Читать книгу A Text-book of Paper-making - C. F. Cross - Страница 47

A very important point in the diagnosis of a raw material, and next in order of treatment, is the degree of purity of the substance, in so far as this is related to structure. The fibres may be associated with cellular tissue, or with cellular debris, if they have undergone the retting process or other treatment for separation; or with “encrusting and intercellular substances” in various proportions. In the latter case the association with the fibres is usually much more intimate; they are in fact essential constituents of the fibre bundles {40} (bast-fibres, fibro-vascular bundles), whereas the former we may regard as “foreign matter.” We may, however, distinguish between the normal incrustation of the fibre-cells, and such an incrustation of the filaments as would be described as a loose adhesion of non-fibrous matter. The latter is seen in such tissues as the bast of the adansonia, and the fibro-vascular bundles of the aloes. These are points with which observation alone can familiarise the student; as experience grows he will find it increasingly easy to follow general distinctions, and in proportion as he uses his own faculties, so he will be able to generalise for himself. He will find this equally true of the second section of the microscopic examination, i.e., the micro-chemical diagnosis of fibres. Under this head is included the observation of the behaviour of fibres towards the various reagents above described. In addition to their microscopical employment it is useful to note their effect on fibres in the gross, both in their natural state and after treatment with bleaching agents.

In applying the iodine reaction, attention must be paid to the following details of manipulation. Place the object (dry) upon the glass slide, moisten with a few drops of the iodine solution, cover with a glass slip and examine under the microscope. Note the effects, which are those of the iodine alone. Then remove the iodine solution by means of blotting paper, and introduce the sulphuric acid by the method of “irrigation.” The colouration of the cellulose (blue-violet) is immediate; it has the effect moreover, of bringing out more clearly a number of the structural details of the fibre.

We have already treated of the resolution of the raw fibres into cellulose and non-cellulose constituents by processes which convert the latter into soluble derivatives. The student will derive much instruction from following up the attendant structural disintegration with the aid of the microscope. The chemical dissection of lignified fibres by the alternate action of bromine water and alkalis, should be studied by mounting specimens of the fibre at all stages and {41} carefully noting all the changes which occur. The more drastic action of chlorine should also be studied by mounting the chlorinated fibre (in water) and then irrigating with the alkaline solvent (caustic alkali or sulphite) and noting the stages in the completion of the disintegration.