The viscosities and densities of methane-propane mixtures were determined a t pressures to 5,000 Ib./,sq.in.abs. for 22.1 and 50.0 mole % methane over a temperature range from -120 to 37.78"C. and for 75.3 mole % methane over a temperature range from -150" to 37.78"C. Reproducibility of the viscosity data was t 276, and the agreement with literature values was, on the average, within -t 2%. The reproducibility of the density data was & 0.8%, and the agreement with literature values was I 1.2% .
Viscosity data for mixtures of light p a r f i n hydrocarbons a t low temperatures are almost nonexistent. Lim et al. ( 10) measured liquid viscosities of methane-propane, methane-n-butane, and ethane-n-butane mixtures. Those data were not well correlated by available methods ( 4 , 9), thereby raising some questions on their reliability. An experimental program was initiated as a result to provide thorough and consistent data coverage on one of these systems, the methane-propane system, since it was recognized that the poor results obtained in applying the data of Lim et al. to existing correlations could also indicate that those correlations were not suitable for mixtures in the region of high values of viscosity and density. The data resulting from this experimental program for methane and propane have been reported by Huang et al. ( 8 ) , and those for mixtures of methane and propane are the subject of this paper.
APPARATUS AND MbirERlALS
The ap aratus used in this investigation is the same as that reported i y Huang et al. ( 8) except for the method of pressure measurement in the viscopeter and the equipment used to pre are the mixtures.
A ifferential pressure indicator of the type described by McCreary and Swift ( 1 1 ) was used, in conjunction with a Heise Bourdon tube gauge, to determine the pressure in the viscometer. By installing the differential pressure indicator, it was possible to confine the experimental mixture within the controlled temperature environment, thereby making it possible to insure that the mixture was maintained in a singlephase condition at all temperature levels investigated. The differential pressure indicator-Heise gauge combination was calibrated with a ressure balance accurate to at least '-c 1 lb./sq.in. The caliEration indicated that the maximum uncertainty in the pressure measurement at any of the pressure and temperature levels investigated in this study was & 15 lb./sq.in. The uncertainty of temperature measurement and control in the viscometer apparatus for this study was the same as that reported by Huang et al.
The equipment used for the preparation of mixtures consisted of two precision bore, variable volume cylinders, a