8 A PRACTICAL TREATISE 



when combined with other substances, and in other stages of 

 preparation, from those of which tliey were possessed in a 

 simple state. 



The process of fermentation likewise requires extreme care, 

 and is an object very imperfectly understood. It is often con- 

 founded with that ebullition, or hissing- noise, which may be 

 noticed when limestone or other alkaline matter is mixed with 

 vinegar or other acids ; but this effervescence is merely oc- 

 casioned by the escape of fixed air, (carbonic acid gas ) and 

 thoug-h the word 'fermentation' may be retained in compliance 

 with common usage, it has nothing in unison with those opera- 

 tions which are properly termed the vinous, the acetous, and 

 the putrefactive Jfer mentations. 



Of these, the first causes the sweet materials to become 

 spirituous, though the latter quality applies more particularly 

 to the juices of fruits ; the second occasions a sourness, which 

 in liquids produces vinegar; and the third is productive of 

 putrefaction. 



During the process of fermentation, as applied to manure, it 

 heats, after more or less time, according to its contents, and at 

 last it is converted into mucilage and salts. The latter part 

 of this operation is the most important, for it requires great 

 care to ascertain, by mixing the whole mass well together, 

 that every part of it is in the same state of fermentation, lest 

 some parts of it should reach the last stage — which produces 

 salts — before the other portion has become mucilaginous, — an 

 accident which frequently happens when lime is laid among 

 dung without being well mixed throughout the heap, by which 

 much of its benefit is lost, as it acts as a stimulant, and becomes 

 hurtful if not used in a very small proportion. 



The materials of which the first-mentioned of these manures 

 are chiefly composed, are stable-dung and litter, urine, night- 

 soil, and all weeds or other vegetable substances which can 

 be converted into muck, together with the putrid remains of 

 animals and fish — which may be all classed under the common 

 name o'l putrescent manures. 



Then chalk, lime, marl, gypsum, shells, ashes, soapers' waste, 

 and burnt clay, which, being fossil, or of the nature of fossil 

 substances, fall under the denomination of mineral manures. 



And lastly, green crops ploughed down, as well as tlie 

 various articles made use of^ as top-dressings and composts, 

 which may be generally designated as JuisccWu/eous manures. 



These will become the subject of separate chapters ; but it 



