DECOMPOSITION OF PROTEINS 497 



the productive capacity of a soil by its ammonia producing power, 

 as will be shown later. 



Among the methods used for determining ammonia in the soil and 

 in solution, only three need be mentioned: (1) the direct distillation 

 of the soil or solution with magnesium oxide; (2) the aeration method; 

 (3) the extraction of ammonia with KC1 solution (followed by distilling 

 the ammonia with magnesium oxide). 



The first is more rapid, but may bring about the liberation of some 

 ammonia from amides and perhaps from other simple nitrogenous 

 substances. 



The aeration method can be used in determining ammonia in liquid 

 culture, but requires a long time for a complete extraction of the am- 

 monia from soils. 70 It consists in placing 25 to 50 cc. of the culture or 

 soil suspension in large heavy glass tubes or flasks, adding some heavy 

 oil, 2 to 3 grams of NaCl and 2 grams of Na 2 C0 3 , then aerating for 

 2 to 3 hours. The ammonia is absorbed in a standard solution of 

 sulfuric acid to which a proper indicator has been added (like sodium 

 alizarine sulfonate). On placing the tubes in a water bath, at 55 to 

 60°C, the process is carried out more rapidly and completely. Where 

 heat is used, there is, of course, always some danger of hydrolysis of 

 undecomposed proteins or their derivatives. 



The extraction of the ammonia from soil by a KC1 solution is based 

 upon the fact that the ammonium base is replaced in its adsorbed 

 condition in the soil by another base when added in excess to the soil 

 (in this case by the potassium of the KC1 solution). The process is 

 usually carried out by extracting 25 grams of the soil successively with 

 five to seven 100-cc. portions of approximately 4 per cent potassium 

 chloride solution (or until the filtrate gives no test for ammonia with 

 Nessler's reagent). Peat soils should be extracted two or three times 

 more. Alkaline soils should be first neutralized with ammonia-free 

 hydrochloric acid. The combined filtrates are then distilled with 

 MgO into standard O.bV H 2 S0 4 . When distillation is finished, the 

 carbon dioxide is removed from the distillate by boiling, before the 

 acid is titrated back with a standard alkali. 71 



70 Potter, R. S., and Snyder, R. S. The determination of ammonia in soils. 

 Jour. Ind. Engin. Chem., 7: 221. 1915; Gibbs, W. M., Neidig, R. E., and 

 Batchelor, H. W. Aeration method for determining ammonia in alkali soils. 

 Soil Sci., 15: 260-268. 1923. 



71 Tarassoff, B. On the methods of determining ammonia in the soil (Rus- 

 sian). Zhur. Opit. Agron., 15: 118-138. 1914; Bengtsson, N. The determina- 

 tion of ammonia in soil. Soil Sci., 18: 255-278. 1924. 



