The determination of traces of ammonium-nitrogen in aqueous solution by optical emission spectrometry with a high-frequency inductively coupled argon plasma source

A method for the determination of low levels of ammonium ion in solution by optical emission spectrometry with an inductively coupled argon plasma source operated at 27 MHz is presented. The ammonium ion is oxidized with sodium hypobromite in alkaline medium, the evolved nitrogen is passed into the argon plasma, and the NH emission intensity produced in the plasma at 336.0 nm is monitored. A practical detection limit of 0.1 μg N ml^-1 for 5-ml aqueous sample solutions has been obtained. The method has been applied to the determination of the exchangeable ammonium content of soil samples.     

The isotropy of Gaussian molecular networks and the stress-birefringence relations for rubberlike materials cross-linked in stressed states

Summary Using the model and some results of theJames andGuth theory of rabberlike elasticity, the relations between stress, birefringence, and strain (measured from the unstressed state) are re-derived by an argument which does not make use of certain assumptions used in previous derivations concerning the isotropy of the distribution of vectors joining junction mean positions and the fixing of junctions in their mean positions. It is proved that in the Gaussian approximation a rubberlike material is necessarily isotropic in the sense that the relations between the stress, strain, and refractive index involve no anisotropic constant tensors. The argument is applicable to networks whose junctions are introduced when the material is in different states of stress, and furnishes strong reasons for regarding the relations between flow birefringence and stress, previously derived on the basis of a network theory for concentrated polymer solutions, as being no longer restricted to solutions of constant viscosity.

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Zusammenfassung Unter Verwendung des Modells und einiger Ergebnisse der Theorie vonJames undGuth für Gummielastizit?t wurden die Beziehungen zwischen Spannung Doppelbrechung und Verformung (gemessen gegen den unbelasteten Zustand) erneut abgeleitet. Es wurde kein Gebrauch gemacht von den in früheren Ableitungen enthaltenen Annahmen über die Fixierung der Bindungen in mittleren Positionen und über die Isotropie der Verteilung der Vektoren, die diese Positionen verbinden. Es wird gezeigt, da? in derGauss-N?herung eines gummiartigen Materials Isotropie in dem Sinne erforderlich ist, da? die Beziehungen zwischen Spannung, Verformung und Brechungsindex keine anisotropen Tensoren der Konstanten enthalten. Diese Ableitung ist anwendbar auf Netzwerke, deren Bindungen eingeführt werden, w?hrend das Material in verschiedenen Spannungszust?nden vorliegt, und liefert eine gute Grundlage für die Annahme, da? die Beziehungen zwischen Str?mungsdoppelbrechung und Spannung, die früher auf Grund der Netzwerktheorie für konzentrierte Polymerenl?sungen abgeleitet wurden, nicht mehr auf L?sungen konstanter Viskosit?t beschr?nkt sind.

     

Synthesis of derivatives of pyrido[2,3-d]pyrimidines condensed with tetrahydropyran and tetrahydrothiopyran

Methods have been developed for obtaining derivatives of W-amino(oxo)-, 8,10-dioxo-, and 10-amino-8-oxo(thio)pyrano(thiopyrano) [4,3:4,5]pyrido[2,3-d]pyrimidine on the basis of 3-amino(benzylamino)-4-cyano (carbamoyl)pyrano(thiopyrano)[3,4-c]-pyridines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1683–1687, December, 1993.     

New approach to the synthesis of 3-amino-1,2-benzothiazine 1,1-dioxides

The possibility of obtaining 3-amino-1,2-benzothiazine 1,1-dioxides by nucleophilic substitution of the chlorine atom in 5-nitro-2-chlorobenzenesulfonamides by carbanions generated from substituted acetonitriles was studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 264–266, February, 1992.     

Recyclization of 3-phenacylidene-3,4-dihydro-2H-1,4-benzoxazin-2-one under the influence of o-phenylenediamine

Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, p. 856, June, 1991.     

Polymérisation anionique amorcée par les composés lamellaires du graphite et du lithium

In the present work, we use the binary insertion compound LiC₁₂ to polymerize styrene, methyl methacrylate, butadiene, isoprene, and to copolymerize isoprene and styrene in various hydrocarbon solvents (aromatics and aliphatic) and etheral solvents. We show that the styrene polymerization in aromatic solvents gives better yields than in the etheral solvents, the polymer being atactic. Methyl methacrylate does not polymerize in toluene but does so completely in DME. More generally, the yields of polymerization are better with KC₃₇ than with LiC₁₂ because of the different capacities of the monomer to get into the carbon layers. The polymerization of dienes with LiC₁₂ shows that the microstructures of the polymer obtained in π-or n-donor solvents are similar to the ones obtained by homogenous polymerization with Li cation in such solvents. However, for isoprene in cyclohexane, the results are different. The isoprene styrene copolymers are statistical ones and the mean length of styrene blocks is less than 5. The monomer interaction with the insertion compound and the growing chain geometry between the carbon layers are the facts which control either the stereospecificity of the polymerization or the selectivity of the copolymerization.