CYANAMID — MANUFACTURE, CHEMISTRY AND USES 49 



Final cyanamide 



Initial after after after 



cyanamide 3 days 6 days 9 days 

 mg. mg. mg. mg. 



Ordinary soil 83.8 52.0 36.0 19.5 



Soil treated with HCl 83.8 63.5 49.1 36.0 



Soil treated with HCl and NaaCOg.. 83.8 55.5 43.2 46.0 



Soil calcined 83.8 — — 77.6 



Each of the above treatments has diminished the ability of 

 the soil to convert cyanamide to other forms. The calcined 

 soil has very little power of decomposition. It is evident, 

 therefore, that it is not the gross, solid, mineral particles of 

 the soil that have this power, but certain constituents of the 

 soil mass that are destroyed by heat. These constituents 

 belong to the class of chemical compounds that form colloids 

 or disperse systems in the soil. 



We will now examine the results of experiments made with 

 various materials that are known to form part of practically 

 all soils. 



EFFECT OF ZEOLITES. 



According to Van Bemmelen^ the colloids of agricultural 

 soil consist principally of amorphous zeolites (amorphous 

 hydrated silicates). These remain for an indeterminate time 

 in suspension in pure water, are coagulated by electrolytes, 

 can be dried into hard compact masses, have in the highest 

 degree the properties of hydrogels, and to their presence is 

 probably due the greater part of the absorptive powers of 

 the soil. Since these substances could not be isolated in their 

 natural state it was necessary to use certain crystallized 

 zeolites, as follows: 



Natrolite of Bohemia, hydrated metasilicate of aluminium 



and sodium. 

 Scolecite of Ireland, hydrated metasilicate of aluminium and 

 calcium. 

 1 Landw. Ver. Staz. Bd. XXXV, (1888) p. 69. 



