38 Farmyard Manure. 



free ammonia, which under all circumstances constitutes but a 

 small fraction of a per cent, of the manure, however, sinks again 

 in February to a mere trace. Direct experiments, made with a 

 view of ascertaining the cause of this difference, have shown me 

 that farmyard manure gives off no ammonia when quite cold, 

 and that free ammonia can only be disengaged when the dung- heap 

 is in an active state of fermentation, which is always accompanied 

 with evolution of heat. In the interior of large heaps the heat of 

 the dung is often very great, and it is in this part of the heap 

 that ammonia is given off largely. Before, however, it can 

 escape into the air it has to pass a portion of manure which is 

 kept cold by the surrounding air. This external and cold 

 part of dung-heaps acts as a mechanical and chemical filter 

 with reference to the ammonia which is given off from the 

 interior and heated portion of the heap. On account of the 

 porous condition of the litter and partly dried excrements the 

 ammonia is fixed mechanically ; but as all organic substances 

 exposed to the atmosphere and moisture are gradually changed 

 into humus, which as we have seen already is an excellent fixer 

 of ammonia, the external parts of dung-heaps may also be called 

 a chemical filter which prevents the loss of ammonia. 



Dung-heaps that have been placed in a field, after a short time, 

 when settled down to a firm mass, do not give off any ammonia, 

 but on turning such heaps a very powerful and pungent smell is 

 readily perceptible. Each turning of a manure-heap thus is 

 attended with a certain loss in ammonia, since it escapes from 

 heated manure. It may therefore be advisable not to turn 

 manure-heaps more frequently than is absolutely necessary. 



In the preceding pages I have given detailed organic and in- 

 organic analyses of the fresh and the rotten dung in the state in 

 which both were used in the experimental heaps. I have like- 

 wise given such analyses of the fresh manure, after it had been 

 kept for 3 months and 11 days in two different ways, and of the 

 rotten dung after having been exposed to the weather for 2 months 

 and 9 days. 



Another detailed analysis of the fresh manure, after having been 

 spread out in an open yard for a period of 6 months, will be 

 found in the succeeding pages. The various experimental heaps 

 were weighed for the second time on the 30th of April, 1855, 

 and at the same time samples for analysis taken from each heap. 



The two heaps made on the 3rd of November, 1855, with 

 fresh mixed farmyard manure and the portion of fresh dung 

 spread out in an open yard, thus were kept for 6 months, minus 

 3 days ; whilst the rotten dung, being placed in a heap on the 

 5th of December, was kept for only 5 months, minus 5 days. 

 The loss in weight having been ascertained in each case, the 



