210 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
by the agency of microscopic organisms. This change is termed 
nitrification, and is due to the Hfe-work of certain micro-organisms 
present more or less in all soils. Amongst these* Bacillus 
tardecrescens, Bacterium iirece, and Bacillus fluorescens all 
nitrify organic matter (like urea), forming small quantities of 
nitrates. 
One of the first products formed during the nitrification of 
organic matter is ammonia. The ammonia is then oxidised and 
becomes nitric acid. The nitric acid combines with certain 
bases (like potash, soda, and lime) already in the soil, forming 
nitrates which are soluble in water, and which thereby become 
valuable plant-foods. 
Other changes besides nitrification occur in the organic 
matter of stable manure during its fermentation. One of these 
is the oxidation of the carbo-hydrates. The carbon of these 
substances is converted into carbonic and organic acids. These 
acids are neutralised by the potash, lime, &c., of the soil, at the 
same time producing active and dormant plant-foods. 
The temperature of fermentation should not be allowed to 
rise in the centre of the heap above 150 Fahr., as loss of am- 
monia is the result. It should be regulated by water, or, as was 
before stated, by pumping liquid manure over the heap. 
The heap should not be drenched, or the valuable nitro- 
genous compounds will run into the drains. A strong odour 
coming from the heap shows that a wasteful fermentation is 
going on. If the manure contains too small a proportion of 
litter, the urea contained in the urine is quickly converted into 
ammonium carbonate, which is a very valuable compound. 
The volatile ammonium carbonate may be " fixed " by watering 
the manure heap with a solution of commercial iron sulphate. 
It is also recommended to spread on the floors of stables, cow- 
houses, &c., sawdust moistened with a solution of iron sulphate. 
Variation in the Composition of Stable and Farmyard Manure* 
1. According to the animals from which it is produced. 
Stockhardt states that, amongst all the herbivorous iinimals, the 
excreta of cows contain the smallest quantity of nitrogen with 
the largest amount of water ; and that they pass but slowly into 
* Sec Nature, Oct. 13, 1892, p. 57G. 
