arV 
 
 19480 
 
 SEWER GAS 
 
 AND 
 
 HOW TO KEEP IT OUT OF HOUSES 
 
 A HANDBOOK ON HOUSE DRAINAGE 
 OSBORNE REYNOLDS M. A . 
 
Cornell University Library 
 
 arV19480 
 
 Sewer gas and how to keep it °u« J* Jjffl! 8 
 
 olin.anx 
 
 3 1924 031 254 497 
 
Cornell University 
 Library 
 
 The original of this book is in 
 the Cornell University Library. 
 
 There are no known copyright restrictions in 
 the United States on the use of the text. 
 
 http://www.archive.org/details/cu31924031254497 
 
SEWER GAS, 
 
 AND 
 
 HOW TO KEEP IT OUT OF HOUSES. 
 
SEWER GAS, 
 
 HOW TO KEEP IT OUT OF HOUSEF 
 
 A HANDBOOK ON HOUSE DRAINAGE. 
 
 BY 
 
 OSBORNE REYNOLDS, M.A. 
 
 Professor of Engineering at Owens College, Manchester; Fellow of Queens' 
 College, Cambridge. 
 
 SECOND EDITION. 
 
 MACMILLAN AND CO. 
 
 1872. 
 
 s 
 
 \Tke Right of Translation and Reproduction is reserved.] 
 
LONDON : 
 CLAY, SONS, AND TAYLOR, PRINTERS, 
 BREAD STREET HILL. 
 
PREFACE. 
 
 The principal part of this book was written nearly 
 four years ago. It has only been waiting in order 
 that some suggestions it contains might have a 
 thorough practical trial, and this being accom- 
 plished, it is now published in the hope that it 
 may help those people who are in doubt and 
 trouble with the drainage of their houses. It 
 would be a public calamity if the wide-spread 
 alarm, caused by the recent illness of the Prince 
 of Wales, were allowed to subside without pro- 
 ducing a beneficial effect ; but there is danger 
 that such will be the case, simply for the want 
 of definite information as to what is amiss, and 
 how it is to be set right. The discussion in the 
 newspapers has been more calculated to cause 
 alarm and bewilderment than to direct anyone 
 how to act. Everyone is crying, " Do ! do ! " 
 
PREFACE. 
 
 while no two agree what is to be done. What 
 appears to be wanted is a book of approved 
 scientific merit, and of such a practical character 
 that a householder or any unscientific person can 
 learn from it how to ascertain if drains are safe, 
 and, if not, how to get them put right. In the 
 absence of such a book, I venture to hope that 
 this little work may be useful. 
 
 My chief object in writing on this subject was 
 to suggest a plan for preventing the evil which 
 is now causing so much alarm — viz. the back-flow 
 of gas into our houses. Of this plan I have 
 now had four years' experience ; and have, without 
 exception, found it to answer perfectly. In the 
 first place, I applied it to my own house at a cost 
 of fifty shillings or thereabouts. This house is 
 of the ordinary type, and is drained into a foul 
 sewer. Before the introduction of the new plan, 
 it was never free from smells ; while, since, there 
 has been no annoyance of the kind, nor have the 
 drains required any attention whatever. 
 
 The plan is very simple, and can be applied to 
 any fairly-drained house at a small cost, and 
 without requiring the drains inside the house to 
 be disturbed. 
 
 I am not aware that this complete scheme has 
 
PREFACE. 
 
 ever been suggested before; but it embodies as 
 its principal features several plans which, I am 
 pleased to see, are daily growing in favour ; 
 among which perhaps the most important is that 
 of having a break or trough in the pipe which 
 connects the house with the sewer. This has now 
 been advocated for several years, but I do not 
 know by whom it was first proposed. 
 
 Besides describing the proposed scheme, I have 
 endeavoured to impress the reader with its sim- 
 plicity, and also to point out other ways in which 
 the drains in a house may be harmful, besides 
 by the admission of sewer gas — in fact, to make 
 this a handbook on house drainage. With this 
 view, I have divided the book into four sections. 
 
 Section I. — A description of the plan recom- 
 mended for disconnecting the house and the 
 sewer, together with the directions necessary to 
 enable an ordinary workman to apply it to every 
 house. 
 
 Section II. — On the purpose and general arrange- 
 ment of house drains. 
 
 Section III. — On the way in which the house- 
 drains themselves give rise to stinks and poison- 
 ous gas, and the best means of preventing them 
 doing so. 
 
PREFACE. 
 
 Section IV. — On the precise way in which 
 the sewer gas enters houses, the inadequacy of 
 measures in use for preventing this, and the 
 advantage of the new plan. 
 
 Throughout the book I have endeavoured to 
 make the language intelligible to everyone, how- 
 ever ill acquainted with technicalities. I have 
 avoided, as much as possible, disputed ground ; 
 but there are two errors frequent among news- 
 paper-writers, which I have found it necessary to 
 point out. The first error is the common belief 
 that there is often an excess of pressure of gas 
 in the sewer beyond that of the atmosphere. 
 Some writers maintain that at times this excess 
 is ten or fifteen pounds on the square inch ; others, 
 that it is at least sufficient to force the gas past 
 a trap. The second error is the belief in the 
 efficacy of mere ventilation for preventing the 
 sewer gases getting into houses. Both these 
 notions are hypothetical, and all experience is 
 against them. 
 
 I do not mean to say that there is never an 
 excess of pressure in the sewer, or that sewer 
 ventilation will not mitigate the evil, but that the 
 evil is not solely or even generally due to such 
 pressure, and cannot be cured by ventilation. 
 
PREFACE. 
 
 I have not gone into or even touched upon the 
 drainage of towns or the disposal of refuse, but 
 confined myself entirely to the drainage of houses. 
 Such readers as wish to study the wider subject 
 are referred to Professor Corfield's able work on 
 " The Utilization of Sewage." 
 
 O. R. 
 
SEWER GAS, 
 
 HOW TO KEEP IT OUT OF HOUSES. 
 
 SECTION I. 
 
 A description of the proposed Scheme for disconnecting the 
 House and the Sewer. 
 
 The art of properly draining buildings is distinct from 
 that of sewering towns or districts. This is fortunate, for 
 be the sewer or cesspool into which a house drains never 
 so foul, it may be beyond the power of the unfortunate 
 inhabitant to get it set right. He must rely on the sub- 
 soil on which his house stands, and on the floor and walls 
 of his house to separate him from the contents of the 
 sewer. He must rely on these and on an artful connec- 
 tion of the drains within his house with the poison gene- 
 rator without, so that they may serve to carry off the 
 refuse without affording a passage back for the poisonous 
 gas. In order to do this effectually it is necessary that 
 
SEWER GAS. 
 
 [sect. 
 
 all the drains in the house should flow into one pipe, so 
 that there may be only one connection between the house 
 and the sewer, and in this pipe there must be a trap of 
 somewhat peculiar construction. This trap is shown in 
 Fig. i. 
 
 Fzty la 
 
 '<ZHL ..„..-^.,,„J. 
 
 A man-hole or shaft is sunk from the surface to the pipe, 
 the floor of the man-hole being about two feet above 
 the bottom of the drain. Across this floor there is an 
 open trough which takes the place of the pipe ; this is 
 about two feet deep, and of the same width as the pipe. 
 The ends of the pipe which are connected with the 
 trough are (as shown in the diagram) so depressed that 
 the water stands in the trough about half an inch above 
 the orifice on the sewer side, and an inch above the 
 mouth on the house side. In this way a trap is formed 
 which effectually closes both the house and the sewer 
 from the man-hole, and doubly closes the house from 
 the sewer. And if care is taken to arrange the orifices 
 of the pipes in the man-hole as recommended, it will not 
 be possible for the water to be sucked out of the trap, 
 
I.] SEWER GAS. 13 
 
 should the pipe run full. The man-hole affords a ready 
 means of examining or cleansing out the trap, but in 
 order to prevent a scum forming on the surface of the 
 water in the trough, the pipe from a roof spout may be 
 arranged so as to discharge itself on to the top of the 
 trough, as shown in the diagram. 
 
 The drain from the author's house is deep, and the 
 shaft is two feet square, built of 4g inches brick work, the 
 bottom formed of bricks and 
 cement : the trough is cemented. 
 The pipe is five inches inside. 
 The charge for constructing the 
 whole was less than 3/. 
 
 In most cases a simpler plan Flg- "• 
 
 will be found to answer quite as well ; instead of having 
 a man-hole and trough, a special earthenware trap is 
 used, such as is shown in Fig. 2. 
 
 The length of the upright branch should be increased 
 with straight pipes until it comes to the surface, where its 
 mouth may be protected but not closed. In one of these 
 pipes there should be a side junction for connection with 
 the down spout, as shown in Fig. 8. 
 
 Such a trap may be put in any position, and need not 
 cost 1/. They are, or should be, kept by all vendors of 
 sanitary pipes. 
 
 The best position for such a trap as this will be deter- 
 mined by circumstances, but it must be somewhere be- 
 tween the house and the sewer, branch sewer, or cesspool 
 into which the house drains. As a general rule the nearer 
 the house the better. 
 
14 SEWER GAS. [sect. I. 
 
 It is, however, to be insisted on that all the drains in 
 the house shall flow into this trap, — that there shall be 
 only one connection between the house and the sewer, or 
 at least if there be more they shall each have a trap, and 
 be certain of a constant supply of water sufficient to 
 maintain the necessary level in it ; for it is to be specially 
 noticed that the essence of this improvement is to in- 
 sure the action of an efficient trap, which can only be the 
 case when the water supply is unfailing. 
 
 The reader will be better able to appreciate the reasons 
 why this particular form of trap and the position assigned 
 to it are specially recommended, when he has read the 
 discussion in the following sections on the general arrange- 
 ment of house drains and traps. The further consider- 
 ation of these questions has therefore been deferred to 
 the Fourth Section. 
 
 It is not necessary to have these traps for cottages and 
 houses without cellars or water-closets, but it is equally 
 important that in such there should be no direct con- 
 nection between the drains from within and the sewer. 
 The only essential drain from the inside of such houses 
 is the pipe from the sink. For reasons which will be ex- 
 plained hereafter, it is not safe to depend on a trap in 
 this pipe. Perfect discontinuity should be insured by 
 bringing the pipe through the wall of the house, above 
 ground, so that it may discharge into an open trough or 
 gutter leading to a yard or street gully. The mouth of 
 the pipe should not be directly over the gully, otherwise 
 the light gas from the gully may rise up it, and thus find 
 a way into the house. 
 
SECTION II. 
 
 On the purpose and general arrangement of House 
 Drains. 
 
 The first thing for the anxious householder to do is to 
 get a clear conception of what the drains in his house 
 are for, and whereabouts he may expect to find them. 
 The accompanying diagram will very much assist him in 
 this. He will at once see that the necessity of the 
 house drains arises from the use of water-closets, baths, 
 sinks, and underground cellars, and that whatever may 
 be their subsequent directions, they start from one or 
 other of these sources. Fig. 3 represents a section 
 of an ordinary town-house, taken so as to show all 
 the usual inlets into the drains : a, the closet ; b, the 
 bath ; c, the sink ; and d, the cellar drains. It also 
 shows the sections of the pipes from these sources, and 
 the manner in which they are usually connected with 
 each other and the outside drain. In this example the 
 house drains are shown connected with a branch sewer 
 which runs at the back of the house (a. very common 
 arrangement in towns), but it is not intended to confine 
 these remarks to houses which drain in this way, for they 
 
SEWER GAS. 
 
 [SECT. 
 
 apply equally to houses which drain directly into a street 
 sewer, or into a cesspool. 
 
 Fig. 3. 
 
 The most important drain in a house is the soil-pipe 
 from the closet (a). It is, generally speaking, metal 
 
n.] SEWER GAS. 17 
 
 between the closet and the ground. Sometimes this part 
 is entirely of lead, but more commonly of lead and iron ; 
 the straight part being of iron, for cheapness, and the rest 
 of lead, for convenience of manufacture. This pipe 
 should be, and generally is, about five inches across 
 inside. There is usually a bend in it immediately below 
 the pan of the closet: a depression which, standing full 
 of water, prevents the smell from coming up the pipe 
 into the closet. 1 In most houses the water-closet is above 
 the ground floor, and the pipe has to descend for some 
 distance before it reaches the ground, and it seems to 
 have been an open question whether it is more objec- 
 tionable to have the pipe with its smells, for these pipes 
 are never smell-tight, inside the walls of the house, and 
 protected from the frost, or to carry it at once through 
 the walls and bring it down outside in the open air. 
 
 If the smells are kept out of this pipe, as will be the 
 case when the house is disconnected with the sewer, in 
 the manner described in Section I., the pipe may be safely 
 kept inside the walls without any fear of its giving out 
 bad smells or sewer poison. 
 
 The minor waste pipes, those from the sinks and bath, 
 often join the down pipe from the closet. They are 
 themselves generally leaden pipes about one inch in 
 diameter, and they are connected with the cast-iron pipe 
 by means of putty joints, and it is at these joints for 
 the most part that the pipe leaks or the smells escape. 
 There are usually depressions in these lead pipes which 
 are supposed to keep full of water and prevent smells 
 1 See Section IV. on Traps. 
 B 
 
iS SEWER GAS. [sect. 
 
 coming up the pipe, but these often fail from a fault in 
 construction (see Section IV. on Traps). 
 
 The closet-pipe brings the refuse from all its tributaries 
 down to the ground, and sometimes as low as the cellar- 
 drain. The metal pipe is then connected with an 
 earthenware pipe of the same size, or larger, which is 
 laid with sufficient fall in the direction of the sewer or 
 outlet. The junction between the vertical iron pipe and 
 the glazed earthenware is of some importance. It is 
 often made with a square elbow or branch. This is 
 particularly the case where the iron pipe descends inside 
 the house, and the earthenware pipe is the continuation 
 of the drain from the cellar, as shown in Fig. 3. 
 This square connection is bad wherever it exists. In the 
 first place, the water falling straight down on to the 
 bottom of the horizontal pipe makes a splash and loses 
 all the impetus it had acquired in falling, which if 
 
 Fig. 4. 
 
 properly directed would have been of great use in 
 carrying it past or removing any obstructions there might 
 be to its subsequent course in the flat-pipe ; and in the 
 second place, where the closet pipe simply branches from 
 
ii.] SEWER GAS. 19 
 
 the cellar or some other drain, the splash at the bottom 
 is apt to leave a deposit, as shown in Fig. 4, on 
 the upper side of the connection, which can only be 
 removed by a flush down the drain from some other 
 source. When practicable, all junctions should be effected 
 with curved bends such as those shown in Fig. 5, so 
 that when the pipes come together their contents may be 
 flowing as nearly as possible in the same directions. 
 
 Perhaps of all the drains in the house that from the 
 cellar is the most liable to be the source of mischief. It 
 is the lowest and consequently has the worst fall, and if 
 its lawful contents are not of an offensive kind, yet, owing 
 to its position, it often receives the contents of its more 
 ill-favoured neighbours. Besides this, it is out of the 
 way, it gets less attention than the others, and in many 
 cases it is not directly used, and so has not the advantage 
 of an occasional flushing. In many old houses in the 
 country it is constructed of brick or of unglazed pipes. 
 In modern houses it is of glazed earthenware pipes about 
 five or six inches across, and sometimes as much as nine. 
 These are all larger than is necessary, a 3 or 4 inch pipe 
 with a fall of f inch to the yard is amply sufficient. 
 
 In many houses, such as those in the neighbourhood of 
 Manchester, there are cellars (not kitchens) under the 
 whole house, and each cellar has its gully and drain. 
 Now, it may be convenient to have sinks all over the 
 house; but when we come to think how seldom these 
 cellars are washed, or indeed have any water in them, it 
 seems almost unnecessary to have drains all over them 
 just to save the servants the trouble of occasionally 
 
 £ 2 
 
SEWER GAS. [sect. 
 
 washing a yard or two of floor. Of course if the drains 
 were harmless that would be all very well, but when we 
 consider that there is difficulty and danger about every 
 drain, and especially the cellar-drains, and that every 
 extra foot or yard is just increasing the danger by so 
 much, we must admit that to have a ramification of 
 drains under the whole house is likely to cost us dear for 
 the convenience it brings. There must be one drain 
 from the lowest part of the cellar, but this need only 
 just come through the wall. 
 
 Besides these drains from the inside of the house, those 
 from the spouts (e), Fig. 3, which carry off the roof-water, 
 often form part of the same system. They are some- 
 times kept distinct, and communicate with the sewer by 
 separate pipes, but more commonly they are connected 
 either with the drain from the cellar or the soil pipe. 
 Some people have recently made a point of doing this 
 with a view to ventilate the drains and form a way of 
 escape for gas that would otherwise force its way into the 
 house. This, however, is a mistaken idea. The plan 
 need not be mischievous, it is often the reverse, but it is 
 done under a similar misapprehension to that which leads 
 people to have openings in their ceilings to take out the 
 hot air from rooms, the fact being that, when there is a 
 fire in the room, the draft up the chimney is so great that 
 it draws air into the room at every crevice, and con- 
 sequently the opening in the ceiling which was intended 
 to take air out lets air in, and thus acts in a manner the 
 reverse of what was intended. So it is with the drains. 
 The suction of the house, especially when fires are lighted 
 
n.] SEWER GAS. 
 
 and windows closed, draws so much air out of the sewers 
 that they have to get it where they can, and all the 
 openings into them from the outside, the down spouts 
 among the rest, are actually letting air into the sewers 
 instead of out of them. 
 
 Such, then, is the most common arrangement of drains 
 in a house, and there are obviously two ways in which 
 these drains may be the means of poisoning the inhabit- 
 ants ; they may introduce the much-dreaded sewer gases, 
 or they may themselves become filthy and give off effluvia. 
 The following parts of this pamphlet are devoted to the 
 consideration of these evils in detail, both in respect to 
 their cause and cure. 
 
SECTION III. 
 
 On the way in which Drains themselves give rise to 
 Stinks and Poisonous Gas, and the best means to pre- 
 vent them doing so. 
 
 If drains are made of a porous material such as brick, 
 or unglazed pipes, they will necessarily be offensive : 
 this will also be the case if they are badly laid so that 
 they have hollows in which water stagnates. It must 
 always be remembered that sewage when fresh is almost 
 innocuous compared with the same when decomposing, 
 and that the rate of decomposition is immensely in- 
 creased by the presence of some already decomposing 
 sewage, which acts in the same way as yeast ; thus 
 sewage stagnating in, or flowing through, dirty drains, 
 will become offensive much more rapidly than if the 
 drains are clean. 
 
 Those drains which are underground are particularly 
 liable to these evils, and in addition are sometimes 
 leaky, in which case they saturate the ground around 
 them with stinking liquid. 
 
 It is of the first importance that these underground 
 drains, especially if under the house, should be well 
 
sect, in.] SEWER GAS. 
 
 laid and composed of the right material. Fortunately 
 there is no difference of opinion as to their proper con- 
 struction, and in most modern houses they are well 
 done. They should be composed of earthenware pipes 
 (not cast-iron), socketed, and jointed with cement. 
 There is an objection to making the joints with cement, 
 which often prevents its being done. It makes the 
 pipes very rigid, and as the ground under new houses 
 is liable to settle, there is fear lest the pipe should be 
 broken. This, however, will not happen if care is taken 
 to lay the pipes on a natural or well-rammed, or, in bad 
 places, a concrete bed. 
 
 The ordinary plan of jointing the pipes with clay- 
 puddle, though probably the best for sewers, is not so 
 good under a house where it will get dry, and where 
 economy in such matters sinks into insignificance com- 
 pared with efficiency and safety. 
 
 The drains above ground are generally of metal, and 
 it is only in the depressions which are intended to form 
 traps that stagnation can take place. This stagnation is 
 the cause of an evil often complained of, viz. that when 
 fresh water is let into a trap a smell comes up ; as, for 
 instance, when the pan of the closet is lifted and its 
 charge sent down into the trap, there is often a bad 
 smell, although apparently none at other times. The 
 fact is, that the trap beneath the pan stands full of filthy 
 water, and the pipe between the pan and the trap is full 
 of the effluvia which the contents of the trap give off. 
 So that when the pan is raised the condition of things 
 below is disturbed and the effluvia rises. The obvious 
 
SEWER GAS. [sect. hi. 
 
 remedy for this is to allow sufficient water to go down 
 each time to change the contents of the trap and leave 
 it full of pure water. More will be said on this subject 
 further on ia the book. 
 
 The size of the pipes is of some importance. It is a 
 common mistake to make some drains too large. It 
 must be remembered that the smaller a pipe is, the better 
 it is flushed, and the less liable it is to get blocked so long 
 as the inlet is properly protected by a grate. From the 
 nature of its work the closet-pipe should not be less than 
 five inches ; but such a pipe is large enough to form a 
 branch sewer to take the sewage from half a dozen small 
 houses ; for the cellar-drains, a pipe of three or four 
 inches is quite large enough. 
 
 With regard to the fall in the underground pipes, it is 
 of more importance that this should be regular than that 
 it should be great. A common rule is to allow f inch 
 fall in the yard. This is quite sufficient, and where 
 necessary a smaller fall may be used, provided the pipes 
 are laid with great regularity. 
 
 In modern houses the drains are generally well laid, 
 and consequently do not commonly generate gas within 
 themselves. Hence, in such houses precautions should 
 be first taken to prevent the gas from the sewers getting 
 into the drains ; after which, if there is any further smell, 
 the drains themselves must be looked to. 
 
SECTION IV. 
 
 On the precise way in which Sewer Gas enters Houses; 
 the inadequacy of means in use for preventing it, and on 
 the advantage of the New Plan. 
 
 The entrance of sewer gas by the house-drains has been 
 the subject of as much discussion within the last few 
 months as if it was a new discovery : but this is not the 
 case, for, if it had been unknown before, why have we 
 traps, and not only traps, but laws to cause the use of 
 traps, on the mouths of all drains? It is not the 
 tendency of this gas to get in that has been recently 
 discovered, but the inadequacy of the measures hitherto 
 taken to keep it out. 
 
 But although the fact that smells and bad air do force 
 themselves from the sewers is well known, it is not so 
 clear why they do so. Judging from the newspapers, this 
 is generally attributed either to an excess of pressure in 
 the sewer arising from the fermentation of its contents, 
 the backing up of water in the outlets of the sewers, or 
 the pressure of wind on these outlets ; or else to the 
 lightness of sewer gas, which causes it to ascend by levita- 
 tion wherever ascent is possible. 
 
26 SEWER GAS [sect. 
 
 The first of these causes is much overrated, in fact 
 it only exists at all under exceptional circumstances, as, 
 for instance, near the outlet of a large sewer on which 
 the wind is blowing. Whenever experiments have been 
 made to ascertain the excess of pressure in the sewers of 
 a town, contrary to expectation the pressure within the 
 sewer has been found less than that without. Nor, as 
 we shall see, is it at all difficult to find a reason for this. 
 Sewers must not be looked upon as so air-tight that 
 a small quantity of gas has a difficulty in escaping from 
 them ; there is generally what may be called free com- 
 munication between the sewer and the outer air, so that 
 it is impossible there should be an appreciable difference 
 of pressure within and without. 
 
 The second cause no doubt exists ; the drains are 
 all laid with a falling gradient from the house to the 
 sewer, and consequently they rise from the sewer to the 
 house; and the light gas will ascend in the opposite 
 direction to that in which the water falls. 
 
 Now, possibly some of the evil is due to this cause, 
 but far more to the following, viz. the suction of a 
 house produced by the chimneys, or even the warmth of 
 the house itself. 
 
 This suction of the house, although a very small quantity 
 in actual pressure, being always less than one-eighth of 
 an inch of water; i.e. not sufficient to suck water up a 
 tube one-eighth of an inch, and consequently never suffi- 
 cient to suck the air past a good trap, is sufficient to 
 cause a great deal of air to enter by a very small open- 
 ing. This will be at once perceived by holding the 
 
iv.] SEWER GAS. 27 
 
 hand over the crevice of a window in a room with a fire. 
 Hence, be there cranny or crevice into a drain, the 
 house will suck gas, whatever be its source. This is the 
 reason why there is a minus pressure in the sewers ; the 
 houses which drain into them are making larger demands 
 for gas than can be supplied by the fermentation of their 
 contents, or wind that may enter at their distant outlets. 
 
 We see, then, that there are two inducements for the 
 gas to enter the house. Now the distinction between 
 them has not received due attention ; they have been 
 confused together, and as the same preventives which are 
 efficient for the one are no use for the other, the attempts 
 to prevent the gas entering have been failures. If the 
 effort of the gas to escape from the sewer were the only 
 reason why it enters the house, this would be satisfied 
 by providing it with a more ready means of exit from the 
 sewer, such as street gullies, shafts, or down spouts. But 
 as the suffocated houses suck away at the drains, air will 
 be drawn out, however many other openings there may 
 be into the sewer, which only serve to let fresh air in. 
 Hence no amount of ventilating shafts can be efficient 
 to cure the evil. Nor is it practicable, as has been pro- 
 posed, to produce effective exhaustion in the sewers by 
 furnaces, for the simple reason that the sewers are not 
 sufficiently air-tight. 
 
 It is not, then, enough simply to prevent the sewer 
 forcing or breathing gas into the houses, we must prevent 
 the house sucking the gas out of the sewer. This is 
 what drains on the usual system, fail to do ; the reason 
 why they so fail will appear when we consider the prin- 
 
28 SEWER GAS. [sect. 
 
 ciple on which they are supposed to act. The drains 
 themselves have free communication with the sewer, and 
 are therefore always filled with sewer gas, and if the 
 house is not to suck this gas from the drains, it is neces- 
 sary in the first place that the inlets or mouths of the 
 drains should be efficiently trapped ; and in the second 
 place, that the drains themselves should be air-tight as 
 well as water-tight. 
 
 Now, to consider the latter of these conditions first, 
 viz. the making the drains within a house perfectly air- 
 tight. It may be possible to make them so for a short 
 time ; but in practice it is found impossible to keep 
 them so. As we have seen, these drains are of different 
 sizes and composed of different materials ; this makes 
 it very difficult to joint them tightly. The metal pipes 
 alter in length with the temperature, and the expansion 
 breaks the putty or cement joints. If, as is the case 
 with gas or water-pipes, leaks manifested themselves 
 with certainty, we might depend on occasional repair 
 to keep these drains tight ; but such is not the case. 
 There is positively no means of ascertaining whether 
 the pipes are sound or not. A smell often shows that 
 they are not tight, but its absence does not prove them 
 to be so. 
 
 It is found practically impossible to make the joints 
 tight (especially those between the lead and iron pipes), 
 and in the face of this fact and that just mentioned, 
 that we have no means of ascertaining when they want 
 repair, it is unscientific to trust to this way of keeping 
 the gas out of houses. 
 
IV.] SEWER GAS. 29 
 
 Again, to go back to the traps, is it possible to close 
 the mouth of the pipes against gases and leave them 
 open to the refuse liquid ? This can only be done under 
 certain circumstances ; then it is done by a water-valve, 
 commonly called a stench-trap. These, though of great 
 variety, are all on the same prin- — 
 
 ciple. This principle is very ^^^k Jr\^ 
 
 simple, as may be seen from the WJL^^Ljf^JWl 
 commonest and simplest form of ifep-"^lBr 
 
 trap — a depression in the pipe, ^^^0r 
 
 which stands full of water, and Fig. 6. 
 
 therefore closed against the gas, after the rest of the pipe 
 is clear. 
 
 Many so-called traps are defective in construction. 
 Sometimes the depression is too shallow, so that when 
 this is full the passage is not completely blocked ; but 
 sometimes, where the depression is deep enough, the trap 
 fails from the fact that of the water which runs through, 
 none, or only a little, remains in it. This is the case 
 with a pipe so small in proportion to its work that it 
 runs full ; for if there is sufficient fall in the pipe below 
 the trap, the water in this portion of it will, by its syphon 
 action, empty the depression. This is a very common 
 fault with the traps in small lead pipes ; most plumbers are 
 alive to it, and make traps in such pipes of a larger size 
 than the pipe itself. 
 
 But it is not only faulty traps that fail : the best trap 
 will not act unless it has water in it ; and, since water 
 evaporates, there must be a constant, at least a frequent, 
 supply of water through the trap to render it effective. 
 
30 SEWER GAS. [sect, 
 
 Now, many of the drains commonly put into a house 
 have no water through them by the month together, and 
 where this is the case, even if the water does not leak 
 out of the trap, it will dry up and the trap be left open. 
 This is particularly the case with the cellar traps, which 
 are often out of the way and unnoticed. 
 
 Again, if dirty water stand in a trap for a few hours, it 
 becomes putrid, especially if there be any putrid water in 
 the trap to begin with. Hence, any trap which is likely 
 to be left full of dirty water is liable to cause nuisance 
 in a house. There is a great liability of this happening 
 with the trap under the pan of a water-closet. This is 
 often so large that there is not enough water in each dis- 
 charge to make a sufficient change in the contents of the 
 trap ; and where with such a construction the closet is 
 only used once or twice a day, the trap is sure to get 
 very dirty. This liability is cured if the trap is left full 
 of clean water, or if there is a frequent flow through it, 
 clean or dirty. 
 
 There is, however, another difficulty with traps : being, 
 as we have said, essentially depressions in pipes, they 
 
 Fig. 7. 
 
 are apt to arrest sediment, and become choked up with 
 it. This is very liable to happen in the cellar drains 
 
iv.] SEWER GAS. 31 
 
 where the dirt from the floor is washed into the gullies. 
 From this reason alone the bell-trap is generally used in 
 cellars, because it can be cleaned out with facility : but 
 it is objectionable from its peculiar liability to dry up. 
 
 To prevent traps from becoming blocked in this way, 
 it is necessary that water should run through them with 
 sufficient velocity to flush them, i.e. carry the sediment 
 out along with it. Where the ordinary flow is not suffi- 
 cient for this, it must be done occasionally by a special 
 effort. 
 
 Thus we see what the conditions are under which 
 a trap will act with certainty ; viz. when the pipe is 
 sufficiently large not to run full, and when there is a 
 frequent flow of water through it. Now, no traps inside 
 a house exist under such conditions, unless it be that 
 in the closet-pipe, and that not always ; hence it will be 
 an advantage to get rid of these inlet traps altogether, 
 and supply their place by another trap placed under 
 more favourable circumstances. 
 
 The sewer gases will be as effectually kept out of the 
 house if they are kept from entering the drains, as if they 
 were prevented from leaving them. In fact, these drains 
 are passages ; and, if we can stop the passages at either 
 end, it will answer our purpose equally well. And, for 
 reasons which are very simple, it is much easier to prevent 
 the sewer gas from entering than from leaving the house 
 drains. These drains, like a river, derive their waters 
 from many sources, and bring them together to one 
 outfall. The water from all the sources will run through 
 this, and hence, if there is a daily flow anywhere, it will 
 
32 SEWER GAS. [sect. 
 
 be here ; and consequently here the circumstances will 
 be most favourable for the action of a trap. Besides 
 this, there is no chance of the gases leaking into the 
 house drains through open joints. Hence we see that 
 an efficient trap in the pipe which connects all the house 
 drains with the sewer or cesspool, will completely cut 
 off the house from the sewer. 
 
 It is difficult to say how it is that such a simple remedy 
 as this has been neglected so long, unless it is that the 
 true nature of the evil has never been clearly appre- 
 hended. There is, it is true, something to be said against 
 complicating the drains when they are buried six or eight 
 feet under the surface, and consequently difficult to get 
 at. And this may have been sufficient to prevent the 
 adoption of the measure so long as it was of doubtful 
 advantage. 
 
 A good syphon trap of glazed earthenware, such as 
 that in Fig. 6, would probably answer all purposes in 
 five cases out of six ; but there is just the chance that 
 the pipe might run full and suck the trap empty, or that 
 the trap might get blocked with sediment, which would 
 be very awkward. 
 
 Now, the plan recommended and described in Sec- 
 tion I. cures both these failings. It secures the trap 
 from being emptied, and furnishes the means of inspect- 
 ing it, either to examine its condition or to set it right. 
 And it will now be understood why this peculiar con- 
 struction is insisted on, and why it is placed in the only 
 connection between the house and the sewer. 
 
 Such connections as these should be adopted for all 
 
IV.] 
 
 SEWER GAS. 
 
 houses having drains from within, whether they are in the 
 town or in the country ; whether they drain into a sewer 
 
 Fig. 8. 
 
 or a cesspool. There will then be no need to have traps 
 within the house, and their riddance will be a great com- 
 
 C 
 
34 SEWER GAS. [sect. iv. 
 
 fort, even if we thereby allow air to enter the house 
 freely from the inlets to the drains. Owing to the fric- 
 tion in the pipes not much will come through, and 
 such as there is can only come from the down spouts 
 or such external connections as there may be on the 
 house-side of the trap, and will therefore be harmless, 
 unless it meets with some stagnant sewage in the house 
 drains themselves which ought not to be there. We 
 have seen that trapping the inlets will not stop the air 
 entering the house, while the stagnant contents of the 
 traps will perhaps turn otherwise harmless air into 
 poisonous gas. 
 
 If the drains within a house are already well laid, it 
 may not be worth while to disturb these simply to do 
 away with the traps ; but where this is not the case, or 
 where after the external trap has been put in there is 
 still annoyance from the drains, then the best plan will 
 be to reduce the whole system of drains as much as 
 possible, as shown in Fig. 8, and do away with all 
 traps except the pan of the closet. And above all things 
 see that the new drains are well laid, and keep a 
 register of their position. 
 
 LONDON : K. CLAY, SONS, AND TAYLOR, PRINTERS. 
 
Second Edition, Corrected and Enlarged. 8m cloth, price 10s. 6d. 
 
 A DIGEST OF FACTS 
 
 RELATING TO THE 
 
 TREATMENT Sf UTILIZATION 
 
 OF 
 
 SEWAGE. 
 
 BY 
 
 W. H. CORFIELD, M.A., M.B. Oxon.; M.R.C.P. Enc 
 
 Professor of Hygiene and Public Health at University College, London ; 
 
 Medical Fellow of Pembroke College, Oxford; Medical Officer of Health for 
 
 Islington ; Assistant Physician to the Victoria Park Hospital 
 
 for Diseases of ike Chest; &>c. 
 
 OPINIONS OF THE PRESS. 
 
 Athenaeum. — "Mr. Corfield's work is entitled to rank as a standard 
 authority, no less than as a convenient handbook, on all matters relating 
 to sewage." — {Jan. 7th, 1871.) 
 
 Spectator. — " It carries out very thoroughly the purpose which 
 its modest title states. The author has evidently used all possible 
 diligence in collecting facts, and, having collected them, knows how to 
 deal with them."— {Jan. 3&th, 1871.) 
 
 Engineer. — "A valuable addition to our scientific books of refer- 
 ence." " Our readers will find in Mr. Corfield's volume a careful, 
 truthful, and valuable digest of all matters relating to the subject of 
 sewage, and we can cordially recommend it to their perusal." 
 
 {Mar. i-jth, 1871.) 
 
Architect.—" The author has good reason to be fully congratulated. 
 The volume is complete and exhaustive, apparently very fair in its 
 arguments and deductions, giving the reader abundant data on which 
 to found his own opinions." — {Oct. 12nd, 1870.) 
 
 Builder "We recommend for a wide study the patient, candid, 
 
 and ample digest of facts upon a momentous subject which has been 
 drawn up by Mr. Corneld."— (Leader, Oct. 29th, 1870.) 
 
 Nature. — "A clear, readable, and reliable risumi of the 'Great 
 Sewage Question.'" — {Jan. 12th, 1871.) 
 
 Chemist and Druggist. — " We do not hesitate to describe this as 
 a book of extreme value, and though its compilation must have been 
 laborious, it has been carried out by Professor Corneld with the utmost 
 patience and ability. " — (Nov. \$th, 1870.) 
 
 Daily News. — "As a repertory of facts, the book will be found 
 most useful to all who wish to study the subject with which it is con- 
 cerned." — (Nov. %th, 1870.) 
 
 Evening Standard "Mr. Corneld will prove an admirable guide 
 
 for persons whose business it may be to make themselves master of the 
 subject in all its details. They will find in his storehouse of facts 
 ample material whereon to work. To such students the volume will be 
 invaluable." — (Jan. loth, 1871.) 
 
 Daily Telegraph.— " Laden with well-distilled information on a 
 subject of high importance to every social reformer." 
 
 (Feb. 14th, 1871.) 
 
 Medical Times and Gazette. — " A very elaborate treatise. We 
 can recommend it to our readers as containing a large amount of infor- 
 mation, and some able reasoning." 
 
 ' ' Professor Corfield's book will well repay the study of all who are 
 interested in the great subject of the increase of national health and 
 national wealth. " — (Sept. 2nd.) 
 
 MACMILLAN AND CO., LONDON.