A new method for the determination of cellulose, based upon observations on the removal of lignin and other encrusting materials

Abstract

IN the analysis of plant materials and woods, one of the chief constituents to be determined is cellulose, which is important since it forms the structural framework of the tissue. The determination of cellulose, however, is for various reasons not always satisfactory. The methods of determination of cellulose in general use do not all give the same product; consequently the results obtained are not always directly comparable. The method selected may be dictated by the purpose for which the cellulose is required. As it occurs naturally, cellulose is always found in the closest association with other constituents of the cell- wall, and these have, by various treatments, to be removed. Originally it was held that a number of distinct compound celluloses existed, e.g. lignocelluloses, pectocelluloses, etc. [Cross and Bevan, 1895], but the more recent view, which is generally accepted, is that all natural celluloses contain a certain fraction which is identical chemically. This fraction, typified by pure cotton cellulose, will from different sources give identical X-ray diagrams, comparable yields of cellobiose octa-acetate, and solely glucose on hydrolysis. It may therefore be regarded as "true" cellulose or "pure" cellulose in the rigid chemical sense. But cellulose as usually isolated does not yield only glucose on hydrolysis. In the case of hardwoods, cereal straws and certain fibre plants, xylose also is obtained, while in the case of softwoods mannose may be found in addition. These sugars are derived from polysaccharide material very intimately asso- ciated with the "pure" cellulose itself, and held either by adsorption or secondary valency forces. The association is so close that these polysaccharides may only be completely removed intact by the most violent treatment with alkali. Mild acid hydrolysis on the other hand removes them rapidly. These associated polysaccharides, which possess the general properties usually de- scribed for the hemicelluloses, have been termed by Hawley and Norman [1932] " cellulosans " and will be referred to as such in this paper. Development studies on the barley plant [Norman, 1933] show that the cellulosans are laid down with the "true " cellulose from the earliest stages and are not produced as the result of changes during lignification or senescence. The inference from this and other work is that the cellulosans must be regarded as forming a normal integral part of the cellulosic fabric of the plant, i.e. natural celluloses consist of "true" cellulose plus associated cellulosan. These two substances together will be taken in this paper to be covered by the word "cellulose."