Five mutually orthogonal Latin squares of order 35

Let N(n) denote the maximum number of mutually orthogonal Latin squares of order n. It is shown that N(35) ≥ 5. © 1996 John Wiley & Sons, Inc.     

Five mutually orthogonal Latin squares of orders 24 and 40

Let N(n) denote the maximum number of mutually orthogonal Latin squares of order n. It is proved that N(24) and N(40)5.     

Reactions of 1,2,4-triazines with nitromethide ion. A convenient method of preparation of 1,2,4-triazin-5-ylcarbaldehyde oximes and their synthetic applications

An efficient procedure for the preparation of 1,2,4-triazin-5-ylcarbaldehyde oximes 2a-f from 1,2,4-triazines 1a-f and nitromethide ion is described. The oximes 2c-d were converted into corresponding 5-cyano-1,2,4-triazines 6c-d . The latter compounds react easily with various nucleophiles to afford 5-substituted 1,2,4-triazines 7a-i and with 1-pyrrolidino-1-cyclohexene to form cyano derivative of 5,6,7,8-tetrahydroisoquinoline 9 .     

Zur Mikrobestimmung des Schwefels in organischen Verbindungen nach dem Bürger-Zimmermann-Verfahren

Zusammenfassung Bei der Schwefelbestimmung durch Aufschluß mit Kalium nachBürger undZimmermann wurde das umständliche Übertreiben des entstandenen Schwefelwasserstoffs umgangen. Die Probe wird nach Lösen des Kaliums direkt mit o-Hydroxymercuribenzoesäure-Lösung in Gegenwart von Dithizon titriert. Die Analysenergebnisse überschreiten im allgemeinen nicht die zulässige Fehlergrenze von ±0,3%.

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The microdetermination of sulfur in organic compounds by the Bürger-Zimmermann method

Summary The laborious distillation of the hydrogen sulfide that results during the decomposition with potassium in the determination of sulfur by theBürger andZimmermann procedure is by-passed. The sample, following solution of the potassium, is titrated directly with o-bydroxymercuribenzoic acid solution. The analytical results in general do not exceed the allowable error limit of ±0,3%.

     

Adsorption from solutions of nonelectrolytes on heterogeneous solid surfaces: A four-parameter equation for the excess adsorption isotherm

A four-parameter single-solute adsorption isotherm equation is generalized to the adsorption of binary liquid mixtures of nonelectrolytes. This equation comprises all isotherms being a simple extension of theEverett isotherm to liquid adsorption on heterogeneous solid surfaces. The benzene—cyclohexane excess adsorption data on silica gel are studied by using this new equation.

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Adsorption aus Lösungen von Nichtelektrolyten an heterogenen festen Oberflächen: Eine Vierparametergleichung für die Excess-Adsorptions-Isotherme

Zusammenfassung Es wird eine Vierparameter-Isothermengleichung für binäre Lösungen von Nichtelektrolyten diskutiert. Diese Gleichung umfaßt alle Isothermen vom Typ der einfachen Erweiterung derEverett-Isotherme für Flüssig-Adsorption auf heterogenen festen Oberflächen. Die Daten für die Adsorption von Benzol—Cyclohexan werden mittels dieser neuen Gleichung behandelt.

     

Poly(3,3′-dimethoxy-2,2′-bithiophene): Synthesis and comparison with poly(3-methoxythiophene)

A new electroactive polymer, namely poly(3,3′-dimethoxy-2,2′-bithiophene) has been prepared by voltammetric polymerization of 3,3′-dimethoxy-2,2′-bithiophene. Due to a different coupling pattern (equivalent to “head-to-head,” and “tail-to-tail” coupled alkoxythiophene rings), poly(3,3′-dimethoxy-2,2′-bithiophene) exhibits different voltammetric properties than the corresponding “head-to-tail” coupled polymer, i.e., poly(3-methoxythiophene). Poly(3,3′-dimethoxy-2,2′-bithiophene) gives very sharp oxidation and reduction peaks indicating an abrupt insulator to conductor transition. This hypothesis was corroborated by the studies of relative resistance as a function of electrode potential. Sharper and better-defined redox peaks may indicate better stereoregularity of poly(3,3′-dimethoxy-2,2′-bithiophene) as compared to poly(3-methoxythiophene) since in this compound the 5,5′-coupling positions are geometrically equivalent and no coupling defects are expected. © 1992 John Wiley & Sons, Inc.     

Fast Simultaneous Adsorptive Stripping Voltammetric Determination of Ni(II) and Co(II) at Lead Film Electrode Plated on Gold Substrate

A fast adsorptive stripping voltammetric procedure for simultaneous determination of Ni(II) and Co(II) in the presence of nioxime as a complexing agent at an in situ plated lead film electrode was described. The time of determination of these ions was shortened due to the application of gold as a substrate for lead film. At gold substrate lead film formation and accumulation of Ni(II) and Co(II) complexes with nioxime proceeds simultaneously. To obtain a stable signals for both ions a simple procedure of activation of the electrode was proposed. Calibration graphs for an accumulation time of 20 s were linear from 5×10^?9 to 1×10^?7 mol L^?1 and from 5×10^?10 to 1×10^?8 mol L^?1 for Ni(II) and Co(II), respectively. The procedure with the application of a lead film electrode on a gold substrate was validated in the course of Ni(II) and Co(II) determination in certified reference materials.