PREPARATION OF MANURE. 250 



duces it. It is well known that the dunnf of cattle, fed during winter 

 upon straw, is greatly inferior to that which they yield wtien con- 

 suming food of a more nutritious quality. 



When the litter mixed with animal excrements is accumulated in 

 sufficient quantity in the pit or on the dung stance, fermentation 

 speedily sets in, and abundance of vapor is disengaged. As car- 

 bonate of ammonia is among the volatile products of this decomposi- 

 tion, it is of importance to hold it under control ; this is done by 

 keeping the heap in a state of proper moistness, and in excluding as 

 much as possible the access of air. The daily addition of fresh 

 quantities of litter from the stables and stalls, contributes powerfully 

 to impede the dispersion of the volatile elements, which it is so im- 

 portant to preserve in manure ; duly spread upon the heap, each ad- 

 dition bbcomes, in fact, a fresh obstacle to evaporation ; it forms a 

 covering which plays the part of a condenser, at the same time that 

 it protects the inferior layers from the direct contact of the air. So 

 long as the dung-heap is kept up and attended to in this way, the 

 fermentation is limited to the inferior layers of the mass. Thaer 

 even satisfied himself that air collected from the surface of a dung- 

 heap, undergoing moderate fermentation, does not contain much 

 more carbonic acid than that which is taken from the mass of the 

 atmosphere. Neither does a vessel containing nitric acid, when 

 placed upon the fermenting mass, produce those dense white vapors 

 which are a certain indication of the presence of ammonia. The 

 slow decomposition which it is of so much importance to effect, is 

 not readily secured save in messes sufficiently trodden down, and in 

 which the litter of different kinds has been spread as evenly as pos- 

 sible. 



It is an important point that the manure should be carried out to 

 the field before the upper portions recently added begin to undergo 

 change, otherwise the whole mass enters into full fermentation, and 

 the volatile elements, being no longer arrested by the upper layer, 

 escape and are lost. One means of preventing this loss in any case 

 (which however can but rarely occur) in which there was a neces- 

 sity for suffering the mass to become made through its whole thick- 

 ness, would be to cover it with a layer of vegetable mould, in which 

 the volatile principles would be condensed ; the layer of earth would 

 in fact thus be converted into a most powerful manure. 



The loss of carbonate of ammonia, during the fermentation of 

 farm-dung, is further prevented by the use of certain salts which 

 have the power of changing the volatile carbonate into a fixed salt. 

 It was with a view of bringing a re-action of this kind into play, 

 tlisrt M. Schattenmann, the able director of the manufactories of 

 Bauchsweiler, proposed to add to dung-heaps, in the course of their 

 accumulation and preparation, a certain quantity of sulphate of iron 

 or of sulphate of lime, either of which is decomposed by the carbo- 

 nate of ammonia evolved, and a fixed ammoniacal salt (the sulphate) 

 is produced.* The loss of ammonia from dung-heaps in the course 



* Annales de Chimie, 3e s6rie, t. iv. p. 116. 



