The organic constituents of plants and vegetable substances and their chemical analysis / by G.C. Wittstein ; authorised translation from the German original, enlarged with numerous additions, by Baron Ferd. von Mueller.

  • Wittstein, Georg Christian, 1810-1887.
Date:
1878
Catalogue details

Licence: Public Domain Mark

Credit: The organic constituents of plants and vegetable substances and their chemical analysis / by G.C. Wittstein ; authorised translation from the German original, enlarged with numerous additions, by Baron Ferd. von Mueller. Source: Wellcome Collection.

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    with an excess of burnt magnesia (or finely pulverised oxycl of lead or white of lead), dry in a gentle heat, pulverise, treat with cold water (in order to remove alkali-salts, chloride of magnesium, iodide of potassium, (fee), boil with alcohol of 90°/^, evaporate the alcoho- lic liqiiid and submit to examination what has remained. (d) The remaining liquid may probably contain traces of dyeing matters, of gum and of resin, the further examination of which h perfectly valueless and involves only loss of time. VII.—Treatment with Diluted Potash-ley. Bring the substance remaining after the treatment with hydro- chloric acid, and while still in a moist state, back into the beaker, add water enough to make the whole up to 500 grams, dissolve in the mixture 10 grams hydrate of potash (or of soda), digest for two days in a temperature of 50° to 60°, let cool, filter and wash the residue thoroughly. Dxy 5 grams of the residue at 110°, weigh, calculate the weight of the whole residue conceived dry, and subtract this weight from the one obtained under VI., the rest representing the weight of the matters dissolved by the ley. Should the mass prove too thick for filtering, it must be diluted previously, and is, if necessary, clarified by subsiding. (a) The alkaline liquid is generally more or less brown, some- times black-brown. By over-saturating with hydrochloric acid, a brown, flocky precipitate is invariably obtained, which contains so-called humic acids, but which may also contain pi'otein-sub- stances. The two substances are only incompletely separable by liquor of ammonia, the humic acids being more soluble in it than the protein-substances. For the quantitative estimation of the two bodies it is sufficient to collect the precipitate produced by hydrochloric acid, to wash, to dry at 120°, and to determine the amount of nitrogen by heating with soda-lime. By multiplying with 6^ the weight of the nitrogen obtained, the quantity of the protein-substances is determined, and by subtracting the latter weight from that of the precipitate, the weight of the humic acids is obtained. (b) The liquid obtained by filtering in a, contains small quantities of humic acids as well as of protein-substances, the closer investigation of which is impracticable. (c) The residue left after the treatment with potash-ley, and the dry weight of which has been calculated, is generally accounted for as vegetable fibre or cellulose, though this name is not correct, as this fibre contains not only colouring matters but also mineral compounds. Regarding the complete removal of the first and the estimation of the latter impurities, see under Fibre, p. 82,