DENSITY AND VISCOSITY IN THE BINARY SYSTEM OCTADECANOIC ACID-HEXANEDIOIC ACID

DensHy. The density measurements were performed by means of the Archimedean method described in the literature (7). A Mettler H 20 T analytical balance mounted above the thermoregulated furnace was used. The level of the furnace was changed by means of a laboratory elevator. From the pan of the balance a gold chain, joined to a steel double cone bob by means of a steel wire (0.05” diameter; 1-cm length), allowed the measurements to be performed. The melt was placed in a Pyrex container positioned in the central zone of the furnace, and the furnace was raised until the bob and half of the steel wire were submerged. This condition was observed by means of a set of mirrors. The temperature of the furnace was controlled by means of a chromel-alumel thermocouple connected to a Leeds and Northrup CAT system, and the temperature of the melt was read with a second thermocouple immersed in the fused substance. The thermocouple was checked against a Pt-resistance thermometer certified by NBS and connected to a Leeds and Northrup K-3 potentiometer. The system was calibrated by using H20, KCNS, LiN03, and NaN03 (7) for which the densities are known. The following equation was obtained for the volume of the bob up to 350 OC: V (cm3) = 1.172,, + 8.71 X 10-5t. In Table I the process of calibration in molten NaN03 is reported. In run I the level of the furnace is settled in order to submerge the bob and half of the steel wire. In run I1 the balance is locked and then released after some minutes. In run 111 the level of the furnace is changed and then brought again to the same level as in run I . A precision on the density of f2 X g/cm3 is obtained. The molar volume of lauric acid (2) measured with this system agrees with that measured by a conventional pycnometric