142 SOILS: PROPERTIES AND MANAGEMENT 



of the organic matter in soils, but none have proved 

 entirely satisfactory, since the composition of this ma- 

 terial is so complicated and so likely to change while 

 under investigation. Other soil constituents also tend 

 to interfere with the determination. Two general methods 

 seem worthy of mention, as they have been used very 

 widely in soil analyses and at least give comparative, if 

 not absolutely accurate, results. 



Loss on ignition. 1 This is a simple method which 

 designs to burn off the organic matter and determine 

 its loss by difference. Five grams of dry soil are 

 placed in a platinum dish and ignited at a low red 

 heat until the organic matter is all oxidized. The 

 cold mass is moistened with ammonium carbonate 

 and heated to a temperature of 150 C. in order to 

 expel the excess of ammonia. The loss is rated as or- 

 ganic matter. 



This method is open to the objection that, besides the 

 loss of organic matter, a certain small amount of water 

 of combination, together with all ammoniacal compounds, 

 nitrates, all carbon dioxide, and some alkali chlorides if 

 the temperature is carried too high, is driven off. The 

 method therefore gives high results, especially in the 

 presence of large amounts of hydrated silicates. An 

 attempt to replace the carbon dioxide is made in the 

 treatment of the cold mass with ammonium carbonate. 

 Notwithstanding these objections, this method is one of 

 the best and is very generally used all over the world 

 in estimating the organic matter of the soil. Very often 



1 Houston, H. A., and McBride, F. W. A Modification of 

 Grandeau's Method for the Determination of Humus. U. S. 

 D. A., Div. Chem., Bui. 38 (edited by H. W. Wiley), pp. 84-92. 

 1893. 



