A Text-book of Paper-making. C. F. Cross
of Contents
—On digesting cellulose with nitric acid (sp. gr. 1·3) at 100° C. (212° F.), a considerable quantity of oxalic acid is formed; but after prolonged digestion, a residue remains, which yields but very slowly to the action of the acid. This substance, which is white and flocculent, when thrown upon a filter and washed with water, combines with the latter to form a gelatinous hydrate. It dissolves in dilute alkalis, but without forming a stable compound with the base. It usually amounts to about 30 per cent. of the cellulose acted upon. Its elementary composition is expressed by the formula {14} C18H26O16 (C = 43·4, H = 5·3 per cent.). Treated with a mixture of concentrated sulphuric and nitric acids, it dissolves, and, on pouring the solution into water, the compound C18H23O13(NO3)3 separates as a white flocculent precipitate. In its essential properties therefore β oxycellulose exhibits a close resemblance to cellulose itself. This oxycellulose is distinguished from the members of the cellulose group by dissolving in concentrated sulphuric acid with development of a pink colour. It appears to stand in very close relationship to the group of pectic substances, which are oxidised derivatives of cellulose.
* Cross and Bevan, Chem. Soc. Journ., xliii. p. 23.
Alkalis.
—Concentrated solutions of the caustic alkalis in the cold attack and disintegrate cellulose but slowly. The action is in many cases merely superficial. Dilute solutions of the alkalis are without action upon cellulose even at the boiling temperature, unless the condition of oxidation is super-added; in this case, acid bodies are found. The extreme product of the oxidation of cellulose in presence of the caustic alkalis is oxalic acid; this acid has indeed been prepared on the commercial scale by the “fusion” of cellulosic substances, with mixture of sodium and potassium hydrates. Malic acid has been obtained as an intermediate product of this decomposition. By potassium permanganate in presence of potassium hydrate, both in solution, finely divided cellulose is oxidised to a syrupy mixture of acids resembling in composition and properties Frémy’s meta-pectic acid. A similar decomposition is effected by concentrated solutions of the hypochlorites, employed cold.
Water at High Temperature.
—Cellulose itself is only slightly affected by exposure to a temperature of 200° C. (392° F.) but in contact with water at this temperature, in sealed glass4 most part into dark brown insoluble products, a portion, however, passing into solution in the water, imparting to it a deep yellow colour. A large quantity of carbonic acid is {15} formed, and the solution contains in addition to formic acid an appreciable quantity of pyrocatechol. The formation of this aromatic substance from cellulose is, perhaps, the most noticeable feature of the decomposition.
4 The action of alkaline substances dissolved from the glass must be taken into account in this decomposition.
Decomposition by means of ferments, &c.
—The soluble ferment of the foxglove has been found to convert cellulose into glucose and dextrin. The fluid from the vermiform appendix of the rabbit has also been found to digest cellulose with liberation of marsh gas and formation of a soluble compound which reduces cupric oxide in alkaline solution.
Humus.
—In the natural decay of cellulosic structures a large quantity of marsh gas is formed, and solid products are formed, which are usually known as humic or ulmic substances. These bodies are amorphous, are largely dissolved by alkaline solutions, and are attacked by chlorine gas in presence of moisture, yielding yellow coloured chlorinated derivatives whose composition has a general resemblance to the chlorinated compounds obtained from the compound celluloses, to be hereafter described.
The most important part which ulmic substances play in the economy of nature, is in the composition of soils. It is doubtful whether they act directly as fertilisers, but by their action upon the mineral constituents of soils they contribute to the supply of these necessary elements of growth to the plant.
Synthesis of Cellulose.
—A transformation of certain soluble carbo-hydrates into cellulose, which may be regarded as a proximate synthesis of cellulose, has recently been brought to light. This is set up spontaneously in beet-juice, and results in the formation of a hard white substance, insoluble in boiling dilute potash, soluble in the ammonio-copper reagent, converted by sulphuric acid into dextrin and sugar, and by nitric acid into oxalic acid. On adding some of these cellulose lumps to a solution of pure cane-sugar, a further transformation of the saccharose into the same substance is brought about. At the same time there is simultaneously produced a gummy substance, which is precipitated by {16} alcohol as a white amorphous caoutchouc-like mass, of the same composition as cellulose, but swelling up with water, and otherwise differing in its physical properties from cellulose. This latter substance is also formed by the action of diastaste upon a solution of saccharose.
The process of cellulosic fermentation may be represented by the equation:
n. (C12H22O11)
Saccharose.
=
n. (C6H10O5)
Cellulose.
+
n. (C6H12O6)
Glucose.
A similar transformation takes place under the influence of certain fatty seeds, e.g. those of rape and colza; and it is probable that the formation of cellulose in living plants may take place at the expense of saccharose and under the influence of ferments. In support of this it has been established that in the sugar-cane, the formation of wood—i.e. cellulose—is accompanied pari passu by a decrease in saccharose. More recently, A. Brown (Chem. Soc. Journ., 432, 1886) has investigated the formation of cellulose by the “vinegar plant” growing in solutions of the carbo-hydrates, e.g. dextrose in yeast-water. The cells elaborate an extra-cellular fibrin, which acts as a “cell-collecting medium,” and they possess therefore a two-sided activity, i.e. the property above mentioned, in addition to their strictly fermentative activity. The cellulose film in question was found to contain 50 to 60 per cent. of pure cellulose. It is noteworthy that in a solution of levulose the growth of the “plant” is unattended by fermentative action, 33 per cent. of the substance being, on the other hand, transformed into cellulose.
Modifications of Cellulose in the Plant. Compound Celluloses.
—It has been already stated that cellulose occurs in nature for the most part in a form different from that in which we have hitherto considered it, viz. either combined or mixed with other substances which are of such a nature that they may be removed by a chemical process, more or less simple. One of the most characteristic of these modified celluloses constitutes the jute fibre, the isolated