VI. MANURING- AND GENERAL MANURES 117 



No free nitrogen was found in the gases, the loss of nitrogen being 

 due to its liberation as ammonia, which would be lost in drying. The 

 oxygen and hydrogen in the gases evolved, including the hydrogen 

 lost as ammonia, exceed by 2-333 grammes and 0-305 gramme respec- 

 tively that lost by the manure, showing that water enters into the 

 reactions by which these gases are produced. 



Preservation of Farm-yard Manure. The best means of using 

 farm-yard manure, whether fresh or rotted, and the most advantageous 

 manner of treating it so as to minimise the loss of fertilising in- 

 gredients, are matters which have received much consideration and 

 about which the greatest diversity of opinion, especially among 

 farmers, exists. 



Such obvious precautions as the prevention of loss of soluble 

 matter by drainage hardly need mention here, unless it be to show 

 how rich in fertilising materials such drainage often is. In fresh 

 manure, the liquid portion consists mainly of urine, which has been 

 shown to be rich in nitrogen and potash. 



The dark- brown drainage from old manure heaps is often rich in 

 manurial matters ; a sample analysed by Voelcker contained nearly 

 2 per cent of solid matter, including 0-04 per cent nitrogen, 0'52 per 

 cent of carbonate and chloride of potassium, and a considerable 

 quantity of phosphoric acid. It is obviously desirable that such drain- 

 ings should be preserved, either by the use of sufficient litter best, 

 peat or peat moss to absorb it, or by collecting it in a tank. 



Of more importance from the chemical aspect is the loss of nitro- 

 gen and other substances which occurs during fermentation. A great 

 amount of attention has lately been directed to this matter, more es- 

 pecially with reference to the methods of minimising the loss. The 

 loss of nitrogen occurs chiefly in two ways, by volatilisation of am- 

 monia from ammonium carbonate and by the liberation of free 

 nitrogen. 



According to Berthelot and Andre, ammonium carbonate dissociates 

 when it volatilises, yielding ammonia, carbon dioxide and water : 



(NH 4 ) 2 C0 3 ^2NH 3 + C0 2 + H^. 1 



In accordance with the law of dissociation, the equilibrium repre- 

 sented above is attained when the product of the square of the number 

 of molecules of ammonia into the number of molecules of carbon di- 

 oxide present in unit volume, reaches a certain value. Now this pro- 

 duct 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 pro- 

 duct 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 carbon- 

 aceous matters in a manure heap can be encouraged, the dissociation 

 of ammonium carbonate will be diminished and the loss of ammonia 



1 See Appendix to Chap. IV. 



