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SCIENTIFIC SUMMARY. 
^c>^ 
AGRICULTURE. 
Value of Sewage as Manure. — It is well that the farming world should 
know that, although the sewage of large towns contains many of the ingre- 
dients of plants, and will, on the first application to a soil produce an increased 
crop, it is, nevertheless, not to be regarded as a true manure. Sewage does 
not contain aU the mineral ingredients of plants, and hence cannot be 
depended on by the agriculturist for the restoration of the plant-ashes to the 
soil. These facts have very recently been urged upon the attention of the 
English public by Baron Liebig, who addressed a long letter upon the sub- 
ject to Lord Robert Montagu, M.P. In what may be termed its natural 
state, says the Baron, sewage is not a universal manure like stable dung, 
which is efficacious at all times and in all localities, but a special manure, the 
continued application of which tends to impoverish the land. Stable dung 
contains all, a special manure only some, of the elements which ought to be 
restored to the soil in order to make it permanently fertile. Peruvian guano, 
for example, belongs to the class of special manures ; and experience has 
shown that in certain countries {e.g., Germany and Scotland), the application 
of guano to meadow land, which produced, in the first year, enormous crops 
of grass or hay, had later no effect at all ; and that the same man who at first 
overrated the use of guano, eventually cursed its employment. Sewage con- 
tains ammonia, potash, and phosphoric acid, like guano, but phosphoric acid 
in much smaller 'proportion. On a soil rich (in its natural state) in phos- 
phoric acid, sewage will have an excellent effect ; it will produce, for instance, 
large crops of grass, turnips, and corn if the soil supplies the quantity of 
phosphoric acid wanting in the sewage ; but, as in each successive crop a 
certain quantity of phosphoric acid is abstracted, the total quantity in the soil 
is, by continual application of the sewage, gradually diminishing every year, 
and a time must arrive when the phosphoric acid will be insufficient for 
further crops, and when sewage will cease to produce its former effects. Such 
being the probable results of the application of sewage per se, there are two 
things to be done : Firstly, it must be made intelligible to all that sewage 
matter in its natural state does not replace stable-manure, and that if used 
exclusively it will produce abundant crops onl'g for a time ; secondly, the 
farmer must be made acquainted with the names of those ingredients which 
it wiU be necessary to add to the sewage in. order to render it a permanent 
and useful manure. Baron Liebig suggests that — the composition of sewage 
being known — a recipe should be placed in the hands of the farmer, for the 
additional elements to be employed. — Vide Letter to the Times, November. 
The Manure Manufactor'y at Auhervilliers. — This enormous factory is 
