Dosage de l'histidine: Étude polarographique et dosage du dinitrofluorobenzene

After polarographic study and determination of dinitrofluorobenzene at varying pH and determination of a number of electron exchanges (n), standardization curves have been constructed at pH 5 and 10. They allow the estimation of DNFB to a concentration of 1γ/ml with a precision of 4–7%. The curve shows 2 or 3 leaps, according to pH.. The E_{$\text{1}\text{2}$} of the first two are less than 1 volt.     

Rupture of wetting films caused by nanobubbles

It is now widely accepted that nanometer sized bubbles, attached at a hydrophobic silica surface, can cause rupture of aqueous wetting films due to the so-called nucleation mechanism. But the knowledge of the existence of such nanobubbles does not give an answer to how the subprocesses of this rupture mechanism operate. The aim of this paper is to describe the steps of the rupture process in detail: (1) During drainage of the wetting film, the apex of the largest nanobubble comes to a distance from the wetting film surface, where surface forces are acting. (2) An aqueous "foam film" in nanoscale size is formed between the bubble and the wetting film surface; in this foam film different Derjaguin-Landau-Verwey-Overbeek (DLVO) forces are acting than in the surrounding wetting film. In the investigated system, hydrophobized silica/water/air, all DLVO forces in the wetting film are repulsive, whereas in the foam film the van der Waals force becomes attractive. (3) The surface forces over and around the apex of the nanobubble lead to a deformation of the film surfaces, which causes an additional capillary pressure in the foam film. An analysis of the pressure balance in the system shows that this additional capillary pressure can destabilize the foam film and leads to rupture of the foam film. (4) If the newly formed hole in the wetting film has a sufficient diameter, the whole wetting film is destabilized and the solid becomes dewetted. Experimental data of rupture thickness and lifetime of wetting films of pure electrolyte and surfactant solutions show that the stabilization of the foam film by surfactants has a crucial effect on the stability of the wetting film.     

A colorimetric method of determination of Borax

A method is described for the rapid and accurate determination of borax. The principle of this method is to cause the boron of the borax under analysis to form a complex by the addition of an excess of a fluoride , the excess of fluorine ions causes decolourization of the violet compound Fe(III) - sulphosalicylic acid by forming the colourless complex (FeF₆)^-3.The extinction coefficient of the solution, measured in the Pulfrich photometer, decreases with increasing content of this excess of fluorine ions, and consequently can be used as an indirect measure of the borax to be determined.     

Zur Diazotierung aromatischer Amine in Schwefelsäure

The diazotization of 2-chloro-4,6-dinitroaniline, 2,6-dichloro-4-nitroaniline, and 4-nitroaniline in concentrated sulfuric acid is very strongly catalysed by water. At a given water concentration the reaction rates of these amines are in the ratio 50/20/1. The relation between the bimolecular rate constants k and the acidity function H₀ is very simple, the plots of log k versus H₀ being linear with a slope of 2.     

Microdosage électrolytique du zine et son application au laiton

Résumé Le microdosage électrolytique du zinc est fait dans l'appareil pour la microélectrolyse dePregl en utilisant une solution d'un zincate à l'électrolyse à froid (5–6 V, 0,2–0,8 A) pendant 20 minutes et en employant préalablement une cathode recouverte de cuivre.On lave la cathode à l'eau, à l'alcool et à l'éther, ensuite elle est séchée et pesée. Les variations des valeurs théoriques s'élèvent à 0,009 mg sur quantités de 0,501 à 3,009 mg de zinc.On applique la même méthode pour le microdosage du cuivre et du zinc à l'alliage de deux métaux.

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Summary For the electrolytic microchemical determination of zinc, this metal is electrolyzed, in form of a zincate solution, inPregls apparatus for microelectrolysis in the cold during 20 minutes, (5–6 V, 0,2–0,8 A); the cathode, before use, use, must be coated with electrolytic copper. The cathode is washed with water, alcohol, and ether, dried and weighed. If the zinc present amounts to 0,501–3,009 mg the results obtained deviate from the theoretical value by ± 0,009 mg. Copper-zinc alloys are analyzed in the same way whereby the copper first, then the zinc, is determined.

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Zusammenfassung Zur elektrolytischen Mikrobestimmung von Zink wird in derPreglschen Apparatur für Mikroelektrolyse das Zink in Form einer Zinkatlösung der kalten Elektrolyse (5–6V, 0,2–0,8A) durch 20 Minuten unterworfen, nachdem vorher die Kathode elektrolytisch verkupfert worden ist. Diese wird mit Wasser, Alkohol, Äther gewaschen, getrocknet und gewogen. Bei Mengen von 0,501–3,009 mg Zink betragen die Abweichungen vom theoretischen Wert bis zu ± 0,009 mg. In Kupfer-Zink-Legierungen werden in gleicher Weise zuerst das Kupfer, dann das Zink bestimmt.

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Communication a été faite de cette méthode à la séance du 2 juillet 1936 de la Société de Physique et d'Histoire Naturelle de Genève.     

Reconstructing curves with sharp corners

In this paper we present a heuristic to reconstruct nonsmooth curves with multiple components. Experiments with several input data reveals the effectiveness of the algorithm in contrast with the other competing algorithms.     

Sur le micro-dosage du cobalt au moyen de l'acide anthranilique

Résumé L'auteur transforme la macrométhode deH. Funk et deM. Ditt pour déterminer le cobalt avec l'acide anthranilique en microméthode gravimétrique. Cette méthode trés exacte, est décrite en détail.

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Summary A gravimetric micro method for determining cobalt by means of anthranilic acid, based on the macro method ofH. Funk andM. Ditt, has been developed. The performance of this accurate method is described.

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Zusammenfassung Die vonH. Funk undM. Ditt angegebene Makromethode zur Bestimmung des Kobalts mit Anthranilsäure wird nach Ermittlung der passenden Reaktionsbedingungen zu einer gravimetrischen Mikromethode umgearbeitet. Die Ausführung dieser genauen Methode wird beschrieben.

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Suite de l'étude sur l'acide anthranilique comme réactif en analyse microchimique quantitative.Ch. Cimerman etP. Wenger: Sur le microdosage du zinc au moyen de l'acide anthranilique. Mikrochemie,18, 53 (1935). Cf.:W. Prodinger: Organische Fällungsmittel in der quantitativen Analyse. Stuttgart 1937, S. 29.