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Apparatus for the determination of the heat of evaporation of liquids of high boiling points

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Abstract

Two new forms of apparatus for determining the heat of evaporation of liquids of high boiling point are described, and their relative merits briefly discussed. In the one the determination is made by a measurement of the amount of liquid vapourised for a given energy supply (radiation loss being eliminated by means of a constant temperature jacket) and in the other, the energy given up on condensing is estimated by means of a continuous flow calorimeter. The latter is thus a modification of the well-known apparatus of Berthelot, but particular attention has been paid to the avoidance of defects inherent in earlier types of apparatus. The apparatus have been tested by determining with them the heats of evaporation of such liquids as alcohol, water, and aniline, whose heats of evaporation are well known. A brief survey of the earlier work is included, and a number of references given.

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This paper reports measurements made within DIPPR2 Project 821 for the 1995 Project Year. Vapor pressures were measured to a pressure limit of 270 kPa or lower decomposition point using a twin ebulliometric apparatus for the nine compounds listed in the title. Liquid-phase densities along the saturation line were measured for each compound over a range of temperatures (ambient to a maximum of 523 K). A differential scanning calorimeter was used to measure two-phase (liquid + vapor) heat capacities for each compound in the temperature region ambient to the critical temperature or lower decomposition point. Where possible, the critical temperature and critical density for each compound were determined experimentally. The results of the measurements were combined to derive a series of thermophysical properties including critical temperature, critical density, critical pressure, acentric factor, enthalpies of vaporization (restricted to within ±50 K of the temperature region of the experimentally determined vapor pressures), enthalpies of fusion if solid at 310 K, solubility parameters, and heat capacities along the saturation line. Vapor-pressure representations were derived for each compound. All measured and derived values were compared with those obtained in a search of the literature. Recommended critical parameters are listed for each of the compounds studied except 1-chloro-2-propanol. The compounds studied were benzenamine, butylbenzene, sec-butylbenzene, tert-butylbenzene, 2,2-dimethylbutanoic acid, tridecafluoroheptanoic acid, 2-butyl-2-ethyl-1,3-propanediol, 2,2,4-trimethyl-1,3-pentanediol, and 1-chloro-2-propanol.
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