Читать книгу A Text-book of Paper-making - C. F. Cross - Страница 24

Table of Contents

—Under the action of dilute sulphuric or hydrochloric acid (5–10 per cent.) at 60°–80° C. (140°–176° F.), a considerable portion of the fibre substance is dissolved. The action of either reagent is of course purely hydrolytic; and the hydrolysis is of the simplest character, since the substance dissolved as well as the residual fibre are found to have the same percentage composition. Moreover, the residual fibre, though having undergone a profound structural modification, and having been converted into a disintegrated mass of brittle fragments, still preserves the chemical characteristics of the original, unaltered. Thus it is converted by the action of chlorine into a similar complex of derivatives, yielding on resolution by sodium sulphite solution 75 per cent. of cellulose; also when acted upon by alkaline hypobromite it yields bromoform. Under the action of these hydrolytic reagents, therefore, the fibre shows itself to be essentially a chemical whole. At the boiling temperature, these acids resolve as well as dissolve the fibre substance, and the volatile products are acetic acid and the peculiar aldehyde {21} furfural C4H3O.COH. The yield of this aldehyde may be raised with suitable precautions to 15–20 per cent. of the raw fibre. The action of dilute nitric acid upon the fibre differs from that of the above-mentioned acids, in effecting its resolution into soluble derivatives and insoluble cellulose; the yield of the latter when the reaction is conducted at 60° C. (140° F.), with 5 parts HNO3 is 60 per cent. only, showing that in the process of isolation some of the cellulose itself is attacked and converted into soluble products.

Schulze’s method of isolating cellulose from wood, and from the ligno-celluloses generally, consisted in macerating them for 12 to 14 days with ⁸⁄₁₀ their weight of potassium chlorate dissolved in 12 parts by weight of nitric acid (sp. gr. 1·10), and completing the resolution by afterwards boiling with dilute ammonia. By the action of a more concentrated acid, 50 per cent. HNO₃, at 80° C. (176° F.), a soluble derivative is obtained which has the composition (C₂₅H₄₀NO₂₅). It is a syrupy, highly acid body, dyeing animal fibres a deep yellow shade, and giving with the earthy bases salts of the formula (C₂₅H₃₂NO₂₅M₄), which are precipitated by alcohol from their aqueous solution in the form of bright yellow flocks that dry to a yellow powder.