126 NATURAL MANURES. VI. 



a limited extent, in accordance with the mass-action law (see 

 p. 86), and according to many recent experiments gypsum is 

 quite useless as a preservative.* These investigators found that 

 kainite and superphosphate or free phosphoric acid are very 

 effective in preventing loss of ammonia. 



As the result of a series of experiments Kreuz and Gerlachf 

 arrived at the following conclusions. Conversion of urea 

 into ammonium carbonate takes . place rapidly either in the 

 presence or absence of air and without any liberation of 

 free nitrogen. The ammonium carbonate dissociates if the 

 dung dries and is easily volatile except in an atmosphere 

 of carbon dioxide ; the loss is greater if a stream of air 

 pass through the dung. The nitrogen of the ammonium 

 carbonate which remains in the dung is gradually, in presence 

 of air, converted into nitric acid, again with no liberation of 

 free nitrogen. The nitric acid so formed, however, is, by 

 the denitrifying bacteria, decomposed with evolution of free 

 nitrogen. This decomposition proceeds either in presence or 

 absence of air, provided the bacteria are furnished with suit- 

 able food materials, such as straw, grape sugar, glycerin, 

 sodium lactate or citrate, the green parts of plants, &c. The 

 whole of the nitrogen of the nitrates decomposed is not evolved 

 as free nitrogen, but about 10% of it is converted into highly 

 complex organic substances resembling albumen. 



The loss of nitrogen which animal refuse undergoes during 

 storage, results from the liberation of ammonia and of free 

 nitrogen. If the manure be kept in a loose, porous condition, 

 the volatilisation of ammonia is favoured ; if compact, so as to 

 exclude air, much free nitrogen escapes, but the ammonia 

 formed is retained. The loss of nitrogen, which is mainly 

 suffered by the liquid portion of the manure, is shared to a 

 small extent by the solid dung and the straw, the nitrogenous 

 compounds of which, by the action of the bacteria, are con- 

 verted into amido-compounds, which suffer the same fate as 

 the urea. If the manure has to be kept long it is desirable to 

 cover the heap with soil, preferably with peaty soil. 



Maercker and Schneidewindj found that in a deep stall the 



* Burri, Herfeldt, and Stutzer, Journ. Landwirt. 1895, 1. 

 t Jahresbericht Agricultur-Chemie 1899, p. 98. J Jahr. Agric. Chem. 1899, 100. 



