THE ORGANIC MATTER OF THE SOIL 105 



they are absorbed again by a crop, the organic cycle is com- 

 pleted. 



56. The partially decomposed organic matter. 1 — The 

 most complicated parts of the organic matter in the soil are 

 the primary and secondary products of decomposition, the 

 materials between the original tissue and the simple products. 

 These compounds are not only complex but they are contin- 

 ually changing. A certain compound present in the soil one 

 week may be altered the next. Again, at least a part of the 

 decomposing organic matter is colloidal, thus possessing spe- 

 cial absorptive and catalytic properties. When the soil 

 organic matter is treated with the various extractive agents, 

 reactions may be induced which would not take place in a 

 normal soil. Compounds are then formed which would prob- 

 ably not exist under natural conditions. 



Many chemists have worked on the problems of the con- 

 stitution of the organic matter of the soil and have published 

 their results. The early conceptions were rather simple. 

 Mulder, 2 for example, considered the soil organic matter to 

 consist almost entirely of carbon, hydrogen, and oxygen. Such 

 a concept ignores the presence of nitrogen, sulfur, and the 

 mineral elements of the original plant tissue, and is much 

 too simple to explain organic transformations. 



Even the investigators 3 of Mulder 's time obtained diseor- 



*See Morrow, C. A., The Organic Matter of the Soil; A Study of the 

 Nitrogen Distribution in Different Soil Types; Dissertation, Univ. 

 Minn., 1918. 



3 Mulder, T. J., Die Organischen Bestandtheile im Boden; Chemie der 

 Ackerkrume, I, pp. 308-360, Berlin, 1863. Also, Wiley, H. W., Agricul- 

 tural Analysis; Vol. I, p. 53, Easton, Pa., 1906. 



Mulder contended that the organic matter consisted of seven distinct 

 compounds, as follows : 1 & 2, Ulmic acid and ulmin ; 3 & 4, Humic acid 

 and humin; 5, Geic acid; 6, Apocrenic acid; 7, Crenic acid. These 

 bodies he considered as arising from one another by oxidation; thus 

 ulmic acid (C 40 H 14 O 12 ) gave humic acid (C^H^O^), which in turn yielded 

 geic acid (C^H^O^), followed by apocrenic acid (C^B.^0^) , and finally 

 by crenic acid (C 24 H 12 16 ). 



8 See Schreiner, O., and Shorey, E. C, The Isolation of Harmful Or- 

 ganic Substances from Soils; U. S. Dept. Agr., Bur. Soils, Bui. 53, pp. 

 15-16, 1909. 



