The gross quantity of wet refuse annually produced in the metropolis, and which consequently has to be removed by one or other of the above means, is, as we have seen,—liquid, 24,000,000,000 gallons; solid, 100,000 tons; or altogether, by admeasurement, 3,820,000,000 cubic feet.
The quantity of this wet refuse which finds its way into the sewers by street and house-drainage is, according to the experiments of the Commissioners of Sewers (as detailed at p. [388]), 10,000,000 cubic feet per day, or 3,650,000,000 cubic feet per annum, so that there remain about 170,000,000 cubic feet to be accounted for. But, as we have before seen, the extent of surface from which the amount of so-called Metropolitan sewage was removed was only 58 square miles, whereas that from which the calculation was made concerning the gross quantity of wet refuse produced throughout the metropolis was 115 square miles, or double the size. The 58 miles measured by the Commissioners, however, was by far the denser moiety of the town, and that in which the houses and streets were as 15 to 1; so that, allowing the remaining 58 miles of the suburban districts to have produced 20 times less sewage than the urban half of the metropolis, the extra yield would have been about 180,500,000 cubic feet. But the greater proportion, if not the whole, of the latter quantity of wet house-refuse would be drained into open ditches, where a considerable amount of evaporation and absorption is continually going on, so that a large allowance must be made for loss by these means. Perhaps, if we estimate the quantity of sewage thus absorbed and evaporated at between 10 and 20 per cent of the whole, we shall not be wide of the truth, so that we shall have to reduce the 182,000,000 cubic feet of suburban sewage to somewhere about 150,000,000 cubic feet.
This gives us the quantity of wet refuse carried off by the sewers (covered and open) of the metropolis, and deducted from the gross quantity of wet house-refuse, annually produced (3,820,000,000 cubic feet), leaves 20,000,000 cubic feet for the gross quantity carried off by other means than the sewers; that is to say, the 20,000,000 cubic feet, if the calculation be right, should be about the quantity deposited every year in the London cesspools. Let us see whether this approximates to anything like the real quantity.
To ascertain the absolute quantity of wet refuse annually conveyed into the metropolitan cesspools, we must first ascertain the number and capacity of the cesspools themselves.
Of the city of London, where the sewer-cesspool details are given with a minuteness highly commendable, as affording statistical data of great value, Mr. Heywood gives us the following returns:—
“House-Drainage of the City.
| “The total number of premises drained during the year was | 310 |
| “The approximate number of premises drained at the expiration of the year 1850 was | 10,923 |
| “The total number of premises which may now therefore be said to be drained is | 11,233 |
| “And undrained | 5,067 |
“I am induced,” adds Mr. Heywood, “to believe, from the reports of the district inspectors, that a very far larger number of houses are already drained than are herein given. Indeed my impression is, that as many as 3000 might be deducted from the 5067 houses as to the drainage of which you have no information.
“Now, until the inspectors have completed their survey of the whole of the houses within the city,” continues the City surveyor, “precise information cannot be given as to the number of houses yet undrained; such information appears to me very important to obtain speedily, and I beg to recommend that instructions be given to the inspectors to proceed with their survey as rapidly as possible.”
Hence it appears, that out of the 16,299 houses comprised within the boundaries of the City, rather less than one-third are reported to have cesspools. Concerning the number of cesspools without the City, the Board of Health, in a Report on the cholera in 1849, put forward one of its usual extraordinary statements.