118 Phenomenon of Absorption in its Relation to Soils 



Absorption hy Humus. 



The part played by humus in the absorption processes in the soil 

 has not been very fully worked out. J. M. Van Bemmelen^ showed 

 that humus is a typical colloid possessing absorbing powers similar 

 to those of the gels. 



A solution of humus in ammonia is precipitated by the addition of 

 salts of metals such as copper, lead, calcium, magnesium — these so- 

 called humates have been and still are in many quarters assumed to 

 be true insoluble salts. Van Bemmelen showed that their composition 

 was very variable and hence defined them as absorption complexes. 



A. Konig2 showed that a sphagnum moor soil consisting almost 

 entirely of organic matter absorbed potassium from its salts with 

 substitution of calcium and magnesium. Humus shows its greatest 

 absorptive power with alkalies; its power of taking up ammonia is 

 well known and is shown by the insoluble portion as well as by that 

 soluble in alkalies. Peat which is almost entirely free from calcium and 

 other bases still absorbs phosphoric acid. It also absorbs neutral 

 salts as a whole. Konig also obtained negative absorption, i.e. the 

 absorption of water instead of dissolved salt from the solution. A peat 

 in contact with N/10 KCl solution absorbed water alone and left the 

 solution more concentrated than before. 



When an alkaline solution of humus is precipitated it carries down 

 with it some of the substances present in the solution. W. Schuhmacher^ 

 using "humus" obtained by the action of sulphuric acid on sugar found 

 an absorption of from 1-7 to 10 % from solutions of 0-5 % of sodium 

 phosphate, potassium nitrate and calcium chloride. Humus is a very 

 difficult substance to work with as there are so many fractions and so 

 far no extensive attempts have been made to deal systematically with 

 its absorptions. 



In the author's experiments the amount of phosphoric acid absorbed 

 by the humus was independent of the concentration of the phosphate 

 solution. A strong solution of humus was made in ammonia the excess 

 of which was then removed by a current of air. The solution was then 

 made slightly acid with acetic acid and dialysed for three days. Con- 

 siderable quantities of phosphate were removed, and finally the solution 

 contained 15 mgms. of PgOg per 100 c.c. Portions of 25 c.c. of this 



1 Landu: Versuchs-Slat. 1888, 35, G7. 

 - Landw. Jahrb. 1882, 11, 1. 

 3 Ann. d. Landw. 18G7, 49, 322. 



