Geology topics
Publications and source records attributed to Leonard Shapiro.
A rapid and simple method for the determination of total water in silicate rocks has been developed by modifying the Penfield procedure. In this method, the time required for a single determination has been reduced to less than 10 minutes. Comparison of the data obtained by this modification and the Penfield method indicates the same degree of accuracy.
Rapid nonsubjective methods have been developed for the determination of calcium and magnesium in carbonate rocks. From a single solution of the sample, calcium is titrated directly, and magnesium is titrated after a rapid removal of R2O3 and precipitation of calcium as the tungstate. A concentrated and a dilute solution of disodium ethylenediamine tetraacetate are used as titrants. The concentrated solution is added almost to the end point, then the weak solution is added in an automatic titrator to determine the end point precisely.
The rapid methods previously used by the U.S. Geological Survey to determine the major constituents of rocks have been modified to introduce atomic absorption spectrometry (AAS) where applicable. Two procedures are available for determining 10 constituents: one, from a single solution prepared by a nitric-acid dissolution of a lithium metaborate-lithium tetraborate fusion, and the other, a two-solution method in which one portion of sample is dissolved in an HF-H 2 SO 4 ,-HNO 3 mixture and another portion is fused with NaOH. In both techniques, SiO 2 , Al 2 O 3 , Fe 2 O 3 , TiO 2 , P 2 O 5 , and MnO are determined spectrophotometrically, and CaO, MgO, Na 2 O, and K 2 O are determined by AAS. Separate portions of samples are used for the following determinations: FeO by titration with K 2 Cr 2 O 7 after decomposition with HF and H 2 SO 4 ; total H 2 O by its weight when evolved on heating a mixture of sample plus flux; H 2 O by loss of weight at 110° overnight; CO 2 by its volume upon evolution with acid; fluorine by a new indirect measurement of SiO 2 evolved with fluorine on heating; and. sulfur by a new procedure based on a turbidimetric measurement of BaSO 4 , after an aqua regia attack. Several mechanical aids and automated devices are used for the analyses.
Solutions containing in excess of 200 μ g/ml of silica form polymers which do not react with molybdate in the spectrophotometric determination of silica. Fluoride ions catalyze the depolymerization of silica so that precise spectrophotometric determinations of silica can be made, even when silica is present predominantly as polymers.
Sulfur is determined turbidimetrically as barium sulfate after an aqua regia attack. The turbidity is formed in an ammoniacal solution from which R2O3 has been centrifuged. Reproducibility of turbidity is obtained by adding barium chloride as a solid rather than as a solution. Sulfur is determined in the range 0.01-4 percent within ±0.02 absolute, or approximately 5 percent of the amount present, whichever is larger. A 100-mg sample is used for sulfur concentrations of up to 0.50 percent S, a 20-mg sample for higher levels. A determination requires about 5 minutes.
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The method is an adaptation of a procedure described by Betz and Noll 1 in 1950. Calcium and magnesium are determined by visual titration using Versene (disodium ethylenediamine tetraacetate) with Murexide (ammonium purpurate) as the indicator for calcium and Eriochrome Black T as the indicator for magnesium.
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About 4 mg of rock powder measured with a scoop is fused with potassium bisulfate in a test tube. Tiron is added to the cool melt and the mixture is dissolved in a buffer solution. Sodium dithionite is added and the approximate concentration of TiO 2 is determined by comparing the resulting yellow solution with permanent standards, which are simple to prepare.The results obtained by this field method for TiO 2 on 72 rock samples of various types are compared with those obtained by laboratory methods.
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