more per mile than a light-steel rail on a cast-iron chair, which would not last one-half as long under steam traction. It will not be overlooked that with the Gowan rail we require no separate sleeper of wood or iron, as the concrete is brought to a smooth surface and the rail laid direct upon it. A Member has suggested that if cast-iron sleepers had been used, a worn steel rail could be taken out, and a new one put in, and the road paving remain undisturbed, but none of us know the duration of a well-laid tram-line with ordinary wear and tear I think it might last from twenty to forty years, and I think if the tram-rails wear even for twenty years, the street paving will likewise want renewing at the end of that time, and the tramway and road paving should all come up and be renewed together. Many systems of tramway construction have come to grief in consequence of faulty construction and defective fastenings, and the great difficulty of finding an efficient mode of fastening the steel rail to the sleeper presents an insuperable obstacle to the adoption of a compound system for steam traction. I think it was Mr. Spencer who mentioned the tie-rods; I agree with him in a great measure, and in a town where the roads are paved from side to side, I do not think a tie-rod is of any consequence whatever, and I am not quite sure that it is in any case. But at present there is not much experience to guide us to the effect of steam traction on tram-rails, and we want our system to withstand a very heavy traffic with steam traction, and as a tie-rod can at any rate do no harm, we have thought it best to use one, and we have put it in as additional security: we hope it will enable the road to last a little longer, and it seems the best thing we can do in a system that is comparatively untried. With regard to the gauge, it is very much to be deplored that we have not uniformity of gauge in tramways, because if we had, the engines and other rolling stock would be constructed at a very much cheaper rate. But there are various reasons why those who are promoting tramways at the present time cannot always adopt the same gauge. The 4 feet 8 inch gauge in tramways was originally adopted with the idea that railway trucks could run upon tramway lines, but that probably has ceased to have any force now, and tramways are constructed as tramways pure and simple. The Corporation of Birmingham are now contemplating altering their 4 feet 8 inch gauge to 3 feet 6 inches so as to correspond with the gauge of other tramways now in course of construction in that neighbourhood, and I should not be surprised to find in the course of time that other owners of tramways will change the gauge, but whether 3 feet 6 inches, or 4 feet or 4 feet 8 inches will be the gauge of the future I don't pretend to say. Last year the gauge of a tramway I was connected with was altered in the Committee of the House of Commons from 4 feet 8 inches to 4 feet in order to fit in with a neighbouring tramway, and I am told General Hutchinson rather advocates a 3 feet 6 inch gauge; we had special local reasons however in Rochdale and Bury for adopting the 3 feet 6 inch gauge. The system of working tramways with a continuous wire rope has not yet been tested in this country, and we have had no experience of it at present, and I look forward with very great interest to the experience we shall gain when that system is brought into practical use. In answer to another question, I have to say that the concrete foundation or bed extends over the whole statutory width of the tramway, including 18 inches outside the outer rails. We think it is a better support to the paving, which we desire to maintain by the best means we can, and so reduce the expenses afterwards. If we had thoroughly well-paved roads such as in Manchester, we might have cut out a space of 2 feet wide in the paving in which to lay the tram-rails; but as the paving had to be entirely reconstructed, we thought it better to take up the whole width of the tramway at once, and put down a continuous width of concrete. I can give no information about asphalte under the rails, it is not so used here. Mr. Spencer has produced a surprise, as he generally does at our meetings, in telling us about the fireless engine that is working in Germany: I shall hope to avail myself of some early opportunity of seeing it, and shall make further inquiries about it: if it continues to work satisfactorily and economically, I shall be very glad to see it extensively used in England. THE VENTILATION OF SEWERS AND By R. READ, Assoc. M. INST. C.E., CITY SURVEYOR, THE water-carriage system of sewerage may be said to have been fairly inaugurated by the Public Health Act of 1848, and although epidemics were of frequent occurrence during the ten or twelve years immediately following, the majority of scientific men took but a very feeble interest in the unsavoury subject of sanitary science until the death of the Prince Consort in 1861; this set everyone to work to discover a remedy for fever epidemics, which doctors and chemists plainly stated were probably caused, and certainly spread, by defective sanitary arrangements. A perfect shoal of patent traps and closets were brought out, all warranted to keep back the much-dreaded sewer-gas, but notwithstanding these, and the timid trial of ventilation, with many precautions in the shape of charcoal-trays and other obstructions, the public were again startled by the illness of the Prince of Wales in 1871. A fresh crop of patent apparatus followed, to the great bewilderment of those whose faith in the magic word "patent" caused them to take the statements of inventors or patentees without the necessary grain of salt. Ventilation in the meantime progressed quietly and steadily, until it has now become the recognised practice to place ventilators from 50 to 100 yards apart upon all new sewers. In a period of forty years the sewers of a town pass through many stages of alteration and development, and it frequently happens that existing sewers are partially retained and become portions of a new system. This may be all right if the old sewers are in good condition, and are laid in the public streets, where they can be examined, flushed, and ventilated by the sanitary authority, but when they are at the backs of houses, crossing private gardens belonging to many owners, and are not ventilated, they become a serious cause of evil. The accompanying diagram shows an arrangement of this kind D as it was unfortunately carried out in Gloucester in 1875, after the extension of the city boundaries to take in several outlying parishes, whose sewers discharged into an open brook. It will be easily understood that the ventilation of the new sewers in the public streets at every 60 yards caused a very great nuisance to arise, the long pent-up gas from the old sewers finding free exit from the vents in the new ones as soon as the two were connected. To allay the fears of the public, charcoal pans were placed in the ventilators, contrary to the advice of the engineer; the nuisance in the streets was thus abated, but as the pans were practically nothing but stoppers, the real sanitary condition of the town was rather worse than before. The writer was called upon soon after his appointment in 1878 to report upon this state of things, and being then ignorant of the existence of a dual system, recommended free flushing, to be followed by more ventilation; accordingly during the winter the charcoal pans were removed, and 100 manholes in the old part of the city ventilated, but a return of warm weather brought with it a recurrence of the nuisance, which no amount of flushing in the new sewers could abate: a thorough investigation revealed the fact that the old sewers were all "picked up" by the new wherever they crossed each other, and the mystery was at once explained. No doubt this was intended as a temporary measure, to give the owners of property time to transfer their housedrains from the old sewers at the back to the new in the front, but with the result that there are still 1200 houses connected with the old sewers, thus preventing the latter from being closed. This point has been dwelt upon somewhat fully, because it is quite possible that something of the kind is of not unfrequent Occurrence. A consulting engineer designs a system of sewers for a provincial town, which of necessity must have some existing system, however bad it may be; a contractor from a distance carries out the work, but the local authorities, to keep down the rates, or for some other reason, leave the transfer of the house-drains from the old system to the new to be carried out by the owners of property at their leisure or discretion, which means that unless the house-drains stop altogether nothing is done; for the majority of owners of house property neither know nor care where the drains go to as long as the water runs off and they can get their rents. Sewer-gas is almost universally dreaded as a highly deleterious compound, but our knowledge of its actual composition and action is by no means extensive nor final. The following table shows the names and specific gravities, compared with hydrogen and atmospheric air, of a number of gases given by several eminent authorities as component parts of sewer-gas: The whole of these are not always present, but the heavier gases as a rule predominate, such as sulphuretted hydrogen, nitrogen, and carbonic acid; the question therefore suggests itself, Why does sewer-gas rise from the sewers, notwithstanding its components are heavier than the air? This is caused-1st, by pressure upon, or displacement of the gas by reason of an increased flow of sewage; 2ndly, by diffusion and natural expansion of the gas itself; and 3rdly, and most commonly, by being absorbed or entangled by the light watery vapour constantly arising from the sewage, which acts as a vehicle to carry it out of the sewers. The first is merely mechanical displacement, but the second and third methods are caused by variations of pressure and temperature of the outer air as compared with that of the sewage. The temperature of sewage in the sewers varies from 40° Fahr. in winter to about 60° in summer, that of the atmosphere at the ground level from several degrees below freezing-point in winter to 80° in the shade in summer; but the temperature of sewage will not vary more than 3° in the 12 hours of a summer day, while that of the atmosphere will vary 6°, 10°, or even 20° in the same time, and during summer is always warmer than the sewage. These differences of temperature are accompanied by constant variations of atmospheric pressure causing the gases to expand, and watery vapour to arise from the sewage; this vapour being lighter than the air carries the gas out at the street ventilators. This action is particularly apparent during a spell of dry weather, when the sewage is in its most concentrated form and evaporation is most active. The action is intensified when a sudden fall of the barometer indicates the near approach of a storm; the |
