26 



resins, and wax, are more susceptible of change than woody 

 fibre when exposed to air and water, but much less liable than 

 the other vegetable compounds: and even the most inflammable 

 substances, by the absorption of oxygen become gradually solu- 

 ble in water. 



Animal matters, in general, are more liable to decompose than 

 vegetable substances: oxygen is absorbed, and carbonic acid and 

 ammonia formed, in the process of their putrefaction. They 

 produce foetid compound elastic fluids, and likewise azote ; they 

 afford dark-coloured acid, and oily fluids, and have a residuum 

 of salts and earths mixed with carbonaceous matter. 



The principal substances which constitute the different parts 

 of animals, or which are found in their blood, their secretions, or 

 their excrements, have been classed and analyzed by Sir Hum- 

 phrey Davy and others. It is unnecessary to describe these mi- 

 nutely, but merely to state that a difference exists in each, and 

 that the ammonia given off from animal compounds in putrefac- 

 tion may be conceived to be formed, at the time of their decom- 

 position, by the combination of hydrogen and azote. Except thia 

 matter, the other products of putrefaction are analogous to those 

 afforded by the fermentation of vegetable substances ; and the 

 soluble substances formed abound in the elements which are the 

 constituent parts of vegetables, in carbon, hydrogen, and oxygen. 



Whenever manures consist principally of matter soluble in 

 water, it is evident that their fermentation or putrefaction should 

 be prevented as much as possible ; and the only cases in which 

 these processes can be useful are when the manure consists prin- 

 cipally of vegetable or animal fibre. The circumstances necessary 

 for the putrefaction of animal substances, and also of vegetables, 

 are, a temperature above the freezing point, and the presence of 

 oxygen at least in the first stage of the process. To prevent 

 manures from decomposing, they should be preserved dry, de- 

 fended from the contact of air, and kept as cool as possible. 



As different manures contain different proportions of the ele- 

 ments necessary to vegetation, so they require a different treat- 

 ment to enable them to produce their full effects in agriculture- 



All green succulent plants contain saccharine or mucilaginous 

 matter, with woody fibre, and readily ferment. They cannot, 



