The adsorption of krypton 011 graphite has been measured above and below its Triple Point. Above the Triple Point, a smooth isotherm was found which showed two types of hysteresis. I11 contrast, the isotherm measured below the Triple Point displayed two discontinuities. The surface area of this graphite measured by means of the krypton isotherm was found to be in agreement with that previously measured by nitrogen adsorption.
INTRODUCTIONThe adsorption of lirypton by artificial graphite has been studied as part of a program directed toward a study of these graphites. The adsorption of krypton by a substance closely related to graphite (P33 carbon black graphitized a t 2700" C) has been studied by Singleton and Halsey (10) ; Amberg, Spencer, and Beebe (I) ; Clark (4) ; and Ross and Winkler (9). In every instailce stepwise isotherms were obtained a t 77' K. The reversibility of the isotherm was demonstrated by Clark. Heats of adsorption measured by Amberg, Spencer, and Beebe were found to show a maximum a t a coverage close to the monolayer. A second smaller maximum coincided with the completion of the second layer. The stepwise isotherms, coupled with the heat curve, are strong evidence that the surface of this graphitized black was homogeneous. Ross and Winkler conducted measurements down to low pressures and presented isotherms which displayed discontinuities characteristic of two-dimensional phase changes. They made measureinents a t 77' and 90" K and showed that the vertical discontinuity signifying two-dimensional liquefactions occurred a t 77" but not a t 90" I<. The two-dimensional critical temperature was estimated to be 82" K. The measurements reported here were undertaken to investigate further the rather unusual hysteresis effects reported previously for artificial graphites manufactured by Acheson Co. Previous papers in this series (6, 7) have presented evidence of two types of hysteresis occurring on the adsorption of oxygen, nitrogen, and argon (6, 7) by artificial graphites a t liquid air temperatures. These measurements have now been extended to lirypton and sulphur dioxide (8). Those with krypton were done above and below the Triple Point. Two types of hysteresis have been reported with the artificial graphites: the normal type of hysteresis due to pores occurring a t high relative pressures and a second type extending down to low relative pressures which has been termed "swelling hysteresis". This type of hysteresis has also been demonstrated for the adsorption of nitrogen by the carbon blacli "Spheron 6" a t 77" K and for the adsorption of diethyl ether by charcoal (2, 7).
E X P E R I M E N T A L AND RESULTSThe graphite used in these experiments was a purified Acheson graphite designated by us as GF-3. Its properties have been given before (7, 11).The krypton was obtained from the Matheson Co. and used without further purification.Isotherms were measured a t 119" I< and 78" K. Before each isotherm was measured, the sample was evacuated for a t least 12 hours a t 200' C. The isotherm a t...
