Pressure on Freezing Points

Specifications for gas turbine fuels prescribe test limits that must be met by the refiner who manufactures fuel however, it is customary for fuel users to define quality control limits for fuel at the point of delivery or of custody transfer. These limits must be met by third parties who distribute and handle fuels on or near the airport. Tests on receipt at airport depots include appearance, distfllation, flash point (or vapor pressure), density, freezing point, smoke point, corrosion, existing gum, water reaction, and water separation. Tests on delivery to the aircraft include appearance, particulates, membrane color, free water, and electrical conductivity. 

In this equation, Pt is the vapor pressure of solvent over the solution, P° is the vapor pressure of the pure solvent at the same temperature, and Xj is the mole fraction of solvent. Note that because Xj in a solution must be less than 1, P must be less than P°. This relationship is called Raoult s law Francois Raoult (1830-1901) carried out a large number of careful experiments on vapor pressures and freezing point lowering. 

Colligative properties are those properties of solutions that depend on the number of solute particles present and not their identity. Colligative properties include vapor pressure lowering, freezing point depression, boiling point elevation, and osmotic pressure. Colloids are homogeneous mixtures, in which the solute particles are intermediate in size between suspensions and true solutions. We can distinguish colloids from true solutions by the Tyndall effect. 

Schardinger himself did not attempt molecular-weight determinations of the crystalline dextrins. The first molecular-weight determinations were based on freezing-point depressions in water" or on osmotic-pressure measurements. " " Other measurements were based on dialysis rates or on cryoscopic measurements rvith the acetates," nitrates, and methyl ethers. In some cases microisopiestic methods were used."-... 

The activity coefficients of sulfuric acid have been determined independendy by measuring three types of physical phenomena cell potentials, vapor pressure, and freezing point. A consistent set of activity coefficients has been reported from 0.1 to 8 m at 25°C (14), from 0.1 to 4 m and 5 to 55°C (18), and from 0.001 to 0.02 m at 25°C (19). These values are all based on cell potential measurements. The activity coefficients based on vapor pressure measurements (20) agree with those from potential measurements when they are corrected to the same reference activity coefficient. 

COlligative property A property of a solvent (vapor-pressure lowering freezing-point lowering boiling-point elevation osmotic pressure) that depends on the total concentration of solute particles present. (Section 13.5)... 

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