ON MANURES. 45 



positive effects upon vegetation are still so doubtful that the 

 degree can only be ascertained by observation. The main 

 agents of the process are water, heat, and air. If a dung-lieap 

 be much wetted, the operation proceeds very slowly; but when 

 only moisture is retained sufficient to condense it, then it pre- 

 sently heats, and the fermentation proceeds so violently that, 

 if not checked, a large portion of its bulk seems to escape by 

 evaporation ; though, if this be only the effect of the condensa- 

 tion of its materials, and if its weight be not also reduced, the 

 residue may perhaps be thus rendered more nutritive. The 

 opposite result may, however, be the fact ; for it may be ob- 

 served that, if a quantity of farm-yard dung be removed from 

 a dung-hill and turned loosely to the air, though it may be 

 cool at first, yet, if moderately wet, it will soon generate 

 heat; it will smoke violently, and emit a very pungent 

 effluvium: from which it may be conjectured, that the nutri- 

 tive properties of the manure would have been better pre- 

 served if it had not been exposed to further fermentation. 

 Care should therefore be taken to preserve those exhalations 

 from being dissipated, and it will be probably found that the 

 object will be sufficiently attained if the vegetative power of 

 seed-weeds be destroyed, and the fibres of the straw be reduced 

 to the state of spit-dung. 



Some fermentation will necessarily be ever going on in 

 the dung-heap; but there is little danger of its being carried 

 too far if the ingredients which it contains be well and pro- 

 perly mixed. If horse-dung alone be employed, it will soon 

 proceed to an excess, occasioned by its own internal heat, that 

 will deprive it of every fertilizing quality; but if mixed with 

 the cooler dung of horned cattle, that risk will be in a great 

 measure avoided. Then, if the dry contents of the covered 

 sheds be also added to the mass of wet litter in the straw-yard, 

 the whole mixture will undoubtedly not ferment beyond the 

 point best suited to render it immediately available. 'In a 

 large dung-hill, of such a mixture, the heat of the active fer- 

 mentation subsides in it long before any of its useful parts are 

 destroyed, and long before even all the water which it contains 

 is evaporated out of it ; for, on examination, the manure will 

 be found to be quite short, and easily lifted with the fork or 

 shovel ; while, at the same time, it will be saturated with the 

 richest black-coloured juices, which appear to be the essential 

 parts of urine deprived of their water.' We, therefore, con- 

 sider it as the opinion of a large majority of the most intelli- 



