An evaluated compilation of equilibrium relative humidities in air versus temperature from pure phase to approximately 105 pascal (1 atm) in pressure is presented for 28 binary saturated aqueous solutions. The relative humidities of the solutions range from about 3 to 98 percent. Using a data base from 21 separate investigations comprising 1106 individual measurements, fits were made by the method of least squares to regular polynomial equations with two through four coefficients. Equations and tables are presented along with the estimated uncertainties in the correlated results. Research, hygrometer calibration, testing and material conditioning often require the accurate control of humidity in a working space. The common methods of controlling the humidity accurately use either a humidity generator (1A)1 or the equilibration of a closed space with a chemical system (IB) which produces the desired equilibrium vapor pressure. Humidity generators tend to be expensive and complex whereas equilibration with chemical systems that provide fixed points is a relatively inexpensive and simple method of humidity control. Among the chemical systems used for this purpose are aqueous sulphuric acid solutions, glycerine and water solutions and single and binary salt solutions. Each such solution offers a degree of humidity adjustment that can be achieved by changing its concentration. On the other hand, special problems are associated with the use of solu- tions because their concentrations must be measured and controlled. Not only must the concentration of the solution be determined initially but the presence of any humidity sources or sinks in the controlled space and even the initial equilibra- tion process of the space can alter the solution concentration. An especially useful method of humidity control by chemi- cal system involves the use of binary saturated aqueous solutions (primarily of single salts) in which the solute is highly non-volatile. At any temperature, the concentration of a saturated solu- tion is fixed and does not have to be determined. By provid- ing excess solute, the solution will remain saturated even in the presence of modest sources or sinks. Where the solute is a solid in the pure phase, it is easy to determine that there is indeed saturation. Due to the ease of its use, this is a popular method of humidity control. Since a given saturated salt solution provides only one relative humidity (RH) at any desired temperature, a different relative humidity must be achieved by selecting another appropriate salt. Though much data on saturated salt solu-

/pdf/humidity-fixed-points-of-binary-saturated-aqueous-solutions-4xfomjtsbm.pdf

Humidity fixed points of binary saturated aqueous solutions

Permeation through nanometer pores is important in the design of materials for filtration and separation techniques and because of unusual fundamental behavior arising at the molecular scale. We found that submicrometer-thick membranes made from graphene oxide can be completely impermeable to liquids, vapors, and gases, including helium, but these membranes allow unimpeded permeation of water (H 2 O permeates through the membranes at least 10 10 times faster than He). We attribute these seemingly incompatible observations to a low-friction flow of a monolayer of water through two-dimensional capillaries formed by closely spaced graphene sheets. Diffusion of other molecules is blocked by reversible narrowing of the capillaries in low humidity and/or by their clogging with water.

/pdf/unimpeded-permeation-of-water-through-helium-leak-tight-50chaotsy2.pdf

Unimpeded permeation of water through helium-leak-tight graphene-based membranes.

There is a special reason for reviewing this book at this time: it is the 50th edition of a compendium that is known and used frequently in most chemical and physical laboratories in many parts of the world. Surely, a publication that has been published for 56 years, withstanding the vagaries of science in this century, must have had something to offer. There is another reason: while the book is a standard fixture in most chemical and physical laboratories, including those in medical centers, it is not as frequently seen in the laboratories of physician's offices (those either in solo or group practice). I believe that the Handbook can be useful in those laboratories. One of the reasons, among others, is that the various basic items of information it offers may be helpful in new tests, either physical or chemical, which are continuously being published. The basic information may relate

Handbook of Chemistry and Physics

Ion permeation and selectivity of graphene oxide membranes with sub-nm channels dramatically alters with the change in interlayer distance due to dehydration effects whereas permeation of water molecules remains largely unaffected. Graphene oxide membranes show exceptional molecular permeation properties, with promise for many applications1,2,3,4,5. However, their use in ion sieving and desalination technologies is limited by a permeation cutoff of ∼9 A (ref. 4), which is larger than the diameters of hydrated ions of common salts4,6. The cutoff is determined by the interlayer spacing (d) of ∼13.5 A, typical for graphene oxide laminates that swell in water2,4. Achieving smaller d for the laminates immersed in water has proved to be a challenge. Here, we describe how to control d by physical confinement and achieve accurate and tunable ion sieving. Membranes with d from ∼9.8 A to 6.4 A are demonstrated, providing a sieve size smaller than the diameters of hydrated ions. In this regime, ion permeation is found to be thermally activated with energy barriers of ∼10–100 kJ mol–1 depending on d. Importantly, permeation rates decrease exponentially with decreasing sieve size but water transport is weakly affected (by a factor of <2). The latter is attributed to a low barrier for the entry of water molecules and large slip lengths inside graphene capillaries. Building on these findings, we demonstrate a simple scalable method to obtain graphene-based membranes with limited swelling, which exhibit 97% rejection for NaCl.

Tunable sieving of ions using graphene oxide membranes

Size, Shape, Volume, and Related Physical Attributes.- Rheological Properties of Foods.- Thermal Properties of Foods.- Electromagnetic Properties.- Water Activity and Sorption Properties of Foods.- Surface Properties of Foods.

Physical properties of foods

Equations are presented which explicitly express the enhancement of water vapor in CO2-free air from 0.1 to 2 MPa. The equations are approximations to the formulation of Hyland and provide the means of obtaining enhancement with very modest computational facilities. The agreement with Hyland's enhancement values is well within his estimated uncertainty.

/pdf/functional-equations-for-the-enhancement-factors-for-co2-48kwcbvhjk.pdf

Functional Equations for the Enhancement Factors for CO2-Free Moist Air.

Some precise measurements of the vapor pressure of liquid water at seven temperatures in the range 25 to 100 °C were reported recently by H. F. Stimson of NBS. These measurements have an estimated standard deviation of 20 ppm or less, except at 25 °C where the estimated standard deviation is 44 ppm. We have derived a formula which yields computed values of vapor pressure agreeing with Stimson's measurements to within 7 ppm. We integrated the Clausius-Clapeyron equation using the accurate calorimetric data of Osborne, Stimson, and Ginnings and the Goff and Gratch formulations for the virial coefficients of water vapor to obtain an equation that has a rational basis. This equation was then adjusted to bring it into closer accord with Stimson's pressure measurements. Two tables are given of the vapor pressure, expressed in pascals, as a function of temperature at 0.1-deg intervals over the range 0 to 100 °C, one on the International Practical Temperature Scale of 1948 and the other on the International Practical Temperature Scale of 1968.

/pdf/vapor-pressure-equation-for-water-in-the-range-0-to-100-c-156yv2n5sc.pdf

Vapor pressure equation for water in the range 0 to 100 C

A low frost-point humidity generator has been developed at NBS to provide a capability for calibration, testing and research at very low levels of water vapor content in such gases as atmospheric air, carbon dioxide and nitrogen. The generator produces frost points from -30 to -100 °C at ambient pressures from 500 to 200,000 pascals (0.005 to 2 atm.). This is equivalent to mixing ratios of 4 × 10-6 to 51 grams of water vapor per kilogram of dry air and to vapor pressures of 1.4 × 10 -3 to 38 pascals. The generated test gas can be fed to a test chamber with independent temperature control between +25 and -100 °C. The uncertainty of the frost point in the test chamber is estimated not to exceed 0.05 deg C. Intercomparisons with a frost-point hygrometer as well as two gravimetric checks gave results which in all cases agreed to within 0.2 deg C in frost-point temperature.

https://nvlpubs.nist.gov/nistpubs/jres/77A/jresv77An5p671_A1b.pdf

Lewis Greenspan

Papers

Humidity fixed points of binary saturated aqueous solutions

Functional Equations for the Enhancement Factors for CO2-Free Moist Air.

Vapor pressure equation for water in the range 0 to 100 C

Low Frost-Point Humidity Generator.

Instrument for measuring the adiabatic saturation temperature (thermodynamic wet-bulb temperature) of a vapor-gas mixture