Part I. Radial Diffusion in a Turbulent Air Stream. Part ll. A. Absorption of Light by the System Nitric Acid-Nitrogen Dioxide-Water. B. Ionization in Solutions of Nitrogen Dioxide in Nitric Acid from Optical Absorbance Measurements. Part Ill. Kinetics of the Decomposition of Sodium Dithionite. Part IV. The Determination of Chromium by Oxidation in the Presence of Silver Nitrate

Citation

Lynn, Scott (1954) Part I. Radial Diffusion in a Turbulent Air Stream. Part ll. A. Absorption of Light by the System Nitric Acid-Nitrogen Dioxide-Water. B. Ionization in Solutions of Nitrogen Dioxide in Nitric Acid from Optical Absorbance Measurements. Part Ill. Kinetics of the Decomposition of Sodium Dithionite. Part IV. The Determination of Chromium by Oxidation in the Presence of Silver Nitrate. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/PFBW-BV22. https://resolver.caltech.edu/CaltechETD:etd-01092004-094500

Abstract

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I. The eddy diffusivity and the eddy viscosity near the center of a pipe have been determined for the case of turbulent, cylindrically symmetric, steady, non-uniform flow*. The eddy properties were calculated from measurements of composition and velocity in a test section 36 in. long and 6 in. in diameter. Natural gas was introduced into a turbulent air stream through an annulus section 1/8 in. thick. Experiments were made at Reynolds numbers of 45,000 and 82,300. Both eddy properties were found to vary appreciably with distance downstream from the annulus. The eddy diffusivity varied much more than did the eddy viscosity, being less in some regions and much greater in others. However, there appeared to be no tendency for either eddy property to approach zero at the center of the channel. The results of the experiments are discussed and compared to the data of other workers.

IIA. The optical absorbance of the liquid phase of mixtures of nitric acid, nitrogen dioxide**, and water was measured at 32[degrees]F at wavelengths of 500 and 425m[...]. At the longer wavelength compositions containing 0.8 or more weight fraction nitric acid were studied. At the shorter wavelength the compositions were limited to a minimum weight fraction nitric acid of 0.93. The results indicate that the absorbance varies linearly with the weight fraction nitrogen dioxide at small concentrations of this component. The optical absorption appears to be a useful intensive property of the liquid phase to be employed as an aid in determining the composition of the ternary system.

IIB. Values of the optical absorbance of solutions of nitrogen dioxide in nitric acid were measured at 32[degrees]F and one atmosphere using light at a wave length of 425m[...]. The data obtained were applied in a study of the ionisation occurring in the solutions. The numerical solution of simultaneous equations based on equilibrium expressions indicated that in nitric acid solutions containing less than one weight per cent nitrogen dioxide the nitrogen dioxide is about 70 per cent dissociated into nitrosonium ([...]) and nitrate ([...]) ions whereas the nitric acid is about five per cent dissociated into nitronium ([...]) ions, nitrate ions, and water. Although the uncertainty is high, the order of magnitude of these values is correct.

III. In aqueous solution, Na2S2O4, sometimes called sodium hydrosulfite but more correctly sodium dithionite, undergoes irreversible decomposition at a measurable rate to give NaHSO3, sodium bisulfate, and Na2S2O3, sodium thiosulfate, as products. Studies of this reaction with initial compositions in the range 0.01 - 0.10 F Na2S2O4 were made with the exclusion of air. A solution of Na2S2O4 alone decomposes in a fashion suggesting that a degenerate branching chain mechanism is involved. An apparent positive salt effect on the reaction rate results when NaCl is added to the solution. At values of the concentration of H[superscript+] above 10[superscript -3] moles per liter this decomposition is extremely rapid. Initial concentrations*** of the products of decomposition, NaHSO3 and Na2S2O3 less than the initial concentration of [...] catalyze the decomposition, indicating that it is autocatalytic in nature. Initial concentrations of [...] up to tenfold that of [...] markedly catalyze the decomposition.

However, in the presence of initial concentrations of NaHSO3 greater than the initial concentration of [...] the chain mechanism is overshadowed, and the reaction is first order with respect to both the species [...] and [...] and is independent of the initial concentration of [...] and of the concentration of H[superscript +] but is slightly dependent on the initial concentration of [...]. With only [...] and [...] added the reaction rate is greatly inhibited, and part of this effect may be attributed to the corresponding lowering of the concentration of [...].

In the presence of initial concentrations of both Na2S2O3 and NaHSO3 which are equimolar or greater than the initial concentration of Na2S2O4 the reaction appears to be approximately first order with respect to the concentrations of the species [...], [...], and [...]. In the presence of both [...] and [...], however, the reaction rate is dependent on both the initial concentration of the H[superscript +] and the concentration of [...]. Superposed on these overall first order reactions is an inherent periodicity in the reaction rate. The bulk of the kinetics measurements were made at 60[degrees] C, although several measurements were made at 50[degrees] and 70[degrees] C to obtain the activation energy of the thermal decomposition reaction.

A few measurements were made at 50[degrees], 60[degrees], and 70[degrees] C of the rapid oxidation of 0.01 F Na2S2O4 in aqueous solution by air. This oxidation reaction appears to be first order with respect to the concentration of [...] and is inhibited in basic solutions. A modified analytical procedure employing methylene blue in a basic aqueous solution of methanol or acetone was used to determine Na2S2O4 in the presence of large quantities of other reducing agents.

IV. A method is described for determining amounts of chromium of the order of a few milligrams. Trivalent chromium is oxidized by fuming perchloric acid in the presence of a small amount of silver ion. The dichromate is then determined iodimetrically. For small amounts of chromium the method gives better results than do other methods listed in the literature. The method has not been tried for large amounts of chromium.

*Flow is defined as steady when the average velocity, temperature, and other properties of interest at a point do not change with time. Flow is defined as uniform when the derivatives with respect to x, the coordinate in the direction of flow, of velocity, temperature, and other properties of interest are zero. Uniform flow is theoretically unattainable but may be closely approached in practice.

**The term nitrogen dioxide is used to designate equilibrium mixtures of nitrogen dioxide and nitrogen tetroxide.

***Unless otherwise specified, concentrations refer to molar or formal concentrations.

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