164 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



plants, such as proteids and lignin, and are soluble in ammonia. 1 

 No doubt they also occur in the soil. In attempts to determine 

 the formation of humus in the soil, these ammonia-soluble 

 materials introduced with the ingredients have been neglected. 

 In experiments 2 in which the ammonia-soluble organic matter 

 originally in the soil and that added to it, were estimated before 

 and after decomposition for several months, there was a loss, 

 and not a gain, of ammonia-soluble material. The following is 

 an example : 



Percentage of humus in original soil 1.36 



Dry soil with meat 2. 29 



Soil with meat moist for 14 weeks 1.68 



Estimation of Ammonia-Soluble Humus. In the estimation of 

 ammonia-soluble humus, 3 the soil is first extracted with I per 

 cent, hydrochloric acid, to remove lime and decompose the com- 

 pounds of humic acid. It is then washed free from acid, and 

 treated with 4 per cent, ammonia for some time. After remain- 

 ing in contact for several days, the solution is allowed to settle, 

 and an aliquot part evaporated to dryness, dried and weighed, 

 ignited and weighed again. The loss in weight is ammonia- 

 soluble humus. 



This method is highly inaccurate on account of the presence of 

 clay. Clay will remain in suspension in ammonia-water for 

 months, and, as it contains chemically combined water, will lose 

 weight on ignition, after drying. It is also present in the humic acid 

 precipitated with the solution, unless previously removed. The 

 clay may be easily removed by precipitation with ammonium car- 

 bonate. 4 The ammonium carbonate is volatilized along with the 

 ammonia when the solution is subsequently evaporated to dryness. 



Humus of Peat and Swamps. As we have already stated, acid 

 bodies are formed in peat and muck soils, which must be 

 neutralized by lime before the soil can be cultivated profitably. It 



1 Hoffmeister, Landw. Versuchs-stat., 1898, p. 347. 



2 Fraps and Hamner, Texas Bulletin 129. 



3 Methods of the Association of Official Agricultural Chemists. 



4 Rather, Bulletin 139, Texas Station. 



