260 PREPARATION OF MAPnJRE. 



of regulated fermentation, must not however be estimated too hignly ; 

 when the decomposition is carefully conducted, the mass having 

 ^een well trodden and properly damped, the loss is really very small. 

 The gentle fermentation, secured by these means, has characters 

 which differ essentially from those that accompany the rapid putre- 

 faction which never fails to take place when matters are not well 

 managed. As an example of the rapid and injurious fermentation 

 of which I speak, I may cite that which frequently takes place in 

 piles of horse-dung : every one must have seen such dung-hills 

 loosely thrown together, left to themselves, without any addition of 

 water, acquiring a very intense heat in the course of a few days, 

 and have even heard of their taking fire. I have seen piles of this 

 kind reduced to their merely earthy constituents! Such are never 

 the results of the moderate and gradual decomposition which farm- 

 dung ought never to exceed. When the pit or stance is emptied, 

 in which a slow and equal fermentation has taken place, the superior 

 layer is seen to be very nearly in the same state in which it was 

 when it was piled ; the layer immediately beneath this one is chang- 

 ed in a greater degree, and sometimes exhales a slight ammoniacal 

 odor. In the lower strata, the modification is yet greater in degree : 

 the straw has lost its consistency, it is fibrous and breaks into pieces 

 with the greatest ease ; the mass is also progressively darker in 

 color as we go deeper, and on the ground it is completely black ; 

 the smell which this part of the heap exhales, is that of sulphuretted 

 hydrogen, and when it is tested, sulphate of iron is discovered ; no 

 doubt these sulphurous products are all the consequence of the de- 

 composition, under the influence of the organic matter, of the sul 

 phates which were contained in the manure. This is the sign by 

 which I know that farm-dung is duly prepared ; the presence of 

 sulphurets and of the hydrosulphate of ammonia will have no ill 

 effect upon vegetation ; for scarcely is the manure spread upon the 

 ground, than these products are changed into sulphates, and then 

 the manure emits that musky smell which is peculiar to it. Fur- 

 ther, there is no doubt but that the state in which a carefully tended 

 dung-heap is found in the end, is due to the circumstances in which 

 it has been placed and kept during the whole time of its preparation ; 

 its constituent elements would have gone through a totally different 

 course in the progress of their modification had they been left ex- 

 posed to the open air. To be satisfied of this, it is enough to re- 

 mark the powerful and purely ammoniacal smell which meets us in 

 a warm stable, especially during the summer season, upon the ground 

 of which the urine of the animals it contains is left to decompose. 



From what has now been said, it will be understood how destruc- 

 tive to good manure is the custom which obtains in certain countries 

 of turning dung-heaps frequently, of airing them as it were, in order 

 to hasten decomposition. Treated in this way, stable litter, &c., 

 does in fact decompose much more rapidly ; but it does so, and I 

 own that I do not myself clearly perceive the object proposed by it, 

 %t the expense of the quality ; for it is very evident that the volatile 



