S34 SCIENCE OF AGRICULTURE. Part II. 



tively small effect, for gases soon become diffused tlirough the mass of the surrounding 

 air. The great object, therefore, in the application of manure should be to make it af- 

 ford as much soluble matter as possible to the roots of the plant ; and that in a slow and 

 gradual manner, so that it may be entirely consumed in forming its sap and organised 

 parts. 



2228. Mucilaginous, gelatinous, saccharine, oily, and extractive fluids, carbonic acid, and 

 water, are substances that in tlieir unchanged states contain almost all the principles ne- 

 cessary for the life of plants ; but there are few cases in which they can be applied 

 as manures in their pure forms ; and vegetable manures, in general, contain a great ex- 

 cess of fibrous and insoluble matter, which must ^mdergo chemical change, before it can 

 become the food of plants. 



2229. The nature of the changes on these substances ; of the causes which occasion them, 

 and which accelerate or retard them ; and of the products they afford, have been scienti- 

 fically stated and explained by our great agricultural chemist. If any fresh vegetable matter 

 which contains sugar, mucilage, starch, or other of the vegetable compounds soluble in 

 water, be moistened, and exposed to air, at a temperature from 55 to 80, oxygen will 

 soon be absorbed, and carbonic acid formed ; heat will l>e produced, and elastic fluids, 

 principally carbonic acid, gaseous oxide of carbon, and hydro-carbonate will be evolved ; 

 a dark-coloured liquid, of a slightly sour or bitter taste, will likewise be formed ; and if 

 the process be suffered to continue for a time sufficiently long, nothing solid will remain, 

 except earthy and saline matter, coloured black by charcoal. The dark-coloured fluid 

 formed in the fermentation always, contains acetic acid ; and when albumen or gluten 

 exists in the vegetable substance, it likewise contains volatile alkali. In proportion as 

 there is more gluten, albumen, or matters soluble in water, in the vegetable substances 

 exposed to fermentation, so in proportion, all other circumstances being equal, will the 

 process be more rapid. Pure woody fibre alone undergoes a change very slowly ; but 

 its texture is broken down, and it is easily resolved into new aliments, when mixed with 

 substances more liable to change, containing more oxygen and hydrogen. Volatile and 

 fixed oils, 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 

 soluble in water. Animal matters in general are more liable to decompose than vege- 

 table substances ; oxygen is absorbed and carbonic acid and ammonia formed in the 

 process of their putrefaction. They produce fetid, compound, elastic fluids, and like- 

 wise azote : they afford dark-coloured acid and oily fluids, and leave a residuum of salts 

 and earths mixed with carbonaceous matter. 



22S0. The principal animal substances which constitute their different parts, or which 

 are found in their blood, their secretions, or their excrements, are gelatine, fibrine, 

 mucus, fatty or oily matter, albumen, urea, uric acid, and other acid, saline, and earthy 

 matters. 



2231. General treatment of organic manures. 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 principally of vegetable or animal fibre. The circum- 

 stances necessary for the putrefaction of animal substances are similar to those required 

 for the fermentation of vegetable substances ; a temperature above the freezing point, the 

 presence of water, and the presence of oxygen, at least in the first stage of the process. 

 To prevent manures from decomposing, they should be preserved dry, defended from the 

 contact of air, and kept as cool as possible. Salt and alcohol appear to owe their 

 powers of preserving animal and vegetable substances to their attraction for water, by 

 which they prevent its decomposing action, and likewise to their excluding air. 



SuBSECT. 2. Of the different Species of Manures of Animal and Vegetable Origin. 



2232. The properties and nature of the manures in common use should be known to 

 every cultivator : for as different manures contain different proportions of the elements 

 necessary to vegetation, so they require a different treatment to enable them to produce 

 their full effects in culture. 



2233. All green succulent plants contain saccharine or mucilaginous matter, with woody 

 fibre, and readily ferment. They cannot, therefore, if intended for manure, be used too 

 soon after their death. Hence the advantage of digging or ploughing in green crops, 

 whether natural or sown on purpose ; they must not, however, be turned in too deep, 

 otherwise, as Mrs. Ibbetson has shown (Philos. Mag. 1816), fermentation will be pre- 

 vented by compression and exclusion of air. Green crops should be ploughed in, if it 

 be possible, when in flower, or at the time the flower is beginning to appear ; for it is at 

 this period that they contain the largest quantity of easily soluble matter, and that their 

 leaves are most active in forming nutritive matter. Green crops, pond-weeds, or the 

 parings of hedges or ditches, require no preparation to fit them for manure, nor does any 



