SECTION II.— SOILS 



CHAPTER V 

 Proximate Constituents of Soils 



Limestone, Humus, Sand, and Clay. 



Soils are popularly classified as loams, clays, marls, peaty, 

 sandy, calcareous, etc., according to their content of the proximate 

 constituents, sand^ clay^ limestone^ and humus. 



36. Limestone. 



{a) The limestone or calcium carbonate content of 

 the soil must be sufficient to ensure a permanently 

 neutral reaction. A rough idea of the amount of CaCOg 

 present in a soil may be obtained as follows : — 



A small quantity of soil (about 5 grams) is dried 

 and powdered, placed in a beaker, and treated with some 

 concentrated hydrochloric acid. If a brisk effervescence 

 is produced the soil contains over i per cent, of CaCOg, 

 which, in general, is ample for fertility. Under i per 

 cent, is indicated by an evolution of COg which can 

 only just be seen. Less than -5 per cent, can only be 

 detected by holding the containing beaker to the ear 

 and listening for the bursting of the small bubbles of 

 carbon dioxide. If no noise is heard in this way the 

 soil contains practically no limestone, and should be 

 tested for acidity with litmus paper. 



{b) Estimation of CO^ in Limestone. — This estima- 



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