324 Chemical Changes in tlic Fermentation of Dung. 
When such differences are found upon what seems so shnple 
a subject among^ persons to whom confessedly agriculture is much 
indebted, we ought at once to recognize a token of our really 
limited knowledge and to wait patiently the period which will 
enable us to employ such methods of investigation as will lead 
to satisfactory results. Instances need not be multiplied to show 
that whatever conclusions we may adopt must be held subject to 
revision, and as merely the best guides to practice warranted by 
existing data. 
Manure is composed of various animal and vegetable sub- 
stances which have served their purpose in the economy of nature 
and are now to return to corruption, that they may form parts of 
new vegetables, and minister subsequently to the wants of other 
animals. 
The elements of which these refuse matters are composed are 
few though the modes of combination are many. Carbon, oxygen, 
hydrogen, and nitrogen may be taken to represent the organic 
parts of plants and animals, while their inorganic portions appear 
to consist of potash, soda, lime, magnesia, silica, alumina, iron, 
manganese, sulphur, phosphorus and chlorine. The combina- 
tions of these elements in the materials of manure have to be 
broken up and a new series to arise out of their destruction 
before living plants can appropriate any portion to their own 
use, and prepare it in their structures to be fitting nourishment 
for animal life. 
The dissolution of existing combinations and the formation of 
the largest number of suitable new ones is, thus, the aim of the 
farmer in his treatment of manure ; and commonly it will be 
found (ca?teris paribus) that he who accomplishes this end most 
completely and with tlie hast loss of manurial constituents Avill 
obtain the best crops. These changes we have now to inves- 
tigate. 
Animal and vegetable substances may be kept unaltered for 
any length of time provided they are perfectly dry and completely 
protected from the atmosphere, but it is nature's invariable law 
that every organized portion of creation shall pass through a 
process of dissolution when it ceases to live and is subjected to 
atmospheric influence at a temperature above 32° Fahr. In every 
known instance tlie chemical forces acting in the direction of disso- 
lution and reconstruction are stronger than those acting in the con- 
trary direction, and the result is a resolution of the elements 
of organic substances into other, and, generally, simpler com- 
binations. 
In the case to which our inquiries are now directed we are 
safe in asserting that the initiation of decomposition is due to a 
nitrogenized substance, and probably also that the rapidity of the 
