FIBROUS SUBSTANCES [derived from Plants] (FL, Fibres Vegetates; GER., Pflanzenfasern).
The "fibrous" portion of plants consists essentially of cellulose C„H,,,0„ a carbohydrate which shows great resistance to reagents that produce a marked effect on the other portions of plants. This resisting property constitutes the value of such fibres for the production of textile and other fabrics. The industrial application and commercial value of a fibre depend principally upon its physical qualities of length, strength, elasticity, firmness, and colour, and upon its capacity for taking dyes. The majority of these qualities are affected more or lees by the mode of cultivation, the period of harvesting, and the method of preparation. .
The varying position of the fibres of different plants has given rise to a threefold classi fication : (1) Monocotyledons, or onilogens, are plants which do not form a true bark, and which grow by virtue of a building up of tissue from within. These plants yield " foliaceous" fibres, imbeilileil in the ecllular tissues and pulp of their roots, stems, and leaves, which fibres rarely attain sufficient development to be of commercial utility, except in tropical and sub-tropical regions, and may, in almost all oases, be separated by simple mechanical processes.
(2) Dicotyledons, ur exogcns, are plants which do possess a bark, and whose growth is purely of an external character. Their fibres reside in the sheath of bark or bast, and hence are called "cortical." They are abundant in temperate eliwates. The fibres are in an agglutinated con dition, held together by means of a tenacious gum, the removal of which necessitates special, and in some cases laborious, treatment.
(3) In a few plants, the seeds are enveloped in a hairy covering within the pods ; these are termed "seed hairs," or " capsular " fibres.
Examin Ition.—Having regard to the fact that many fibre-yielding plants still remain to be examined, and for convenience of reference to the characters of, and means of distinguishing, fibres treated of in a subsequent part of this article, instructions for conducting chemical and micro scopical investigations, as suggested by Vdtillart and others, may here be briefly given.
The first step is the separation of the fibres from the remaining portions of the plant, which may be effected by boiling the sample in a solution containing 6 per cent. of carbonate of potash or
soda. When the separation is accomplished, the sample is well washed, pressed, and dried. If the washing does not suffice to complete the disunion of the fibres, they may be bruised under water in a porcelain mortar, with a pestle of hard polished woo I. The separated fibres are then divided into three portions :—(1) For examination longitudinally, in neutral liquids ; these are at once Placed to macerate in water and glycerine ; (2) for longitudinal examination, under reagents, are put aside to dry ; (3) for examination in transverse section ; this sample is straightened as well as possible, and then put to dry.
A.—Of sample (1), some threads are taken, and placed on a glees slab under a microscope ; they are then bathed in pure concentrated glycerine, two or three entire isolated fibres are picked out, laid parallel, and moistened with sufficient glycerine to keep them in place. Care must be taken that the ends are intact, and the fibres entire. Their length is then estimated; and the operation is repeated upon a number of samples. The mean length is, perhaps, most correctly stated no that which occurs tlie greatest number of times.
B.—Theso fibres are next examined in neutral liquids having a refractive power as nearly as possible like that of the object itself; such as a solution of chloride of calcium, of the consistence of clear syrup, or glycerine, either alone or with the addition of a little camphor-water and a few drops of acetic acid. One or two fibres are laid in the liquid on a glass plate, being curled spirally, to diminish their length, and are covered with another thin sheet of glass. Repeated observations are then made as to whether the fibres are solid, or in flattened bands ; whether rounded or prismatic ; whether smooth, or fluted, or striated; whether an internal cavity is visible, and whether it is large, continuous, or Interrupted. A number of measurements of the diameter of the fibres are then made, carefully noting the maximum, miuimum, and mean, and the degree of tapering or irregularity.