FERTILIZERS. 93 



When the fermentation is going on rapidly, ammonia 

 is sometimes foi-med so fast as to i)roduce a strong, pun- 

 gent odor. ^Ve may determine whether it is cseaping to 

 some extent by suspending over the manure hea}) a piece 

 of litmus ])a[)er in which the l)lue color has been changed 

 to red by dipping it in some ac!d. If there is any ammo- 

 nia escaping, it will gi-adually restore the color from red 

 to blue. 



Slight fermentation would do no harm, and in fact 

 may be of some advantage in converting the elements of 

 manure into availaljle forms, ))rovided there are other 

 substances present ready to unite with the gases, and re- 

 tain them as soon as they are formed, so as to prevent 

 their escape. It is in this way sometimes desirable for 

 special purposes, as in compost heaps. Generally, how- 

 ever, it is to be avoided, since any advantages gained 

 by the process are overbalanced by the loss of escaping 

 gases. 



The ordinary methods of checking fermentation are : — 



(1.) By mixing the manure of different animals. 

 Some kinds of manure are slow to ferment. When 

 these are mixed with other kinds, the fermentation of 

 the mass is checked. 



(2.) By keeping the manure heap wet. A certain 

 amount of moisture aids fermentation, but an excess 

 checks it. It is therefore of some advantage to keep 

 the heap as moist as possiI)le without causing loss by 

 drainage. 



(3.) By keeping the heap trodden down, so as to 

 exclude the air. As the process requires the presence 

 of the atmosphere, it is evident that it may be largely 

 prevented by excluding the air as much as possible. 



F'or this reason it is often of great service to allow 



