Imágenes de páginas

much more expensive in construction, and require much attention and labor for repairs, and cleansing, than do the stone-ware pipe sewers which are now universally adopted wherever measures are taken to investigate their comparative merits. An example of the difference between the old and modern styles of sewers is found in the drainage of the Westminster School buildings, etc., in London. The new drainage conveys the house and surface drainage of about two acres on which are fifteen large houses. The whole length of the drain is about three thousand feet, and the entire outlet is through two nine inch pipes. The drainage is perfectly removed, and the pipes are always clean, no foul matters being deposited at any point. This drainage has been adopted as a substitute for an old system of sewerage of which the main was from 4 feet high, by 3 feet 6 inches wide, to 17 feet high and 6 or 7 feet wide. The houses had cess-pools beneath them, which were filled with the accumulations of many years, while the sewers themselves were scarcely less offensive. This condition resulted in a severe epidemic fever of a very fatal character. An examination instituted to discover the cause of the epidemic resulted in the discovery of the facts set forth above, and there were removed from the drains and cesspools more than 550 loads of ordure. The evaporating surface of this filth was more than 2000 square yards. Since the new drainage, not only has there been no recurrence of epidemic fever, but “a greater improvement in “the general health of the population has succeeded than “might be reasonably expected in a small block of houses, “amidst an ill-conditioned district, from which it cannot be “completely isolated.” The principle which justifies the use of pipe sewers is precisely that which has been described in recommending small tiles for agricultural drainage, to wit: that therapidity of a flow of water, and its power to remove obstacles, is in proportion to its depth as compared with its width. It has been found in practice, that a stream which wends its sluggish way along the bottom of a large brick culvert, when concentrated within the area of a small pipe of regular form, flows much more rapidly, and will carry away even whole bricks, and other substances which were an obstacle to its flow in the larger channel. As an experiment as to the efficacy of small pipes Mr. Hale, the surveyor, who was directed by the General Board of Health of London to make the trial, laid a 12-inch pipe in the bottom of a sewer 5 feet and 6 inches high, and 3 feet and 6 inches wide. The area drained was about 44 acres. He found the velocity of the stream in the pipe to be four and a half times greater than that of the same amount of water in the sewer. The pipe at no time accumulated silt, and the force of the water issuing from the end of the pipe kept the bottom of the sewer perfectly clear for the distance of 12 feet, beyond which point some bricks and stones were deposited, their quantity increasing with the distance from the pipe. He caused sand, pieces of bricks, stones, mud, etc., to be put into the head of the pipe. These were all carried clear through the pipe, but were deposited in the sewer below it. It has been found by experiment that in a flat bottomed sewer, four feet wide, having a fall of eight inches in one hundred feet, a stream of water one inch depth, runs very sluggishly, while the same water running through a 12inch pipe, laid on the same inclination, forms a rapid stream, carrying away the heavy silt which was deposited in the broad sewer. As a consequence of this, it has been found, where pipe sewers are used, even on almost imperceptible inclinations, that silt is very rarely deposited, and the waste matters of house and street drainage are carried immediately to the outlet, instead of remaining to ferment and poison the atmosphere of the streets through which they pass. In the rare cases of obstruction which occur, the pipes are very readily cleansed by flushing, at a tithe

[ocr errors]

of the cost of the constant hand-work required in brick Se WerS. For the first six or seven hundred feet at the head of a sewer, a six inch pipe will remove all of the house and street drainage, even during a heavy rain fall; and if the inclination is rapid, (say 6 inches to 100 feet,) the acceleration of the flow, caused partly by the constant additions to the water, pipes of this size may be used for considerably greater distances. It has been found by actual trial that it is not necessary to increase the size of the pipe sewer in exact proportion to the amount of drainage that it has to convey, as each addition to the flow, where drainage is admitted from street openings or from houses, accelerates the velocity of the current, pipes discharging even eight times as much when received at intervals along the line as they would take from a full head at the upper end of the sewer. For a district inhabited by 10,000 persons, a 12-inch pipe would afford a sufficient outlet, unless the amount of road drainage were unusually large, and for the largest sewers, pipes of more than 18 inches diameter are rarely used, these doing the work which, under the old system, was alloted to a sewer 6 feet high and 3 feet broad. Of course, the connections by which the drainage of roads is admitted to these sewers, must be provided with ample silt-basins, which require frequent cleaning out. In the construction of the sewers, man-holes, built to the surface, are placed at sufficient intervals, and at all points where the course of the sewer changes,so that a light placed at one of these may be seen from the next one;—the contractor being required to lay the sewer so that the light may be thus seen, a straight line both of inclination and direction is secured. The rules which regulate the laying of land-drains apply with equal force in the making of sewers, that is no part of the pipe should be less perfect, either in material or construction, than that which lies above it; and where the inclination becomes less, in approaching the outlet, siltbasins should be employed, unless the decreased fall is still rapid. The essential point of difference is, that while land drains may be of porous material, and should have open joints for the admission of water, sewer pipes should be of impervious glazed earthen-ware, and their joints should be securely cemented, to prevent the escape of the sewage, which it is their province to remove, not to distribute. Drains from houses, which need not be more than 3 or 4 inches in diameter, should be of the same material, and should discharge with considerable inclination into the pipes, being connected with a curving branch, directing the fluid towards the outlet. In laying a sewer, it is customary to insert a pipe with a branch opposite each house, or probable site of a house. It is important that, in towns not supplied with water. works, measures be taken to prevent the admission of too much solid matter in the drainage of houses. Water being the motive power for the removal of the solid parts of the sewage, unless there be a public supply which can be turned on at pleasure, no house should deliver more solid matter than can be carried away by its refuse waters.

The drainage of houses is one of the chief objects of sewerage.

In addition to the cases cited above of the model lodging houses in Lambeth Square, and of the buildings at Westminster, it may be well to refer to a remarkable epidemic which broke out in the Maplewood Young Ladies’ Institute in Pittsfield, Mass., in 1864, which was of so violent and fatal a character as to elicit a special examination by a committee of physicians. The family consisted, (pupils, servants, and all,) of one hundred and twelve persons. Of these, fifty-one were attacked with well-defined typhoid fever during a period of less than three weeks. Of this number thirteen died. The following is extracted from the report of the committee: “Of the 74 resident pupils heard from, 66 are reported “as having had illness of some kind at the close of the “school or soon after. This is a proportion of # or nearly “90 per cent. Of the same 74, fifty-one had typhoid fever, “or a proportion of nearly 69 per cent. If all the people “in the town, say 8000, had been affected in an equal pro“portion, more than 7000 would have been ill during these “few weeks, and about 5500 of them would have had “typhoid fever, and of these over 1375 would have died. “If it would be a more just comparison to take the whole “family at Maplewood into the account, estimating the “number at 112, fifty-six had typhoid fever, or 50 per “cent., and of these fifty-six, sixteen died, or over 28.5 per “cent. These proportions applied to the whole population “of 8000, would give 4000 of typhoid fever in the same “time; and of these 1140 would have died. According “to the testimony of the practising physicians of Pittsfield, “the number of cases of typhoid fever, during this period, “aside from those affected by the influences at Maplewood, “was small, some physicians not having had any, others “had two or three.” These cases amounted to but eight, none of which terminated fatally. The whole secret of this case was proven to have been the retention of the ordure and waste matter from the kitchens and dormitories in privies and vaults, underneath or immediately adjoining the buildings, the odor from these having been offensively perceptible, and under certain atmospheric conditions, having pervaded the whole house. The committee say “it would be impossible to bring “this report within reasonable limits, were we to discuss the “various questions connected with the origin and propaga“tion of typhoid fever, although various theoretical views “are held as to whether the poison producing the disease

« AnteriorContinuar »