: injurious before it putrefies, and it is both foolish and wrong to incur any avoidable danger, still more so to expose others to it. Sewers should, therefore, be so constructed, first, that as little foul air shall form in them as possible; and, secondly, that any foul air which does form shall escape where it will do least mischief. To those who contend that the prevention of deposit in sewers will prevent all formation of foul air, and that therefore no provision for its escape is needed, the reply is-Be it so. If no foul air be formed, to provide for its escape can do no harm; while, if there be any formed, not to provide for its escape where it will be harmless, will. be to compel its escape where it may be deadly, for example, through the house-drains into dwellings. To prevent the possibility of this very common danger, two simple expedients are indispensable and effectual free ventilation of sewers outside our dwellings, and absolute non-connection of sewers with the interior of them. The external ventilation of sewers, even in the rude way common in London, namely, by openings from the crowns of the sewers to the middle of the streets, though the cause of frequent annoyance, is almost infinitely safer than no ventilation at all. The escape of foul air into the streets is annoying; but if forced into the dwellings it would be destructive; and London, instead of being one of the least, would become one of the most unhealthy of large cities. The danger may, however, be entirely avoided without encountering the annoyance, by providing channels for the escape of sewer air at places where it will not annoy, and, better still, by compelling it to pass through charcoal, by which any putrescent matter it may contain will be absorbed and decomposed before the air is allowed to escape. We are indebted for this invaluable invention to Dr. Stenhouse, F.R.S., the eminent chemist, who many years ago discovered that charcoal, like other very porous substances, has the power not only of absorbing, as was always known, a large quantity of putrescent matter, but of continuing to do so indefinitely, as decomposition as well as absorption are constantly going on between the oxygen and the putrescent matter, both absorbed in the pores of the charcoal, and thereby brought into close contact and chemically united. The effect is, that if air, carrying putrescent matter, be passed slowly through, not merely over, a layer of crushed charcoal a few inches thick, the putrescent matter will be not merely absorbed, but decomposed as completely as if the putrescent matter had been burnt; in fact, it will be burnt, though very slowly, the products being water, carbonic acid, and either nitrogen or nitric acid; but with even less of what will decolourize permanganate of potash than common air in towns often contains. For complete success, it is essential for the charcoal to be dry, and for the foul air to be carried through a layer of it very slowly. If the charcoal be fresh, foul air can be rendered inoffensive by passing it slowly over a considerable surface of it, as is done at Croydon; but that plan requires the charcoal to be frequently renewed or reburnt, and does not ensure the complete decomposition of the impurities; neither is the air filtered and freed from floating particles which many believe to be the real germs of disease. When sewers receive much hot water, as they do at Liverpool and elsewhere, the action of air-filters is impeded by the charcoal soon becoming damp. If the sewer air be conveyed to the tops of the houses by the rainwater pipes, at the top of which air-filters are fixed, most of the steam will be so condensed in the pipes that little of it will reach the filters. It has been objected that roof-pipes are unfit to be the ventilating channels of sewers, because liable to be filled with water during rain, whereby, instead of allowing the air from the sewer to escape, the descending water will force it elsewhere. I think those who make this objection can never have noticed how very large rain-water pipes commonly are in proportion to the water they ever have to convey, so that unless obstructed they cannot be filled by any probable fall of rain. It is very common for the water from the roof gutters to be conveyed to the rain-water pipe by a short pipe about half its diameter, and rare for the small pipe to be running half full; but unless four times as much rain falls on the roof as the smaller pipe provided for it can carry, it is impossible that the larger rain-pipe, twice its diameter, can be filled. And, in fact, such pipes never are filled, unless there be a fixed obstruction or other occasional accident, so that the roof-pipes are often the best as well as the cheapest ventilating channels, unless a window happen to be near. It is safest, however, to provide each with an air-filter, which need cost very little. The other necessary precaution is effectually cutting off all communication between the sewers and the house-drains, by which sewer air can be conveyed into any dwelling. It is not enough merely to interpose a water-trap, though that is a great protection, especially if it be itself ventilated by a pipe from the centre of an inverted syphon to the roof-pipe. The only safe plan is, as Mr. Rawlinson has so often and so wisely recommended, to allow of no direct communication at all between the sewers and the house-drains, so that if any air enter the house by the drains at all, it shall be outer air, not sewer air. Another important precaution also strongly insisted upon by the same high authority, is to have the house-drains themselves as short as possible, to have them conducted directly through the outside wall, and not along the floors of the basement, as is too common, so that there may be no possibility of any collection of filth or filthy water within the walls. With these precautions, and with careful trapping of all drains within a house, and ventilation of all sewers outside, the entrance of sewer air may be effectually prevented; but without them the danger is great and constant, and many a death from diarrhoea, typhoid fever, and other disease has owed its origin to this often unsuspected cause. Sewer air is not dangerous to those only who breathe it. Many cases of poisoning have been caused by its absorption by water that has afterwards been drank, and have been very puzzling to account for until the cause was discovered. This mischief often arises from the very common fault of leading the overflow pipes of a cistern into a drain or even into the soil pipe of a closet. This is one of the many evils arising from not supplying water continuously. Often no precaution at all is taken to guard against a danger so evident, and generally no better precaution is adopted than that of giving a bend to the overflow pipe, so that when the bend is filled with water it may act as a trap; but as no water enters the overflow pipe except when the cistern is overful, it may easily happen that there is none in its bend, when, of course, there is free passage for the drain air. Few plumbers seem to have common sense enough so to fix the overflow pipe as to make the water run from the bottom instead of the top of the cistern, when the water reaches the level of the upper bend of the overflow pipe; yet nothing can well be more easy. Common sense is, however, a very uncommon quality amongst practical men, who will persist in doing their work in the usual way, although it is usually found to be very unsatisfactory. Many seen to think that if the solid excrement could be kept out of the sewers, the sewage could be disposed of without difficulty. But though the difficulty might be diminished it would not be removed, while the necessity for sewers and the cost for making them would be same. The sewage, though less offensive, would still pollute any stream it entered; if putrid it would kill fish, and if allowed to collect, would be an intolerable nuisance to all in its neighbourhood. On the other hand, if nothing further be sought than to cleanse ordinary sewage to such a degree as to render it possible to pour the effluent water into any stream not used for water supply, without creating a nuisance, there are few places where a sufficient quantity of land is not easily accessible for merely cleansing the sewage, as is done at Merthyr, to such a degree that the effluent water may be safely allowed to flow into any river not used for water supply; while in many places such effluent water would form a fertilizing stream of inoffensive liquid that might be turned to profitable account. This part of the question will, however, be more properly discussed on another occasion. Mr. G. N. STEVENS, M.R.C.S., also read a paper on the question. He was of opinion that the very best material for the construction of drains that can be used is Roman cement, in large blocks, fitted closely together, and surrounded by a thick bed of concrete, as through these no percolation of the sewage could take place; whilst the old plan of perforated bricks, to a small extent, in the centre of the sewer, the rest being made of ordinary stone and mortar (unless the latter is made of the best hydraulic lime), will admit of such percolation, and consequently of the escape of mephitic gases through the soil into the atmosphere. Secondly, as to the levels. These being the work of the engineer, he need say no more on this subject, but that they should be at such an angle as will allow a ready and rapid flow of the sewage to the outfalls. Thirdly, as to their size and shape. They should invariably be of large size as regards the main sewers; in fact, to such an extent as to admit of a man's passing easily through them. The interior should be as smooth as possible, so as to hasten the onward flow of their contents, and for the attainment of the same desirable and self-evident purpose, they should be oval or egg-shaped, which has been proved to create a force of expulsion greater than the circular form. His own belief is, that wherever main sewers are constructed in the manner mentioned, and on the principles named as to material for construction-the levels, shape, size, &c., supplemented with a sufficient number of ventilators opening on the street, having trays of charcoal and chloralum in immediate connection with them, so as to completely deodorize and disinfect the sewers, no poisoning of the atmosphere could by any possibility take place. The charcoal should be steeped in chloralum solution and drained. This liquid attracts moisture and absorbs ammonia greedily-an ammonia chloride of aluminum is thereby formed, and this may be utilized in various ways. If, therefore, this disinfection renders inert the materies morbi contained in the poisonous gases of sewers, the question under discussion appears to me to be solved." DISCUSSION. Dr. HEARDER (Holland) remarked that, in all the propositions which were made for the prevention of sewage poisoning, much importance was attached to the chemical means proposed to be employed; but it appeared to him that in almost all these cases those who proposed the use of chemical means overlooked the difficulty of keeping the chemical process in proper train. It was all very well to suggest that charcoal should be used for the filters, but who was to look after the filters? If the servant of the house were to do it, she would have to risk her neck to get into a position so as to reach the filter, because it was necessary that it should be placed so high and so far out of the reach of garret windows, and so on, as to be incapable of conveying obnoxious effluvia into those windows. In order that it might be carried out, there must be a regular systematic change of charcoal, because charcoal only absorbs a small quantity of matter; it would have to be changed over and over again, and ultimately it would be worth nothing at all. Therefore the attempt to ventilate sewers by bringing tubes to the top of the house would be impracticable. There was one remark by which the author seemed to suppose it was impossible for water in descending a shoot to carry air with it, unless the shoots were full, and they were so large that they rarely filled. It seemed the author forgot that water carried air down by friction. To ventilate drains through the rain-pipes would be impracticable, in consequence of the trap which they were supposed to have at the bottom. With regard to shutting off houses from all external communication with their drains, every drain was supposed to have a trap of its own, every closet had a trap, and every drain at its junction with the main sewer was furnished with a trap; consequently we had a quantity of foul air and sewage always lying and accumulating between those traps. This showed that ventilation was necessary, and therefore he should hail with pleasure any plan that could be devised for the practical working of any system; but he must confess all he had seen and heard as yet of individual draining of houses was quite inadequate to the purpose. He did not see why we might not, in certain towns and localities, put up large shafts which should serve as outlets; or church towers might serve the purpose. That, he thought, would be no desecration; but by so doing the impurities of the sewers might be carried up and delivered high in the atmosphere. There was some little danger in applying heat for the purpose of destroying noxious gases, but that ventilation was requisite there was not the slightest doubt; and he hoped some plan which could be well carried out might be suggested. Dr. HARDWICKE (London) stated, the question, he believed, centered itself in two or three points. They were the ventilation of sewers either by charcoal or by street gullies, and the ordinary ventilation in the streets; the flushing of sewers; and the adoption of chemicals, which he for one put little faith in. With regard to the ventilation of sewers by pipes, it would never do to ventilate full sewers opposite a drawing-room window, or in a street in which children were playing all day long; and it was just as doubtful whether disinfecting charcoal or shafts would prove advantageous. As to ventilation by means of shafts, he might mention that Mr. Bazalgette had spent much money in the metropolis in the years 1866 and 1867 in trying this system, and that he came to the conclusion that tall shafts were of no use whatever, besides being ridiculously expensive. Ventilation by stack pipes was also not a very good thing to rely upon, and, besides, people would not allow the pipes to go up the sides of their houses, because the foul air would come into their windows and quickly fill the rooms with a nuisance. Then came the question what was to be done? The chemical method was equally as difficult to work as any of the preceding ones, for carbolic acid was of itself a nasty, filthy agent. He had succeeded in proving that, and he was at Sedan, when it was being used in every possible way. There, he believed, it really poisoned the patients, and the medical men admitted they could not save a case. With regard to chloralum, he thought that it was a tolerably safe thing; but it could not be used on a large scale in a town where there was a large amount of fecal matter going through the drains. The only practical remedy was flushing where there was a proper water supply, and where the drains were laid in the proper way. If this were the case, and if there were thirty gallons of water per diem for each of the population, with an ordinary fall, all matters would most decidedly be carried away before the gases or any nuisance formed. The great thing to aim at was to have such a flush of water as to be enabled to carry matters away in ten or twelve hours, and this could be done by the expenditure of 150. a year, supposing the supply of water to be all that could be desired. Storm waters could be carried down when desired. Looking practically at the subject, he thought no more could be done than by flushing, although he did not say that chemical substances might not be used to supplement the scheme. Dr. NANKIVELL (Tregony) expressed his entire concurrence with the views set forth in Mr. Holland's paper, and he entertained no doubt that the great protection from all sewer poisoning must be the prevention of gases from such matters entering their houses, or any part where it was likely to be dangerous. There was no doubt that the great object in constructing main sewers should be to get a great and continuous flow of water through them. There was this objection to shafts -they would never act except upon small portions of sewers, in consequence of the number of small drains running into the sewers. He counselled the fitting of a "mason's trap" near the sewer, so as to cut off the connection between houses and the main sewer, and another near the house, so as to cut off all communication between the pantry and the scullery and the house-drains. This would free the house, he believed, almost entirely. The application of chemical means must always be uncertain, and attended with great difficulty, while, after all, we were not quite certain that we had any means of entirely disinfecting gases. We might deodorize them, but could not destroy them. Mr. CHRISTOPHER BULTEEL (Devonport) remarked that the people in the three towns had not long emerged from the old system of cesspools, and it was only within the last two years that a complete system of sewers and proper drainage had been introduced into Stonehouse. Now, although the medical profession were fully alive to the immense improvement such a system was upon the old system of cesspools, if it were properly carried out, yet, unless there was a thorough attention to detail, he very much questioned whether in some instances sewers and drains do not become a more fruitful source of danger than even a properly managed cesspool. What he meant was this-and facts which would bear him out had occurred under his own notice in several parts of these towns-in adopting the recent improvements, especially in regard to earthenware pipes and properly constructed sewers, it was of immense importance that the work should be most |