The x-ray scattering from liquid copper, silver, tin, and mercury was measured at temperatures of 1125 °C, 1050 °C, 335 °C, and 28 °C, respectively, from the open surface of horizontal samples using a focusing theta-theta diffractometer, quartz crystal monochromator positioned in the dif fracted beam, scintillation detector, and pulse height discriminator. The effect on the measured intensities of the positioning of the sample with respect to the diffractometer axis and the meniscus of the liquid were considered. Calibration of the primary beam intensity by measurements on liquid mercury provided an alternate check of the standard normalization procedures for copper, silver, and tin. After calculation of the interference functions, atomic and radial distribution functions were evaluated from which interatomic distances and coordination numbers were obtained. The interatomic distances in the liquid were in good agreement with the G o l d s c h m id t diameters of the respective elements.X-ray diffraction is one of the more important methods that may be employed to investigate the liquid state of matter. The arrangement of the atoms determines the angular distribution of the scattered x-rays. This arrangement is usually described by the probability W {r)dv of finding the center of another atom in the volume element dt> at a distance r from a given atom. Then, W (r) = Q (r )/g 0 , where o(r) is the atomic density function and ,o0 the average atomic density in the liquid. It can be shown that, for monatomic liquids, the radial distribution func tion (R D F ) 4 ; r r 2 o(r) is given by1: 4 n r2 Q (r) = 4 n r2 o0 o o + (2 r/ji) f K [ I ( K ) -l]-(sin£r) d K ,(1 ) o where K = 2 ji s = 4 ji sin © //, s = 2 sin G/X, and I( K ) is the interference function:

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149we have plotted the reduced temperatures and densities and also the critical ratios of various substances against X and compared these with the results of our model, ' In the case of the critical ratio there is experimentally an increase of about 5%%uq as X increases from Xe to Hes, After completion of this paper M. E. Fisher supplied us with more recent experimental data collected by him for Ref. 4. However, use of those results makes only about 1% change to Fig. 2.

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