -f 1 -P,)(0.2094)1 = 0.3386~/(Pb + P st -P 1 -P 2)where poo (g ~m -~) is the density of oxygen gas (0 OC, 101.3 002t-956a1a411729-02at3$0 1.5010 Table I. Oxwen Solubilities in Water a0 temu. "C obsda lit.* re1 dev. % _ . 15.0 0.0338 0.0342 -1.2 25.0 0.0279 0.0284 -1.8 37.0 0.0235 0.0240 -2.
