Untersuchungen zur thermischen Zersetzung von Boraten

In spite of numerous investigations the literature data on the thermal decomposition of borax are contradictory. On the basis of thermal, X-ray, gas analytical and optical investigations this fact can be attributed to the complex decomposition mechanism. After the release of about 8 mole water the reaction product is an X-ray amorphous phase, having the thermal behaviour of glass. From this glass sodium diborate (Na₂O.2B₂O₃) crystallizes between 500–600? with further mass loss. Sodium diborate decomposes from about 700? incongruently yielding NaBO₂ vapor and B₂O₃ glass phase. After evaporation of NaBO₂ is completed the rate of evaporation of B₂O₃ increases considerably.     

A theory of glass electrode response

Summary The response of glass electrodes to rapid changes in ion concentrations is considered from a theoretieal viewpoint. An expression is derived which describes the potential vs. time behavior of glass eleotrodes in terms of a new constant which may be useful in the characterization and selection of glass compositions. Agreement between glass electrode response predicted by the theory and available experimental data is excellent.

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Zusammenfassung Die Ansprechbarkeit von Glaselektroden auf rasche Änderungen der Ionenkonzentration wird vom theoretischen Standpunkt aus erörtert. Eine Gleichung wird abgeleitet, die das Elektrodenpotential als Funktion der Zeit erfaßt und eine neue Konstante enthält, die zur Beurteilung und zur Auswahl der Zusammensetzung von Gläsern dienen kann. Es besteht eine sehr gute Übereinstimmung zwischen theoretisch vorausgesagter und experimentell geprüfter Ansprechbarkeit von Glaselektroden.

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The financial support of NIH Grant GM-10086-03 and NSF Grant GP-1093 is gratefully acknowledged.

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Alfred P. Sloan Research Fellow.     

Spectrometric determination of the fineness of gold

The use of the glow discharge source has been tested for the analysis of refined gold by direct reading emission spectrometry. Careful investigations of the discharge parameters and the introduction of the sputtering rate as internal standard led to a very precise and accurate analytical procedure which has been proved by analysing 100 unknown samples of refined gold. The proposed spectrometric analysis is at least as accurate as the conventional fire assay method and is much faster and laboursaving.     

Electronic structure of octacyanides of molybdenum IV and V according to the SCCC MO method

The SCCC MO method has been used to calculate the electronic structure and spectrum of Mo(CN) ₈ ^4– and Mo(CN) ₈ ^3– ions of a D _4d symmetry. All metal-ligand and ligand-ligand interactions and all overlap integrals (over products of HF atomic orbitals) have been included within the SCCC MO scheme. Basing on these calculations a new assignment of some absorption bands is proposed. The overall agreement between the calculated and observed electronic spectrum is satisfactory.

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Zusammenfassung Elektronenstruktur und Spektrum der [Mo(CN)₈]^–4- und [Mo(CN)₈]^–3-Ionen in D _4d -Symmetrie wurden mit der SCCC-MO-Methode berechnet. Alle Metall-Ligand- und Ligand-Ligand-Wechsel-wirkungen und Überlappungsintegrale wurden berücksichtigt. Die Bandenzuordnung wurde neu vorgenommen. Die Übereinstimmung der berechneten und gemessenen Spektren ist befriedigend.

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Résumé Application à Mo(CN) ₈ ^4– et Mo(CN) ₈ ^3– de la méthode SCCC MO basée sur des orbitales atomiques HF approchées, en tenant compte du recouvrement et de toutes les interactions ligand-ligand. Dans la partie I on discute le cas de la symétrie D _4d . L'accord global avec l'expérience est satisfaisant en ce qui concerne les spectres. On montre aussi que toutes les attributions antérieures basées sur la théorie du champ cristallin semblent inadéquates.

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The authors are grateful to Prof. W. Jakób, Dr. Z. Stasicka and Dr. A. Samotus for many interesting discussions, to Prof. J. Chojnacki for providing us with new X-ray results before publication and to Dr. A. J. Sadlej for a help in dealing with the computer.     

High-performance liquid chromatographic analysis of bile acids in hamster bile

A high-performance liquid chromatographic procedure has been developed for the determination of pentamidine concentrations in serum samples. A microbore, reversed-phase column was used with a mobile phase consisting of methanol and water with sodium heptanesulfonate and triethylamine as modifiers. Pentamidine could be extracted from serum only by the addition of an ion-pairing agent, di(2-ethylhexyl) phosphoric acid, to the chloroform used for extraction. The method can be used to reliably detect levels as low as 5 ng/ml. The pentamidine concentration in the serum of eleven patients 24 h after their tenth daily dose of pentamidine averaged 60 +/- 34 ng/ml.     

Trace-Aktivitätskoeffizienten und Ionenassoziation von Natriummetawolframat im System Natriummetawolframat-Natriumperchlorat-Wasser

Zusammenfassung In der vorliegenden Arbeit wird das Sedimentations-gleichgewicht des Systems Na₆[H₂W₁₂O₄₀]-NaClO₄-H₂O bei 25 °C untersucht. Die scheinbare Ladungszahl des Natriummetawolframats wird als Funktion der NaClO₄-MolalitätmNaClO₄ ermittelt. Aus dieser Abhängigkeit kann für die summarische Dissoziation des NatriummetawolframatsNa₂[H₂W₁₂O_4o] 6Na⁺ + [H₂W₁₂O₄₀]^6– die DissoziationskonstanteK in Gegenwart von NaClO₄ als Fremdelektrolyt zuK=0,08 mol⁶·kg^–6 bestimmt werden.Der Kreuzdifferentialquotient ( _PXz , ist der Trace-Aktivitätskoeffizient des Natriummetawolframats) wird ebenfalls als Funktion der NaClO₄-Molalität ermittelt.Die Konzentrationsabhängigkeit des Trace-Aktivitätskoeffizienten zeigt einen Verlauf, wie er unseres Wissens nach noch nicht von anderen Autoren beobachtet wurde.

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Summary An ultracentrifugal study of the sedimentation equilibrium of the system Na₂[H₂W₁₂O₄₀]-NaClO₄-H₂Oat 25 °C is presented. The dependency of the apparent charge of the sodium metatungstate on NaClO₄-molality is investigated. From these data the dissociation constant for the dissociation of the sodium metatungstate in the presence of NaClO₄ according to the equationNa[H₂W₁₂O₄₀] 6Na⁺ + [H₂W₁₂O₄₀]^6– is calculated toK=0.08 mol⁶·kg^–6. The cross differential quotient ( _PXz is the trace activity coefficient of the sodium metatungstate) shows a behavior in its dependence on NaClO₄-molality which to our knowledge has not yet been reported by other authors.

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Mit 5 Abbildungen und 1 Tabelle     

ESCA-Analysis of tin compounds on the surface of hydroxyapatite

The formation of tin compounds on the surface of hydroxyapatite, the main crystalline component of teeth, is discussed controversially. SnF₂ is used as an anticaries agent in toothpaste preparations. Pure hydroxyapatite (HAP) is treated with extracts of commercially available toothpastes containing tin fluoride and analyzed by electron spectroscopy (ESCA). Survey spectra and depth profiles are recorded. The chemical shifts measured for the HAP samples are compared with those of standard tin compounds. It is concluded that on the surface of hydroxyapatite a mixture of two-valent fluoro-phosphato compounds is formed. SnO is not found in the mixture.     

Intersequence cyclization in copolymers of N-vinyl carbamates

Monomer reactivity ratios determined for the copolymerization of tert-butyl N-vinylcarbamate (r_A = 0.55 ± 0.05) with phenyl N-vinylcarbamate (r_B = 2.08 ± 0.15) indicate that the monomer units are distributed randomly along the polymer chains. The following sequence of reactions was used to cause intersequence cyclization between tert-butyl N-vinylcarbamate and phenyl N-vinylcarbamate units in the copolymers. The extent of cyclization obtained was in accord with that expected for random copolymers.      

Measurement of the Compton profiles of CH4 and C2H4 by high energy electron impact spectroscopy

We present a new experimental determination of the Compton profiles of CH₄ and C₂H₄ molecules using high energy electron impact. The observable q range has been extended up to 10 au (6 au for C₂H₄). Good agreement is found with an earlier X-ray scattering experiment and with new theoretical calculations.