The results when plotted on a log N vs. 1 ¡T basis show that the urea-water solutions appear ideal when the mole fraction of urea is greater than approximately 0.6.3. The heat of fusion of urea is calculated to be 3470 cal./mole. Wilmington, Delaware
On the basis of results obtained from small-scale laboratory work, equipment for the production of 60 pounds of zirconium sponge a cycle has been placed in operation.Zirconium carbide, prepared from zircon and earl)on in an electric arc furnace, is chlorinated in improved equipment capable of producing over 300 pounds a day. The raw zirconium chloride is purified in a unit which accommodates nearly 200 pounds. Reduction by magnesium is carried out in the same furnace as the purification. Excess magnesium and magnesium chloride are removed by a combination melting and vacuum distillation method. The zirconium sponge is pressed into briquets and melted in graphite crucibles in a new graphite resistor vacuum furnace capable of melting over 10 pounds of zirconium a charge.
The influence of water on the halogen-hydrogen combinations is discussed. Reasons are advanced for the hypothesis that the primary chemical reaction takes place between halogen atoms and hydrogen. Halogen molecules excited either by light in the visible portion of the spectrum or by thermal collision do not dissociate into atoms except on collision with water molecules. While dissociation does not affect the thermal decomposition of hydrogen iodide, the thermal and photochemical union of hydrogen and bromine and the thermal combination of hydrogen with iodine can be stopped by desiccation.In the combination of hydrogen and bromine the commencement of the chain mechanism, so marked in the hydrogen-chlorine reaction, can be detected a t high temperatures and high pressures of hydrogen. The relationship between the mean life of the excited bromine molecule and the water-vapor pressure required for the attainment of a velocity maximum of combination is developed.sec., this pressure is found to be of the order of 0.1 mm. A mechanism for the combination of hydrogen with iodine based upon the primary dissociation of iodine into atoms is advanced and this system is shown to be photochemically sensitive a t high temperatures (450') in accordance with theoretical considerations. I t is considered unnecessary to assume that the chain mechanism involves water.With a value of 7 =
CAMBRIDGE, ENGLANDThis article is the last of three dealing with the free energy of formation of zinc oxide. Four possible methods of experimentally determining the standard free energy of stable oxides usually are available: (1) measurement of high-temperature equilibria and extrapolation of the results; ( 2 ) measurements dependent on the electromotive force of reversible galvanic cells ; (3) calculation from low-temperature specific-heat data and the third law of thermodynamics; (4) calculation from solubility values and standard electrode potentials. The present work reports new experimental resultsPublished by permission of the Director, United States Bureau of Mines.
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