672 PRINCIPLES OF SOIL MICROBIOLOGY 



mineral soils may contain as much as 0.154 per cent wax and 0.03 per 

 cent fat. 14 The high content of wax is due to its accumulation in the 

 soil, since it is not readily decomposed by microorganisms. The so- 

 called soil "humus" may contain 10 per cent of material soluble in 

 ether and in alcohol (dihydroxystearic-, oxystearic-, lignoceric, and other 

 acids), in the case of virgin soils rich in organic matter, and as much as 

 4:) to 50 per cent of ether and alcohol soluble substances in the case of 

 soils poor in organic matter. 15 



The nitrogen of the soil organic matter is made up of complexes 

 which give, on hydrolysis, amino acids and acid amides. 16 By boiling 

 the soil with hydrochloric acid, 75.8 per cent of the soil nitrogen was 

 extracted in the form of these compounds, while boiling water alone 

 extracted only 2.92 to 9.96 per cent of the total soil nitrogen. The amino 

 acids and acid amides do not exist in the soil in a free state but in com- 

 bination, probably as constituents of the cells of microorganisms, 

 modified or unmodified by secondary processes of decomposition. 

 When the soil "humus" is obtained from the alkali extract by precipita- 

 tion with an excess of hydrochloric acid and is carefully washed with 

 acid and water, it is found to contain about 3 per cent nitrogen. The 

 nature of this nitrogen has been the subject of considerable controversy; 

 some 17 have claimed that it is an extraneous material (as protein nitrogen) 

 and can be separated from the non-nitrogenous "humic acids," while 

 others 18 have claimed that it forms an important constituent of the soil 

 "humus" or "humic acids." 



Various organic acids, such as formic, acetic, butyric and propionic, 

 as well as alcohols, are often found in the soil, especially when the soil 

 is kept under anaerobic conditions. These substances do not remain in 

 the soil as such for a long time, but are used, under favorable conditions, 



14 Reinitzer, 1900 (p. 266). See also Fraps, G. S., and Rather, J. B. The 

 ether extract and the chloroform extract of soils. Texas Agr. Exp. Sta. Tech. 

 Bui. 155. 1913. 



15 Piettre, M. Recherches, au moyen de la pyridine, des matieres humiques 

 et des matieres grasses du sol. Compt. Rend. Acad. Sci., 176: 1329-1336. 1923. 



16 Jodidi, S. L. Organic nitrogenous compounds in peat soils. Tech. Bui. 4, 

 Mich. Agr. Exp. Sta. 1909; The chemical nature of the organic nitrogen in the 

 soil. Iowa Agr. E^p. Sta. Res. Bui. 1. 1911; Jour. Amer. Chem. Soc, 32: 396. 

 1910; 33: 1226. 1911; 34: 94. 1912. 



17 Detmer, W. Die naturlichen Humuskorper des Bodens und ihre land- 

 wirtschaftliche Bedeutung. Landw. Vers. Sta., 14: 248-300. 1871; Oden, 

 1919 (p. 671). 



18 Eggertz, C. G. Studier och undersokninger ofver mullamnen i aker-och 

 mossjord. Diss. Lund. Centrbl. Agrik. Chem., 18: 75-80. 1888. 



