CHAPTER IV. AN ACCOUNT OF THE CHEMICAL AND PHYSICAL CHARACTERISTICS OF THE PRINCIPAL RAW MATERIALS.

This chapter contains the results obtained from an investigation of the different plant fibres by the methods indicated in the two previous chapters.

In the following table the fibres are classified according to the reactions which they give with iodine solution.

Microscopic features.—Fibres simple, opaque, flattened, always more or less twisted upon itself, side wall membranous, showing striæ. {47}

Sections.—Simple, oval, irregular, central cavity often containing granules.

Micro-chemical reaction.—Blue with iodine solution.

General chemical characteristic.—Pure cellulose basis with slight admixture of colouring matters, &c.

E. Schunck in his investigation of cotton bleaching (Chem. News, 17, p. 11) finds that in boiling with sodium carbonate solution the fibre loses 5 per cent. in weight. Some portion of the dissolved substances is precipitated on acidifying and is found to contain a wax, brown resinous and colouring matters, and pectic acid. {48}

Forms in which employed.—Fibrous refuse from the decortication of the seeds; spinning waste, threads, rags, new and old.

Microscopic features.—Fibres transparent, regular, with tapered ends, side walls thick, consequently central canal small, smooth externally, sometimes slightly striated. Filaments easily split up into fibres.

Sections.—Polygonal, regular, angles more or less acute, lumen represented by point; slight indications of concentric arrangement of fibre substance.

Micro-chemical reaction.—Blue with iodine solution.

General chemical characteristic.—Pecto-cellulose.

Composition of raw fibre.—This varies with the different species, and is doubtless also influenced by variations in the {49} processes of retting. The following are the analyses of two samples of Belgian flax (heckled):—

The chemistry of the flax fibre has been investigated by Kolb.

Forms in which employed.—Scutching refuse, spinning waste, threads, rags, new and old.

Microscopic features.—Compact bundles. Fibres show striæ and fissures, and often fibrillæ, detached or adherent. The central canal almost obliterated, ends of fibres large and flattened. The bundles show fine transverse markings. {50}

Section.—Well marked concentric zones of fibre substance, irregular in outline.

Micro-chemical reaction.—Blue and yellow reaction with iodine solution, the joint result showing green colouration.

General chemical characteristic.—Pecto-cellulose.

Forms in which employed.—Scutching refuse, spinning waste, threads, cuttings and rope ends.

Microscopic features.—Generally similar to those of hemp.

Micro-chemical reactions.—With iodine various, from blue to yellow. With aniline sulphate, slight yellow.

General chemical characteristics.—Pecto-cellulose (with some ligno-cellulose).

The following are the results of analysis of the raw fibre (H. Müller):—

This fibre, exported from India and the Sunda Islands, has found employment in Spain and Portugal, but up to the present has not been adopted to any extent in other parts of Europe.

Microscopic characteristics.—Irregular in form and length; often conspicuous in respect of latter (see Table, p. 39); fibre sometimes cylindrical, either smooth or striated, sometimes flattened; central canal well developed, often containing granules; extremities of fibres rounded, spatulated or lance-shaped. Sections marked by numerous concentric layers, often showing radiating striæ.

Micro-chemical reaction.—Blue to violet, with iodine solution.

General chemical characteristics.—Pecto-cellulose.

Composition of raw fibre (H. Müller):—

Forms in which employed.—Up to the present the price has been prohibitive. Has been the subject of successful {52} experiments; imparts great tensile strength to paper. The portions available will be as in flax.

The fibres of this plant were, in the olden times, separated in the same way as flax, and worked up into cloth. At present it has no practical interest to the paper-maker, but deserves attention at the hand of the student, as the most easily accessible for the purpose of study. It is, moreover, possible that, under cultivation, it may yet become a source of raw material for paper-making.

Microscopic features.—Compact bundles; fibres smooth.

Micro-chemical reactions.—Yellow brown, with iodine; yellow, with aniline sulphate; bright yellow, with chlorine water; changed to carmine by treatment with sodium sulphite solution. {53}

General chemical characteristic.—Ligno-cellulose. The chemistry of jute as the type of ligno-cellulose has been treated on p. 17.

Composition of raw fibre (Müller):—

Forms in which employed.—Threads, butts, bagging.

The fibres give a yellow colouration with aniline sulphate, but they contain only a small proportion of lignose. The following are the results of analyses of this bast:—

Order, Gramineæ. Bast fibres of fibro-vascular bundles. Length, 1·5 mm.; diameter, 0·012 mm.; ratio, 125. Illustrated in Figs. 10, 11. In Fig. 10, the fibro-vascular {56} bundles f are seen spread throughout the interior of the leaf, but the intervals, instead of being occupied by parenchyma, with large cells and thin walls, are filled with a compact mass of fine solid fibres f ′ ; e, external epidermis; e′, internal epidermis; mag. 100. In Fig. 11, a is a section of a group of fibres; b, fibres seen longitudinally; c, ends; mag. 300.

Microscopic features.—Short, smooth, cylindrical, uniform in diameter, central canal very small, extremities rounded, truncated and bifurcated.

Section.—Minute, generally oval, sometimes polygonal; central cavity represented by a point.

Micro-chemical reaction.—Both blue and yellow with iodine solution.

In examining a paper containing esparto under the microscope, the pulp will be found to contain, in addition to the fibres of the fibro-vascular bundles, a certain number of the cuticular cells (see Fig. 12), together with some of the fine hairs which are seen in the section (Fig. 10). These are very characteristic.

General chemical characteristics.—Pecto-cellulose mixed with some ligno-cellulose. {57}

Composition (Hugo Müller):—

Microscopic features.—Generally similar to those of esparto. There are, however, differences of shape and dimensions of the serrated cuticular cells, which differentiate the various kinds of straw from each other and from esparto.

In Fig. 12 are shown these cells, from maize-straw (a and b); from rye-straw (c) and from esparto (d). The {58} following table gives the dimensions of the cells from different kinds of straw:—

Another distinctive feature of straw-fibre is the presence in it of a number of oval cells, derived from the pithy matter attached to the inside of the stem. These are clearly shown at b (Fig. 13), which represents the general appearance of straw pulp.

General chemical characteristics.—Both ligno-cellulose and pecto-cellulose.

The following are the results of analyses of straws (Hugo Müller):— {59}

From the close botanical relationship of these products to the stems of the gramineæ of our own climate, their microscopic features are, as might be expected, similar to those of straw. The similarity is further shown by the chemical composition (Hugo Müller):—

Microscopic characteristics.—Length of fibres, 9 mm., diameter 0·016 mm., ratio, 560. Fibres are fine, regular and smooth; the walls are uniform, central canal small, extremities vesicular. The fibres have little cohesion in the bundle. Sections round or polygonal. Illustrated in Fig. 4, p. 35.

Micro-chemical reaction.—Yellow, with iodine solution. Characteristic deep red colouration with concentrated nitric acid (Müller).

General chemical characteristic.—Ligno-cellulose. It contains 86·3 per cent. of cellulose.

Microscopic characteristics.—Length of fibres, 6 mm.; diameter, ·024 mm.; ratio, 250. Fibres, white lustrous; the walls are uniform; central cavity large and very apparent. Fibres easily detached. {60}

Sections round or polygonal. Illustrated in Fig. 14: a, section of bundle of fibres; b, fibres seen longitudinally; c, ends; mag. 300.

Micro-chemical reaction.—Yellow with iodine solution.

Composition (Hugo Müller):—

In America, however, poplar and other woods are largely employed. The coniferæ yield a larger proportion of pulp than most other woods, the individual fibres, moreover, are longer, and for these reasons it is generally preferred. On the other hand, however, poplar is more readily acted upon by reagents. Fig. 15 gives the microscopic appearance of {61} the fibre of the common white fir. It is characterised by the presence of numerous pitted vessels (Fig. a).

Pine wood consists essentially of a compound cellulose, resembling in most of its properties the jute fibre (see p. 16). With iodine solution it gives a deep yellow colour. The chemical composition of some of the more important woods will be seen from the following analyses. (Müller.)

The above results are calculated on the ash-free wood. The ash varies from about 0·3 to 0·7 per cent.