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parts of them as are rendered gaseous, and that pass into the 

 atmosphere, must produce a comparatively small effect, for gasea 

 soon become diffused through the mass of the surrounding air. 

 The great object in the application of manure should be to 

 make it afford 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 organized 

 parts. Mucilaginous, gelatinous, saccharine, oily, and extractive 

 fluids, and solution of carbonic acid gas in water, are substances 

 that, in their unchanged state, contain almost all the essentials 

 necessary for the life of plants; but there are few cases in 

 which they can be applied in their pure form : and vegetable 

 manures, in general, contain a great excess of fibrous and in- 

 soluble matter, which must undergo chemical changes before 

 they can become the food of plants. 



It will be proper to explain the nature of these changes, of 

 the causes which occasion them, and which accelerate or retard 

 them ; also of the products they afford. 



"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 

 degrees, oxygen will soon be absorbed, and carbonic acid formed : 

 heat will be produced, and elastic fluids (principally carbonic 

 acid gas, gaseous oxide of carbon, and hydro-carbonate) will be 

 evolved, and a dark-coloured liquid, of a slightly sour or bitter 

 taste, will likewise be formed ; and if the process be suffered 

 to continue sufficiently long, nothing solid will remain except 

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

 coloured fluid formed in the fermentation always contains acetic 

 acid, and when albumen or gluten exists in the vegetable sub- 

 stance it likewise contains volatile alkali. In proportion as there 

 is more gluten, albumen, or matter 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 elements when mixed with substances more liable to change, 

 containing more oxygen and hydrogen. Volatile and fixed oils, 



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