1866. | Sewage and Sewerage. 191 
vegetable filter. The growing vegetation, besides setting free into 
the foul water an abundance of purifying oxygen, would build up 
into its own substance a quantity of valuable manurial salts, which 
would make it werth the tarmer’s while to dredge it up and plough 
it into his land. ‘The positive return from such a harvest as this 
would be small indeed as compared with that of the Italian or other 
grass from the meadow, which, in such cases, is unattainable 
ex hypothesi. Still, such a plan, if not positively profitable, would 
at least be negatively so, by destroying the mischievous and morbific 
properties of the sewage it dealt with; and thus, as, with the 
exception of vice, nothing is so expensive as disease, it would effect 
a real economy. We believe that if a sufficient amount of ditch 
network were employed, the water which would flow out from the 
further outlet of the maze would be wellnigh as clear and pure as 
that which has received the orthodox amount of filtration through 
four feet of soil, prescribed and followed at Croydon. The account 
recently given to the world by the Metropolitan Main Drainage 
Committee, of the application of the irrigation system to this place 
and of its results, we herewith append. 
“ After Rugby, your Committee visited Croydon, where they found 
the application of the sewage carried out with far greater complete- 
ness. The land treated is immediately adjoming Boddington Park, 
and consists of 250 acres of loamy soil, running into sand and 
resting on the chalk. There is a gentle inclination of the service 
of the whole towards the Wandle, very favourable to the operation 
to be performed. The sewage is coarsely filtered, and carried by 
gravitation through an open cut to the edge of the farm; from this 
cut it is distributed by small grips or drains, and made to overflow 
by extemporized sluices inserted here and there by the labourers. 
The population whose excreta flows over this land 1s about 17,000 
in number, from which 3,000 tons per acre per annum are said to 
be derived ; one-tenth of the land is under irrigation at a time, and 
each acre is under treatment thirty-six days in the year. The 
sewage takes about five hours in flowing over the land from the 
time of leaving the inlet; that period is sufficient entirely to 
deodorize it, and to enable the herbage to abstract from it the 
fertilizing salts; after the process has been continued two or three 
days, it flows off nearly tasteless, colourless, and inodorous. The 
greater portion of the farm is sown with Italian rye-grass, which 
requires resowing every three years, and appears to produce the 
largest results; but some parts are still in natural pasture. It is 
rented by the Croydon Local Board at 47. per acre, and is sub-let 
to Mr. Marriage at 5/. per acre, so that the Local Board obtain an 
improved rent of 250/. per annum, which goes in reduction of their 
local rates. Your Committee could not ascertain the exact weight 
of grass produced. It is cut four times a year, and each cutting 
