Volumes de Mistura de Liquidos a Baixas Temperaturas

A new differential densimeter was designed and built for measurements at cryogenic temperatures in saturated liquids as a function of temperature. Two weights are immersed in the liquids, each suspended from one end of a lever arm. The difference in their apparent weights alters the tension of vibrating wire whose resonance frequency is related with the difference in densities. The gaseous phases in equilibrium are separated, the tension being transmitted through the separating wall via a magnetic coupling. A first prototype was used at 298K with samples of liquids of known density. The differences in density of different pairs of liquids were determined with a maximum uncertainty of #+-#0.03Kg.m"-"3. The density of saturated liquids are obtained with a precision of #+-#0.02% and an accuracy of #+-#0.05%. At cryogenic temperatures the differences in density ethane-propane between 150 and 190K were measured showing deviations from the literature no greater than 0.1% from the literature. The density of ethane was measured with a precision of #+-#0.02% and an accuracy of #+-#0.04%. New values for the difference in density were obtained for cyclopropane-propane and propane+cyclopropane mixtures-propane. The excess volumes were determined between 152 and 176K with an estimated precision of #+-#0.02cm"3.mol"-"1Available from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga