PHYSICAL PROPERTIES OF ORGANIC MATTER 127 



are such as to have a large influence on its produc- 

 tiveness. 



56. Solubility. The organic matter may be divided 

 into two general classes of materials: (a) If an ordinary 

 soil or peat or muck be leached with water, particularly 

 if the water contain a little ammonia, a dark brown 

 or black color will be imparted to the extract. This 

 is due to a mixture of organic compounds which have 

 a colloidal or gelatinous consistency. It is the material 

 to which the specific term humus is applied which 

 gives the brown color to the drainage water from 

 swamps and to the leachings from the manure heap. 

 This color is an indication of the loss of the humus 

 constituent, and should remind one of the necessity 

 for precautions against the loss, as far as possible. When 

 the humus is united with salts like lime to form humates, 

 this loss is very much reduced. It follows from this 

 that the loss of humus, by leaching from soils rich in 

 lime, is very much less than in those soils poor in lime. 

 Many of the soils in the southern states are very low 

 in lime, and the streams are generally bordered by 

 swampy areas. As a result, the drainage water is usually 

 of a brown coffee-color. On the other hand, in those 

 northern states where the soils are rich in lime, this 

 brown color is much less pronounced and is usually 

 absent. If lime or some other flocculating agent be 

 added to this brown liquid, the humus separates out 

 in fluffy masses, which settle to the bottom, leaving 

 the liquid above almost colorless. This is, in part, what 

 takes place in the soil when these flocculating materials 

 are present. 



