PRESERVATION OF MANURE. 125 



nitrogen and other substances which occur during fermenta- 

 tion. A great amount of attention has lately been directed to 

 this matter, more especially with reference to the methods of 

 minimising the loss. The loss of nitrogen occurs chiefly in 

 two ways, by volatilisation of ammonia from ammonium car- 

 bonate and by the formation of free nitrogen. 



According to Berthelot and Andre, ammonium carbonate 

 dissociates when it volatilises, yielding ammonia, carbon 

 dioxide, and water : 



(NH 4 ),C0 8 ^ 2NH 8 + C0. 2 +H 2 0. ::: 



In accordance with the law of dissociation the equilibrium 

 represented above is attained when the product of the square 

 of the number of molecules of ammonia into the number of 

 molecules of carbon, dioxide present in unit volume reaches a 

 certain value. Now this product may be reached by an increase 

 of both or of only one of the two factors ; if either be increased 

 the other factor will diminish if the product is to remain the 

 same. It is obvious, therefore, if the amount of carbon 

 dioxide in the surrounding air be increased, the amount of 

 ammonia set free by dissociation will be diminished. Hence, 

 if the production of carbon dioxide by the fermentation of 

 merely carbonaceous matters in a manure heap can be en- 

 couraged, the dissociation of ammonium carbonate will be 

 diminished and the loss of ammonia hindered.! Another 

 important consideration affecting this source of loss of nitro- 

 gen as ammonia is the renewal of the gas in the interstices of 

 the manure by diffusion. If the gaseous carbon dioxide and 

 ammonia are removed by, say, a current of air, the dissocia- 

 tion 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 O) over the heap or in the stall. This was sup- 

 posed to act by producing calcium carbonate and ammonium 

 sulphate. This reaction could, even in solution, only go on to 



* See Appendix to Chap. IV. 



t Deherain recommends (Cornpt. Rend 1898, 1305) that the soiled litter be removed 

 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. 



