210 Farmyard Manure. 



It is clear therefore that, during the fermentation of dung-, 

 much of the organic substances must become changed into com- 

 pounds which are either readily soluble in water, and easily 

 washed out by heavy rains, or into gaseous products, which are 

 readily volatilized. In point of fact, both volatile gases and 

 readily soluble organic compounds are formed. Amongst the 

 former, carbonic acid and ammonia deserve especial mention ; 

 amongst the latter, soluble humates and ulmates may be named. 

 These ulmates and humates are dark-brown-coloured compounds 

 of humic and ulmic acids, with the alkalies, potash, soda, and am- 

 monia. Ulmic and humic acids in a free state are scarcely 

 soluble in water, and for this reason colour it only light brown. 

 These organic acids have a very powerful affinity for ammonia, 

 in consequence of which they lay hold of any free ammonia, 

 which is generated in the fermentation of dung, and fix it per- 

 fectly, as long as no other compound is present or produced in 

 fermenting dung, which at an elevated temperature again destroys 

 the union of ammonia with humic, ulmic, and similarly consti- 

 tuted acids. Now, ammonia is generated during the putrefaction 

 of the nitrogenized constituents of dung in large quantities, and 

 would be dissipated into the air much more rapidly than is the 

 case in reality, if there were not formed in the dung itself a 

 group of organic compounds, which act as most excellent fixers 

 of the volatile ammonia. I refer to the humus substances, 

 which are gradually produced from the non-nitrogenized consti- 

 tuents of dung. In other words, the straw employed as litter 

 during the putrefaction of dung is to a great extent c jnverted 

 into humic and ulmic acids, which fix to a certain extent the 

 ammonia produced from the more nitrogenous excrementitious 

 matters. The pungent smell of fermenting dung, however, shows 

 that the volatile ammonia cannot be fixed entirely by these 

 means. In the course of this inquiry I shall point out the reason 

 of this, and content myself in this place by saying that the pro- 

 portion of ammonia which passes into the atmosphere from fer- 

 menting dung-heaps, and the loss which hereby is occasioned, is 

 much less considerable than it is generally assumed to be. In 

 fermenting dung-heaps the carbonaceous constituents at first are 

 changed into humus substances, but these are rapidly oxidized 

 by atmospheric oxygen, and partly changed into carbonic acid, a 

 gaseous substance which, in conjunction with oxide of carbon and 

 carburetted hydrogen, is given off abundantly from all putrefying 

 organic matters. 



I have endeavoured to describe briefly the principal changes 

 which take place in the fermentation of farmyard manure. It 

 has been shown : — 



