The ability of a solid catalyst to promote a gaseous reaction depends upon the amount of surface which the solid possesses as well as upon the specific activity of the surface. Methods of surface area measurement, such as that based on the theory of Brunauer, Emmett and Teller,3 afford a means of distinguishing between changes in quality and in extent of a catalyst surface. Aluminum oxide is known to undergo changes on thermal treatment, and the purpose of this investigation was the determination of how the resulting variations in its effectiveness as a catalyst for the dehydration of ethanol are related to the two aspects of surface alteration. ExperimentalAlumina catalysts were prepared from 8/14 mesh Alorco Activated Alumina by heating a t temperatures between 500 and 1000", both in vacuum and in the presence of water vapor. Surface areas of the catalysts before use were measured by the BET method using n i t r~g e n ,~ following outgassing of the samples a t 400'.The catalytic reaction was carried out a t 350 and 400"in an electrically heated, vertical tube, of 25 mm. inside diameter. The 200-proof ethanol was pumped a t constant rate into an electrically heated evaporator and then passed as vapor into the reactor. The upper part of the reactor tube contained a preheater section packed with quartz chips and provided with manual temperature control; the middle section of the tube contained the catalyst bed of 49 cc. volume, and the temperature of this part was controlled to about * 1 O by means of a Micromax potentiometer controller. The liquid products of the reaction were condensed in receivers cooled in ice and in dry ice and were analyzed by distillation. The uncondensed gas was measured in a wet-test meter and analyzed for ethylene by absorption in HgS04-H2S04 s~l u t i o n .~ Before the reaction was begun the catalyst tube was brought up to temperature under vacuum and then filled with nitrogen ; the first portion of the products was discarded while the system was reaching a steady state, Results and Discussion Surface Areas.-Catalysts prepared by evacuation a t 600 to OOOo show an approximately linear decrease cf area with increasing temperature (Table I). The areas of aluminas treated with water vapor are always lower than are those of the aluminas vacuum-treated a t corresponding temperatures; the magnitude of the difference depends somewhat upon the pressure of water vapor as well as upon the duration of vapor treatment.All materials prepared by heating a t temperatures between 500 and goo', either in vacuum or in (1) Based on the thesis of Wallace S. Brey, Jr., presented to the Faculty of the Graduate School of the University of Pennsylvania in partial fufillment of the rquirements for the degree of Doctor of Philosophy. (2) Present address: St. Joseph's College, Philadelphia, Pa. (3) Brunauer, Emmett and Teller, THIS JOURNAL, 60, 309 (1938). (4) Francis and Lukasiewicz, I n d . E n g . Chem., Anal. Ed., 17, 703 (1945).the presence of water vapor, were shown by X-ray diffraction powder photographs t...

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