Page:Paper and Its Uses.djvu/74

62 The twisting, the division into fibrillæ, make for strength, good felting, and, with the softness in addition, the best and most durable papers are those of cotton.

The flax fibre is a bast fibre. Its yield of pure cellulose is 70 to 80 per cent. The fibre consists of a thick walled canal, which is easily seen in the unbeaten state. Beating tends to crush and remove the early characteristics. The fibres are regularly rounded or polygonal, and easily split into numerous fibrillæ, the ends of the fibres beat out into bunches of small fibres, and these, together with the nodules which occur on many of the fibres, produce strength in the paper. The flax fibre is straighter than the cotton fibre, and so linen papers are stiffer and harder than cotton papers.

Wood, produced as fibres by chemical means, consists largely of tracheids, long ribbon-like cells, which are easily broken into shorter lengths. It is not possible to subdivide the fibres longitudinally by prolonged beating. This only tends to shorten the fibres. Hence Mitscherlich, or similarly produced wood pulp, gives strong tough papers, unattainable by those pulps which are strongly bleached and much reduced. The tracheids, being smooth and flat, do not tend to make soft papers. But, blended with rag or esparto fibres, excellent papers may be produced. Only 50 per cent. of fibre is produced from the original wood.

Esparto gives a smooth, cylindrical fibre, pointed, short, with small canal. Being small, the fibres do not receive much treatment in beating. Separation and cleaning are the principal ends of the preparatory stages. Esparto is, to the papermaker, synonymous