Equations describing the flow of a Newtonian liquid on a rotating disk have been solved so that characteristic curves and surface contours at successive times for any assumed initial fluid distribution may be constructed. It is shown that centrifugation of a fluid layer that is initially uniform does not disturb the uniformity as the height of the layer is reduced. It is also shown that initially irregular fluid distributions tend toward uniformity under centrifugation, and means of computing times required to produce uniform layers of given thickness at given angular velocity and fluid viscosity are demonstrated. Contour surfaces for a number of exemplary initial distributions (Gaussian, slowly falling, Gaussian plus uniform, sinusoidal) have been constructed. Edge effects on rotating planes with rising rims, and fluid flow on rotating nonplanar surfaces, are considered.

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Recent developments in the aqueous solution chemistry of nitrogen are described.with particular attention to the low positive oxidation states + 1 and + 2 . The compounds discussed include hyponitrous acid and hyponitrites, nitrosyl hydride (HNO, "nitroxyl"), trioxodinitrate, nitric oxide, and nitroamine. The numerous redox pathways in which these and other nitrogen compounds are participants illustrate the versatility of that element, and bear important relation to current problems in nitrogen cycle research that focus upon the identity and reactivity of nitrogen species in intermediate oxidation states.

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The rate of decomposition of trioxodinitrate monobasic anion (HN2O3-) in aqueous solution is unaffected by the presence of hydroxylamine, but the primary product nitroxyl ("0) experiences a competition between dimerization to N 2 0 and reduction to N2. The proportion of N2 increases with pH and with NHzOH concentration; at pH 8, with N H 2 0 H in 10-fold excess over HN203-, the reaction product is more than 97% N2. The reaction between NO and N H 2 0 H produces equimolar amounts of N2 and N 2 0 at pH >13, but the ratio N Z / N 2 0 decreases with pH; at pH 8 the product is almost entirely N20.The rate of reaction declines sharply with decreasing pH. Observations of reaction product ratios are complicated by simultaneous contributions of ",OH disproportionation, which produces N2 and NzO in pH-dependent proportions. Tracer experiments employing 15N180 reactant confirm a previously proposed mechanistic interpretation of the NO-NHzOH reaction in detail: an N-bound H atom is abstracted by NO to form H N O and the radical NHOH. The radical combines with a second N O molecule to form nitrosohydroxylamine, which in turn produces two kinds of N20: I, predominantly 14N15N180, and 11, predominantly I5Nl4Ni6O. The asymmetry of the intermediate is reflected in a higher proportion of I than I1 in the product at high pH, but these proportions become equalized at pH 8, probably because of tautomerism in the intermediate. Nitroxyl is entirely reduced by NHzOH to N2 at high pH but undergoes dimerization to produce a third kind of N 2 0 , predominantly 15N1SNis0, to an extent that increases with decreasing pH. The tracer experiments also provide support for the hypothesis that nitroxyl is a primary product of hydroxylamine disproportionation. Since the nitroxyl produced in "203-decomposition is preferentially reduced to Nz at pH 8 in the presence of ",OH, while the nitroxyl produced in the NO-NH20H reaction is almost entirely consumed by self-reaction at the same pH, different intermediate species are produced in these two reactions. Possible explanations for this difference are discussed.

Ground‐water samples from two heavily fertilized sites in Suffolk County, New York, were collected through the 1978 growing season and analyzed for nitrate‐N concentrations and nitrogen‐isotope ratios. Six wells were at a potato farm; six were on a golf course. The purpose of this study was to determine whether the 15N/14N ratios (δ15N values) of fertilizer are increased during transit from land surface to ground water to an extent which would preclude use of this ratio to distinguish agricultural from animal sources of nitrate in ground water. Ground water at both sites contained a greater proportion of 15N than the fertilizers being applied. At the potato farm, the average δ15N value of the fertilizers was 0.2%0; the average δ15N value of the ground‐water nitrate was 6.2 %0. At the golf course, the average δ15N value of the fertilizers was ‐5.9%0, and that of ground‐water nitrate was 6.5%0. The higher δ15N values of ground‐water nitrate are probably caused by isotopic fractionation during the volatile loss of ammonia from nitrogen applied in reduced forms (NH+4 and organic‐N). The δ15N values of most ground‐water samples from both areas were less than 10%0, the upper limit of the range characteristic of agricultural sources of nitrate; these sources include both fertilizer nitrate and nitrate derived from increased mineralization of soil nitrogen through cultivation. Previous studies have shown that the S15N values of nitrate derived from human or animal waste generally exceed 10%0. The nitrogen‐isotope ratios of fertilizer‐derived nitrate were not altered to an extent that would make them indistinguishable from animal‐waste‐derived nitrates in ground water.