328 Chemical Changes in the Fermentation of Dung. 
as every one knows by experience, and as he might perceive must 
he the case by inspecting the chemical formulae of the substances 
undergoing decomposition. A large quantity of ready formed 
water is added in the excrements of animals, which probably 
never contain less than 90 per cent., and the sum of this existing 
and generated moisture is increased b}^ the rainfall. Yet we 
see every heap, made of horse dung alone, burnt, and often those 
of an ill-managed farm-yard are in the same condition. What 
renders the case more noticeable, is, that the burning is tlie worst 
when the evaporation is the greatest, and no spectacle is more 
lamiliar to an observer of the fermentation of manure tlian a 
cloud of white vapour which completely conceals the workmen 
who are removing a heap of ' firefanged ' horse dung. 
But every particle of that exhaling moisture was designed by a 
beneficent Providence to be condensed into a liquid chai-ged with 
the precious burden which it is now bearing away on the wings 
of the wind. Elements of corn and cattle are volatilizing with 
every grain of the steam, and (in towns) are becoming sources of 
disease and death to those whom, if differently managed, they 
might feed ! And why ? Simply because man will defeat nature. 
Nature designed putrefaction (combustion) to he sloro, and to that 
end required all decomposing refuse to be buried, in which case 
its slow but useful conversion was certain. Man on the other 
hand places the waste substances so that the combustion may be 
rapid. He employs the light porous material straw to mix with 
animal excreta, and places the whole so as to ensure a free passage 
of oxygen among the putrefying mass. The rapid burning of 
sticks is ensured by their being laid carefully across each other 
so as to afford the readiest access to the atmospheric oxygen, 
and this is a close approximation to the state of dung tlirown 
lightly into a pit. The heat generated during its combustion 
converts the water of the burning wood into steam which passes 
freely and rapidly up the chimney, and that of dung may be seen 
in a still dewy morning forming a column of some twenty feet in 
height above its source. 
But suppose all the water had been retained by the heap. 
Suppose tlie oxygen had been supplied to the decaying mass as 
it is supplied in the soil, abundantly but yet slowly, would there 
have been any firefang, or would the ammonia and other valu- 
able products have flown away almost as quickly as they were 
generated ? We are always wrong when we can perceive a law 
of nature and do not conform to it. 
It has been already observed that the fermentation of the mass 
of materials which constitute a manure heap is begun by the 
putrefaction of some of the nitrogenized compounds which abound 
in it, and which act upon those in contact with them as yest 
