The average size of the cesspools throughout the metropolis is said, by the Board of Health, to be 9 feet by 6½, which gives a capacity of 58½ cubic feet, and this for 150,000 houses = 8,775,000 cubic feet. But according to all accounts these cesspools require on an average two years to fill, so that the gross quantity of wet refuse annually deposited in such places can be taken at only half the above quantity, viz. in round numbers, 4,500,000 cubic feet. This by weight, at the rate of 35·9 cubic feet to the ton, gives 125,345 tons. This, however, would appear to be of a piece with the generality of the statistics of the Board of Health, and as wide of the truth as was the statement that there was scarcely a house in London without a cesspool, while many had three, four, and even more. But I am credibly informed that the average size of a cesspool is rather more than 5 feet square and 6½ deep, so that the ordinary capacity would be 5¾ × 5¼ × 6½ = 197 cubic feet, and this multiplied by 150,000 gives an aggregate capacity of 29,550,000 cubit feet. But as the cesspools, according to all accounts, become full only once in two years, it follows that the gross quantity of cesspoolage annually deposited throughout the metropolis must be only one-half that quantity, or about 14,775,000 cubic feet.
The calculation may be made another way, viz. by the experience of the nightmen and the sewer-cesspoolmen as to the average quantity of refuse removed from the London cesspools whenever emptied, as well as the average number emptied yearly.
The contents of a cesspool are never estimated for any purpose of sale or labour by the weight, but always, as regards the nightmen’s work, by the load. Each night-cart load of soil is considered, on an average, a ton in weight, so that the nightmen readily estimate the number of tons by the number of cart-loads obtained. The men employed in the cleansing of the cesspools by the new system of pumping agree with the nightmen as to the average contents of a cesspool.
As a general rule, a cesspool is filled every two years, and holds, when full, about five tons. One man, who had been upwards of 30 years in the nightman’s business, who had worked at it more or less all that time himself, and who is now foreman to a parish contractor and master-nightman in a large way, spoke positively on the subject. The cesspools, he declared, were emptied, as an average, by nightmen, once in two years, and their average contents were five loads of night-soil, it having been always understood in the trade that a night-cartload was about a ton.[72] The total of the cesspool matter is not affected by the frequency or paucity of the cleansing away of the filth, for if one cesspool be emptied yearly, another is emptied every second, third, fourth, or fifth year, and, according to the size, the fair average is five tons of cesspoolage emptied from each every other year. One master-nightman had emptied as much as fourteen tons of night-soil from a cesspool or soil-tank, and a contractor’s man had once emptied as many as eighteen tons, but both agreed as to the average of five tons every two years from all. Neither knew the period of the accumulation of the fourteen or the eighteen tons, but supposed to be about five or six years.
According to this mode of estimate, the quantity of wet house-refuse deposited in cesspools would be equal to 150,000 × 5, or 750,000 tons every two years. This, by admeasurement, at the rate of 35·9 cubic feet to the ton, gives 26,925,000 cubic feet; and as this is the accumulation of two years, it follows that 13,462,500 cubic feet is the quantity of cesspoolage deposited yearly.
There is still another mode of checking this estimate.
I have already given (see p. [385], ante) the average production of each individual to the wet refuse of the metropolis. According to the experiments of Boussingault, confirmed by Liebig, this, as I have stated, amounted to ¼ lb. of solid and 1¼ lb. of liquid excrement from each individual per diem (= 150 lbs. for every 100 persons), while, including the wet refuse from culinary operations, the average yield, according to the surveyor of the Commissioners of Sewers, was equal to about 250 lbs. for every 100 individuals daily. I may add that this calculation was made officially, with engineering minuteness, with a view to ascertain what quantity of water, and what inclination in its flow, would be required for the effective working of a system of drainage to supersede the cesspools.[73] Now the census of 1841 shows us that the average number of inhabitants to each house throughout the metropolis was 7·6, and this for 150,000 houses would give 1,140,000 people; consequently the gross quantity of wet refuse proceeding from this number of persons, at the rate of 250 lbs. to every 100 people daily, would be 464,400 tons per annum; or, by admeasurement, at the rate of 35·9 cubic feet to the ton, it would be equal to 16,670,950 cubic feet.
A small proportion of this amount of cesspoolage ultimately makes its appearance in the sewers, being pumped into them directly from the cesspools when full by means of a special apparatus, and thus tends not only to swell the bulk of sewage, but to decrease in a like proportion the aggregate quantity of wet house-refuse, which is removed by cartage; but though the proportion of cesspoolage which finally appears as sewage is daily increasing, still it is but trifling compared with the quantity removed by cartage.
Here, then, we have three different estimates as to the gross quantity of the London cesspoolage, each slightly varying from the other two.
| Cubic Feet. | |
| The first, drawn from the average capacity of the London cesspools, makes the gross annual amount of cesspoolage | 14,775,000 |
| The second, deduced from the average quantity removed from each cesspool | 13,462,500 |
| And the third, calculated from the individual production of wet refuse | 16,670,950 |