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up to 1800" C, and on pure silica up to 2050" C, using a rotating crucible viscometer.The viscosity isotherms exhibit no appreciable inflection and show an exponential increase in viscosity with increasing silica content. From the slope of the linear relation between log 7 and 1/T, the heat of activation for viscous flow is evaluated.A fundamental change in the silicate lattice occurs on the addition of about 10 mole % alkali metal oxide and about 20 % alkaline earth oxide. Thereafter, up to the orthosilicate composition, the results are consistent with the concept that discrete ions constitute the units of flow. Recently available partial molar volume results which indicate the magnitude of the Si-0-Si angle in liquid silicates are combined with the present measurements to ascertain the constitution of these ions. Si3096-rings are the fundamental building units, and the ions obey the general formula (Sin02n+3)6-. They are present in melts containing from about 10 to 60 mole % metal oxide. The model is shown to satisfy both molar volume changes and the variation of the activation energy for viscous flow with composition.* All compositions refer to the molar percentages.

An investigation of the permeation rate of electrolytic hydrogen through Armco iron single crystals and polycrystals by an electrochemical technique is described. The variation of the permeation rate with cathodic overpotential has been determined in alkaline false(0.1N normalNaOHfalse) , alkaline cyanide, acidic false(0.1N H2SO4false) , acidic iodide, acidic napthalene, and acidic nitrile (valeronitrile, napthonitrile, benzonitrile) solutions. The potential‐permeation behavior as a function of temperature has been investigated in acid false(0.12N H2SO4false) solutions. The permeation potential behavior in alkaline solutions indicate a coupled discharge recombination mechanism for hydrogen evolution at low overpotentials while at higher overpotentials the mechanism is slow discharge‐fast electrochemical. The effects of CN−, I−, and napthalene which increase permeation rate has been interpreted in terms of a lowering of the M‐Hnormalads bond energy. Nitriles were found to decrease the permeation rate, and their effect on the permeation rate is interpreted in terms of their vertical adsorption on the electrode hindering the discharge process. The results indicate that hydrogen goes through an adsorbed intermediate state on discharge before entering the metal lattice. Grain boundaries play no part in the hydrogen evolution kinetics or in the entry of hydrogen to the metal.

The parameters of the H2 evolution reaction on Pt have been determined as a function of current density (c.d.) pH, salt addition, mode of electrode preparation, aging and degree of preelectrolysis; and as a function of c.d., and degree of preelectrolysis for W and Ag. On Pt, Tafel slopes (b) and exchange currents (if) varied with mode of preparation, that in air giving a slope of 2.303 RT/F compared with the more usually observed slope of 2.303 RT/2F; anodic activation gives high and reproducible ¿o's. Aging decreases i0 and extends the c.d. range in which b = 2.303 RT/F. Successive increase of preelectrolysis causes it, to increase to a limiting value. Anodic activation occurs only at a c.d. > 10 "2 amp. cm. ~2 and is independent of the amount of current passed and subsequent reduction. The stoichiometric number (v) is unity. On W and Ag Tafel lines had two distinct slopes; v = 1 in 0.1-0.4 N solution. There is no intrinsic screening effect due to a Luggin capillary. Previous work on Pt in pure solutions indicating b > 2.303 RT/F is reinterpreted in terms of partial diffusion control. Anodic activation on Pt is due to both mechanical cleaning and oxidation. The limiting c.d. for activation is that at which H2 depolarization is negligible. Tafel slopes of RT/F are consistent with migration of H atoms over the surface as rate determining. Calculation of the rate of change of the potential of the layer of ions in contact with the electrode with that of the electrode indicates that near the electrocapillary maximum Tafel slopes may be changed to lower values.slopes occur in pure solutions depending on current density.3(1) .

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