OF all quantitative determinations in the analysis of plant materials the lignin determination is subject to greatest uncertainty since in the first place the constitution of this component is unknown and secondly all attempts to isolate it in the form in which it is believed to occur in the plant have, so far, failed. At the present time any so-called quantitative determination of lignin is at best a compromise, for the yield and composition of the product depend to a great extent on the analytical method employed. The best available methods for the routine determination of lignin in wood are those which involve the removal of the carbohydrates by hydrolysis with mineral acids. The details of the original methods and various modifications of them which have appeared from time to time are fully discussed by Schorger [1926, p. 518] and Hawley and Wise [1926, p. 163]. A number of modifications of the original methods [Ost and Wilkening, 1910; Willstatter and Zechmeister, 1913] have been suggested. Most of these aim at the preparation of a lignin complex, free from carbohydrate condensation products, and broadly speaking they involve either (1) preliminary treatment to remove those carbohydrates which are liable to form condensation products at some stage in the isolation of the lignin residue [Paloheimo, 1925; Ritter et al., 1932; Norman and Jenkins, 1934], or (2) control of experimental conditions, such as the temperature of the wood samples during digestion with concentrated acid [Sherrard and Harris, 1932; Peterson et at., 1932; Ritter et at., 1932; Komarov, 1934]. Cohen and Dadswell [1931] have shown that with certain Australian woods the accurate determination of lignin is further complicated by the presence of gums or kinos which are resistant to concentrated mineral acids. These substances are, however, soluble in dilute sodium hydroxide, and the above authors have therefore proposed a modification of the Ost and Wilkening method which involves a preliminary treatment with this reagent. A further modification has since been suggested by Cohen [1934]. Since the crux of the lignin determination lies in the efficient removal of carbohydrates, it is essential that uniformity of method should be established for the digestion with concentrated acid and the subsequent hydrolysis with dilute acid. Although the method of Willstatter and Zechmeister [1913], which
IN the great majority of woods which have been investigated there is a strong correlation between specific gravity and certain mechanical characteristics. As a rule the higher the specific gravity the stronger the wood, although it is known that, in any single species, wide variations in strength may occur throughout a range of matched specimens ofequal specific gravity. These latter variations have been ascribed [Clarke, 1935;1936] to concomitant variations in the chemical composition of the wood cell walls which at the present time are not fully understood. Despite its obvious importance the relationship between chemical composition and strength in woody plants has hitherto received comparatively little attention. Dadswell & Hawley [1929] observed a higher cellulose content in tough white oak than in a single brash specimen of the same species, and Uno [1932] concluded that the strength of various species of bamboo increases with increasing cellulose content. The investigation by Luxford [1931] of the influence of minor components or extractives on the strength of wood will be referred to later.The object of the present study was in the first instance to determine whether the chemical composition of ash wood varies within a single tree as well as from tree to tree in a single locality, and in the second instance to attempt to correlate chemical composition with strength figures already obtained for the same material [Armstrong, 1936].EXPERIMENTAL. A 2-ft. bolt was cut at the same height from the ground from each of six representative English ash trees (Fraxinus excelsior) obtained from Holkham, Norfolk. Each bolt was sawn into two discs measuring 15 and 9 in. in diameter respectively and the pairs of discs were marked out on the transverse surfaces exposed by the common cross-cuts into the following concentric zones.A. Sapwood containing starch. B, C. Intermediate zones containing small amounts of starch decreasing from B to C. D. Heartwood containing no starch. The 15-in. discs being reserved for mechanical tests [Armstrong, 1936] each 9-in. disc was sawn into the respective zones which, after air-drying, were separately converted into sawdust. The 80-100 mesh material was analysed according to the method of Schorger [1926] except that the digestion with 72 % sulphuric acid in the lignin determinations was carried out at 10 + 0.50 using 12-5 ml. of acid per 2 g. sample of air-dry wood flour (Table I).
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