FARMYARD MANURE. 13 



some more readily, others more slowly. Those organic substances 

 which, like straw, contain but little nitrogen, on exposure to air 

 and moisture at a somewhat elevated temperature decompose 

 spontaneously and slowly, without disengaging any noxious smell. 

 On the other hand, the droppings of animals, and especially their 

 urine, which is rich in nitrogenous compounds, rapidly enter 

 into decomposition, producing disagreeable-smelling gases, In a 

 mixture of nitrogenous substances and organic matters free from 

 nitrogen, the former are always first affected by putrefaction ; 

 the putrefying nitrogenised matters then act as a ferment on 

 the other organic substances, which by themselves would resist 

 the process of spontaneous decomposition much longer. Without 

 air, moisture, and a certain amount of heat, organic matters can- 

 not enter into putrefaction. These conditions exist in the drop- 

 pings of cattle and the litter of the stables, hence putrefaction 

 soon affects fresh dung. Like many chemical processes, putre- 

 faction is accompanied with evolution of heat. Air and water 

 exercise an important influence on the manner in which the de- 

 composition of organic matters proceeds. Both are absolutely 

 requisite in order that putrefaction may take place. Perfectly 

 dry organic substances remain unaltered for an indefinite period, 

 as long as they are kept perfectly dry. But too large an amount 

 of water, again, retards the spontaneous decomposition of organic 

 substances, as it excludes the access of air and prevents the ele- 

 vation of temperature, both of which conditions greatly increase 

 the rapidity with which organic matters are decomposed. Al- 

 though air is an essential element in the putrefaction of organic 

 matters the unlimited access is unfavourable to this process of 

 spontaneous decomposition, and is productive of new changes. 

 In farmyard manure the unlimited access of air is prevented by 

 the compact nature of dung-heaps, consequently only a limited 

 quantity of air can find its way into the interior of the mass. 

 During the fermentation of fresh dung, disagreeable smelling 

 gases are given off. These arise principally from the sulphur, 

 and from the phosphorus of the nitrogenized compounds present 

 in dung. A considerable proportion of this sulphur and the 

 phosphorus combine with hydrogen, and form sulphuretted and 

 phosphoretted hydrogen two extremely nauseous gases, which 

 both escape from fermenting dung-heaps. Another portion of 

 the sulphur and the phosphorus unites with atmospheric oxygen, 

 and in the presence of porous substances becomes changed into 

 sulphuric and phosphoric acid, two non-volatile compounds, 

 which are left behind. 



We have seen the relative proportion of inorganic matters in 

 well-rotten dung is much greater than in fresh. This increase 

 in mineral matters can have only been produced at the expense 



