Sixty organic compounds were tested qualitatively in concentrated sulfuric acid for their suitability as either colorimetric or fluorometric reagents for boron. Twenty of these gave color and seventeen fluorescence changes. Further testing in a quantitative way led to a choice of 1-amino-4-hydroxyanthraquinone as a fluorescent and 1,l'-dianthrimide as a colorimetric reagent. The more satisfactory colorimetric method is described in detail and compared with other methods. In the usual procedures for determining boron in plant material, losses of boron during ashing of the sample may occur. A method for wet ashinp snrh samples. by which losses of baron can he minimized, is also given.HE iriipurtance of t r w e s of boron in such diverse fields a< T agriculture and the steel industry makes of intered an] new reagent for its determination. The one dealt Kith here i. not ideal, but seems to have some points of superiority over quinslizarin. Of a large number of compounds dissolved in conrentrated sulfuric acid and tested qualitatively, 20 gave a color f*hange with boron and were tested further. The final choice was 1,l'-dianthrimide (1,l'-dianthraquinoylamine) and a colorimetric method using this reagent is described.The two most widely used colorimetric methods emplo! quinalizarin ( 2 ) or curcumin ( 4 ) as reagents. Quinalizarin seem?to be the more widely used because it is less subject to interference by other elements and because determinations may be made easily and quickly. The reagent, however, is not particularly suited for use with a filter photometer or spectrophotomder, for there is a considerable overlapping of the absorption bands of the reacted and unreacted reagent (7). Consequently, there is a wide divergence from Beer's law and a colorimeter can be used over only a limited range of boron concentration The authors have had difficulty in finding concentrated sulfuric wid low enough in boron to permit utilization of this limited range. The color change (from greenish yellow to blue) in the present method is suitable for use with a filter photometer and less difficulty has been experienced in finding sulfurir Rrid sufficientlv low in horon EXPERIMENTAL t'he reagents were tested qualitatively as follows: Sufficient reagent waa dissolved in C.P. concentrated sulfuric acid to give a moderately deep color. [It was necessary to obtain sulfuric acid from several sources and test each bottle to find lots sufficiently low in boron for most of this work. A good test reagent is quinalizarin (1,2,5,&tetrahydroxyanthroquinone) which gives a pink solution in concentrated sulfuric acid low in boron and becomes increasingly blue as the boron concentration is increased.] This was divided into six portions of approximately 6 ml. each in lowboron glass test tubes (Corning's alkali-resistant). To three of these tubes was added approximately 1 mg. of C.P. boric acid. One pair of tubes was kept in a desiccator a t room temperature (approximately 20' C.). Another pair was heated for 5 hours at 80" C., and the remaining pair wa...
Wasser gekocht, lost es sich rnit geringer Trubung im Verhaltnis 1 : 40.Um eine klare Losung von Wismutnitrat mit Zuhilfenahme von Natriumcblorat z u erhalten, nimmt man zweckmaflig zu 24 g Wismutnitrat 64 g Chlorat und 500-600 g Wasser. Es entsteht hierdurch eine vollkommen klare Liisung, welche nach tagelangem Stehen keinen Niederschlag abscheidet und durch weiteren Zusatz keinerlei Veranderung zeigt. Die Liisung besitzt eioen ganz schwachen Geruch, der an unterchlorige Saure erinnert. Sie reagiert sauer, zeigt aber auch die Eigentumlichkeit, Curcumapapier schwach braun zu farben. Diese schwilche Farbung ist aber nicht die Farbung alkalischer Reaktioo, d a sie durch Zusatz verdunnter Sauren nicht aufgehoben wird. Offenbar bildet sich eine komplexe Wismut-Curcuma-Chlorsaure-Verbindung. Eine ahnliche Reaktion beobachtet man bekanntlich auch bei der Borsaurel), ebenso bei eioer vollkommen neutralen Bleiacetatliisung, wenn man sie mit Curcurnafarbstoff zusammenbringt. Allerdings wird in letzterem Falle die riitliche Fnrbe durch Saurezusatz riickgangig gemacht.Die Losung zeigt ferner alle Reaktionen der Wismutsalze, wodurch bewiesen wird, da13 keine komplexe Verbindung vorliegt.Hervorzuheben ist noch, daB das chlorsaure Kalium an Stelle des Natriumchlorates ahnliche Erscheinungen zeigt; es erwies sich jedoch infolge seiner Schwerloslichkeit a19 weniger geeignet. Analoge Versuche mit bromsauren und jodsauren Salzen fuhrten zu keinem Resuitate; ebenso negativ verliefen die Reaktionen beim basischen Wisrnutnitrat sowie Wismutchlurid an Stelle des neutralen Wismutnitrates.
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