118 PRESERVATION OF FARM-YARD MANURE 



hindered. 1 Another important consideration affecting this source of 

 loss of nitrogen as ammonia is the renewal of the gas in the interstices 

 of the manure by diffusion. If the gaseous carbon dioxide and am- 

 monia are removed by, say, a current of air, the dissociation of the 

 ammonium carbonate will proceed more rapidly. 



A method of preventing, or rather of lessening, the loss of ammonia 

 from manure heaps which has been recommended and used for many 

 years, is the strewing of powdered gypsum (CaS0 4 .2H 2 0) over the heap 

 or in the stall. This was supposed to act by producing calcium car- 

 bonate and ammonium sulphate. This reaction could, even in solution, 

 only go on to a limited extent, in accordance with the mass-action law 

 (see p. 80), and according to many recent experiments gypsum is quite 

 useless as a preservative.' 2 These investigations show that kainite and 

 superphosphate or free phosphoric acid are very effective in prevent- 

 ing loss of ammonia. 



As the result of a series of experiments, Kreuz and Gelach 3 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 atmo- 

 sphere 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 pre- 

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

 able food materials, such as straw, grape sugar, glycerine, sodium lactate 

 or citrate, or the green parts of plants. The whole of the nitrogen of 

 the nitrates decomposed is not evolved as free nitrogen, but about 10 

 per cent of it is converted into highly complex organic substances re- 

 sembling albumin. 



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 am- 

 monia 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 converted into 

 amino-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. 



JDeherain recommends (Compt. Rend., 1898, 1305) that the soiled litter be re- 

 moved to the manure heap as often as possible and the stable or cow-shed gutters 

 be rinsed with water to carry the liquid excreta into the liquid manure tank and 

 that the dung heap be well heaped up and watered with the liquid from the tank. 

 In this way a constant production of carbon dioxide by fermentation is produced 

 and loss of ammonia hindered. 



2 Burri, Herfeldt and Stutzer, Jour. Land., 1895, 1. 



3 Jahr. Agric. Chem., 1899, 98. 



