Plumbing and household sanitation

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J. Pickering Putnam.

PLUMBING

AND

HOUSEHOLD SANITATION

BY THE SAME AUTHOR

Lectures on The Principles of Household Drainage

Delivered before the Suffolk District Medical Society, and the Boston

Society of Architects, at the Massachusetts Institute of Technology.

With over 300 Illustrations.

From the Editor of the Sanitary Record, London.

By permitting me to reproduce these "admirable articles in the Sanitary Record, you will greatly oblige me and serve the cause of Sanitary Science in England."— The Editor.

Sanitary Plumbing

Reprinted from the American Architect and Building News. With over 400 Illustrations.

"These investigations have been set forth quite fully in illustrated communications to the American Architect, which papers certainly mark a very important step forward in Sanitary Literature." — Col. Geo. E. Waring, Jr., in the Century Magazine for December, 1884.

"This important work of the laboratory has been under the direction of Mr. J. Pickering Putnam, of Boston, and I am sure that his experiments and investigations are the most comprehensive, and thorough and valuable that have ever been made on the subject of Household Sanitation " — Address before the Academy of Sciences at Rochester. New York, by Wm. E. Hoyt, C. E., S. B., Chief Engineer of the B., R. & P. R. R. Co.. and at «ne time Chief Engineer of the Massachusetts State Board of Health. Ticknor & Co., 1886.

The Open Fireplace In All Ages

Republished from the American Architect and Building News. Quarto, with over 300 Illustrations.

"This is undoubtedly the most extensive and critical work on this subject in the language. The author takes up the subject of heating and ventilation and treats it in extenso, showing existing defects, giving a full historical resume of the theme, and ends by criticism and practical suggestions."— Chicago Journal.

"A very beautiful book, artistically and practically,.'' — Louisville Courier- Journal.

" It is brimful of good suggestions." — N. Y. Graphic.

" The book is excellent from cover to cover, and a real contribution to useful literature." — Boston Advertiser.

ALSO THE FOLLOWING MINOR WORKS:

"Architecture Under Nationalism," pub. by "Am. Architect," 1890. "The Metric System of Weights and Measures." pub. by Library

Bureau, 1877.

"The Outlook for the Artisan and His Art." pub. by C. H. Kerr &

Co., Chicago.

"Improved Plumbing Appliances," pub. by Wm. T. Oomstock. N. Y..

1887.

"General Principles of House Plumbing," in Buck's Handbook of Medical Sciences. Wm. Wood & Co.. N. Y., 1886. Etc.. Etc, w^^tik^x

t. Recipient of the Grand Prize of Rome, Academy of France. ques." Firmin — Dido et Cie, Paris, 1890.

PLUMBING

AND

HOUSEHOLD SANITATION

BY

J. PICKERING PUTNAM

MEMBER OF THE BOSTON SOCIETY OF ARCHITECTS AND OF THE AMERICAN INSTITUTE OF ARCHITECTS

A COURSE OF LECTURES DELIVERED BEFORE THE

PLUMBING SCHOOL OF THE NORTH

END UNION, BOSTON

Garden City New York

DOUBLEDAY, PAGE & COMPANY

A r*

COPYRIGHT

BY J. PICKERING PUTNAM.

TO THE BOSTON SOCIETY OF ARCHITECTS

WHOSE UNTIRING AND' DISINTERESTED EFFORTS IN BEHALF

IF BETTER BUILDING LEGISLATION ENTITLE THEM TO PUBLIC

RECOGNITION AND GRATITUDE, THIS LITTLE WORK

IS RESPECTFULLY DEDICATED.

Contents

Page

PREFACE.— Purpose and Scope of the Work. Boards of Health are urged to provide themselves with Testing Apparatus enabling them to demonstrate the superiority of the Simple or One Pipe System of Plumbing over the complicated one now in vogue in most Cities and Towns, and relieve the Public of a very great and unnecessary Burden, Cut the Cost of Plumbing in Two, and yet at the same time increase Its Safety and Convenience. Authorities Consulted 11

INTRODUCTION.— The Significance in Sanitary Plumbing of the Modern Science of Bacteriology and Chemistry, and a Summary of the Conclusions in the direction of greater simplicity to which they lead. Important Benefits which would result from Filtering the Air of Cities of Dust and Bacteria through Proper Sewer Ventilation. The Ten Laws or Commandments of Plumbing 18

CHAPTER II.— Influence on the Community of Sanitary Engineering 43

CHAPTER III.— Bacteria in their Relations to Sanitary Engineering. The Marvelous and Intensely Interesting Recent Discoveries in Bacteriology and the Great Importance of this Science to the Sanitary Engineer 49

CHAPTER IV.— Sewer Air. Ancient and Modern Views of Its Nature and Composition. Conclusions of Modern Science as to the Freedom from Disease Germs of Sewer Air, and as to why they are unable to survive long in Sewage itself, and why they Cannot Rise from Liquids nor Damp Surfaces. Researches and Conclusions of Modern Scientists on the Effects of Breathing Sewer Air 66

CHAPTER V. — Dr. Carmichael's Experiments and Conclusions as to the Reliability of Water Traps for Excluding Gases and Germs. Similar conclusions by other well-known Scientists. Experiments on Filtration 90

CHAPTER VI.— Further Studies on Micro-Organisms in Sewer Air, and in the Outer or Street Air of Cities Above the Sewers 110

CONTENTS.

Page CHAPTER VII.— The Main House Trap and the Reasons why its Use should be Prohibited by Law. Why the House Drains should be Used as Sewer Ventilators. Author's Experiments, Calculations and Conclusions as to the Immense Value of Such Ventilation and the Amount of Air Filtration and Purification from Dust and Germs of the Air of Cities it would effect 125

CHAPTER VIII.— Sewer Ventilation, and the Reduction of the

Death Rate of Cities through Proper Sewerage 140

CHAPTER IX.— Traps. General Considerations and Classification 151

CHAPTER X.— Mechanical Seal Traps and Their Tendency

to Clog 154

CHAPTER XI.— Water Seal Traps and Their Classification into Cesspool and Self Cleansing Traps. Dangers of Cesspool Traps 168

CHAPTER XII.— Street Gullies. Why They Should be Made

to Aid Sewer Ventilation 175

CHAPTER XIII.— Seal Retaining or Anti-Siphon Traps, and

Their Philosophy and Development 184

CHAPTER XIV.— The Two Plumbing Systems, the Simple and the Complicated. The Hydraulics and Pneumatics of Plumbing ' 233

CHAPTER XV.— Trap-Testing Apparatus. Experiments on Siphonage, Back Pressure, Evaporation, and Clogging of Traps, and Author's Researches and Demonstiations Before Sanitary Engineers, Boards of Health and others 241

CHAPTER XVI.— Self Siphonage and Momentum 288

CHAPTER XVII.— Water Flushing. Its Great Importance and

Deplorable Neglect in Practice and Plumbing Legislation.. 290

CHAPTER XVIII.— Evaporation of Trap Seals 304

CHAPTER XIX.— Capillary Action on Trap Seals 315

CHAPTER XX.— The Evils of Back Venting Traps 331

CHAPTER XXI.— Wash Basins, Ancient and Modern, and the

General Principles which Should Govern Their Construction 339

CHAPTER XXII.— Classification of Lavatories. Plug and Chain

Waste Cock Outlet Lavatories 350

CHAPTER XXIII.— Valve Outlet Lavatories 362

CONTENTS.

Page

CHAPTER XXIV.— Plnnger Outlet Lavatories 369

CHAPTER XXV.— Standpipe Outlet Lavatories. Improved Lavatories 379

CHAPTER XXVI.— Kitchen and Pantry Sinks. Should be Constructed on Principle of the Automatic Flush Tank 393

CHAPTER XXVII.— Public Baths. Interesting Examples, Ancient and Modern 411

CHAPTER XXVIII.— Latrines and Water Closets and Their

Classification 419

CHAPTER XXIX.— Defects of Valve and Plunger Closets 440

CHAPTER XXX.— Interesting Ancient, Modern and Foreign

Examples and Wherein They are Unsatisfactory 450

CHAPTER XXXI.— Improved Closets 462

CHAPTER XXXII.— Modern Trap Jet Closet: their origin and

development. Latest Improvements 471

CHAPTER XXXIII.— Soil and Drain Pipes and Their Classification 502

CHAPTER XXXIV.— Lead Calked Joint. Its Serious Defects; Its Use Doubles the Cost of the Piping by necessitating Extra Heavy Pipe ' 516

CHAPTER XXXV.— Flange. Sleeve, and Screw Joints 538

CHAPTER XXXVI.— Leakage of Pipes and Joints and the Grave Danger of Gas and Water Leakage, and the Immense Volume of Loss Sustained by the Public 561

CHAPTER XXXVII.— Improvements in Pipe Jointing. Rigid

and Flexible Joints 570

CHAPTER XXXVIII.— General Arrangement of Plumbing Work.

Bath Room Ventilation Outside Windows Unnecessary . . 595 CHAPTER XXXIX.— Author's Report to Boston Board of

Health on Siphonage and Evaporation of Traps 601

CHAPTER XL.— Critical Review of Dr. Teal's interesting illustrated ''Dangers to Health," in the Light of Modern Bacteriology 630

CHAPTER XLL— Slow Sand Filtration 661

CHAPTER XLII.— Plumbing Laws. Critical Analysis. Corle

Recommended by the Author 672

CHAPTER XLIII.— Recapitulation 696

CHAPTER XLIV. — Author's Address before Am. Inst. Archts. 707

Preface

To the Header.

Since the purpose of this course is to treat of the best and simplest method of obtaining healthy homes and to show by what means the utmost convenience in plumbing work may be obtained with safety and economy, no attempt will be made to describe in catalog form all the interesting appliances manufactured to-day. Indeed, it would be impossible in a small volume to do even partial justice to their almost countless numbers. Each enterprising manufacturer requires for the cataloging of his sole individual productions, a ponderous volume, sumptuous and costly enough to pay for a small king's ransom. Before long, of course, in accordance with a law of economics which allows of no exception, a very big Trust will take charge of the whole business and place the goods before the public in a simplified form. Then the consumers will constitute the stockholders and price lists will become less mysterious and more satisfactory.

But in the meantime the work of combining the descriptions of all the myriads of artistic and tempting creations in a single volume or set of volumes for ready reference must be left to some specialist in business cataloging like "Sweet's" Indexed Catalog of Building Construction which

Preface.

will place them all before the architect and his client in such a form that they can actually be found when they are wanted. But "Sweet's" will not be able to discriminate against some of these goods in favor of others, even in the interest of the public, because the same individual cannot to-day serve both as business agent and critic at the same time. An old and reliable authority assures us that a man cannot at one time serve two masters.

The business cataloging, therefore, being provided for elsewhere, the public will now only require a knowledge of the scientific principles which should guide them in their selection and use of these goods. It will be found that all the plumbing appliances and methods of construction in use to-day may be grouped under certain classes or types, and that by means of such classification any one may, without laborious technical training, be enabled to discriminate independently between the good and the bad, even though the bad may possess in some cases the most pleasing external appearance.

Accordingly we have arranged in this volume a classification and explanation not of appliances but of types and methods of construction which will enable the reader to judge for himself independently, and acquire all the modern plumbing conveniences and sanitary advantages with the greatest safety and at the same time with the least expense.

The reader is warned that he will find in these pages many ideas and conclusions which are not considered orthodox among many plumbers and framers of plumbing legislation.* The existing state of things has been freely criti-

♦Some practitioners, very properly estimating- highly the "practical" side of the plumber's work, have questioned the ability of a non-practitioner in plumbing or a "theoretical" man to fully comprehend an art which is so technical in its nature. While an architect does not deny that he must be something of a theorist in the interest of progress, he nevertheless contends that the nature of his work requires him to be essentially and first of all practical Although he may be unable to wipe a joint or set a fixture with skill, he is nevertheless trained to fully comprehend the philosophy and purpose of these proceedings. The very first thing he discovers in the practice of his profession is that there is no sound theory which is not based on facts and on facts alone.

Defects in Plumbing Laws.

cized whenever it has appeared, after exhaustive experimentation and investigation, that simpler and better methods are possible. It is now possible for anyone to demonstrate for himself with little expense whether or not the contentions made herein are correct, without going through all the tedious and costly experiments which have led up to them, and if the writer wished to lay claim to having performed some slight service in his several years of effort along these lines, perhaps an item might be in his having called attention to and in a measure having developed the means and implements needed for such demonstration.

His chief claim, however, is in having labored for many years to show to legislators and to the public in general (with definite, favorable results on plumbing legislation in more than one city), the importance of very greatly simplifying our plumbing ; in having first pointed out the significance of recent bacteriological discoveries in providing further justification for these simplifications, such, for instance, as the omission of the main house trap, whereby an exceedingly important purification and dust and germ filtration of the air of cities through the agency of the moist surfaces of the sewers and individual house drains, is effected ; and finally in having devised certain practical means for obtaining these simplifications hitherto considered impossible.

It is hoped that Boards of Health will avail themselves of some simple standard form of apparatus and methods of demonstration which any plumber can construct of ordinary piping, with cistern, vacuum gauge, and ordinary quickclosing valves, and relieve a long-suffering public of a. burden in plumbing construction, still required in the majority of cities and towns of the United States, which is, to express it in the mildest terms, a most gigantic blunder. The cost of such apparatus would be more than paid for by the saving in the plumbing of a single building.

Preface.

It is quite as important and useful a part of the work of an investigator to build up as it is to tear down. It is indeed, in a certain sense, useless to criticize an existing state of things unless some practical remedy can be offered to take its place. No apology seems, therefore, required for the presentation here of certain new methods and appliances which have been developed in the course of these studies to meet the new conditions advocated, nor for the protecting of some of them by patents. Yet the writer recognizes that however much the public may desire to see an inventor share with it a small part of any benefit which may be derived from his efforts, he is nevertheless, and, so long as a destructive form of competition continues to form the basis of the business relations between men, must be, regarded rather in the light of an "innovator" to be opposed and punished by all who are financially interested in the existing order of things.* Therefore, it is the industrial system and not the individuals affected which .is responsible for the long continuation of abuses from which the public might otherwise be quickly freed, and for the tardy recognition the inventor receives. Any return at all should really be regarded by him as more than he ought to expect under such conditions, and the writer should feel really much gratified that he has so far been able to escape from this unequal contest with some of his bones unbroken.f

♦Pipe dealers are financially interested in maintaining the elaborate system of piping required by back venting and main house trap installation, while plumbers have nothing to gain by it, but rather much to lose, since what money goes into unnecessary piping is lost for better fixtures and more of them, and the public, alarmed by all the complication, becomes distrustful of all plumbing and tends to do away with its benefits as far as possible.

tin spite of these discouragements, some words of recognition have now and then been received from disinterested parties which have given renewed courage and perseverance at times when they seemed most needed. Among them are the following from no less of an authority than William E. Hoyt, C. E., S. B., Chief Engineer of the Buffalo, Rochester & Pittsburg Railroad Company and at one time chief engineer of the Massachusetts State Board of Health : "Not long after the adoption of the fallacious device of back venting, it became evident that more efficient means of guarding against the

Original Investigations.

It should be added that these investigations and innovations have been made in the course of regular professional practice, and have, therefore, been conducted in the unprejudiced spirit of an architect working for the interest of his clients, and in some cases with their substantial aid and co-operation. The improvements and their protection, are the result and not the cause or original purpose of the

dangers of sewer-air were necessary and persistent effort was directed toward devising better methods of house drainage. The result has been the attainment of a new order of things by the recognition of scientific principles previously ignored. Without referring now directly to the experiments and investigations, we may consider briefly certain principles which have been established by them. The first and cardinal principle of science as applied to house-drainage is simplicity. In the place of a wilderness of pipes tangled in hopeless confusion about every fixture, modern science demands that there shall be only a simple and positive system which shall act with directness and certainty in every case. The old air pipes from traps are discarded. There are fewer joints and the danger from leakage is lessened. Instead of traps that easily lose their seal, notwithstanding the relief pipes attached, traps are now used that in themselves will resist the hostile influences of evaporation and siphonage. The new system demands that basins, sinks, baths and water closets shall be so constructed as to act after the manner of flush tanks, and scour the whole system of waste pipes at each discharge. It requires that there shall be no hidden and inaccessible recesses in plumbing fixtures, where filth may collect and putrefy so as to become offensive and dangerous. The absolute prevention of serious evils is considered of far greater importance than means to palliate them.

For the development of this science credit must be given mainly to an accomplished sanitarist of Massachusetts, Mr. J. Pickering Putnam, whose experiments and investigations on subjects relating to household sanitation are unquestionably the most thorough and complete that have ever been put on record. The first of this series of experiments was made for the Board of Health of Boston in 1883. Subsequently, special demonstrations were shown before the Suffolk District Medical Society of Massachusetts, the Boston Society of Architects, and others. The results have been published in the "Boston Medical and Surgical Journal," the "American Architect," the "Sanitary Record" of London, and other periodicals." Wm. E. Hoyt, C. E., S. B., in an article on "Safety in House-Drainage," published in "The Popular Science Monthly." for July, 1888.

If Mr. Hoyt has been a little over generous In his words of encouragement, it will not be allowed to have a permanently injurious effect upon the writer's character, but be considered as in a measure offsetting the rebuffs received from others not so favorable to progress as Mr. Hoyt.

The late Col. George E. Waring, in an article published in the Century Magazine for December, 1884. on the "Principles and Practice of House Drainage." wrote of the writer's investigations and writings equally pleasantly, saying of them that "they certainly mark a very important step forward in sanitary literature."

In another place equally encouraging words by other well known authorities will be quoted, only enough here being needed to reassure the reader and cheer him forward in the study of this somewhat dry subject, if a treatise on hydraulics may be so designated.

Preface.

investigations. If they are actually improvements on what existed before (the need of improvement being clearly recognized) then they are the best in the particular class to which they belong up to the date of their presentation, and as the purpose of this writing is to advocate the best, they will necessarily have to be described as such irrespective of their authorship, and even in some cases to the exclusion of other things in the same class, which are believed to be not so good. It must be left to the common sense of the reader to judge of the soundness of the reasoning in each case, and of the just motive and sincerity of the author. The quotations in the foot-note are only given for the purpose of placing the reader, who might naturally be prejudiced by these circumstances, in a more impartial and receptive frame of mind for judgment.

An apology should be made for the name "plumbing," which has curiously enough been taken from the very metal, lead (Latin, plumbum) , which we are learning should rarely be used in its unalloyed form in plumbing at all. Brass and iron are rapidly taking its place. Lead is inelastic, inert, feeble, treacherous, unreliable for plumbing and dangerous on account of the fire it requires in the house for its manipulation. The ancient alchemists called it Saturn. The modern plumber should modify this name to Satan, and debar his entrance and his fire altogether from the house.

To sanitary engineers one of the most important works which have been published in the last decade is the record and critical examination of the researches of bacteriologists entitled "Sewer Gas and Its Influence Upon Health," by H. Alfred Roechling, C. E., which the writer has freely quoted in these lectures, and for which he desires here to express his obligation. More recent and equally valuable are the researches in the same field of our own Professor Charles Edward A. Winslow, of the Massachusetts Insti-

Acknowledgments.

tute of Technology, whose aid is gratefully acknowledged.* Thanks are also extended to Professor Edward S. Morse for his courtesy in permitting the use of his remarkably interesting sketches which have been taken from one of his masterpieces entitled "Japanese Homes and Their Surroundings," published by Harper Brothers, New York.

Also to William Paul Gerhard, C. E., for valuable aid in connection with furnishing copies of the plumbing laws of a very large number of cities and towns of the United States ; to Mr. David Craig for many practical suggestions ; Mr. Craig, while acting as President of the National Association of Master Plumbers and of its sanitary committee, has performed a valuable public service in furthering the investigations conducted for the committee by Prof. Winslow,f and later their publication ; to the writings of Dr. Antoine Magnin, Prof. H. W. Conn, Dr. Niel Carmichael, Mrs. and Prof. Percy Frankland, Yiollet le Due, Col. George E. Waring, Dr. Teale, and many others whose works are referred to and duly acknowledged in the text, to "Domestic Engineering" for a number of valuable articles which have been quoted and credited where mentioned, and, finally, to Mr. Samuel Hubbard, Director of the North End Union, of Boston, through whose invitation the course of lectures forming the nucleus of this work, was given before his pupils. J. PICKERING PUTNAM.

535 Beacon St., Boston.

*The National Association of Master Plumbers has within the last few months through its Sanitary Committee, made some very important investigations on the question of the carriage of bacteria by sewer air. This most careful and valuable work was entrusted to Prof. Winslow. and seems to entirely remove the doubts on the subjeet cast by the publication of Major W. H. Horrocks of the English Army Medical Corps, and corroborates the conclusions of Laws and Andrewes. Roechling and others. The work is being printed by the Master Plumbers' Association. and is a very valuable contribution by them and its author to the literature of the subject, and to the welfare of the public.

tThese conclusions of Prof. Winslow as published in this report agree with and corroborate the results attained by the author and published in the "Inland Architect" of Nov. 8. 1908, and in "Domestic Engineering" in 1900, 1903. 1906 and 1908.

Introduction

Fig. 2. Complexity and Fig. 3. Simplicity and Danger. Type of system Safety. Type of system of extreme complication recommended as a subto which we are tend- stitute. ing.

At the time when these lectures were first delivered, in the winter of 1899- 1900, the plumbing laws of Bost o n and of nearly every other city of the United States enforced a system of piping and trapping which almost doubled the cost of the work in new buildings and more than doubled it in repair work over what was necessary, besides greatly lessening its convenience and safety.

Every fixture was required to have a separate trap, and every trap had to be independently revented by a special "back vent" pipe extending up to the highest fixture in the building. A disconnecting trap was required between every building and the public sewer, which prevented the best and only known really effective method of ventilating the sewers ; and no better method of jointing cast iron pipes was allowed than the unscientific, unreliable and very costly lead calked bell and spigot joint.

These worse than useless and very burdensome requirements have held the people like a vise for the last quarter

Simplification of Plumbing.

of a century in spite of the protests during all that time of many of the leading sanitary engineers and plumbers.

Within a very few years, however, some of the more wide awake and progressive cities have seen the folly of this course and have given their citizens the benefits which the modern simpler and more scientific methods and discoveries have provided, and every year is adding to their number. But as the plumbing laws of the majority of places are based upon the ideas of more than a decade back, the only possible way to present anything of the least value in this important department of architecture is to break entirely away from the conventions of ordinary practice and base all our conclusions upon direct personal investigations and absolute demonstration. Our treatment must therefore necessarily become largely critical and argumentative throughout, and, although this method of handling the subject is certain to arouse from many quarters adverse criticism and possibly some bitterness, it is nevertheless evidently unavoidable, and will also have the great advantage. of making the matter vastly more interesting and we hope much more intelligible to the reader.

The arguments used by the writer as early as 1884 in behalf of this simpler plumbing system have been of late greatly reinforced by the discoveries of the bacteriologists. The data they have furnished and their significance from a sanitary standpoint have been summarized by him in his publications before 1909. as follow r s :

(1) A sound water seal affords a reliable barrier against the entrance of sewer air and all kinds of germs.

(2) Dust and germs falling into water or against the wet surfaces of sewers and drain pipes are, under normal conditions in the drains, arrested and prevented from rising again into the air so long as the surfaces remain wet.

(3) Abnormal conditions prevail in the drains when

Introduction.

splashing or bubbling occurs in the sewage under the influence of which fine droplets may be projected into the surrounding air. If these droplets contain germs and are minute enough to be wafted in the air currents passing through the pipes the germs therein may remain in the air until they again fall against the wet surfaces. Even germs have a definite weight and the speed of their descent under the influence of gravity has been calculated, which gives also the speed of an air current necessary to support or move them.

(4) It is possible that small particles of sewage which have dried against the upper parts of the walls of the sewers may be detached therefrom by air currents and in this manner under rare instances allow of the escape of germs into the sewer air. The probability of this action is denied by some investigators, but affirmed by others. It may be admitted as a possibility.

(5) Disease germs seem to be unable to survive long in sewage, the non-pathogenic germs therein far outnumbering them and destroying them by their products.

(6) Fewer germs are found in the air of sewers than in the outer air above the sewers, and those which are found in the sewer air are dissimilar in kind from those in the sewage but similar to those in the outer air.

(7) The number of germs present in the air of well ventilated sewers exceeds that in less well ventilated sewers, and varies with variations in the content of the street air, implying that their origin is from without and not from within the sewer.

(8) The majority of investigators have failed to isolate specific disease germs from the air of sewers, and it may be stated in general terms that they are not to be found there under normal conditions. Yet a few well known investigators have obtained cultures in the air of sewers of germs

Recent Discoveries in Bacteriology.

apparently coming from the sewage under normal conditions, and it is generally admitted that the splashing, bubbling or drying of the sewage may release them under rare conditions in good practice. Their numbers in sewer air must, however, in properly constructed sewers be so small in the whole volume of the sewer air, that their effect regarded from a sanitary standpoint may be considered as negligible.

From the above data and from his own experiments the writer has derived the following general conclusions affecting Sanitary Engineering.

(i) It is known that disease germs, especially those of consumption, may be disseminated in the air above the sewers, and may, especially in times of epidemic, abound there in large numbers, and unquestionably in larger numbers than in the air of the sewers themselves.

Under such circumstances street air passing through the sewers and house drains becomes filtered by them and emerges from the pipes freer from its dust and germs than when it entered, and must in fact before reaching the tops of the stacks above the roof be entirely freed therefrom.