The analysis of picomolar lithium, sodium, and potassium by electrothermal atomic absorption spectrophotometry was studied using a Perkin-Elmer Zeeman 3030 spectrophotometer. With ordinary pyrolytically coated graphite tubes, a number of interference effects associated with the sample matrix were observed. In particular, the lithium and potassium absorbance signal was depressed by chloride, an effect shown to be dependent on the preatomization heating. When an in situ tantalum-coated atomization surface was used, matrix interferences observed in lithium and potassium analyses were abolished, and the linear range for the potassium assay was extended. Technical difficulties encountered during sodium analysis at the primary wavelength were effectively circumvented by analysis at a less-sensitive wavelength (303.3 nm), at which tantalum coating also prevented significant chloride interference. The improved microanalyses were employed to reevaluate the handling of lithium, sodium, and potassium along the proximal convoluted tubule (PCT) of the anesthetized rat. The average tubular fluid-to-plasma concentration ratios for lithium [(TF/P)Li] and sodium [(TF/P)Na] were 1.13 +/- 0.08, n = 26, and 0.99 +/- 0.07 (n = 26), respectively. The tubular fluid-to-plasma ultrafiltrate concentration ratio for potassium [(TF/UF)K] was 1.09 +/- 0.05 (n = 13). Ratios did not change significantly with puncture site along the PCT for any of the ions. (TF/P)Li and (TF/UF)K were significantly greater than (TF/P)Na, indicating that lithium and potassium reabsorption do not directly parallel sodium reabsorption in the PCT.

The elastic constants C′ = (C11 – C12)/2, C 11S and C italicnS = C 11S – C′ + C44 of lithium single crystals were measured in the temperature interval 85 to 300°K and the pressure interval 0.001 to 3.5 kbar. Of special interest is the behavior of C′ near the martensitic transformation (which at 1 bar occurs near 78°K) to determine the applicability of either a bulk or a microscopic instability criteria to the transformation. A pulsed ultrasonic interferometer was employed to measure the transit times of the lithium samples from which the elastic constants were calculated. The resulting data indicate that the elastic constants do not change in any drastic manner and are continuously increasing as the temperature is lowered. In addition, all pressure derivatives remain positive to the lowest temperatures and highest pressures studied. Comparisons of the presently reported quantities with those previously measured and theoretically calculated are made.

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The elastic constants of a commercial tungsten carbide cermet (3% cobalt binder) were measured as a function of pressure at room temperature. As pointed out in a recent publication by Ruoff, the pressure dependence of the elastic constants affects the maximum possible pressure which a vessel can contain. This dependence is discussed in light of the present data.

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