The ultrasonic sound velocity has been measured at 2WC and at 4OoC for a number of triglycerides in the liquid state. From these data we have computed molar sound velocities according to Rao. Using published data on fatty acid methyl esters and a previously derived relation for triglycerides, an equation is given which relates the ultrasonic sound velocity of a mixture of triglycerides to its refractive index, density, and iodine value. The applicability of this relation to fatty oils is checked against a number of original fatty oils.Physikalische Eigenschaften der Triglyceride 111: Ultraschall-Geschwindigkeit Bei einigen fliissigen Triglyceriden wurde die Ultraschall-Geschwindigkeit bei 200 und 4OoC ermittelt. Aus diesen Werten wurden die molaren Schallgeschwindigkeiten nach Rao berechnet. Mit Hilfe der bereits bekannten, bei Fettsaure-methylestern gewonnenen Daten und einer friiher abgeleiteten Beziehung fur Triglyceride wurde eine Gleidmng aufgestellt, die die Beziehungen zwischen der Ultrascfiall-Geschwindigkeit eines Gemisches von Triglyceriden und dem Brechungsindex, der Dichte und der Jod-
I n t r o d u c t i o nThe field of ultrasonics is comparatively new. Many techniques, based on the knowledge of the velocity of sound in a compound have, however, already found wide-spread application. The sound velocity in ;L compound is closely related to many physical properties of the medium and knowledge of this magnitude has expediently been applied to the evaluation of otherwise more inaccessible values. Reviews on the applicability of ultrasonics to chemical and physical problems have been presented by T. W. Ridzards et all, L. Berginann 2, W. Schaaffs and many others.The velocity of a wave due to longitudinal vibrations in a liquid medium is expressed as: the propagation taking place adiabatically and independent of the frequency. In this equation u is the sound velocity, pad and pis are the adiabatic and the isothermal compressibilities of the liquid respectively and d is the density. K is the ratio of the specific heats at constant pressure and a t constant volume (=C,/C,), which is also equal to piS/pad.The derivation of the adiabatic compressibility is one of the major applications of ultrasonics in the field of thermodynamics. Another application is the derivation of C,, the specific heat at constant pressure. We then make use of the following expression:where a is the coefficient of thermal expansion and T is the absolute temperature. The isothermal compressibility can be obtained from relatively simple measure-* Present address: Chevron Research Comp., Richmond, Calif. USA 94 802.
