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The compressibility of a sample of very pure methane has been measured with high precision from 0°C to 150°C and over a pressure range of about 20 to 230 atmos. The precision attained is of the order of 1 part in 104. Small but consistent discrepancies exist between the present results and earlier measurements, and it is believed these discrepancies are the result of a small impurity of ethane in the methane used earlier. The virial coefficients of methane are redetermined from the present measurements, and the intermolecular forces of methane are calculated from the second virial coefficient for several forms of force laws. These force laws are then used to calculate the third virial coefficient, the crystal properties at 0°K, and the viscosity for comparison with experiment. All the force laws fit the second virial coefficient very well, but some can be eliminated on the basis of the other properties.

An interferom eter has been used to m easur e t he change in index of r efracL ion wiLh change in pressure or temperatm e. Absolu te indices of refraction are l'eporLcd Lo fi v(' d ec imals for benzene, carbon tetr ac hloride, a nd water a t eight diffcren t wavelcngt hs it} t he v i~ibl e region of the sp ectrum at press ures as hi gh as 1100 bars an d tempenl,tu res as high as 55 0 C. The data for benzene and carbon tetrac hloride ha ve been fi tted Lo one Lc rm, dis persion equation s of t he Dru de and Lorentz-Loren z types. Th e observed changes in in dex of r efrac t ion for t hesc two liquids h ave been attribu ted to change in density p lus a shift in t he fundamental a bs orption fr equ ency, assuming t hat the oscillator strengt h r emain s consLant. The data for water have bee n Lr eated and ex plain ed in t he same lTlann er but w iLil Lhe a ddi t ional postulate that water co nsists of two differ ent molecular typ es.

The compressibility of nitrous oxide (N2O) has been measured with high precision from 0° to 150°C and over a density range of about 18 to 180 amagat. The agreement with results of others using somewhat different experimental techniques is good. The virial coefficients are calculated, and the intermolecular potential of nitrous oxide calculated from the second virial coefficient for several forms of force laws, both spherical and nonspherical. A comparison with the physically similar molecule carbon dioxide is made.

A novel method for measuring the isothermal compressibility of liquids has been devised. This method can be used to obtain compressibilities over a wide range of pressure quite rapidly. The compressibilities of C6H6, CCl4, and CH2Cl2 have been measured from 200 to 900 bars. When the Tait equation is used to extrapolate the present results to lower pressures, the agreement with other works is good.

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