the Progress of English Agriculture. 
831 = 565 
a a suffices to purify effectually large volumes of sewage. The 
jvverful oxidising properties of the air condensed within the 
J res of the soil, and the renewal of the air in the soil, effect an 
a lost perfect destruction of the organic constituents of sewage, 
al their conversion into harmless inorganic compounds. Land 
pperly prepared, and managed so as to admit of downward 
i ermlttent filtration being practised successfully, may be com- 
j ed to a furnace charged with burning fuel. Like the fire in 
a^ood-drawing furnace, a well-drained and fully aerated soil 
I'ns up, or, in chemical language, oxidises, most perfectly the 
pxescible nitrogenous organic matters in sewage, and transforms 
t m into nitrates and other final products of decomposition of 
amal matters, products having no smell, colour, or injurious 
p perties. The soil, it may be observed, has not the power of 
a orbing and retaining chemically the nitrates thus produced, 
a I in consequence the effluent drainage and the liquid mechani- 
cly retained in the land are alike poor in nitrogen and other 
frilising matters, when liquids as dilute as town-sewage are 
pired upon the land. It naturally follows that an accumulation 
0 litrates or organic refuse-matters can as little take place in a 
tl roughly drained and porous soil, so managed as to give full 
stpe to downward intermittent filtration as there can occur an 
aiumulation of half-burned foul products of combustion in the 
clmney of a lighted furnace with a good draught, in which 
ft id gases and organic refuse matters are effectively destroyed 
b fire and air. 
.and, deeply drained, and thoroughly impregnated with air, Soluble 
e:rts the same beneficial influence upon the soluble oraranic 5°''" 
, « • 1 1 • stituents of 
Ci stituents of sewage for any number oi years, provided its dilute sewage 
o; lising powers are not overtaxed in a given time, and a not concen- 
81 icient interval is allowed between the successive operations I'^^^f^' 
, . . - , .p-*, , land by irri- 
01 oncentrated irrigation for the admission of a plentiful supply gation. 
oliir, whereby the purifying oxidising powers of the soil are 
wstantly renewed. With good management, land suitable for 
C(centrated irrigation can never become overcharged with the 
feilising matters of sewage so as to become sewage-sick. 
Iieed, no amount of sewage passed through a soil is capable of 
merially raising its permanent fertility, for no soil has the 
P'er of abstracting from dilute sewage the most valuable fer- 
ti ing matters, of concentrating them in the land, and allowing 
th effluent to pass away deprived to a large extent of its fer- 
ti! ing constituents. In other words, the soluble manuring con- 
st lents of dilute sewage cannot be concentrated in the land by 
ir j;ation. The land is not rendered more fertile if the clear 
seage of 10,000 persons is filtered through an acre, than it is 
w n the sewage from only 1000 persons is passed through the 
OL. XIV.— S. S. 3 K 
