48 HUMUS 



ponding in composition to the formula C 20 H 1S O 9 was obtained ; it still, 

 however, contained 0*179 per cent of nitrogen. It is described as being 

 soluble in 8300 parts of cold or 625 parts of boiling water, it reddens 

 litmus, and expels carbon dioxide from carbonates, forming humates 

 which are all insoluble with the exception of those of the alkalies. 



The ammonium compound, C 60 H 48 (NH 4 ) 6 27 , is very soluble in 

 water. With calcium chloride a compound, 60 H 46 Ca 3 (NH 4 ) 2 O 27J is 

 precipitated. Ulmic acid is stated by Detmer to be identical with 

 humic acid. Crenic and apocrenic acids are produced by oxidation of 

 humic acid. The former is said to be found in moist soils, the latter 

 in dry, loose ones. Crenic acid is said to have the composition 

 C 24 H 24 O 16 + 3H 2 O, apocrenic acid, C 24 H 12 O 12 + H.p. 1 The free acids are 

 soluble in water. 



In 1889, a study of the black soils of Eussia was published by Kostyt- 

 cheff, 2 in which he found that the humus contained from 4-0 to 6 -65 

 per cent of nitrogen, a quantity greatly in excess of that in the original 

 vegetable matter from which it was produced (1*6 to 2 per cent). He 

 found that when wet vegetable matter (hay) was allowed to decay 

 under a bell jar, air being injected daily, the dry matter considerably 

 diminished, but that no loss of nitrogen occurred, so that the per- 

 centage of nitrogen increased from 1'27 to 2-04. He concludes 

 that the nitrogen in humus exists mainly as proteid bodies, very little 

 being as amide; that both bacteria and moulds aid in the conversion 

 of vegetable matter into humus ; that if decay occurs beneath water, 

 the vegetable structure is retained and peat results, if in air, all trace of 

 structure is destroyed by the leaves being passed through the bodies of 

 worms, caterpillars, etc. He states that fungi aid greatly in dis- 

 seminating humus (say from a dead root) through the soil. In black 

 earth the humic acid is almost exclusively in combination with lime. 



Humic acid and the soluble humates are colloidal bodies. Accord- 

 ing to Grandeau, humic acid and the humates combine with phosphoric 

 acid, lime, potash, oxide of iron, or silicic acid to form double com- 

 pounds, which, though soluble in ammonia, do not give the reactions 

 characteristic of their constituents. When solutions of these double 

 compounds are submitted to dialysis, decomposition occurs and the ash 

 ingredients pass through the membrane entirely free from the organic 

 matter. This has, to some extent, been confirmed by Simon. 3 These 

 absorptive properties of humus for substances in solution, as well as 

 those of clay, are of great importance in agriculture and will be con- 

 sidered hereafter. The alleged power of humus to absorb nitrogen 

 from the air and convert it into ammonia, described by Simon and 

 others, is denied by Prevost. 4 



Much work on the chemical nature of .the organic matter of soils 

 has been published recently, but a detailed account of these investiga- 

 tions cannot be given here. 



1 Mulder, Ann., 361, 243. 



2 Jour. Chem. Soc., 1891, Abstracts, 611. 



3 Landw. Versuchs. Stat., 18, 452; Jour. Chem. Soe., 1876, 731. 

 4 Jour. Chem. Soc., 1881, Abstracts, 371. 



