146 § 89. SPECIAL METHODS OF ANALYSIS. 



Cyanogen is sometimes to be found among the products 

 of the decomposition of nitrogenous organic matter in 

 the presence of strong bases, particularly if the decom- 

 position has been aided by heat. 



Ferrocyanogcn is a product of the decomposition of 

 nitrogenous animal matters by heat, in the presence of a 

 strong base and iron. 



Iodine is very widely but sparingly diifused. 



Lead may sometimes be found in Avater that has been 

 in contact with it, and in superphosphates ; in this latter- 

 case it is derived from the sulphuric acid used in the 

 manufacture of the fertilizer ; it is also a common ingre- 

 dient of pigments. 



Manganese occurs in nearly all soils, and is generally 

 found, at least in traces, in plants, and whatever is pro- 

 duced from them. 



Zinc may occur in soils in the neighborhood of beds of 

 zinc ore, and in the ashes of j)lants grown on such soils. 



II. 



SPECIAL METHODS OF QUANTITATIVE SEPARATION OF 

 SUBSTANCES. 



Under this head a few special methods of quantitative 

 separation of substances, that often occur in agricultural 

 chemical analysis, are described with full details and di- 

 rections, and in a manner convenient for reference. In 

 this way much repetition is avoided in the chapters treat- 

 ing of special analyses. 



By consulting Table X, at the close of the book, the 

 analyst may ascertain how much he will probably find of 

 each of the constituents of the compound he is about to 

 analyze, and, knowing the strength of his reagents, he 

 can form some idea as to the quantities of these to be used 

 to pro'duce complete precipitation. 



