TOTAL NITROGEN. 93 



be decomposed by the heating into carbon dioxide, which 

 would escape, and quick-lime) back into its original form. 

 Otherwise the loss on ignition would include the carbon 

 dioxide thus expelled. 



Care must be taken that the temperature be as low as is 

 consistent with the oxidation of the carbon, or loss, due to 

 volatilisation of alkaline chlorides, may occur. 



Determination of Nitrogen. The nitrogen in a soil may exist 

 in three states of combination : 



1. As nitrates. 



2. As ammonium compounds. 



3. As organic compounds of complex but little known con- 



stitution, associated with the " humus." 



The nitrogen existing at any given time in a soil in the state 

 of nitric acid or ammonia is usually very small in amount and 

 in most cases does not require separate determination. 



Total Nitrogen. Several methods are in use for the deter- 

 mination of nitrogen in soil, but of recent years the well- 

 known Kjeldahl process for the determination of nitrogen in 

 organic substances generally, has, with various modifications 

 in detail, been adopted in soil analysis. 



Broadly speaking, the method is based upon the behaviour 

 of strong sulphuric acid towards organic matter ; by continued 

 heating with strong acid the carbonaceous matter is oxidised 

 into carbon dioxide and water, the nitrogen which it contains 

 being converted into ammonia, which in the presence of the 

 large excess of acid, remains behind as ammonium sulphate. 

 A large proportion of the sulphuric acid is reduced with the 

 evolution of sulphur dioxide. It is found that the oxidation of 

 the organic matter is facilitated by the addition of small quan- 

 tities of certain metallic salts, e.g., of mercury or copper. 

 They apparently act as carriers of oxygen from the acid to the 

 organic matter. 



The following are the details of the method which the 

 author uses : 



10 to 15 grammes of the air-dried "fine soil" (i.e., which 

 has been crushed and passed a 1mm. sieve) are introduced into 

 a 16oz. spherical flask and treated with 20 to 25 c.c. of pure 

 sulphuric acid (which must be free from ammonia, the 



