“13. During the fermentation of dung, ulmic, humic, and other organic acids are formed, as well as gypsum, which fix the ammonia generated in the decomposition of the nitrogenized constituents of dung.
“14. During the fermentation of dung, the phosphate of lime which it contains is rendered more soluble than in fresh manure.
“15. In the interior and heated portions of manure-heaps, ammonia is given off; but, on passing into the external and cold layers of dung-heaps, the free ammonia is retained in the heap.
“16. Ammonia is not given off from the surface of well-compressed dung-heaps, but on turning manure-heaps, it is wasted in appreciable quantities. Dung-heaps, for this reason, should not be turned more frequently than absolutely necessary.
“17. No advantage appears to result from carrying on the fermentation of dung too far, but every disadvantage.
“18. Farm-yard manure becomes deteriorated in value, when kept in heaps exposed to the weather, the more the longer it is kept.
“19. The loss in manuring matters, which is incurred in keeping manure-heaps exposed to the weather, is not so much due to the volatilization of ammonia as to the removal of ammoniacal salts, soluble nitrogenized organic matters, and valuable mineral matters, by the rain which falls in the period during which the manure is kept.
“20. If rain is excluded from dung-heaps, or little rain falls at a time, the loss in ammonia is trifling, and no saline matters, of course, are removed; but, if much rain falls, especially if it descends in heavy showers upon the dung-heap, a serious loss in ammonia, soluble organic matter, phosphate of lime, and salts of potash is incurred, and the manure becomes rapidly deteriorated in value, whilst at the same time it is diminished in weight.
“21. Well-rotten dung is more readily affected by the deteriorating influence of rain than fresh manure.
“22. Practically speaking, all the essentially valuable manuring constituents are preserved by keeping farm-yard manure under cover.