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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    This latter operation, though comparatively easy with ethereous and alcoholic liquids, often engenders great difficulties with aqueous extracts on account of the presence of colloidal matters, as albumin and gum. It is therefore better to first try a small quantity, and if filtering is found practicable,^ to give the whole into the displacement apparatus and to wash with water, until the latter passes ofi clear. Any decomposing efiect of heat has to be avoided by performing the operation in a cool place. If, on the contrary, filtering through paper should prove incomplete and slow, it is necessary to strain the mass through miller's gauze (silk bolting cloth), not through linen, calico, or flannel, because the meshes of these latter fabrics would soon become filled up by swelling, and so prevent the liquid from pass- ing thi-ough. Spread a cii'cular piece of the silk gauze (preferably of No. 10 to 13) over a wide glass jar, press it in the middle slightly into the vessel, secure the part of the gauze resting on the edges by means of a wide porcelain ring, pour the contents of the flask into the bag-like cavity, and rinse the flask with a little water. After the liquid has ceased dripping, take hold of the cloth, tie it together close over the contents with pack-thread, and press out as much liquid as possible. Or use a small bookbinder's press, the side wedges (those parts that come in contact with the liquid) of which are covered with glass or porcelain plates. Again, mix the pressed-out substance in a porcelain dish with water to a pulp, strain and press, and repeat these operations once more. Mix the whole of the liquids well together, and allow them to subside in a cool place. An amount of starch or inulin, surpassing mere traces, may be separated from the vegetable substance in a merely mechanical way, i.e., by kneading. A partial separation is even effected in straining through gauze, but may be considerably improved in case of any starch or inulin having been observed in the first liquid by kneading the substance after the second pressing, and after the gauze-bag containing it has been tied as before, under water and for a considerable time, adding the milky water to the other liquids and kneading again under fresh water until the substance is entirely exhausted. From the united liquids, starch or inulin subside gradually. Filter, or, if impracticable, decant the clear liquid, collect the sediment of starch or inulin on a filter, dry at 110°, and weigh. By filtering the aqueous extract in the displacement apparatus, starch or inulin are, of course, left in the remnant. The presence of starch is easily ascertained by shaking a small quantity of the substance with solution of iodine, when it will assume a violet or blue colour. The presence of inulin can only be ascertained by kneading. Starch and inulin have, as yet, not been observed in the some plant; and, whereas the former occurs in widely