IC-NRLF 272 SANITARY ENGINEERING GERHARD LIBRARY OF THE UNIVERSITY OF CALIFORNIA. Class SANITARY ENGINEERING SANITARY ENGINEERING BY WM. PAUL GERHARD, C.E. CONSULTING ENGINEER FOR SANITARY WORKS; MEMBER OF AMERICAN PUBLIC HEALTH ASSOCIATION, AMERICAN FORESTRY ASSOCIATION; CORRESPONDING MEMBER OF AMERICAN INSTITUTE OF ARCHITECTS, ETC NEW YORK PUBLISHED BY THE AUTHOR 36 UNION SQUARE, EAST 1898 8RARy 11 or ( UNIVERSITY J or t>~\ ( ft \J^' COPYRIGHT, 1898, BY WM. PAUL GERHARD, C. CONTENTS. PAGE ARCHITECTURE AND ENGINEERING 6 DEFINITION OF CIVIL ENGINEERING, ... 9 ENGINEERING SPECIALTIES, 11 DEFINITION OF SANITARY ENGINEERING, . 13 COURSE OF STUDY IN SANITARY ENGINEERING, . . 14 ACTUAL PRACTICE OF THE SANITARY ENGINEER, . 20 Water Supply of Cities and of Dwellings, . . 21 Sewerage, ........ 27 Prevention of Pollution of Water-courses, . . 35 Sewage Disposal 39 Street Pavements 44 Street Cleaning 52 Removal of Ice and Snow, 60 Street Sprinkling 62 Cleansing Footways and Sidewalks, ... 64 Removal of Refuse Garbage Disposal Scavenging, 65 The Laying Out of Cities and Towns, ... 69 Sanitation of Towns, ...*... 88 Sanitary Engineering in Relation to Habitations, . 89 Railway and Ship Sanitation, .... 91 Sanitary Inspection of Buildings and Building Sites, 92 The Sanitary Engineer's Services as Expert in the Courts, 93 Sanitary Engineering in Case of Epidemics, in Time of War, and in Sudden Calamities in Civic Life, 95 4 CONTENTS. PAGE THE TITLE "SANITARY ENGINEER," .... 95 GENERAL QUALIFICATIONS OF THE SANITARY EN- GINEER, 99 THE SANITARY ENGINEER IN PUBLIC LIFE AND MUNI- CIPAL GOVERNMENT, 100 APPENDIX : Work of the Sanitary Engineer in case of Sudden Outbreaks of Epidemics, 103 Work of the Sanitary Engineer in Time of War, 117 Work of the Sanitary Engineer after Sudden Calam- ities, Catastrophes, and Great Disasters in Civic Life, . . . . 127 SANITARY ENGINEERING,* THE subject discussed in these pages was, up to within a few years, comparatively unknown. Sanitary engineering like electrical engineer- ing is one of the recent branches of civil engi- neering ; sanitary science, the researches of which form one of its foundations, may like- wise be considered a new science, although it has, in the last few years, made such rapid strides that its importance is beginning to be more universally recognized. The general public has but a vague idea of the meaning of the term " sanitary engineer- ing." Many mistaken or narrow views exist in regard thereto, which, I trust, this book may help to dispel. Having lived for many years in each of the three continents of Europe, * A lecture delivered by the author before the Franklin Inst. of Phil, Feb. 15, 1895. 6 SANITARY ENGINEERING. Africa, and America, and being, therefore, some- what of a cosmopolitan, some of the statements which I shall make do not refer exclusively to American conditions. ARCHITECTURE AND ENGINEERING. As soon as a science, art, or profession ex- pands to such an extent, both in theory and in practice, that its entire field can no longer be mastered by one mind, it divides itself naturally into departments or specialties. We know this has been the case in law, in medicine, in the fine arts, and in the natural sciences. In fact, ours is the age of specialists in all branches of learning, in all arts and sciences. Such a sub- division has also gradually taken place in the profession or art of engineering ; thus it came about that sanitary engineering was made a special and distinct branch of the profession of civil engineering. Let us glance briefly at the origin, and define the meaning, of this new branch. ARCHITECTURE AND ENGINEERING. y Centuries ago the whole science and art of building construction were concentrated in one profession. At that time there existed even no division into engineers and architects. Archi- tecture and engineering were not only com- bined, but merged together with other profes- sions or arts. In those bygone times a man could be, at the same time, a painter, a sculp- tor, an engraver, a designer, and builder of church edifices, a constructor of fortifications, an engineer of canals. The thought of a Mi- chael Angelo Buonarotti, of a Leonardo da Vinci, of an Albrecht Durer, will readily recur to you. To-day, however, all this has been changed. The complex requirements of mod- ern civilization, the multiplication of human wants not to mention the exigencies of busi- ness competition render it well-nigh impossi- ble for such universal genius or master-mind to rise to success. While there may occasionally be exceptional instances of accomplished men who are proficient in many things, as a general rule those will succeed best who limit them- g SANITARY ENGINEERING. selves to the study and practice of one spe- cialty.* It is now a little over a century ago that in building construction the first division into the two independent professions of architecture and engineering took place. Broadly speaking, architecture deals with the ornamental, whereas engineering embraces the purely utilitarian, branches of construction. It should be said, however, that while, from a * After writing down the above, I happened, for the first time, to come across a passage in the poem " Lucile," by Owen Meredith, which expresses exactly the same views. It is as follows : " The age is gone o'er When a man may in all things be all. We have more Painters, poets, musicians and artists, no doubt, Than the great Cinquecento gave birth to ; but out Of a million of mere dilettanti, when, when Will a new Leonardo arise on our ken ? He is gone with the age that begat him. Our own Is too vast, and too complex, for one man alone To embody its purpose, and hold it shut close In the palm of his hands. There were giants in those Irreclaimable days, but in these days of ours In dividing the work, we distribute the powers." Lucile, Part /, Canto /, ///. DEFINITION OF CIVIL ENGINEERING. 9 purely business aspect, in the practice of the art, this division exists, the line cannot be quite so strictly drawn as regards the preparation and training required for the subsequent practice of the professions. It lies in the nature of their work that architects must be, to some extent, engineers ; they must understand construction in order to be able to design, whereas the reverse of this proposition is not quite so evi- dent, for to find artistic talent and skill in an engineer is rare. To some extent, nevertheless, these two professions have always remained in close touch, and in recent years architects and engineers have once more been drawn together, particularly in such works as pertain to land- scape and to domestic engineering. DEFINITION OF CIVIL ENGINEERING. The profession of civil engineering has been defined as " the art of directing the great sources of power in nature for the use and convenience of man." The organization of the first State IO SANITARY ENGINEERING. engineer corps occurred in France, in 1791, when the Corps des Ingenieurs des Fonts et des Chaussees was established. As the name implies, the work of these civil engineers con- sisted largely in the development of means for better transportation for passengers, as well as goods, such as the construction of roads, bridges and canals ; whereas the military engineers constructed works of fortification, and applied engineering construction to military operations. Soon after, followed the construction, equip- ment and management of railways and the im- provement of rivers, harbors and other aids to navigation. Other branches were added from time to time, such as the manufacture and im- provement of machinery and mechanical appli- ances ; the operating of mines ; the establish- ment of telegraph and telephone lines ; the erection of gas works ; the application of elec- tricity for producing light, heat and power ; the fire protection of buildings ; the water supply, sewerage and lighting of cities ; the drainage, lighting, heating and ventilation of buildings ; ENGINEERING SPECIALTIES. TI the reclamation of marshes and agricultural drainage ; the laying out of streets and towns, squares and parks ; the construction of piers, docks, sea-dykes, jetties, breakwaters and light- houses. Broadly speaking, engineers deal both with structures and with machines, the former being, according to Rankine, combinations of materials, the parts of which have no relative motion ; and the latter, mechanical appliances whose function is to perform useful work, and the parts of which move. ENGINEERING SPECIALTIES, At the present day we may distinguish the following divisions of engineering, viz. : Military Engineering, Electrical Engineering, Railroad Engineering, Gas Engineering, Hydraulic Engineering, Municipal Engineering, Marine or Naval Engineering, Sanitary Engineering, Bridge Engineering, Landscape Engineering, Mechanical and Steam Engi- Fire Protection Engineering, neering, Architectural Engineering, Mining Engineering, Agricultural Engineering. 12 SANITARY ENGINEERING. As previously stated, it is impossible for one man to acquire a complete knowledge and prac- tice of all branches, and the tendency to spe- cialization leads engineers to devote themselves to some one particular field. Notwithstanding this division into separate branches, made nec- essary largely by business considerations, the various branches often meet. Much of the work of the municipal or city engineer, for example, refers to sanitary, to hydraulic, and to gas engineering ; the landscape engineer and the architect meet in the laying out of country estates, city gardens and public parks ; the sanitary and the mechanical engineer meet in the planning and construction of heating and ventilating plants ; the sanitary and the hydraulic engineer, in works of water supply or sewerage for cities, villages and institu- tions ; the architect and the sanitary engi- neer, in all that pertains to healthfulness of habitations ; the architect and the bridge engi- neer, in the iron or steel construction and the foundations of large and tall buildings. These DEFINITION OF SANITARY ENGINEERING. j^ examples might be multiplied, but what is said will suffice to explain my meaning. DEFINITION OF SANITARY ENGINEERING. If we accept the above definition of civil engineering, then sanitary engineering may be defined as the art and science of applying the forces of nature in the planning and construc- tion of works pertaining to public or individual health ; or, to put it in other words, the purpose of all works of sanitary engineering is the pro- motion of healthful conditions, the avoidance of disease caused by outside influences, which may be brought under control of mankind, and the increase of the duration of life. It is obvious, therefore, that a general knowledge of civil en- gineering, of architecture and of sanitary science, in all their branches, should form the basis of the education of the sanitary engineer. I will make an attempt to outline briefly the course of studies and the special training re- quired to enable one to attain the qualifications 14 SANITARY ENGINEERING. necessary to practise the profession of sanitary engineering. Following this, I shall describe and discuss the principal subjects or problems with which the sanitary engineer deals in his practice. In order to become a competent en- gineer, the course of study should embrace both theoretical (scientific and technical) education and practical or manual training. The practi- cal education differs according to whether the special branch, which the engineer will follow later on, belongs to mechanical, civil, electrical or sanitary and hydraulic engineering. COURSE OF STUDY IN SANITARY ENGINEERING. In order to be able to make use of the forces of nature for the promotion of the comfort, health and welfare of mankind, it is necessary to study and to become conversant with them ; hence, training in the natural sciences and in mathematics forms the basis of sanitary as well as of all other branches of engineering. The study should include mathematics (arithmetic, STUDY OF SANITARY ENGINEERING. 15 algebra, geometry, trigonometry and stereome- try), astronomy and descriptive geometry ; like- wise, of the physical sciences, mechanics and dynamics, hydrostatics and hydraulics, aerostat- ics and aerodynamics ; the theory of heat, op- tics, acoustics, magnetism and electricity. It is also necessary for the engineer to have some knowledge of meteorology, climatology, phys- ical geography, mineralogy and geology ; fur- thermore, of general chemistry, metallurgy, and, in particular, of chemical technology. The study of botany, of the trees of commerce and of forestry, is also useful in many ways. In none of these studies, however, must the young engineer student expect to become complete master ; even in mathematics, which is to the engineer the basis of all learning, he cannot expect to cover the whole field. He must become acquainted with the proper- ties of the materials employed in engineering structures, and gain a knowledge of the princi- ples of construction, of the theory of strength of materials, and of the stability of structures. l6 SANITARY ENGINEERING. Without this knowledge, he cannot attain emi- nence in his profession. All engineers should be good draughtsmen ; therefore, the student should practise not only general drawing and sketching, but become skilful in particular in mechanical drawing, in the preparation of engineering drawings, and, to a certain extent, of architectural plans, sec- tions and details. He should also learn geod- esy, surveying, levelling, the laying out and staking out of work, and should aim to thor- oughly master topographical and map drawing. All these studies are fully as useful to the sani- tary engineer in his practice as they are essen- tial to the civil engineer. The studies mentioned so far comprise the general or preparatory course in engineering. After this should follow special courses in engineering as related to commerce, which comprises the means of transportation and communication on land and on water ; in en- gineering as related to agriculture ; in engineer- ing as related to manufacturing industries and STUDY OF SANITARY ENGINEERING. 17 mining ; in engineering as related to buildings, and, finally, in engineering as related to public health. He should learn road and street con- struction, railroad and tramway building, hy- draulic engineering, sewerage, water supply, measurement of water power, bridge, roof and tunnel construction, works of drainage and irri- gation, canals and locks, river improvements, harbor and sea-coast works, machine construc- tion, and the application of the different classes of motors. A general course in architecture or building construction is also desirable for the well-qualified sanitary engineer, and this should include some knowledge of the trades of car- pentry, bricklaying and stone masonry, plaster- ing, blacksmith work, plumbing, gas-fitting and drain-laying. In addition to these, there should be a course in sanitary science, comprising public and per- sonal health, and a study of the causes and methods of preventing the spread of infectious and contagious diseases. A fundamental knowl- edge of anatomy and physiology, so useful to 1 8 SANITARY ENGINEERING. men in all conditions of life, is of paramount value to the sanitary engineer, and this should be followed by a special course in " First Aid to the Injured," as now made a feature in all German polytechnic schools. This will prove eminently useful in the subsequent practice of the engineer, in case of accidents or emergen- cies, whether in the machine shop, on buildings, in railroad disasters, or in sanitary and hydraulic works. Finally, the general knowledge of language and grammar should not be overlooked, as engineers are frequently called upon to write reports. The study of foreign languages will prove useful in travelling and in many other ways. And, finally, there should be added a general knowledge of law, so necessary when drawing up contracts or preparing specifica- tions; the cultivation of business habits, and the faculty of dealing with foremen and work- men in the superintendence of works. From all this it is seen that the extent of theoretical knowledge and practical acquire- STUDY OF SANITARY ENGINEERING. \g ments which the sanitary engineer should pos- sess is quite formidable. It has been truly said that " no man in an ordinary lifetime can prop- erly learn engineering," and that " the learn- "ing period of an engineer ends only with his death." Although it follows clearly from what has been said that the foundation for the special study of sanitary engineering, should be a reg- ular course in civil engineering, it by no means follows that every civil engineer is also a well- qualified sanitary engineer. In order to become competent for the duties of a sanitary engineer, the civil engineer should in study as well as in practice give special attention to, and gain knowledge and experience of, all those problems which are correlated to, and which influence, public health. Sanitary engineering covers a very wide field, and is a profession requiring years of preparation and hard work. 20 SANITARY ENGINEERING. ACTUAL PRACTICE OF THE SANITARY ENGINEER. I will now attempt to give in outline a very general and condensed review of the various classes of work and of the problems arising in the professional practice of the sanitary engi- neer. I would overstep the limits of the book were I to discuss any of those questions or topics in detail. I can mention many subjects only casually, and my difficulty is the constant embarrassment of deciding what to omit rather than what to mention. Speaking generally, much of the work per- formed by the salaried city or municipal engi- neers is sanitary engineering. If the sanitary engineer has a private practice, he will often be called upon to act as consulting or advisory engineer for municipal works ; or his work will be more in the nature of private architectural engineering and domestic work, such as heat- ing and ventilating of buildings, plumbing and drainage, water supply, sewerage and sewage disposal. PRACTICE OF THE SANITARY ENGINEER. 21 WATER SUPPLY OF CITIES AND OF DWELLINGS. One problem which belongs to sanitary, and likewise to hydraulic engineering, is the pro- vision of a bountiful supply of pure and whole- some water for cities and towns. A project for water works requires investigations as to the quantity needed ; as to the quality and avail- able sources of supply ; as to the pressure re- quired and the division into pressure districts ; as to the means for conducting the water from its source to the places of consumption and the systems of pipe distribution ; as to the methods of storing the water, protection against con- tamination, and, finally, as to the means of purification. Water is required for many uses, such as for drinking, cooking, washing, bathing and general ablutions ; for cleaning ; for sprinkling side- walks and streets, areas and yards and watering gardens ; for fire-extinguishing purposes ; for flushing water-closets, drains and sewers ; for washing carriages and watering horses and 22 SANITARY ENGINEERING. cattle ; for feeding steam-boilers, supplying fountains, running hydraulic elevators ; for in- dustrial establishments, laundries, dyeing estab- lishments, paper factories, breweries and sugar refineries, etc. From a sanitary point of view, the chief con- siderations are the sources of supply, quantity, quality, pressure, storage, the material of dis- tributing pipes and the artificial improvement of the water. The sources for a water supply are rivers and lakes, springs and gathering ponds, which are naturally good, but liable to be polluted by surface washings or by sewage ; rain water, which is pure in the country, but contaminated in cities ; subsoil and ground water, which, away from habitations, is good ; shallow wells, which are always open to suspicion ; and deep artesian or driven wells, which, as a rule, furnish an uncontaminated water supply, but which is not in every instance available for use. A sani- tary examination of the source of supply should always be instituted, and comprises a chemical. PRACTICE OF THE SANITARY ENGINEER. 23 microscopical and bacteriological analysis of the samples, in the gathering of which particular care is required. The quantity of water required should be de- termined according to the rate of growth of pop- ulation, and according to the special needs of water for domestic and personal, for industrial and for public use. The amount of water re- quired per head per diem will naturally fluctuate with the customs, desire for cleanliness, and the social conditions of the inhabitants of a place, likewise with the extent of manufacturing in- dustries, the number of public baths, public institutions and public fountains, and, finally, according to the mode of supply ; /. e., whether this is unlimited or metered. The consumption also varies at different hours of the day, on different days of the week, and in different sea- sons of the year, and this should be borne in mind in the design of a water works system. The quality of the water is another considera- tion of importance. The fact needs to be empha- sized, that clear water is not necessarily whole- 24 SANITARY ENGINEERING. some water ; and, inversely, water may be good without being absolutely pure from the chemist's point of view. Good water, suitable as a bever- age, should be transparent, colorless, odorless, tasteless, moderately hard and cold and free from organic impurities and disease germs. The pressure at which v/ater is supplied is of interest mainly from the point of view of fire protection, but also as regards the supply in dwellings, for a deficient pressure points to the need of storage cisterns in houses, and in some places necessitates the use of domestic pumps to lift the water to the tanks. Deficiencies in quality, quantity or pressure of the water supply may be the cause of dis- astrous calamities to life as well as property. To guard against these, stand-pipes or storage reservoirs often form a part of the distribution system. In the reservoirs, the water stored is frequently subject to vegetable growths, or algae, which impart to it a bad taste or odor, or both. The method of supply is either constant or intermittent ; the former is far preferable for PRACTICE OF THE SANITARY ENGINEER. 2 $ sanitary reasons, and may be either a free and unlimited supply, or the supply may be con- trolled by water meters. The system of supply- ing consumers by meter measurement prevents unnecessary waste of water, due to leaky house- fittings or carelessness and negligence in use, and is not, from a sanitary point of view, objec- tionable, as many suppose. The supply of water to a city may either be brought to it by open or covered gravity con- duits, or it must be pumped, by hydraulic or steam power, into reservoirs or into pressure conduits. The distribution in the city streets is usually by a network of underground iron pipes, and the domestic water service is effected by smaller distributing pipes, the material of which may have a bad influence on the quality of the supply. Finally, the artificial improvement of the supply is a problem which concerns the sanitary engineer. It may be accomplished on a large scale, either by sedimentation, by sand filtra- tion on filter beds, by distillation, by aeration, 26 SANITARY ENGINEERING. or by chemical precipitation processes, requir- ing the addition of substances like alum, lime, or perchloride of iron. In the home, small domestic filters may effect some purification, but nearly all the household filters merely strain the water without actually purifying it, and, unless they are frequently and regularly cleaned and recharged with fresh filtering material, be- come worse than useless. There are a few household filters which do remove the germs from the water ; but all those which have any merit necessarily filter the water very slowly and require occasional cleaning and sterilizing. Incidental to the use of water as a beverage is the employment of water in its solid form as ice, for the purpose of rendering the tempera- ture of the water more agreeable. It is a popu- lar fallacy that ice is water purified by freezing. Recent progress made in bacteriology has es- tablished the fact that germs of disease, such as typhoid germs in drinking water, are not killed by the process of freezing. Danger, therefore, lurks in the indiscriminate use of ice. The business PRACTICE OF THE SANITARY ENGINEER. 27 of ice-cutting requires careful watching, and should be under the control of sanitary engi- neers of Boards of Health. The cutting of ice from ponds or rivers subject to organic con- tamination, and rendered unfit as a source of ice supply, should be prohibited. Careful house- holders should, for like reasons, as a matter of precaution, make use of water coolers so ar- ranged that the ice is kept in a separate com- partment, so that in melting it cannot mix with the drinking water, or they should order their ice supply only from dealers in artificial ice, manu- factured from distilled water. SEWERAGE. The water supplied to a city from its water works must be removed after use. To accom- plish this is one, though not the-only, object of a sewer system. Town sewerage, in the wider meaning .of the term, signifies the removal, by underground conduits or sewers, of the sewage of a city, which may include a portion or all of the following liquid wastes : house wastes, in- 28 SANITARY ENGINEERING. eluding excreta and urine ; stable wastes, manu- facturing wastes from industries using in their processes large volumes of water ; waste from water motors and hydraulic lifts ; subsoil water; and, finally, surface or storm water, falling on roofs, yards, areas, courts, paved streets and unpaved spaces. From a sanitary point of view, the continuous and instant removal, before pu- trefaction begins, of all liquid waste products from habitations, must be the chief considera- tion in order to avoid the pollution of soil and air in and about dwellings, and the contamina- tion of the ground-water. To be able to devise a sewerage system, it is necessary to institute many preliminary investigations, which refer to the present and future extent of the drainage area, the configuration or topography of the city, the geology and physical character of the drainage district, the meteorological observa- tions, particularly as to the rainfall of the place, including the frequency and amount of sudden heavy showers ; the proportion of rainfall, if any, which is to be admitted into the sewers ; PRACTICE OF THE SANITARY ENGINEER. 29 the character and quantity of the daily and hourly water supply ; the size of population, present as well as prospective, which will derive practical benefit from the sewers, and the com- parative density of population in different sec- tions of the city. Another question of prime importance in the establishment of a sewerage plan, is the final disposal of the sewage ; the location of the sewer outfalls ; the nature, volume of flow and velocity of current of the water course intended to receive the sewage, the requirements of pumping stations, or the need of sewage purifi- cation works. It maybe laid down as an axiom that no engineer can give intelligent advice con- cerning a proposed sewerage system of a city, without having a correct general contour map of the place. Following these preliminary investigations the sanitary engineer should consider the vari- ous sewer systems, the combined and the sepa- rate system, the gravity, suction and compressed air systems of sewage removal, and decide 30 SANITARY ENGINEERING. which is best adapted to the locality in question. Often it may be advantageous to admit into the sewers only a portion of the liquid wastes enu- merated. In many towns storm water may be left out of consideration, as, for instance, where it can be taken care of quite sufficiently by open or covered street gutters, or by a few shallow and short rain-water sewers, discharging in a straight line into the nearest water-course. Wherever sewage must be pumped to the out- fall, and in all cases where it must be purified before discharge into a water-course, the advan- tages of the separate system predominate. After deciding upon the system of sewerage best adapted to the needs of a community, a general sewerage plan should be developed, and according to the topography of the city, various lay-outs for the division into sewer districts may be followed, such as the direct or perpen- dicular system, the intercepting system, the zone or parallel system, the fan system and the radial system, the details of which I cannot describe here. The grade and inclination of PRACTICE OF THE SANITARY ENGINEER. 31 the sewers, the resulting velocity of flow, the importance of making sewers self-cleansing, the depth at which they are laid below the street level, the sectional forms and sizes; the material and construction, whether cement or vitrified pipe or iron pipe sewers, concrete, brick or stone-masonry sewers these are all matters of importance, which the experienced sanitary en- gineer has to consider. In the construction of the sewers many questions of detail come up, upon which the ultimate success of the system will depend, such as the trenching, the provi- sion of proper foundations in loose soils, the use of invert blocks, the making of water-tight joints in pipe sewers, the proper junction of sewers, the careful alignment and the adjust- ment of the grade, the smoothness, hardness and durability of sewer pipes, and other consid- erations. Sound, practical judgment will deter- mine the position and number of man-holes and lamp-holes for purposes of inspection, location and removal of obstructions, the advisability of using devices for flushing sewers, either flush- 32 SANITARY ENGINEERING. ing man-holes, gates or tanks with automatic siphons, and the details of sewer outfalls. Where rainfall is admitted to the sewers, the construction of catch-basins at street corners and of storm overflows to relieve the sewers in case of sudden heavy showers must be studied. Where sewage cannot be discharged by gravity, pumping stations and sewage pumps must be designed ; finally, the house connections must be provided, in wet soils subsoil drains must be laid in the sewer trenches, and in all cases the sewers must be well ventilated. The problem of sewer ventilation presents many practical difficulties. The prevailing method, by means of perforated man -hole covers, is open to objections, particularly in narrow streets or courts, and the alternative of untrapped catch-basins aggravates the evil, ow- ing to the proximity of the latter to the win- dows of dwelling houses. Among the various other methods suggested from time to time, I mention ventilation by means of the rain-water pipes of buildings, which is objectionable, first, PRACTICE OF THE SANITARY ENGINEER. 33 because during rain-storms, just when sewers require a free vent, owing to the displacement of the air by water, the rain-water conductors cannot act as ventilators ; second, because the joints of outside metal leaders are rarely tight; and third, because rain-water leaders often terminate under windows of living rooms or sleeping apartments. Ventilation by lamp-posts or special columns rarely ac- complishes much, because they are of too small diameter. The carrying of special sewer vent pipes along the outside of buildings would be somewhat more effectual, but the method is difficult to enforce, expensive, and often troublesome in case of adjoining buildings of various heights. Ventilation of sewers by connection with chimney shafts or boiler flues, involves the possibility of explosion, or is ob- jected to by the owners, as it may injuriously affect the chimney draft. Special tall shafts, at the upper ends of sewer lines, are, to some de- gree, effective, but very expensive. Other prop- ositions include charcoal ventilators in the top 3 34 SANITARY ENGINEERING. of man-holes, which require frequent removal/ material placed in sewers to absorb gases, and the passing of disinfecting vapors or chemical gases into sewers. Unfortunately, most of these devices suggested are costly or difficult to apply, and the problem is by no means satis- factorily solved. One other method deserves special mention, it being a successful feature of the separate system ; this is the omission of the running trap on all house drains, thus making use of the house soil and vent pipes, which are carried up to the roof. With a well-flushed, well-arranged and well-maintained sewer sys- tem, under complete control of the municipal engineer, the simple method is perfectly feasi- ble, and gives good results, provided the drain- age works of the houses are absolutely air-tight. A public water supply and a sewer system are improvements which usually go together, and exercise a marked sanitary effect upon the gen- eral health of a community. The problem be- comes more difficult when there is a water supply without sewerage, in which case the PRACTICE OF THE SANITARY ENGINEER. 35 filthy and health-destroying cesspool, or the vault, is the usual receptacle of the sewage pending removal by cartage. Where there is neither sewer nor a water supply, the disposal of filth must be accomplished by dry removal systems, such as the earth or ash closets, or the pail system. Finally, there are certain special systems, such as the pneumatic systems of Liernur and of Berlier, and the mode of pump- ing sewage by compressed air by the Shone system, of which a practical application could be seen at the recent World's Fair in Chicago, with all of which the sanitary engineer should be quite familiar. Of all systems, that one will be by far the best, from a hygienic point of view, which effects cleanliness by a constant, systematic and quick removal of all manner of liquid organic refuse from houses, streets and towns. PREVENTION OF POLLUTION OF WATER-COURSES. Rivers and water-courses have been utilized as the natural outfalls for the sewage of towns. 36 SANITARY ENGINEERING. As the amount of town sewage increases, owing to growth of population, and of its industrial establishments, the streams and water-courses become more and more polluted, to the great detriment of the people living further down- stream. River pollution, in numerous instances, has been the result of improved town sanitation by sewerage. Too much reliance has often been placed in the assumed self-purification of rivers. In many instances, furthermore, clear streams flowing through the heart of a city, have been made the receptacle of all its liquid wastes, with the result of turning a once pure water-course into an extremely foul open sewer, contaminating the air of the town. This offen- sive practice cannot be too strongly condemned from a sanitary point of view. The experienced sanitary engineer will uphold the axiom that in cities all natural water-courses must be kept unpolluted. Even the smallest open streams should, under no circumstances, be covered or arched over and used as sewers. Filth should be prevented from reaching these open streams, PRACTICE OF THE SANITARY ENGINEER. 37 and they should be kept pure with plenty of water and by a free circulation of air, and may, by proper rectification, be used to serve as a natural embellishment of a city. Regarding larger water-courses flowing past a city, the question whether or not sewers may discharge directly into them depends upon a number of factors which must be carefully con- sidered by the engineer. A certain amount of self-purification is, no doubt, always going on, due largely to the sedimentation or subsidence, to oxidation and aeration and to dilution ; and with this in view there is a certain degree of permissible pollution. Speaking generally, the larger the volume of the water-course, and the greater its velocity of current, the more sewage can be admitted to it without danger of undue pollution. The condition of the water-course before it reaches the town should also be con- sidered, but the chief question will always be whether the water of the river is, or may in the future be, used at a point below the sewer out- fall as a source of potable water. In that case 38 SANITARY ENGINEERING. the direct discharge of unpurified sewage should never be permitted, for the preservation of the purity of water used for public water supply is of paramount importance. We may even go a step further and demand a certain amount of purification of sewage, before discharge into rivers or lakes, in order to keep these inoffen- sive even where they are not drawn upon to supply the drinking water, making the required degree of purification variable according to the circumstances of each case. Small lakes, stag- nant ponds, coves, bays or inlets should never be used as receptacles for town sewage. In manufacturing districts difficulty often arises from chemical wastes, and from the fact that the volume of water of the stream is consider- ably reduced on account of the flumes which divert part of the water to use it as motive power. On the other hand, artificial dams, like rapids and natural waterfalls, aid the puri- fication by aeration and oxidation. PRACTICE OF THE SANITARY ENGINEER. SEWAGE DISPOSAL. 39 The question of the proper disposal of the sewage of populous places is one of the most important, and often difficult, problems which the sanitary or municipal engineer encounters. In many sewered cities of Europe, particularly in the case of inland towns, sewage purifica- tion systems have long ago been devised and adopted, while in the United States the diffi- culty is only beginning to be appreciably felt with the increasing pollution of our rivers. A direct discharge of sewage into a water-course or into lakes and tidal rivers is seldom permis- sible. Even the casting away of crude sewage into the sea can only be countenanced under special conditions, as it quite often leads to a defilement of the beaches, and tends to create mud-bars and silts up the navigable channels at the entrance of harbors. Frequently the argu- ment is used against this method of disposal, that it is a waste of fertilizing materials. It should be said, however, that none of the 40 SANITARY ENGINEERING. methods of sewage disposal can be carried out with a view to financial gain. The purification of the sewage is, in all cases, the chief object. The methods of purifying sewage may be divided into natural and artificial methods. To the former belong the simple sedimentation or subsidence, filtration through soil and broad surface irrigation. Among artificial methods, I mention the simple straining of sewage, mechanical filtration, chemical precipitation, aeration processes, and the purification by elec- trical currents. Quite often a combination of two of these methods is adopted, and it is im- possible to say, in a general way, which is the method that will yield the best success. The sanitary engineer must study each problem separately and use sound judgment in selecting a method best adapted to the existing condi- tions. Certain scientific experiments, however, and the actual experience gained in cities having various processes in operation will serve as a useful guide. Simple sedimentation or subsidence is a slow PRACTICE OF THE SANITARY ENGINEER. 41 method, which rarely effects more than a mere clarification of the sewage, and removes none of the matters in solution. This is also true of the cruder methods of straining or filtering sewage in mechanical filters, and these processes may be considered rather useful as preliminary methods to be followed by broad irrigation or intermittent downward filtration. Chemical precipitation consists in the addition of certain chemicals, such as lime, or sulphate of alumina, or salts of iron, which act as precipitants, caus- ing the suspended matters and a part of the dissolved impurities to be removed. The pre- cipitation takes place in large sewage tanks, and is effected in a variety of ways. In some the sewage comes to a complete rest for several hours, and this method requires, therefore, a large number of tanks. Or the sewage, after the addition of the chemicals, is made to move slowly through shallow tanks, or it is compelled to follow up and down movements in the same. Finally, instead of large shallow tanks, deep upright tanks, cylinders or wells, placed either 42 SANITARY ENGINEERING, above or below the ground, are used in certain chemical precipitation processes. None of the numerous chemical processes effect a complete removal of all foul matters, and where the effluent is required to be very pure, the chemi- cal method is often supplemented by irrigation over, or filtration through, soil. In all pre- cipitation processes a new difficulty arises on account of the unavoidable accumulation of sewage sludge, which contains a large per- centage of water. This sludge must be dried, either by spreading it out on well-underdrained land, or by pressing it in filter presses. The sludge cakes have some value as manure, but a financial return from their sale is seldom realized. In some cities the solid house and street refuse is mixed with the sludge and burned in garbage-cremating furnaces. In the natural method of sewage disposal, sewage is made to flow either over or through land prepared for the purpose, and an excellent degree of purification is usually attained. Sew- age irrigation over cultivated land is assisted PRACTICE OF THE SANITARY ENGINEER. 43 during part of the year by the vegetation, the cultivation of certain crops on the sewage dis- posal field being perfectly feasible. The diffi- cult feature of the system is the need of large areas of well-drained land. Near cities these are not always available, or when they are to be found they require a large outlay of money. Irrigation and filtration through soil also in- volve the constant need of manual labor. Aeration processes are seldom adopted, al- though the oxidation of the organic matters in sewage, either by forcing air through it, or by causing it to run over a series of terraces or waterfalls, or by dripping it down on wire meshes, appears to be practicable. The treatment of sewage by electricity was introduced experimentally in England several years ago ; more recently it has teen tried in the United States on a small scale, but suffi- cient practical experience is not yet available to permit definite conclusions to be formed as to the results to be attained by the pro- cess. 44 SANITARY ENGINEERING. STREET PAVEMENTS. All roads and streets serve for purposes of intercommunication and traffic ; city streets, however, are planned with the further object of providing light and air to the adjacent houses, and, incidentally, are utilized as receptacles for a network of underground pipes, conduits, and wires which afford drainage and sewerage facil- ities and furnish water, gas, heat, light, steam, and electric power, etc., to the buildings. When we demand even of our country roads that they should not be dusty in dry weather, nor muddy and impassable in wet seasons, it is ob- vious that city streets, in which our habitations, offices, and places of work are located, should be subject to much stricter requirements. We are, as far as this book is concerned, interested chiefly in the sanitary aspects of street con- struction or the paving of its surface. The essential requirements of a good city street pavement are quick surface drainage, good foundations, impermeability and hardness of PRACTICE OF THE SANITARY ENGINEER. 45 surface, avoidance of slipperiness, least resis- tance to traffic, cleanliness and noiselessness. Impermeability and noiselessness are the chief desiderata, from a sanitary point of view. There is plenty of medical testimony available tending to prove that the ceaseless noise, from early morning till late at night, due to vehicles passing over rough stone pavements, affects the nervous system and reduces the duration of life. A street surface should be as water-tight as possible, to prevent a downward soakage into the ground of liquids, or the retention of filth in the joints and cracks of the paving stones. The street surface should drain off quickly, and there must be no depressions or inequalities where water can stagnate and become offensive. A street pavement should not be slippery, as this not only causes horses to fall, but is equally dangerous to life and limb of pedestrians. Cleanliness of pavements is essential to prevent dangerous exhalations and illness due to pol- luted air. Finally, paved streets should be 46 SANITARY ENGINEERING. noiseless, for the continuous jarring and rum- bling of heavy vehicles, the shaking of the foun- dations and the accompanying vibrations of window panes, doubtless affect the nerves of town-dwellers, disturb sleep, aggravate the suf- fering and retard the recovery of the sick. For these and similar reasons the selection and construction of a good street pavement is a sanitary problem of much importance. Leaving out of consideration some kind of pavements which are not used to any great extent, the choice lies between macadam, wood, cobble- stone, granite block, and asphalt pavements. Macadamized roads are not well suited for city pavements. Under a heavy street traffic the broken stones particularly if the softer limestones are used are quickly ground to powder, causing clouds of disease-breeding and irritating dust in dry weather, while in wet weather the dust is quickly changed into the worst kind of soft mud. The surface of macad- amized roads wears out very quickly, and al- most the only advantages worth mentioning PRACTICE OF THE SANITARY ENGINEER, 47 are that such roads are noiseless, and that they afford a firm footing for horses. Wooden pavements have formerly been em- ployed, to a large extent, in American cities, but, of recent years, they have been given up, partly, no doubt, on account of the growing scarcity of timber, due to the barbarous destruction of our forests. From a hygienic point of view, wooden pavements, unless the blocks are impregnated to prevent decay, offer several important objec- tions. In the first place, wood absorbs not only dampness, but likewise putrefying matter, and exhales bad odors, and, being alternately wet and dry, the surface soon rots. It is a well- known fact that decaying wood is detrimental to health. Wooden pavements, on account of their elasticity, are more noiseless than stone pavements, but they are expensive to maintain, and soon their surface becomes quite unequal, except when the precaution is taken to lay the blocks on a concrete or sand foundation. Cobblestone pavements are of a very inferior character, on account of the uneven surface, 48 SANITARY ENGINEERING. due to absence of proper foundation and the rough joints and numerous pockets, due to the irregularity of the stones. The joints of such pavements soon fill up with putrefying street filth and create obnoxious odors. Such pave- ments are very difficult to maintain in a clean condition, and, taken altogether, they are unfit for the thoroughfares of large cities. Granite pavement, if composed of stones of regular size evenly laid, well bedded on a good concrete foundation, and with the joints care- fully filled with sand or cement, or tar and gravel, is a good city pavement for heavy traffic. The stone blocks should not be too hard, as they otherwise become quite slippery from abrasion, and the evenness of the pave- ment is usually disturbed by the frequent tear- ing up required for underground pipe connec- tions. The improved stone pavements, with well-filled joints, have the one disadvantage of causing increased vibration of buildings. The best pavement, from a sanitary point of view, is, without doubt, the asphalt pavement, PRACTICE OF THE SANITARY ENGINEER. 49 and it is destined to become the favorite pave- ment for streets with light traffic. It is water- tight and quite impermeable ; it prevents soakage into the subsoil ; it is free from the noxious odors so often found on pavements with joints ; it is durable, smooth, and very readily cleaned ; it renders all traffic noiseless, does not cause jar- ring or vibration of buildings, and creates no dust due to abrasion and wear. About its only disadvantage is its liability to become slippery when the pavement is damp or greasy, as dur- ing foggy weather, or where soft mud is carried to it from adjoining stone pavements, by horses' hoofs, pedestrians' shoes and carriage wheels. It is principally adapted to the residential parts of cities, where there is no heavy traffic ; owing to its noiselessness it is also preferred in the neigh- borhood of courthouses, schools, hospitals, etc. Other durable pavements are the vitrified paving blocks, the asphalt blocks and brick pavements, in the laying of which particular care should be given to the rilling in of the joint spaces. 5