THE ORGANIC MATTER OF THE SOIL 113 



dized. The cold mass is moistened with ammonium carbonate 

 and heated to a temperature of 150° C. in order to expel the 

 excess of ammonia and replace the carbon dioxide. The 

 change in weight is rated as loss on ignition. 



This method is open to the objection that, besides the loss 

 of organic matter, a certain amount of water of combina- 

 tion, and all ammoniaeal compounds, nitrates, carbon dioxide, 

 and some alkali chlorides, if the temperature is carried too 

 high, are driven off. The method, therefore, gives high results, 

 especially in the presence of large amounts of hydrated sili- 

 cates such as are likely to occur in residual soils. Notwith- 

 standing these objections, this method has been used to a very 

 great extent in soil analysis.^ 



Chromic acid method.- — This method, proposed by Wolff, 

 has been modified and improved by various chemists. War- 

 ington and Peake ^ have perhaps done more with the method 

 than any other investigators. In the United States the modi- 

 fication by Cameron and Breazeale ^ has been very generally 

 accepted.* It consists in the treatment of the soil sample with 

 sulfuric acid, and chromic acid, or potassium bichromate. 

 The organic matter, in the presence of the sulfuric acid and 

 an oxidizing agent, evolves carbon dioxide until, if the mix- 



^Eatlier offers a modification to this method which seems to obviate 

 some of its difficulties. The soil is first extracted with dilute HCl and 

 HF to remove the hydrated aluminum silicates, the organic matter being 

 little influenced thereby. The sample is then ignited in the usual 

 manner. Eather, J. B., An Accurate Los&'0%-Ignition Method for the 

 JDetermination of Organic Matter in Soils; Jour. Ind. and Eng. Chem., 

 Vol. X, No. 6, pp. 439-442, June, 1918. 



^ Warington, R., and Peake, W. A., On the Determination of Carbon in 

 Soils; Jour. Chem. Soc. (London), Trans., Vol. 37, pp. 617-625, 1880. 



^Briggs, L. J., and others, The Centrifugal Methods of Mechanical 

 Soil Analysis; U. S. Dept. Agr., Bur. Soils, Bui. 24, pp. 33-38, 1904. 

 Also, Cameron, P. K., and Breazeale, J. F.^ The Organic Matter in Soils 

 and Subsoils; Jour. Amer. Chem. Soc, Vol. 26, pp, 29-45, 1904. 



^Waynick offers a simplification of this method: Waynick, D. D., A 

 Simplified Wet Combustion Method for the Determination of Carbon in, 

 SoiU; Jour. Ind. and Eng. Chem., Vol. XI, No. 7, pp. 634-637, 1919. 



