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first discontinuity with respect to water content, considering the 4% point as the lowest percentage water content gel obtainable without destruction of gel activity. Calculating the area covered by 0.04 g. of water one molecule thick also gives a value of about 1 X 10s sq. cm.

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Vol. 59 experiments continued for an hour, and, in a test case, for many hours. If the criticism were here valid, the liquid must be supposed to occupy perhaps ten minutes in developing about 95% of its equilibrium vapor pressure and thereupon to reach a state stationary for hours.d. The possibility of superheating cannot come in question with our method of work.e. The likelihood of phosphorus pentoxide reacting with benzene to produce a soluble impurity of lower volatility than benzene29 is negatived by the results of expts. 1, 9, 10, 11, 12 and 18 which, over many weeks, showed no elevation of boiling point; of expts. 2, 13 and 15 whose boiling points reverted to normal upon heating; and of expts. 5 and 8 which reverted to normal b. p. upon opening to the atmosphere. Summary When purified benzene was desiccated with purified phosphorus pentoxide with precautions to exclude or destroy dust, its vapor pressure,

Adsorption of Nitrogen by Iron Ammonia Catalysts 3f> were carried out in an unsilvered Pyrex Dewar of about 250 cc. capacity, surrounded by an eutectic mixture of CaCla-HjO. A rubber stopper covered with tin foil closed the neck of the Dewar. Through this stopper projected the thermocouple tube, a hand stirrer of glass and a tube for admitting nitrogen or dry air. It was found best to employ a mixture of about 3 parts of carbon tetrachloride to 1 part of methanol, by weight, since this gave a mixture which was about 50% solid and 50% liquid at the transition point. About 75 cc, of this mixture, previously cooled into the transition, was introduced into the Dewar and slowly stirred while readings were taken on the thermocouple. Three determinations gave -47.67, -47.68 and -47.65°, respectively, as compared with the accurate value of -47.66°. The deviations are barely greater than the limits of reproducibility of the thermocouple and are certainly within the limits of error with this simple apparatus. The melting point of the carbon tetrachloride employed in these determinations was also measured in a nearly similar piece of apparatus,24 and found to be -Colxjmbus, Ohio