Abstract
LONDON. Society of Chemical Industry, November 4.—Mr. R. J. Friswell in the chair.—The determination of indigotin in indigo-yielding plants: Cyril Bergtheil and R. V. Briggs. The accurate determination of indigotin in the indigo plant is of considerable importance, since a correct estimate of the efficiency of the process of indigo manufacture depends thereon. A method of precipitating indigotin from an extract of the plant in boiling water by means of ammonium persulphate, proposed by Rawson in 1904 and modified by the present authors, has been shown to giye correct results by comparison with those obtained by fermentation of the extract by means of the indigo, enzyme (Journ. Soc. Chem. Industry, 1906, xxv., 729). This method has been criticised by Orchardson, Wood and Bloxam,.and two alternative methods proposed, one of which, depending on the same principle, is said to give results identical with those obtained by the authors' method, whilst the other, depending on the precipitation of indirubin by the action of isatin in acid solution, indicates a considerably higher potential yield of indigotin in the plant extract used Qourn. Soc. Chem. Industry, xxvi., 4). The authors' original method is now verified, and some minor modifications are recommended. The conclusion that the isatin method may in certain circumstances indicate a higher indican con-tent in a given extract than the persulphate method is not borne out by the authors' experiments.—Analysis of indigo (part iii.) and of the dried leaves of Indigofera arrecta and J. Sumatrana: R. Gaunt, F. Thomas, and W. P. Bloxam. A summary is first given of the results of the work on indigo carried out for the Government of India at the University of Leeds during the years 1905-7. In the present paper the exact conditions were prescribed for the preparation of pure indigotin to serve as the standard on which the tetrasulphonate process for the estimation of indigotin is based. A reply was made to certain criticisms on the tetrasulphonate process; the defects complained of were shown to be due to want of proper precaution on the part of the operators. The methods in use for the estimation of indigotin in the leaf were described. The persulphate method was found altogether faulty, as the results obtained by it were too low. The new “isatin” method was found to give much higher results, and, moreover, the method is quantitative, as proved by its action on the glucoside indican, which has recently been isolated in quantity by Messrs. A. G. Perkin and W. P. Bloxam. As a result of employing the isatin process, the indigo leaf is demonstrated to be capable of yielding more indigotin than had previously been supposed. Again, the percentage of leaf present in the green plant has been underestimated in India. It is insisted that these facts are in favour of the survival of the Indian indigo industry. Finally, it was submitted that the work on the indigo ferment or enzyme had not been properly followed out, and that the present reports on the Indian manufacture are eminenlly unsatisfactory, for (1) the colour-giving value of the raw materials was seriously underestimated, whilst (2) the indigotin value of the manufactured cake was overestimated, and this owing to the persistent use of unsatisfactory methods of analysis in lieu of adopting the tetrasulphonate process.
Article PDF
Rights and permissions
About this article
Cite this article
Societies and Academies . Nature 77, 118–120 (1907). https://doi.org/10.1038/077118a0
Issue Date:
DOI: https://doi.org/10.1038/077118a0