14 FARMYARD MANURE. 



of organic substances, the quantity of which during the process 

 of fermentation must decrease in a corresponding relative degree. 

 Thus the total amount of organic and inorganic matters in fresh 

 dung, dried at 212 Fahr., is, , 



Organic matters 83*48 



Inorganic matters 16*52 



100-00 

 Whilst in rotten dung there are in 100 



Organic substances 68*24 



Mineral substances 31*76 " 



100*00 



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 

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

 soluble in water, and for this reason colour it only a 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 constituents 

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

 the putrefaction of dung is to a great extent converted 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 proportion 



