X-Ray Diffraction in Ethyl Ether near the Critical Point

X-ray diffraction ionization curves were obtained for ethyl ether at 43. 50. 7 kg/cm^2 pressure with temperatures in the range from 25^ to 210^. The critical pressure and temperature of ether are 36. 70. 2 kg/cm^2 and 194. 60. 3^, respectively. In the region of the higher temperatures the ionization curves are a combination of the liquid and polyatomic gas types, falling rapidly near 0^ with increasing angle, then rising to a distinct peak and again falling. Liquid semi-orderly "cybotactic" groups are in evidence from room temperature to 199^ but not for specific volumes greater than the critical specific volume. It seems reasonable to expect vanishing of these groups at the critical point. The influence of the polyatomic gas type begins to appear at the low temperatures and increases with temperature. The liquid type decreases almost linearly until 155^ where it begins to fall off very rapidly. The observations are in excellent accord with the "cybotactic" view of the interior of a liquid.