458 PRINCIPLES OF SOIL MICROBIOLOGY 



Powell and Whittaker suggested the following formula for flax lignin: 

 C4oH 3 o0 6 (OCH 3 ) 4 (OH)5-CHO 



For rye lignin the formula C40H44O15 has been suggested. The car- 

 bon content of lignin is thus found to be about 63.0 per cent. 



The methods of determination of lignin in natural organic sub- 

 stances are based either upon the destruction of all the carbohy- 

 drates with concentrated acids, or upon the oxidation of lignin with 

 chlorine dioxide or other oxidizing agent, or upon the determination 

 of some chemical constituent of lignin, such as the methoxyl groups. 953 

 However, none of these methods are very accurate. Alkalies ex- 

 tract, under pressure, only a part of the lignin; but this method can 

 be applied most readily to soils. 



For the study of its decomposition by microorganisms, lignin can be 

 added, either in crude or pure form, to soil or to a solution containing 

 a source of nitrogen and the necessary minerals. The growth of the 

 organisms, the evolution of C0 2 , or the disappearance of the lignin added 

 can be taken as quantitative indices of decomposition. 



Pringsheim and Fuchs 96 dissolved 10 grams of lignin (obtained by 

 treating spruce wood with 11.5 per cent NaOH under pressure, then 

 precipitating the lignin with HC1 and heating in the presence of an 

 excess of 2 per cent acid) in NH 4 OH and then warmed the solution to 

 drive off the excess of ammonia. The solution thus obtained was 

 added to 5 liters of a nutrient medium containing 20 grams (NH 4 ) 2 S0 4 , 

 3 grams K 2 HP0 4 , 2.5 grams MgS0 4 and 2 grams CaC0 8 . The medium 

 was inoculated with soil and incubated at 37°; decomposition was found 

 to take place. It resulted in the complete disappearance of the pento- 

 san content and in the reduction of the methoxyl content of the lignin. 

 The ability of certain bacteria to decompose lignins has also been 

 pointed out by Schrader. 97 Attention must be called here to the fact 

 that alkali lignin usually contains some pentosans and probably some 

 proteins; it is these substances which frequently undergo decomposition 



96a Schorger, 1926 (p. xvi); Schwalbe, C. G., Die chemische Untersuchung 

 pflanzlicher Rohstoffe und der daraus abgeschiedenen Zellstoffe. Papier. Ztg. 

 Bd. 13. 1920. 



96 Pringsheim, H., and Fuchs, W. tJber den bakteriellen Abbau von Lig- 

 ninsaure. Ber. deut. chem. Gesell., 56: 2095-2097. 1923. 



97 Schrader, H. Uber das Verhalten von Cellulose, Lignin, Holz und Torf 

 gegen Bakterien. Ges. Abh. Chem. der Kohle., 5: 553; Chem. Centrbl., 4: 1044. 

 1922; 3-4: 1649. 1923. 



