Vii.]CBEMICAL CHANGES DURING DUNG-MAKING 189 



same time the proportion of this gas falls to such an 

 extent because of its dilution with the air, that 

 ammonia can be lost by volatilisation. By consolidat- 

 ing the heap and pumping the liquid over it afresh, 

 the anaerobic fermentation rapidly sets in again and 

 the proportion of carbon dioxide is restored, thus 

 checking the dissociation and volatilisation of the 

 ammonium carbonate. After the first outburst of 

 fermentation, the evolution of hydrogen ceases and 

 the marsh-gas fermentation takes its place. 



A considerable proportion, amounting to one-quarter 

 or more, of the dry matter of the original dung is lost 

 during this process of humification, by the conversion 

 of carbohydrates into carbon dioxide, marsh gas or 

 hydrogen, and water. The various acids which are 

 also produced are neutralised by the liquid part of 

 the manure, which is alkaline from the presence of 

 ammonium and potassium carbonates resulting from 

 the fermentation of the nitrogenous constituents and 

 salts of the urine ; the dark brown liquid to be seen 

 draining from a dunghill is a solution of the humus 

 formed in this alkaline liquid. 



The changes going on during the making and 

 storage of farmyard manure are thus exceedingly 

 complex ; it is in the early stages that the bacterial 

 actions are most rapid, and they fall chiefly upon 

 the soluble nitrogenous compounds like urea. At this 

 time the greatest losses of nitrogen take place both by 

 volatilisation of ammonia and by evolution of nitrogen 

 gas, and so active is the oxidation that the temperature 

 of the mass rises continually. If the rate of oxidation 

 b2 promoted by occasionally turning over the mass, as 

 in preparing a hot bed or a mushroom heap, the rise 

 in temperature is much increased ; at the same time 

 the losses of nitrogen rise rapidly, and the amides and 



