Chemical Changes in the Fermentation of Dung. 
329 
acts upon a solution of pure sujjar. The bodies in question 
absorb oxygen when they are subjected to the influence of the 
ferment and they then enter upon a state of change. Each fer- 
menting portion becomes itself a cause of fermentation to other 
portions which are in contact with it — as the rotten apple de- 
stroys the sound ones which touch it — and thus the action con- 
tinues till tlie whole is fermented. 
Originally the nitrogen of the decaying substances was vari- 
ously combined with carbon, oxygen, and hydrogen, but when it 
leaves its former arrangement in obedience to the action of de- 
caying bodies it uniformly adopts one and only one new one. 
Every azotized compound exposed to air and moisture liberates 
its nitrogen to finite witli free hydrogen and form ammonia. This 
is a principle of fermentation lohich admits of no exception. Wc are 
acquainted with no instance in which the nitrogen of organic com- 
pounds, fermenting under those conditions, combines with oxygen 
until it have first formed ammonia with hydrogen, but after the 
formation of ammonia oxides of nitrogen are formed with facility. 
Tliis is a well-known cause of difficulty in nitrogen determinations 
in organic analysis, and it brings before us the important fact that 
before the farmer can obtain any nitrates for his crops he must 
incur risk of loss by the formation of volatile ammonia. Does 
it not also press upon him the wisdom of taking all possible 
precaution to consei've the latter that, by its oxidation in the pre- 
sence of lime and other alkaline bases, his fields may be supplied 
witli abundance of the former ? 
All known fixers of ammonia, &c. are too costly for use, and, 
if they were not, are every way inferior to nature's fixer Earth. 
I shall not extend the limits of this paper by a chemical discussion 
of tliis topic, but will refer the reader to the experiments by 
Mr. Thompson and Mr. Way which have been published in the 
Society's Journal, and to the following from Liebig : — 
" The oxides of iron and alumina are distinguished from all other metallic 
oxides by their power of forming solid compounds with ammonia. The pre- 
cipitates obtained by the addition of ammonia to salts of alumina or iron are 
true salts in which the ammonia is contained as a base Some 
varieties of alumina (pipeclay for instance) emit so much ammonia when 
moistened witli caustic potash that even after they have been exposed for two 
days reddened litmus paper held over them becomes blue Soils 
therefore wliich contain oxides of iron and burnt (?) clay act precisely as a 
mineral acid would do if extensively spread over the surface (or among the 
manure) ; with this difference, that the acid would penetrate the ground, 
enter into combination with lime, alumina and other bases, and thus lose in a 
few hours its property of absorbing ammonia from the atmosphere 
The ammonia absorbed by tlie clay or ferruginous oxide is separated by every 
shower of rain and conveyed in solution to the soil." 
Having made an extensive series of experiments extending 
over four years I shall merely give a few of them to illustrate 
