MEASUREMENT OF THERMODYNAMIC QUANTITIES OF MINERAL-OIL BY LOASER INTERFEROMETRY

In previous attempts to find bulk modulus of liquids, the difficulty h as always been in how to accurately measure minute volumetric changes in the fluids when pressure changes. The present paper describes the a pplication of laser interferometry to this measurement in a mineral oi l in order to develop a more reliable substitute for the conventional methods. Firstly, the basic relationship between density and refractiv e index of the oil was established by the use of the interference frin ge method. Thereafter, the heterodyne interferometer was used to measu re thermodynamic changes of state in the oil, giving adiabatic and iso thermal compressibilities, specific heats at constant pressure and at constant volume, and specific heat ratio. The velocity of sound in the oil derived from adiabatic compressibility thus obtained agrees well with that determined experimentally through wave transmission tests. T he same interferometer has also been shown to be applicable to the mea surement of pulsating pressures in oil.