Argentometric determination of iodide and cyanide using a depolarisation end-point

It has been shown that the depotarisation end-point technique, based on the phenomenon of a sudden out-of-balance current, produced by the establishment of a new redox potential at the indicator electrode in a pre-balanced circuit, can also be applied to precipitation titrations. The use of a platinum indicator electrode instead of one made of silver, and determination in very dilute solution, yield better results than those obtained using the classical potentiometric method.     

Spektroskopische Untersuchungen der Metallkomplexe des 2,5-Dibenzoyl-3,4-dihydroxyselenophens

Zusammenfassung Eine Reihe von Metallkomplexen des 2,5-Dibenzoyl-3,4-dihydroxy-selenophens wurden spektroskopisch untersucht. Das Verhalten des Wismutkomplexes und die Möglichkeiten einer spektrophotometrischen Wismutbestimmung auf diesem Wege wurden eingehend studiert.

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Summary A spectroscopic examination was made of a series of metal complexes of 2,5-dibenzoyl-3,4-dihydroxyselenophen. The behavior of the bismuth complex and the possibilities of a spectrophotometric method of determining bismuth in this manner were studied thoroughly.

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Herrn Univ.-Prof. Dr.Hans Lieb zum 80. Geburtstag gewidmet.     

The effect of morphological changes on the coprecipitation of strontium by calcium phosphate

The coprecipitation of strontium by a calcium phosphate phase formed at an elevated pH 10.8 was investigated. The first phase obtained under these conditions in the amorphous calcium phosphate (ACP) which is transformed into crystalline hydroxyapatite (HA) after the induction period. Is has been shown that this transformation together with morphological changes of the precipitated solid phase, influences the amount of the sorbed strontium significantly. The possible consequences of this finding on practical application of coprecipitation of strontium by calcium phosphate have been discussed.     

Corrosion of Cu-xZn alloys in slightly alkaline chloride solutions studied by stripping voltammetry and microanalysis

The mechanism of corrosion of Cu-xZn alloys (x = 10-40 wt %) in slightly alkaline chloride solutions was investigated by analysing solid reaction products by energy dispersive X-ray analysis (EDS) and dissolved reaction products by differential anodic pulse stripping (DAPS) voltammetry. The corrosion process was studied under open circuit and under potentiostatic conditions at selected potentials. Pure metals were studied comparatively so that an interacting effect of particular metal components in the alloy could be determined. All four Cu-xZn alloys show an improved behaviour compared to pure metals. Under open-circuit condition both components dissolve simultaneously in the solution. With increasing immersion time the preferential, dissolution of zinc in the solution becomes pronounced. It is the highest for Cu-10Zn and the lowest for Cu-30Zn alloy. Under potentiostatic control the dissolution mechanism depends on the electrode potential and changes from exclusive dissolution of zinc to simultaneous dissolution of both components with preferential dissolution of zinc. The latter decreases, as the electrode potential becomes more positive.     

The electronic structure of the aqua-oxo complex of vanadium(IV)

The Jorgensen [16] and Ros-Cotton [9, 10] methods have been used to calculate the electronic structure of VO(OH₂) ₅ ²⁺ . The results are compared with those obtained from the simple Wolfsberg-Helmholz method and with the electronic absorption spectra. Good agreement with the experimental data is obtained in the latter case. When calculating the transition energies associated with charge transfer, we took into account the interaction of an excited electron with the effective charges in the complex and the redistribution of these charges when the excited state is populated.     

A simple procedure for the quantitative microdetermination of rhamnose

Summary A simple spectrophotometric procedure for microdetermination of rhamnose is described. It is based on breakdown of the sugar with sulphuric acid followed by treatment withp-hydroxydiphenyl. The coloured product is measured spectrophotometrically at 560 nm. A linear relationship exists between the amount of rhamnose (10-0g–) and the absorbance. The method is recommended for determination of rhamnose in samples containing rhamnose, different neutral sugars, amino-sugars, sugar alcohols, uronic acids, and muramic acid.

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Zusammenfassung Ein einfaches spektralphotometrisches Verfahren zur Mikrobestimmung von Rhamnose wurde beschrieben. Es beruht auf der Spaltung des Zuckers mit Schwefelsäure und nachfolgender Behandlung mit p-Hydroxydiphenyl. Das gefärbte Reaktionsprodukt wird spektralphotometrisch bei 560 nm gemessen. Die Extinktion steht mit der Rhamnosemenge in linearer Beziehung. Das Verfahren wird für die Rhamnosebestimmung in Proben empfohlen, die verschiedene Neutralzucker, Aminozucker, Zuckeralkohole, Uronsäuren und Muramsäure enthalten.

     

Elektronenspektren einiger Thioamide und ihrer S- und N-Derivate

Zusammenfassung Wir diskutieren und veröffentlichen die Elektronenspektren einiger Thioamide und die einiger S- und N-Derivate (N-Aryl-, N-Methyl-N-aryl-, S-Methyl-N-aryl-, N-Acyl-) davon.

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The electronic spectra of some thioamides and their S- and N-derivatives (N-aryl, N-methyl-N-aryl, S-methyl-N-aryl, N-acyl) have been reported and discussed.

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Aus der vonN. Stojanac eingereichten Dissertation, die einen Teil der zur Erlangung des Titels eines Doktor der Chemie (Ph. D.) der Universität Zagreb gestellten Anforderungen erfüllt.     

On the evaluation of the characteristic polynomial via symmetric function theory

The use of power sum symmetric functions leads to Newton's identities, which relate the traces of various powers ofA, the adjacency matrix of a graph, and the coefficients of the characteristic polynomials. While it is possible to solve Newton's identities and generate the coefficients by recursion or, alternatively, to derive them by sequential manipulations (yielding the explicit formulas), we show how the results can be expressed using a combinatorial approach and relate the evaluation of the coefficients to selected Young diagrams.     

Critical behaviour of the compressible magnet with exchange anisotropy

Then-component magnet with exchange anisotropy on a compressible lattice, with isotropic elastic properties, is studied. The renormalization group method is applied ind =4 — dimensions. The fixed points and the stability regions are explored to the order ², and the analysis is concentrated upon the casen<4—2 +O( ²). Investigation of the fixed points reveals various crossover phenomena which are not present in the corresponding rigid model. Renormalization of the anisotropy crossover exponent is demonstrated. It is shown that macroscopic instabilities, leading to the first order phase transition, may appear.     

Raman scattering in SnSe

Zone center optical phonons in SnSe were investigated using Raman scattering data obtained here and previously reported far infrared reflectivity measurements. The values of the ratio of the pairs of interlayer force constants were calculated te be between 3·3 and 4·5. Thus it can be concluded that SnS is a layer like semiconductor but less layer like than GeS, GeSe or SnS.