456 PRINCIPLES OF SOIL MICROBIOLOGY 



present in the cell wall. Pentosans are considered 89 as intermediate 

 products in the formation of lignin. The latter is believed to be made 

 up of hydrosols of high molecular weight which are adsorbed from the 

 sap by the cellulose fibers. 90 Maximum lignification corresponds with 

 maximum percentage of adsorbed material; this may be followed by 

 chemical reactions, such as dehydration. The lignin content of rye 

 straw was found 91 to increase with age, the greatest increase occurring 

 during the period preceding ear formation. In the ligno-cellulose 

 complex the cellulose is linked with two non-cellulose substances one 

 of which contains an aromatic nucleus, while the other is presumed to 

 be a pentosan since it yields furfural on distillation with HC1. 



Two different processes are available for the preparation of lignin, 

 based upon the fact that it is insoluble in concentrated acids and is 

 soluble in alkalies, when heated under pressure; acid or alkali lignin are 

 thus obtained. To prepare acid lignin, finely ground straw or wood is 

 extracted with ether and then treated with a concentrated acid, using 

 either 72 per cent H2SO4, or fuming HC1 solution (specific gravity 

 1.21), or a mixture of 1 vol. HC1, specific gravity 1.07, and 6 vol. 72 

 per cent H 2 S0 4 . 92 



Alkali lignin can be prepared by extracting the plant material with 

 NaOH. The actual amount of lignin thus obtained will depend on the 

 concentration of the alkali used, temperature and period of extraction. 

 The following method may be used : 93 Ten parts of a 10 per cent NaOH 

 solution are added to one part of finely ground straw, wood, or soil 

 containing these materials, and the mixture is heated at 130° under 



89 Rassow, B., and Zschenderlein, A. t)ber die Natur des Holzes des Hanfes. 

 Ztschr. Angew. Bot., 34: 204-206. 1921. 



90 Esselen, G. J. A few high spots in the chemistry of cellulose. Jour. Ind. 

 Engin. Chem., 15: 306-307. 1923. 



91 Beckmann, E., Liesche, D., and Lehmann, F. Lignin als Winterrogen- 

 stroh. Ztschr. Angew. Bot., 34: 285-288. 1921; Biochem. Ztschr., 139: 491- 

 508. 1923. 



92 Klason. Beitrage zur Kenntnis der chemischen Zusammensetzung des 

 Fichtenholzes. Berlin. 1911; Willstatter, R., and Zeichmeister, L. Zur Kenntnis 

 der Hydrolyse von Cellulose. I. Ber. deut. chem. Gesell., 46: 2401-2412. 1913; 

 Hagglund, E., and Bjorkman, C. B. Untersuchungen fiber das Salzsiiure- 

 Lignin. Biochem. Ztschr., 147: 74-80. 1924; Cellulosechemie, 4: 74-77. 1923; 

 Schwalbe, H. Eine neue Methode zur Bestimmung des Lignins. Papierfabr., 

 23: 174-177. 1925; Wenzl, H. Papierfabr., 23: 305-306. 1925; Schorger, 1926 

 (p. xvi). 



93 Powell, W. J., and Whittaker, H. The chemistry of lignin. I. Flax lig- 

 nins and some derivatives. Jour. Chem. Soc. Trans., 125: 35-36. 1924. 



