These results substantially confirm the observations previously made in this Laboratory [Barry, This Journal, 44, 933 (1922)] which yielded the approximate value for the total heat similarly developed on a goldplated surface of 0.035 cal. per sq. cm. 5. The phenomenon, which is certainly not an adsorption in the usual sense of the term, awaits full explanation. It appears to involve the occlusion of water vapor by gold, and to be affected, at least, by capillary imbibition.

In 1821, Michael Faraday' found that a solution of chlorine in tetrachloroethylene yielded hexachloroethane when exposed to sunlight. This reaction should offer perhaps the simplest possible case for kinetic study of photochemical chlorination of a double bond; there is no opportunity for complication arising from simultaneous substitution, and there is little likelihood of the formation of more than one chlorination product; moreover, a t room temperature dark reaction apparently does not occur. On the other hand, it has been found2 that tetrachloroethylene and oxygen alone give on prolonged exposure to sunlight, trichloroacetyl chloride and phosgene. We have undertaken a study of the kinetics of the chlorination in carbon tetrachloride solution using light absorbed only by the chlorine; we have found: (I) that this photochlorination, in common with many others, is strongly inhibited by dissolved oxygen; and (2) that in the presence of sufficient oxygen, oxidation of the tetrachloroethylene occurs to the practical exclusion of the chlorination although chlorine remains the light absorber. The present paper is concerned mainly with the products and kinetics of this photochemical oxidation sensitized by chlorine. ApparatusThe Reaction Vessel.-Most of the illuminations were carried out with the solution in the vessel shown in Fig. 1. This vessel consisted of two flat-windowed Pyrex cells so joined together that the solution could be transferred from one to the other by inverting the vessel: the solution was placed in the thin cell A for illumination and in the thick cell B for photometric analysis. The cell A, which was of 5 mm. internal thickness and about 35 mm. diameter, was made thin in order that light absorption in it be low and all parts of the solution under nearly the same intensity of illumination. The cell B, which was of 3.30 cm. internal thickness and of slightly smaller volume than A, gave a longer optical path through the solution. The light absorption measured with the solution in B was used to compute the chlorine concentration and to compute the smaller absorption occurring in the cell A. The vessel was filled through a ground-glass stopper C which was protected with a water-tight cap D, since the vessel was placed in a water thermostat for illumination.The Light Thermostat.-This was a tank of water provided with a window, stirrer and heater; temperatures were kept constant to one-half degree or better. The reaction vessel was mounted in a position accurately reproducible from one experiment to another, and about 1 cm. from the window. M. Faraday, Ann. chim. phys., [Z] 18, 55 (1821). M. A. Besson, Comfit. rend., 121, 125 (1895).

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A new hydrate of hydrazonium dibromide is reported.2. Dissociation pressures over a range of temperature are given for four of the five known hydrated hydrazonium salts, and transition points determined for two of them.3. Calculations of the change in heat content and standard free energy change of hydration are made. Corvallis, Oregon