DECOMPOSITION OF NON-NITROGENOUS ORGANIC MATTER 



457 



pressure, for one hour or more. Two volumes of water are then added 

 to the digested mixture and the dark-colored solution containing the 

 lignin is filtered off. The warm filtrate is acidified with hot hydrochloric 

 acid, brought to boiling and the precipitated lignin is centrifuged or 

 filtered off. To obtain pure lignin, this preparation is washed with 

 hot dilute hydrochloric acid, dried, redissolved in a mixture of acetone 

 and water, and reprecipitated by pouring into a mixture of hot hy- 

 drochloric acid (20 per cent) solution. The lignin is now filtered off, 

 washed with hot water and dried at 40 °C. The yield of lignin by 

 alkali extraction is considerably lower than that obtained by treatment 

 with strong acids. By raising the temperature of extraction to 180°C, 

 a yield almost equivalent to that of acid lignin may be obtained. 94 



It is doubtful whether lignin is a single chemical compound, Ritter 95 

 having shown that it can be separated even by mechanical means into 

 two forms, one of which is located in the middle lamella of the tree and 

 has a methoxyl content of 10.8 to 13.6 per cent and the other is cell 

 wall lignin with a methoxyl content of 4.3 to 4.8 per cent. By treat- 

 ment with alcohol or with (3 naphthol, lignin can also be separated into 

 two fractions, one soluble and the other insoluble. A close relation- 

 ship was found to exist between certain alcohol-soluble resins, tan- 

 nins, and lignin. 



Various formulae have been suggested to account for the chemical 

 composition of lignin. It is sufficient to give the formula of Klason: 



CH, 







CH 



/\ C/\ 



H 2 C 





CO • CH 3 Cl 



/ 



o 



c/ N:— CH:CH-C 



/ 



CH 



CH, 



v/ 



\ CO ■ CH, 

 N^O • CH 3 



SH 



94 Mehta, M. M. Biochemical and histological studies on lignification. I. 

 The nature of lignin: its physiological significance and its estimation in timbers. 

 Biochem. Jour., 19: 958-978. 1925. 



96 Ritter, G. J. Distribution of lignin in wood. Jour. Ind. Engin. Chem., 

 17: 1194^1197. 1925. 



