Page:The Building News and Engineering Journal, Volume 22, 1872.djvu/21

 F JAN. 5, 1872. THE BUILDING NEWS. 5 to abolish, and which they stigmatised as sewers of deposit. ‘‘ But look,” said the de- fenders of these large sewers, ‘‘ at the men who are regularly employed in them: they look healthy enough.” Now this notion has reference solely to the experience of London and other places where the sewers are un- usually large. In these the obnoxious gases are largely diluted with atmospheric air. It is in the higher and smaller branches, in the house drains, where the concentration takes place that isso injurious. These places the Sewer men never approach. When house drains have to be repaired, or taken up and re- laid, itis by another set of workmen altogether that the work is done, and many of these have suffered illness and death that have been traced without doubt to the act of opening a drain at its upper end, and inhaling the pent- up gases. In smaller towns, where there is no parti- cular set of men working regularly in the sewers, but where sewers have occasionally to be opened for the purpose of connecting branches with them, or for the purpose of repair, the men who do this work are not exempt from illness caused by the inhalation of sewer gas to the same extent that the other class of menare, but, on the contrary, itis a very common thing for them to go home ill after having done their work. It is all a question of dilution. A given quantity of poisonous sewer gas largely diluted with atmospheric air may do no harm, but the Same quantity breathed in a concentrated form may be fatal. On the 12th, Mr. Haywood, engineer to the City Commissioners of Sewers, answers Mr Gibbs thus :-— ; Sa “Tt is popularly thought that a system of sewers resembles a mine. Now, both are subterranean cHaeae _but were the resemblance ceases, and in e conditions affectin eir lati eaten ate ee g their ventilation they are ‘“ A mine consists of a series of passages ‘ally of about the same sectional cee WThaiver thew Jength may be, they are carefully adjusted with the view specially to transit and ventilation; there is ordinarily but one entrance to a mine, or if more the mine is divided so as in respect of ventilation practically to form distinct mines; and whether the ventilation be by natural or artificial means, there is but one downeast shaft for the entrance of air and one upeast shaft for its exit. “Whatever, therefore, may be the length of channel im @ mine, and however much the air currents in them may be turned, divided, and re- united (and this is largely done), the quantity of air Set in motion neither loses ner gains materially on its passage; practically, that quantity which goes down comes up, and no more; thus the ventilating power can be calenlated, and within the limits of the power the quantity of air can be diminished or sae according to exigencies. x © sewerage of a town consists of tubes vary- ing from three inches in diameter to others a re dved times that capacity, and in London even from 3 inches to 13 feet in diameter. They are laid with various directions, inclinations, and levels, and at every 90 fect at least of their length is agulley, sink- pipe, water-pipe, or other inlet, all of which must admit water through them, and most of which at times do, although they should not, admit air to escape through them. In 1858, when Dr. Letheby and myself investigated this subject, we found that peo the City of London alone there were 260 re ge channel and more than 47,000 in- ““ Under existing conditions sewers, therefore, are but tubes perforated with air holes at intervals along their entire length, and the application of air exhaus- ters would be practically useless, for wherever placed the air currents would rush in with great velocity towards them from the nearest inlets, the current becoming feebler and feebler from other inlets as the distance increased, until the exhausting power would no longer operate at all.” On the same day, ‘“ Paterfamilias ” says :— “At present our architects and builders appear to ze to ‘lay on” to every dwelling-house a supply of ae Sewer gases as carefully as they do water and il uminating gas. Isitnecessary that thesewershould be brought into the house at all? I think that it is Be ony unnecessary, but that it should be probibited y law. “T have suffered greatly by this system, and I shall be glad if my experi e ¢ rte & Riko y experience be turned to the ad- a A I have disconnected the sewer. All my drains and water-pipes discharge themselves over the mouth of a water-trap outside my house. ‘Lhere is a space between the pipes and the trap; thus the sewer gas cannot force its way into the house. In my case the trap has placed immediately over it the rain-water pipe, so that ifany gas should pass the trap it would immediately rise above the house. “T have had this system in operation for two years, and it answers admirably.” And Mr. B. W. Gibsone, M.A., of Eaton- square, says :— ‘1. What substances, may I ask, do we use on a large scale as antiseptics and disinfectants? Sul- phurous acid, carbon, and carbolic acid. That these three are the very ingredients present in a most transportable form in coal-smoke is too evident to every eye and nose above ground. To the sewers. then, let us consign the offender, there it would be ‘the right thing in the right place, for miasma ‘a perfect cure.’ “2. What simpler ventilation for sewers than that each house should contribute its now wasted hot-air in creating a draught down into them and out at a distant exit, rather than up from them into, possibly, some exhausted sleeper’s lungs? ‘Tons of force are now expended every winter day by our house fires in sucking up into the rooms through the sinks and closets (all other entrances for air being carefully closed) the mephitis of the cesspool. “ Let me hope, then, sir, that both your great ob- jects, ventilation of the sewers and smoke drainage, may at no very distant time simultaneously be effected by one and the same comprehensive sub- ordination of our efforts as above indicated. Mean- while, as instalments of the future perfected good, we might gradually— “1. Adopt grates, in some measure at least, smoke- consunnneg, “2, Erect on rising grounds, tentatively, lofty furnace-chimneys, exhausting our cloace ; the heat would be utilised for public washhouses. “3. Connect the house flues with the sewers, and trap the openings to the latter.” We have quoted from this letter, not because there is anything at all practicable in the mode of ventilation proposed, for we shall see by-and-by that the idea of ventilating sewers and drains by ‘lofty furnace chimneys” is impracticable, but because the mention of sulphurous acid and carbon shows that the writer has a germ of the true idea of ventila- tion, which is to dilute the gases with atmospheric air to the utmost possible extent, and when the atmosphere contains sulphurous acid and carbon, as it always does in towns, so much the better, for these sewer gases are then not only diluted but destroyed by their action. ——_oa>—_—_ NOTES ON BRICKWORK.—VIUII. OR small arches and inverts it is necessary to have bricks moulded purposely to the different radii, because in using the common building bricks the back of the joint is too thick for sound work. Culverts and sewers especially require the sides of the bricks to coincide with the radius of the circle of which the arch or invert forms a part, so that the joints may be as nearly as possible of the same thickness at the back as at the front, other- wise the unequal extent to which the mortar joints would be compressed would distort the work; and besides that the use of square ‘bricks is wasteful of mortar. Arches and inverts are generally turned in half-brick rings, all the bricks being laid as stretchers, and in using square bricks, in arches of greater radius, that system makes better work than if the bricks were laid as headers, because the back of the joint would then be double the thickness; but with radiated bricks there does not seem to be the same reason for this system of half-brick rinys, for it would seem to be as easy to mould the bricks with the thin edge at the end as at the side, and it would also seem that that method would make sounder work. It is usual to retain nearly the same bulk in radiated bricks as in the common square bricks, about Yin. long, 44in. wide, and a mean thickness of 23in. ; but for sewers, where it has been judged that a single half-brick ring was not sufficient and that two made the work unnecessarily thick, bricks have been moulded for the occasion of the dimensions of 9in. long, Gin. wide, and 2#in. mean thick- ness. ‘These were not found to be incon- venient in the handling. When sewers or culverts are laid in trenches in the solid ground they need no footings, as is shown in Fig. 17 and 18, for the ground can be got out to the shape of the invert in most cases ; but when culverts are laid to carry streams under embank- ments a footing of brickwork is necessary, as shown in Fig. 19, which represents a cul- vert 4 feet diameter. For large culverts the form shown in Fig. 20 is preferable. It has been considered best to make sewers egg-shaped, as shown in Fig. 18, with the object of increasing as much as possible the hydraulic mean depth when the flow of sew- age is small in comparison with the whole capacity of the sewer, by concentrating the flow instead of allowing it to spread over a greater width and attain a less depth. The best proportions of height and width of an egg-shaped sewer are—height 3, width 2;radius of sides 3, of arch 2, and of in- vert 1. FiIc.I3 FICG.A7 eee Fig. 21 isa bridge of 12 feet span, with semicircular arches. All arches should be backed up at the haunches, but semicircular arches especially so, for that is their weak point. Fig. 22 is a bridge with segmental arches, in which case the abutments require to be thicker than with semicircular arches ; either, that is to say, thicker bodily, or to be strengthened with counterforts, the spaces between which may be arched oyer. The rise of the arch in this example is one-fifth of the span. In all the examples hitherto mentioned the arches are struck from one centre. In Fig. 23, which is a section of a bridge which carries a road over a railway, the arch is struck from three centres. The proper names of the parts of bridges are as follow. The foundations are those parts of the abutments and piers below the plinth, the plinth being formed by a set- off just above the ground level. The abut- ment is the mass of masonry—brickwork is included in the generic name of masonry— which is placed so as to oppose its resistance to the horizontal thrust of the arch, the di- mension of which mass horizontally is re-