Determination of silica in silicates by formation of 12-molybdosilicic acid and redox titration of molybdenum(III).
An indirect titrimetric method for the determination of silica in silicates is described. A boron trioxide-lithium carbonate (10:1) mixture is used as flux and the melt is dissolved in an acidic molybdate solution to form 12-molybdosilicic acid. The yellow complex is extracted with methyl isobutyl ketone (MIBK) and, after removal of the co-extracted molybdate reagent, is decomposed with alkali. The resultant aqueous phase is acidified and passed through a Jones reductor to convert the molybdenum(VI) into molybdenum(III), which is then titrated with potassium permanganate. The method has high precision and accuracy. Phosphorus, titanium, zirconium and vanadium, in amounts that may occur in silicate rocks, do not interfere; at least 5% P(2)O(5), 5% TiO(2), 2% ZrO(2) and 0.5% V(2)O(5) are permissible. Fluorine (at least 2%) can also be tolerated when lithium metaborate is used as flux.
A selective amplification-titration procedure for the determination of microgram amounts of phosphate
Phosphate is converted into phosphomolybdic acid, which is separated from excess of molybdate by extraction. The phosphomolybdate is back-extracted into aqueous solution, and the twelve molybdate ions accompanying each phosphate ion are reduced on a silver reductor column and titrated with 10–3M cerium(IV) by use of a 50-ml burette. Other heteropoly acid-forming elements, e.g., arsenic, antimony, germanium and silicon do not interfere, and there is no interference from a wide range of other ions. The method is both precise and rapid, and has been applied to the submicro determination of phosphorus in a standard organic compound.
Testing the Core Empirical Implications of Gottfredson and Hirschi's General Theory of Crime
In A General Theory of Crime, Gottfredson and Hirschi propose that low self-control, in interaction with criminal opportunity, is the major cause of crime. The research reported in this article attempts to test this argument while closely following the nominal definitions presented by Gottfredson and Hirschi. A factor analysis of items designed to measure low self-control is consistent with their contention that the trait is unidimensional. Further, the proposed interaction effect is found for self-reported acts of both fraud and force (their definition of crime). Inconsistent with the theory are (a) the finding that criminal opportunity has a significant main effect, beyond its interaction with low self-control, on self-reported crime and (b) the substantial proportion of variance in crime left unexplained by the theoretical variables. Suggestions are offered for modifying and expanding the theory.