■Ill llll ■I II Ml iiii"i!i. n.i ■ I 1 ■' "i ' • in. H t I1HI ,/ V' CORNELL UNIVERSITY. THE BostueU p. dottier ftibrarg THE GIFT OF ROSWELL P. FLOWER FOR THE USE OF THE N. Y. STATE VETERINARY COLLEOIgCU / Digitized by Microsoft® \Zl ..cS? *> da .~r »£? r . ne " Uni «sreity Library RA 425.P24h 1907 Hygiene and public health. 3 1924 000 236 889 DATE DUE coffX w w^_^>^ GAYLORD PRINTED IN USA Digitized by Microsoft® This book was digitized by Microsoft Corporation in cooperation with Cornell University Libraries, 2007. You may use and print this copy in limited quantity for your personal purposes, but may not distribute or provide access to it (or modified or partial versions of it) for revenue-generating or other commercial purposes. Digitized by Microsoft® HYGIENE AND PUBLIC HEALTH Digitized by Microsoft® 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/cu31924000236889 Digitiz&a by Microsoft® HYGIENE AND PUBLIC HEALTH BY LOUIS C. PARKES, M.D., D.P.H. Univ. of Lond. CONSULTING SANITARY ADVISER TO H.M. OFFICE OF WORKS J CIVILIAN SANITARY MEMBER OF THE ADVISORY BOARD FOR ARMY MEDICAL SERVICES; MEDICAL OFFICER OF HEALTH OF THE METROPOLITAN BOROUGH OF CHELSEA; EXAMINER IN HYGIENE AND PUBLIC HEALTH TO THE UNIVERSITY OF LONDON; FELLOW OF THE ROYAL SANITARY INSTITUTE AND HENRY R. KENWOOD, M.B. Edin., D.P.H. Lond. PROFESSOR OF HYGIENE AND PUBLIC HEALTH AT UNIVERSITY COLLEGE, LONDON; MEDICAL OFFICER OF HEALTH AND PUBLIC ANALYST OF THE METROPOLITAN BOROUGH OF STOKE NEWINGTON ; FELLOW OF THE ROYAL SANITARY INSTITUTE THIRD EDITION, WITH ILLUSTRATIONS. PHILADELPHIA P. BLAKISTON'S SON & CO. Digitized bytMJapsoft® V "y '• I il'i 111); i i ;.•>[.■! vii; 1 1 II /: 1! ii i i Digitized by Microsoft® PREFACE This, the third edition under the conjoint authorship, has been carefully revised. A certain amount of new matter has been introduced, but some parts of the previous edition have been compressed and abbreviated, so as to maintain the work in a convenient form for handiness of reference. With this object also the size of the page has been slightly "enlarged, so as to avoid undue bulkiness. L. C. P. H. R. K. August, 1907. Digitized by Microsoft® V Digitized by Microsoft® CONTENTS CHAP. I Water .... II The Collection, Removal, and Disposal of Excretal and other Refuse III Air and Ventilation IV Warming and Lighting V School Hygiene VI Soils and Building Sites VII Climate and Meteorology VIII Exercise and Clothing IX Food, Beverages, and Condiments X The Contagia — Communicable Diseases and their Pre vention — Hospitals . XI Disinfection ..... XII Statistics ..... XIII Sanitary Law and Administration page i 66 162 -3i 246 262 274 300 309 382 502 53i 559 Digitized by Microsoft® Vll Digitized by Microsoft® LIST OF ILLUSTRATIONS FIG. PAGE 1. Underground Water Curves . . . . . .21 2. Depression of Water in Shallow Well by Pumping . . 24 3. Diagrammatic Section through London Basin ... 29 4. Diagrammatic Representation of Strata, showing Shallow, Deep, and Artesian Wells . . -31 5. Suction Pump ... . . . 33 6. Single-acting Suction and Force Pump ... 33 7. Double-acting Suction and Force Pump . . 33 8. Centrifugal Pump ...... 34 9. Hydraulic Ram . ... 35 10. Berkefeld Filter . .... 56 1 1 . Cesspool with House Drain Inlet and Overflow to Filter Bed 74 12. Privy constructed for Pail System .... 13. Field's Annular Siphon Flush Tank for Flushing House Drains 14. Long Hopper Water-closet with Side-inlet for Flushing 15. Wash-down Water-closet 16. Wash-out Water-closet . . . . 17. Century Siphonic Closet 18. Pan Closet with D trap, supplied from Drinking Water Cistern 19. Era Valve Closet . . . . . 20. S trap, with Water Seal ..... 21. P trap, with Water Seal .... 22. Trough Water-closet ...... 23. New Form of Trough Closet or Latrine with Isolated Pans 24. Day's Waste-water Closet .... 25. Wiped Soldered Joint ...... 26. Joint made with a Copper Bit or Blowpipe 27. Soil Pipe and Ventilator, with Anti-siphonage Pipes from the Water-closet Branches 28. Section of Disconnecting Chamber 29. Flushing Grease Gulley 30. Semi-detached Houses ; Flans of Drainage 31. Dean's Silt Gulley .... 32. Sink with Double l9^^ fyMM ^ ix 75 80 83 83 83 85 87 88 91 91 92 93 94 97 97 99 104 107 109 "3 116 LIST OF ILLUSTRATIONS FIG. PAGE 33. Diagrammatic Sketch of Various Provisions for Ventilation . 215 34. Rifle-back Stove with Economizer ..... 2 3 2 35. Euthermic Ventilating Gas Stove .... 2 3& 36. House Foundation with Damp-proof Course in Wall and Dry Area . 269 37. Synoptic Chart showing Cyclonic System . . . .283 38. Synoptic Chart showing Anticyclonic System . . 284 39. Fortin's Standard Barometer ...... 286 40. Diagram of Barometer Scale and Vernier . 286 41. Robinson's Anemometer ...... 289 42. Daniell's Hygrometer . . . 290 43. Regnault's Hygrometer . . . 291 44. Wet and Dry Bulb Hygrometer . . . . 292 45. Rain Gauge ... 294 46. Six's Thermometer . . . . . 296 47. Solar Radiation Thermometer . . 297 48. Sunshine Recorder . . . 298 49. Cotton Fibres ... . 303 50. Linen Fibres . . . 303 51. Wool Fibres 304 52. Silk Fibres . . . 305 53. Hemp Fibres . 306 54. " Measly " Pork . 326 55. Head of Taenia solium . . 326 56. Head of Taenia mediocanellata . . . 327 57. Brood Capsule of an Echinococcus . . 327 58. Trichina Spiralis encysted in Muscle . . . 328 59. One of Rainey's Capsules .... 328 60. Distoma hepaticum ...... 331 61. Percentage Composition of Solids of Human and Cow's Milk 348 62. Aspergillus Glaucus . . 352 63. Penicillium Glaucum . . . 352 64. Mucor Mucedo ... . - 353 65. Puccinia Graminis . . . 361 66. Smut Spores : Uredo segetum ... . 362 67. Acarus farinae . . . . 362 68. Vibriones tritici . . 362 69. Weevil ...... . 362 70. Section of Wheat Grain . Outer Coat ..... 363 71. A, Ear of Rye with Ergot; B, a Slice of Ergot . . 363 72. Potato ....... . . 365 73. Arrowroot Digitized •■by Microsoft® • • 365 74. Maize . ... .... 365 LIST OF ILLUSTRATIONS XI FIG. 75- 76. 77- 78. 79- 80. 81. 82. S3- 84. 85. 86. 87. 89. 90. 91- 92. 93- 94 94 95- 96. PAGE Rice ... 365 Barley . .•"'■. . . . ■ • ■ 3 66 Pea . $& .... 366 Bean 366 Oatmeal ... . . . 366 Wheat . . .367 Sago . . 367 Tapioca ........ . 367 Coffee : Cells of Testa and Cellular Structure .... 368 Chicory : Dotted Ducts and Cellular Structure . . . 368 Tea Leaf ..... 369 Cocoa Starch Cells ...... .370 Torula cerevisiae : Yeast Plant . . . . . 371 Fulham Small-pox Hospital. Special Area divided into Sec- tions, showing Number of Houses invaded by Small-pox . 396 Chart showing Average Death-rates in different Infectious Diseases in Corresponding Weeks of a Period of Years . 400 Small-pox Epidemics, 1871, 1881 ; Mortality per cent, in Fever Hospitals (London) ....... 404 Hospital Slop-sink with Flushing Rim and Bed-pan and Slipper Douches . . . ... 497 Borough Hospital, Croydon. First-floor Plan . . 499 Isolation Hospital Block (as recommended by the Local Govern- ment Board) . . . . . . * . . 499 (a). Disinfecting Station. Infected Side . . . .511 (b). Disinfecting Station. Non-infected Side . . .512 Graphic Expression of Male Population : Number Living or Lives at Risk . . . . . . . .551 A Sanitary Cowshed. Double Byre with Central Feeding Passage ...... 582 Digitized by Microsoft® Digitized by Microsoft® HYGIENE AND PUBLIC HEALTH CHAPTER I WATER Water is a prime necessity of life. Without it, terrestrial animal and vegetable life must cease to exist. The earliest settlements in all countries were, therefore, made in the neigh- bourhood of water. Towns and villages sprang up on the banks of streams and rivers, on the shores of lakes and in the neigh- bourhood of springs ; or water was obtained from the soil around these early settlements by shallow excavations or wells. In modern times, sites for dwellings are not necessarily limited to a small area around a natural source of water. Our engineer- ing knowledge enables us, on the one hand, to obtain water by means of wells and borings from great depths beneath the surface of the earth, and on the other, to convey water from a distance by means of conduits to the places where it is required. This latter method was well known to the ancient Romans, many of whose aqueducts and reservoirs are, after the lapse of many centuries, still standing and serving their original pur- pose. In Rome the total supply per head was certainly not less than 300 gallons daily for a population of about 1,000,000 people, the greater portion of this vast supply of water being required for public baths and fountains. London is an instance of a settlement founded originally on the banks of a river, and subsequently spreading away from the neighbourhood of the river only in those directions where a water-bearing gravel overlaid the impermeable London clay. The bed of gravel being of but slight thickness — 10 to 30 feet — water was easily reached by shallow excavations or wells ; whilst at some places'^'sprrngs 'ffowea out where the gravel 1 B 2 HYGIENE AND PUBLIC HEALTH terminated, as at Bagnigge, Holywell, and Clerkenwell. Eighty years ago, parts of London where the clay came to the surface, and which are now densely populated owing to the introduction of a public water supply, were quite uninhabited. Sources of Water — Collection and Storage. The natural sources of water are the rain and snow which fall on the surface of the earth. When the rain has reached the surface of the ground, it is disposed of in the following ways : a portion (a) is evaporated ; another portion (b) flows off in the direction of the inclination of the surface ; whilst a third portion (c) sinks into or percolates through the interstices of the soil. The amount of rain that evaporates depends upon the tem- perature of the air. The higher the temperature, the greater the evaporation. If the inclination of the surface is nil, or only very slight, and the soil is of some depth and of a porous nature, the larger portion sinks into the soil or -percolates. If, however, the inclination of the surface is great and the soil is not porous, but more or less impermeable to water, the greater portion of the unevaporated rain flows down the incline. It is this portion which forms or helps to swell the brooks, streams, and rivers, which are the natural drainage channels of the locality. In very porous soils, such as pure sand or coarse gravel, the rain so rapidly sinks into the interstices of the soil that the evaporation, even in summer, is but slight. In nearly all other soils, however, the amount of rain evaporated greatly exceeds the percolation, even in winter. The portion that percolates, after a certain deduction that must be made for the moisture absorbed by the roots of vege- tables and grasses growing on the surface, and which is subse- quently evaporated from their leaves, helps to form and renew the underground sources of water. These are made available to man by natural outlets as springs, or by artificial tappings in their subterranean depths through wells. Rainfall. The rain that falls on the roofs of houses can be collected and made available as a ftMfig'W WafgP^pply. To calculate the amount of water supply per head from this source, we must WATER 3 know the amount of roof space per individual (the slope of the roof must not be taken into account, but merely the area of horizontal surface covered by the roof), the average amount of yearly rainfall, and the average amount of evaporation of the rainfall. The amount of yearly rainfall varies considerably in different parts of England. In the Eastern Counties the average is less than 25 inches per annum. Throughout the remainder of England the average is from 30 to 40 inches per annum, with very much larger amounts in the mountainous and hilly districts of Devon- shire, Wales, Cumberland, and Westmorland (60 to 200 inches per annum). The expression " an inch of rainfall " signifies that one cubic inch of rain-water has fallen upon each square inch of horizontal surface. (For description of rain gauge see Chap. VI). During the past 15 years the least annual rainfall, measured at Greenwich, has been i8"85 inches (1898), and the greatest 35 '54 inches (1903). In the latter year (1903) ex- ceptionally heavy falls of rain occurred ; thus on July 23, 2^47 inches fell in 24 hours, and on numerous occasions over an inch feU in the same period. During the 13 years 1890-1902, the annual rainfall at Greenwich had been below the average (24-53 inches) in 11 years, and only twice slightly exceeded the average, namely in 1891 and in 1894. Rain is also sometimes collected from prepared surfaces of ground, which, together with the storage reservoir or tank, should always be railed off to keep live stock away. The surface of a certain area of land in an exposed situation is rendered impermeable by a covering of slates, asphalte, or cement, and sloped towards an outlet pipe or pipes leading to a tank or reservoir. In estimating the amount of water that can be obtained from such a surface, calculations may be facilitated by remembering that one inch of rain delivers 4-673 gallons on every square yard, or 22,617 gallons (101 tons) on each acre. The amount of evaporation from the surfaces of roofs may be taken as averaging throughout the year 20 per cent, of the rainfall. There is more evaporation from tiled than from slated roofs, and from roofs of low than of steep pitch. The evaporation is greatest where the rainfall is least, and vice versa. If the amount of roofc8$>aaa/ $ew/headfftfs 60 square feet, and the rainfall 30 inches in the year, deducting one-fifth for evaporation, 4 HYGIENE AND PUBLIC HEALTH 120 cubic feet or 748 gallons is the amount available for each person in a year, which is equal to about two gallons daily. This is the amount available from the rainfall — 30 inches — of an average year. It has been found from a great number of records of rainfall extending over a long series of years in different places, that the rainfall in the driest year in usually one-third less than the average fall, whilst in the wettest year it is one- third greater than the average. So that in a very dry year, in the example given above, the amount of water available may be only i| gallons daily per head, whilst in a very wet year it may be 2f gallons. Rain, as it leaves the clouds, is water pure and simple, free from all foreign ingredients. In its passage through the air to the earth it may collect various impurities, gaseous and suspended. The rain falling in towns is found to have absorbed sulphurous and sulphuric acids, which are always present in the air of towns from combustion of coal and coal gas, and to contain numerous sooty particles. It also appears that the rain washes out of the air countless bacterial and fungoid organisms and their spores. The rain which first falls after a period of dry weather contains far larger numbers of bacteria than that which falls later in a storm ; 200,000 germs per litre is not an unusual quantity under such circumstances. During the warm months of the year, the number of bacteria in the rain exceed those found in the rain of winter and early spring. The greater number of the organisms in rain are micrococci. Besides bacteria, pollen of grasses and flowers, microscopic plants, such as Protococcus pluvialis and spores of fungi, are occasionally found in rain, the latter being on rare occasions in sufficient quantity to cause a localized fall of what is known as " coloured rain " ; but dust, possibly of volcanic origin, or derived from vast sand deserts, is sometimes responsible for falls of coloured rain. Rain is thus seen to be a great purifier of air, for it washes out of it gaseous and solid impurities, organic and inorganic. For this reason the rain which falls in the impure smoke and soot-laden atmosphere of large towns is unfit to drink. When roofs are used as collecting surfaces for rain-water, the first portion of rain which falls and descends from the roof should be rejected, as lFis liaole '£0 ^e much polluted with soot, vegetable matter (leaves), and animal matter (excrement of WATER 5 birds, etc.) washed off from the slates or tiles. After the first washing the remainder of the water may be collected and stored. Robert's Rain-water Separator, which can be fixed on the downward course of the rain-water pipe, effects this purpose by allowing the .first portion of water that passes through the apparatus to run to waste. After a certain time, a part of the apparatus which is balanced on a pivot cants over, owing to its centre of gravity being altered as one of its compartments fills with water, and the water escapes into another pipe, which conducts it to a storage cistern. Rain-water should always be stored in as pure a condition as possible, otherwise the storage receptacle becomes coated with foul matters, which contaminate the water. The advantage of underground storage is that the water does not get frozen in the winter or unpleasantly hot in the summer. But, on the other hand, the tanks are often difficult of access. Underground tanks must be built of sound masonry or brickwork and lined with hydraulic cement. They should rest upon a bed of concrete and be covered over with arches of masonry or brickwork ; and if there is a special danger of polluting material gaining access to the tank, they should be surrounded with at least a foot of well-puddled clay. Rain-water is especially useful for cooking and washing on account of its softness — that is to say, its freedom from the salts of lime or magnesia in solution. When these salts are dissolved in a water they render it hard. Hardness is usually reckoned as equivalent to so many grains of chalk (or carbonate of calcium) per gallon of water. A water containing more than 10 grains of chalk or its equivalent in other salts (sulphate of lime or magnesia, carbonate of magnesia, etc.) to the gallon is said to be hard. Hardness due to the presence of carbonate of calcium, held in solution by carbonic acid, is said to be tempor- ary ; for when the water boils, the carbonic acid is driven off, and the chalk, no longer able to remain in solution, is precipitated. It is this deposit of chalk which causes the fur on the bottom and sides of boilers and kettles. When meat or vegetables are cooked by boiling in hard water, a certain amount of the hard material is deposited on their surfaces, which either hinders the proper penetration of the heat into the interior, or prevents solution of the soluble materials when this is desired. The fur lining is also a : of heat from the t> HYGIENE AND PUBLIC HEALTH causing a waste of fuel. This fur lining is one of the causes of the boiler explosions from which loss of life not infrequently results. To reduce the possibility of such explosions the follow- ing precautions are desirable : — The boilers should be of wrought iron, properly tested ; they should be periodically inspected and cleaned ; pipes connected with them should not be carried up external walls where they may be affected by frost, and the cisterns should also be in well-protected positions ; the safety valve should be accessible, easily adjusted, and sensitive to variations of pressure. Great waste of soap, too, is caused by the use of hard water in washing. When the water is hard, the lime or magnesia combines with the fatty acid of the soap, forming a curdy pre- cipitate ; and all the lime or magnesia of the water must be so combined before a lather can be formed. -Consequently a certain amount of soap is wasted. One grain of chalk wastes about eight grains of soap. The hardness of rain-water is generally less than half a degree ; that is to say, there is less than half a grain of chalk or its equiva- lent salts to the gallon of water ; hence its value for domestic purposes. Rain-water should never be allowed to run to waste where the water derived from other sources is hard. There is one great disadvantage possessed by rain and other soft waters, namely, their liability to dissolve lead, iron, or zinc if left in contact with these metals. Consequently cisterns of lead, iron, zinc and even galvanized iron in some cases should not be used to store soft water ; and such water when collected from lead roofs should not be used for drinking. Upland Surface Waters. In hilly districts, the water which flows off the hills in the form of rivulets or streamlets can be collected and stored by building an earth and masonry dam or barrier across the outlet of the valley to which the streams converge. By this method of collecting in " impounding reservoirs," large artificial lakes may be formed — capable of holding a supply sufficient for several months — at suitable elevations above the towns which they supply with water. A certain amount of " compensation " water (usually estimated at one- third the amount impounded) must be allowed to pas3/^(&isaib^owa«^dfiR8ll-owners on the streams from which the waters have been diverted. WATER 7 Large storage reservoirs for such waters are made by excavating or embanking the soil, and then lining the floor and sides with concrete or well-puddled clay ; common mortar must not be used, as the water takes up the lime. Their position should be such that a jet reaching 20 feet above the highest house to be supplied is assured by gravitation alone, otherwise the water has to be pumped to a higher elevation. Means are generally taken for diverting the tributary streams from the storage reser- voir when these get foul in times of flood, by means of a by-wash. The size of a storage reservoir for a catchment area will depend upon the numbers of the community requiring the water, and upon the mean rainfall of the district. Hawksley's formula is of value in estimating the number of days' supply (x) which must be stored when a community is dependent on a rain- 1000 water supply. In this formula x = , ; where y = the mean rainfall during the three driest consecutive years — which is usually about one-fifth less than the average. In this country from 120 to 130 days' supply have to be stored. The average annual amount of evaporation from an exposed body of water reduces the depth by some 30 inches over the whole surface ; therefore there is an advantage in diminishing the exposed area of the water by constructing deep reservoirs, rather than shallow ones. The probable daily yield (in gallons) of a catchment area (x) may be arrived at by Dr. Pole's formula, in which x = 62 A ( Rm — Ej- In this formula A = the area of the gathering ground in acres ; Rm=the estimated average rainfall of the three driest conse- cutive years ; and E = the loss of rainfall by evaporation, per- colation, and unavoidable waste. The value of E may be as little as 10 inches, and may even exceed 20. Peaty matter is very frequently present in the upland surface waters of mountainous districts, often imparting a decidedly yellow or brownish hue to the water. It may be removed by filtering the water through beds of fine, sharp sand, as is done at Vartry (Dublin). Under the heading of Upland Surface Waters may also be considered the waters gsftW^W^ptf^ral lakes in mountainous. 8 HYGIENE AND PUBLIC HEALTH districts, of which Glasgow furnishes a good example. Glasgow is supplied with water from Loch Katrine, 34 miles north of the City. This beautifully soft and pure lake- water, which replaced in 1859 the grossly-polluted supply drawn from the Clyde, has been of inestimable advantage to Glasgow, not only by raising the standard of health of its inhabitants, but also by effecting an enormous saving in manufacturing and industrial pursuits, from the fact of the hardness being equivalent to only one grain of chalk per gallon of the water. Upland surface and lake waters approach more nearly to the composition of rain-water than water derived from any other source in their comparative freedom from mineral matters. Many of the manufacturing towns in Lancashire and Yorkshire are supplied with upland surface waters. Manchester has lately obtained a new source of supply from Thirlmere, 90 miles from the City. By the construction of a dam, the level of the lake has been much raised, and its storage capacity increased. Liverpool, by immense engineering works, has impounded the waters of the Vyrnwy, in Wales, by a massive masonry wall built across a narrow part of the valley, creating an artificial reservoir 4| miles in length and conveying the water a distance of 68 miles ; and Birmingham is now engaged in the task of bringing water from the upper sources of the Wye. Occasionally the water of lakes and open reservoirs becomes con- taminated by the growth and subsequent decay of algse and other microscopic organisms. In some instances so abundant is the growth of the organism that the water becomes coloured red or green-blue, according to the nature of the organisms, and is also turbid and evil-smelling. Beyond the unpleasantness arising from the odour and turbidity of the water, and the disturbance of the sand filter-beds when the reservoir water is subjected to filtration, it does not appear that this contamination induces any injurious effect upon the health of the consumer. The quantity of water that can be collected and stored in an impounding reservoir amongst hills can be calculated with some approach to accuracy if the area of the catchment basin, the average rainfall, and the average amount of percolation, evapor- ation, and flow of the rainfall off the surface, are known. Re- cords of the rainfall, percolation, etc., extending over a long series of years are nem§a&gp bjaeiidtesfflpmpose. The loss from evaporation in open reservoirs may reach to £ of an inch per WATER 9 day in summer, the average throughout the year varying from -^ to y 1 ^ of an inch daily. The area of the catchment basin or gather- ing ground can be ascertained from a 6-inch ordnance map. It is in many cases a district enclosed by a ridge line, which is continuous except where the water finds exit ; or if the ridge line is complete and the water does not find an exit, a lake or natural reservoir is formed. The main ridge line may give off branches, and thus produce subsidiary or secondary catchment basins. In 6-inch ordnance maps, contour lines, which are lines of equal altitude, are drawn at every 25 feet of elevation. Ridge lines, or watershed lines, indicate where the ground is higher than that immediately adjacent on each side, the land sloping from them on both sides. On the ordnance map will also be found the Bench Mark figures, which indicate in feet the height of the particular spot above ordnance datum. If the place noted by any of these figures be visited, there will be found aB. M. or broad arrow marked on some object, such as a milestone, church- wall, rock, etc. The maps of the Ordnance Survey of the United Kingdom are published in the following scales : (1) J inch to the mile, or o-tjV^it the actual measurements of the ground. This map shows a considerable area of country in one sheet. (2) One inch to the mile, or eraec? the actual measurements of the ground. This is the general road map of the country. The outline edition shows contours at 1 00 feet intervals up to 1 ,000 feet, and above that height at 250 feet intervals, and numerous spot levels along the roads. (3) Six inches to the mile, or Tirses the actual measurements of the ground. This map shows houses and fields and boundary lines. Altitudes are shown as on the 25-inch map, and contours are shown at 50ft., 100ft., and at 100ft. intervals up to 1,000 ft. above sea level. (4) Twenty-five inches to the mile, or 2 s'oii the actual measurements of the ground. This map shows the details of buildings, and the boundaries and areas of fields, etc. It shows levels of bench marks along the roads to one place of decimals, but does not show contours. (5) Town maps, with the exception of London, Dublin, Belfast, and some smaller towns, are on the scale of 10-56 feet to the mile, or 555 the actual measurements of the ground, for all towns which at the time of the survey had 4,000 inhabitants and upwards. The scale is large enough to show doorsteps, the thickness of walls, and the divisions between buildings. It also shows all objects con- nected with water-supply, lighting, and drainage, such as hydrants, lamp- posts, sewer-manholes, and gratings. Levels are shown along many of the streets, and bench marks showing to two places of decimals the altitude above mean sea level. Areas are not shown on town plans, nor are con- tours. In London, Dublin, and Belfast the scale adopted is 5 feet to the mile, or T5 Va the actual n®fgmgMspiV}im&mgr°und. The altitudes on the maps are those above ordnance datum or mean 10 HYGIENE AND PUBLIC HEALTH sea-level at Liverpool, which is 0-65 feet below the mean level of the sea round the coast. Trinity high water mark at the entrance of the London Docks is 12-48 feet above ordnance datum. Surface levels are shown in feet along the roads on the 6-inch maps thus + : on 10-feet town plans one decimal is given. Levels are shown thus " ^ B. M. 57-4." B. M. means the Bench Mark cut on buildings, walls, etc., and at this spot the Bench Mark is 57-4 feet above ordnance datum. Waters collected from upland surfaces are liable to pollution from shepherds' huts and the droppings of animals allowed to feed upon the collecting area. The water collected upon these areas ought always to be carefully protected from such pollutions. Streams and Rivers. Streams near their sources, and passing through uncultivated land on hills and moorlands devoid of human habitations, are good sources of water-supply ; they form, in fact, those upland surface waters which have already been considered. Streams and rivers in their course through cultivated valleys, with towns and villages on their banks, furnish water which must always be regarded as undesirable, and in many cases as dangerous for drinking purposes. The composition of river water, as regards its mineral ingre- dients, is most variable. Fed from a variety of sources, by springs and streams in the uplands, by surface drainage, by springs in their beds, and by other streams and rivers through- out the whole of their course, rivers are a combination of spring and surface waters, and present sometimes mainly the char- acteristics of the one and sometimes those of the other. All rivers, as being the natural drainage channels of the surrounding land, must be subject to pollutions of animal origin. The surface and subsoil drainage from manured land under culti- vation, the sewage effluents from isolated houses, the slop waters and the sewage of villages and sometimes even of towns, and the waste products of industries on their banks frequently flow into the river. Towns, as a rule, draw their supply of water from a river above the spot at which the sewage of the town is dis- charged. But the intake of the next lower town on the banks of that river must necessarily be from a stream already polluted with sewage ; and the question arises, can a river once polluted with sewage, and with all the possibilities of specific disease contamination thereby^te&WchAfecbsog^er be a safe source of supply below the point of pollution ? WATER II When sewage or other polluting liquids are discharged into rivers, they are more or less diluted with the river water, the amount of dilution depending on the comparative volumes of sewage and river water which are thus mixed together. If the river into which the sewage is discharged consists of clean and hitherto unpolluted water, the oxygen dissolved in it will, to a certain extent, oxidize the organic matters of the sewage, this destruction being very largely effected through the agency of aerobic or oxygen-requiring bacteria. If, too, the dilution of the sewage with clean water is considerable, plant life is not interfered with but continues to give off oxygen, reoxygenating the water, and enabling the process of purification by oxidation to continue. No doubt, also, as the oxygen dissolved in the water is used up, fresh oxygen is absorbed from the air. Besides water, plants, minute animals (infusoria, anguillulidaa or water worms, entomostraca or water fleas, etc.) aid the process of purification by feeding on the organic impurities of sewage. These organisms are found in countless numbers in the polluted reaches of rivers. Fish, too, if the pollution is not sufficiently great to cause serious diminution of dissolved oxygen in the water, feed on some of the elements of sewage, and aid in the process of purification ; and when the current is sluggish, or in the deep and quiet pools of a rapid stream, the suspended matters of the sewage will be largely deposited. Delepine has shown that this sedimentation, which occurs when the flow is sluggish, is a very important factor in promoting bacterial purification in river water. The result of all these processes is that, under certain con- ditions and within certain limits, streams and rivers which have been polluted are capable of undergoing a certain amount of self-purification by natural means. The Rivers Pollution Commissioners (Sixth Report) came to the conclusion, as the result of their experiments, that " the oxidation of the organic matter in sewage proceeds with extreme slowness, even when the sewage is mixed with a large volume of unpolluted water, and that it is impossible to say how far such water must flow before the sewage matter becomes thoroughly oxidized. It will be safe to infer, however, from the above results, that there is no river in the United Kingdom long enough to effect the destruction of sewage by oxidation." The truth of the mau§Y^nen / appears'' to be, that under favour- 12 HYGIENE AND PUBLIC HEALTH able conditions, when the dilution of the sewage - with clean water is very considerable and the oxidation and purifica- tion exerted by aquatic animal and vegetable life can have free play, a stream or river, especially if it undergoes agitation and exposure to the air by flowing over rapids or by falling over weirs, is capable of being so far purified that, although it may never quite regain its original purity, it becomes at least very much improved. The oxidation of the organic matters in sewage is not, how- ever, the only process with which the self-purification of rivers is concerned. Of more importance is the destruction or elimination of the bacterial organisms introduced into the water by the polluting agents, more especially of those of " intestinal type," e.g., Bacillus coli, Bacillus enteritidis sporogenes, Bacillus enteriti- dis (Gaertner), and streptococci, with which are occasionally associated the Bacillus typhosus and other pathogenic organisms. It is probable that organisms of this type may persist in a polluted water which has freed itself from all other evidence of sewage contamination, and be present in such numbers as to indicate recent contamination with animal matter with all its attendant dangers. There' is evidence that organisms of the intestinal type, after obtaining admission to water, undergo after a time changes of a degenerative nature, probably accom- panied by loss of virulence, so that they no longer comply with all the tests characteristic of the types they represent. When the river into which sewage is discharged is already much polluted, or if the dilution is not sufficiently great, oxidation and purification are brought to a standstill. The dissolved oxygen is then greatly diminished in amount ; many forms of animal and vegetable aquatic life are injuriously affected or destroyed ; decomposition or fermentation of organic matters is started, with the production of foul gases ; the bed of the river becomes silted up with decaying matters, which, buoyed up by gases, occasionally rise to the surface and sink again, and a most serious nuisance results. The process is one eventually tending to purification by resolution of complex organic bodies into their simpler elements, but in the meantime the effects of the process are most offensive. A considerable rise of temperature will produce a like result on rivers which are h^#g 3< tM¥ / p"eg < $fing powers tested to the height of their capacity. Purification goes on so long as the WATER 13 weather is cool, but with a rise in temperature, certain forms of bacterial growth are stimulated and decomposition sets in, replacing the oxidizing processes. Sewage in drinking water is chiefly dangerous from the fact of its being liable to contain the specific poisons of disease. Cholera and enteric fever, diarrhoea and dysentery, we know to be sometimes spread by means of infected and polluted water. A considerable mass of evidence, based largely on laboratory experiments, was submitted to the Royal Commission on Metro- politan Water Supply (1893), as to the behaviour in water of the bacilli of typhoid fever and cholera. The statements of the bacteriological witnesses before the Commission, therefore, represent knowledge obtained under artificial conditions of disease organisms cultivated under such conditions, and are consequently only inferentially applicable to similar microbes in a state of nature and subjected to a natural, as opposed to an artificial, environment. With this reservation, the general results of the bacteriological evidence may be summed up as follows : The bacilli of typhoid fever and cholera tend to lose their vitality, and ultimately to disappear, when placed in water. In water which is sterile, or devoid of other organisms, these bacilli may retain some kind of vitality for several weeks or months if the water contains organic pabulum. But in water containing actively growing non-pathogenic organisms, such as ordinary river water, the destruction of the pathogenic organisms is effected much more rapidly. This statement helps to throw light on certain outbreaks of enteric fever due to specific contamination of deep well-water. Pure deep well-waters contain relatively few bacteria; consequently the typhoid bacillus when introduced into such a water (as occurred in the Caterham outbreak) may possibly retain its vitality and virulence sufficiently long to render large volumes of water infective. It appears possible, also, that under such conditions, deep underground, with an absence of light, the typhoid bacillus for a space of two or three days might in- crease in numbers, thus enabling a relatively small amount of polluting ingredient to contaminate large volumes of water. The process of sedimentation which occurs in the deep and sluggish reaches of a river tends to the elimination of bacteria, the suspended matters in their subsidence entangling them and carrying them dcMf ed fhe^ / e r rfl cf ) of aeration and of flow 14 HYGIENE AND PUBLIC HEALTH are less apparent qua bacterial destruction ; whilst as regards the undoubted powerful germicidal action of bright sunlight, in the case of a river like the Thames, with an average depth of over six feet, it is doubtful what effect the water has in cutting off the actinic light, and, therefore, what is the precise germi- cidal action of sunlight or daylight at different depths from the surface, and under different conditions of clearness or turbidity of the water. The process of storage and purification of Thames water pursued by the Metropolitan Water Board, on the efficiency of which the health and freedom from disease of so large a population depends, is as follows : — The water taken from the river is passed into a storage reser- voir, capable of holding several days' supply. It is important that the capacity of this reservoir should be sufficiently great, both to obviate the necessity of drawing water from the river when it is in flood (and therefore very turbid), and to allow time for the clarification of the water by the deposition of suspended matter. The Thames storage reservoirs are of an aggregate capacity of over 500 million gallons, and the average daily supply from them is 133 million gallons. From the storage reservoirs the water is conducted to the surface of the filter beds, which con- sist of layers of fine sand (average thickness 3 feet) lying upon layers of gravel, fine above but coarse below, and of a total depth varying from 3 to 8 feet. The average filtering area per million gallons of daily supply is 079 acres. In the coarse gravel or rough stones are the open mouths of the outlet pipes, which convey the filtered water from the filter beds to a central filtered-water well, from whence it is pumped through iron mains to the Metropolis, or to a high-level reservoir near London. Vents run up from the deeper layers of the filters to above the water level to permit of the escape of displaced air when the bed is being filled with water. The large reservoirs for the storage of filtered water in or near towns should be covered ; they are not infrequently made to feed supplementary reservoirs, especi- ally where the demand in one part of the district greatly exceeds the average for the district generally. The depth of water on the filter beds is never more than 2 feet, the average rate of filtration per square foot of filter-bed being ij gallons per fcigi£t£?<£by 4^>f§op8 gallons per acre in 24 hours. The upper layers of fine sand must be occasionally WATER 15 renewed, as they become choked with sediment. The old sand is washed with water jetted from a hose under high pressure, before being used again in the filter-beds. Houston has shown that in fresh, healthy, human faeces 85 per cent, of the organisms known as Bacilli coli communis are typical B. coli, answering to all the known tests for this organism, the remaining 15 per cent, being atypical, in the sense that they do not respond to all the tests. In sewage and sewage effluents the percentage of typical B. coli is slightly reduced, and in sewage polluted waters there is a further reduction. In filtered waters derived from polluted sources, such as the water of the Thames at Hampton, the percentage of typical bacilli is reduced as low as 38 after storage and sand nitration, such as is practised by the Metropolitan Water Board, in addition to the 98 per cent, reduction in total num- ber of organisms as compared with the unfiltered crude river water. Dr. Houston is of opinion that the smaller proportion of typical B. coli in the stored and filtered water is evidence of elimination from the water of bacilli which are specially char- acteristic of fascal matter, and therefore of purification by change of type of bacilli, apart from reduction in numbers. The disappearance of the typical bacilli is relative and not absolute, as 30 per cent, of the samples of filtered water analysed contained typical B. coli either in 100 c.c. (15 per cent.), 10 c.c. (n per cent.) or 1 c.c. (14 cent.) of the water. In the latter case only, however (B. coli present in 1 c.c), would the water be considered decidedly unsatisfactory. Sand acts almost entirely as a mechanical filter, but a small amount of purification by oxidation takes place. This purifica- tion results mainly from the condensation of oxygen, which takes place upon the upper surface of the sand. Dr. Percy Frankland has shown that the micro-organisms (harmless) present in unfiltered Thames water at Hampton are reduced in number on the average 97-7 per cent, by the sedimentation and filtration which the water undergoes at the hands of the Water Board, and that this reduction is largest in the case of those installations which have the largest storage capacity for unfiltered water, and the slowest rate of filtration, these being factors of much influence on the chemical, as well as on the biological, charac- teristics of the water. All the witnesses beW^Mpf Commission of the Metro- l6 HYGIENE AND PUBLIC HEALTH politan Water Supply (1893) were agreed that the efficiency of the sand filter-beds in intercepting bacteria is due to the forma- tion of a superficial gelatinous deposit on the top of the sand. Green and blue algae interweave their filaments into one felted sheet ; diatoms, with their siliceous frustules and gelatinous envelopes, fill up the meshes; zooglea adhere to every particle; and innumerable bacteria dot the whole mass (Thresh). The bacteria become attached to and entangled in the colloidal mass, and are consequently prevented from passing down into the deeper beds of sand and gravel. This filtration has been likened to the dialysis through a fine jelly, which is capable of inter- cepting the very smallest bacteria, if there is no rupture or loss of continuity in the material. This gelatinous film which forms on the top layer of sand consists therefore very largely of intercepted organic matter and bacteria. It appears to be sufficiently well formed to be effective in intercepting bacteria within two or three days after the filter-bed has been in use, subsequent to renewal of the top layer of sand. It follows, therefore, that the filter-bed does not attain its normal efficiency in the inter- ception of bacteria until it has been in use at least two days after the periodical renewal. On the other hand, there is no evidence of the efficiency of the sand filter-beds, qua bacterial interception, being reduced by prolonged use, even for so ex- tended a period as sixty-eight days. It would seem that the organisms tend to grow down deeper and deeper into the beds, and might possibly in time grow quite through the interstices of the filter, and so reappear in the filtered water. But owing to the thickness of sand this process must occupy a very long time. The reason why the top layers of sand should be removed and renewed periodically is to prevent other filter-beds being overtaxed, because the filtration becomes slow in old beds, owing to the thickness of the gelatinous coating, and consequent clogging of the top layers. If certain filter-beds are working too slowly, others have to be pressed, possibly resulting in inefficient.filtration, in order to make up the volume of filtered water necessary for the daily supply. The result of the Massachusetts experiments on the purifica- tion of water by filtration may be briefly summarized as follows : (a) By reducing thea§ipiiify MJb/filfcffiition, and employing the finer sands, increased efficiency is obtained. WATER 17 (b) With moderate rapidity of filtration (2,000,000 gallons per acre per diem) 1 foot of sand appears to be as effective as 5. (c) The scraping off of the upper layer of clogged sand enables more organisms to pass through the filter ; and it is not, as a rule, until three days after scraping that the filters regain their highest efficiency. (d) Fifty-five per cent, of the organisms removed were found in the upper £ inch of sand, and 80 per cent, in the upper inch. (e) Much less water at 32 F. passes through a filter than when the water is at 70 F., owing to the increased viscosity of the colder water. . (/) Shallow filters require more frequent scraping than the deeper ones, due to the greater head available in the deeper filters. (g) Filters used continuously require less frequent scraping than when used intermittently. The connection between the cholera outbreak in Hamburg in 1892 and its water supply, and the value of sand filtration are clearly demonstrated by the following facts : — -Hamburg, Altona, and Wandsbeck are three towns which are con- tiguous to each other, and really form a single community, not differing from each other except in so far that each has a separate and different kind of water supply. Wandsbeck obtained filtered water from a lake which is hardly at all exposed to contamination with faecal matter ; Hamburg obtained its water unfiltered from the tidal Elbe above the town ; whilst Altona drew its water from the Elbe, but below Hamburg, after the river had received the sewage of 800,000 people. The water so taken, however, was subjected to careful sand filtration, before being supplied to the people of Altona. Whereas Hamburg in 1892 was severely visited by cholera, nearly 17,000 attacks and 8,600 deaths occurring in the autumn of 1892, Wandsbeck and Altona were nearly free from the disease. About 500 cases of cholera occurred in Altona, but at least 400 of these were infected in Hamburg. The water supplied to Hamburg was taken from the Elbe above the sewage outfalls into the river, but was nevertheless contaminated at times by the tidal action carrying sewage back above the outfalls. This water, supplied in an unfiltered condition ^p th^ogDulatgi, was the cause of the cholera epidemic. Careful sand nitration of the Elbe water, in a C l8 HYGIENE AND PUBLIC HEALTH much more grossly sewage-polluted condition, saved Altona from the disastrous epidemic which raged in Hamburg. Professor Koch lays stress upon the following three points as to the efficacy of sand filtration : (i) That a proper thin layer of mud or slime should be formed on the top of the filter-bed ; that it should not be disturbed during the process of filtration, and that when the deposit becomes too thick and impermeable it should be removed ; (2) that the thickness of sand should never be less than 30 cm. (11 -8 inches) ; (3) that the downward movement of the water through the sand layer must not exceed 100 mm. (3-94 inches) in the hour, or 4,800,000 gallons per acre per diem. He recommends that, after a filter has been scraped, the slimy deposit should first be allowed to form before the water is conducted to the filtered-water well or reservoir ; that each separate filter should be bacteriologically investigated daily, and water containing more than 100 germs, capable of develop- ment in a cubic centimetre, should not be allowed to reach the pure water reservoir. The majority of the bacteria in ade- quately filtered water are attributable to post-filtration sources, the filter-beds below the slime layer, the channels, collecting drains, culverts, and wells being, of course, not sterile. The slightest disturbance, however, in the process of filtration, as, for instance, the quickening of the pace of filtration to over 100 mm. per hour, or the disturbance of the slimy covering, as in periods of frost or immediately after a filter is cleaned, tends to create an immediate increase of germs in the filtered water. The conclusion that we may come to, then, in the case of the London water supply from the Thames, is, that as long as it is efficiently filtered and not taken from the river when in flood, it is fairly pure and reasonably wholesome ; but that the Thames is not really a safe source of supply, for should the filtering arrange- ments break down at a period of epidemic prevalence in the upper reaches of the river, disease would in all probability arise amongst the consumers of the water in London. The same may be said of any other polluted river used as a source of drinking water ; and all attempts to purify by filtration organically polluted water, whether it be on a public or a domestic scale ought to be deprecated. The yield of a smallra£ffearl^>cW/rfeSSrr'S0fter-bearing strata below, 28 HYGIENE AND PUBLIC HEALTH though often at no great distance from the surface. In sinking a deep well, as soon as the water-bearing strata are reached the water often rises rapidly, and may even overflow at the surface. If the sides of a deep well of this nature are properly steened with brickwork set in cement as far down as the impermeable stratum, surface waters and underground water resting on this stratum are entirely excluded, and the well is freed from those sources of pollution which so often contaminate shallow- well waters. In hard chalk, new red sandstone, oolite, and limestone, the wells require no lining, but in clays, marls, and in all free and broken strata they should be steened. The water collected from deep wells has usually travelled a long distance since it fell as rain on the surface of the earth ; for the outcrop of the water-bearing strata on the surface, which are the catchment areas for the rain, may be many miles from the spot at which the well is sunk, as is the case with the deep wells in the chalk sunk into the London basin. The London basin is interesting as an example of a geological formation with water-bearing strata in different rocks at varying depths from the earth's surface (fig. 3). Most superficially are the subterranean waters in the beds of gravel or alluvium of but slight thickness (10 to 30 feet) upheld by the London clay. These waters supplied the shallow wells which formerly formed so large a part of the water supply of London. After boring through the London clay (100 to 400 feet in the neighbourhood of London) water is again reached — or was before these strata were exhausted — in the Lower London Tertiaries, beds of sand, gravel, and clay of variable thickness (20 to 100 feet), withlimited out-crops beyond the edge of the London clay, and more or less surrounding it as they rise from the margin of the basin. Having such a limited outcrop exposed to rainfall, the water which accumulated in the deep strata of these beds under the London clay was soon exhausted, when numerous wells were sunk into them. Beneath the Lower London Tertiaries comes the chalk, with its outcrop in the chalk hills and downs, north, south, and west of the Thames basin, and many miles from its centre. The outcrop forms a very extensive catchment area for rain, which percolating through the joints and fissures of the chalk rives Digitized by Microsoft® , ' b rise to vast reservoirs 01 Subterranean water in the underground water 29 extensiofx of this rock beneath the tertiary beds of the London basin. As the London basin is hollowed into the form of a shallow trough, the sides of the trough being the outcrop of the chalk in hills and downs, it follows that the water in the chalk is also trough-shaped, and that when wells or borings are sunk into it near the centre of the London basin, the water tends to rise in the boring, and may even overflow at the surface, forming • true Artesian wells. In conse- quence of the number of borings drawing water from the chalk near London, the water-level has been lowered ; and borings have now to be made deeper than formerly. Owing to the joints and fissures in the chalk allowing a free passage for water, the distance which a well or bor- ing drains, when its water-level is depressed by pumping, is very great ; and thus borings at con- siderable distances from one another are mutually affected by continued pumping in any one of them. If a boring in the chalk should not happen to open up any fissures or cracks, it may supply but a limited quantity of water, or none at all. Beneath the chalk is the upper greensand in thin beds (10 to 30 feet) with a very limited out- crop around the edge of the chalk ; and beneath this again is the gault, a bluish clay with an average thickness of 130 to 200 feet, the lower greensand in very thin beds, often completely thinned out, and therefore absent. Although the greensands are rocks permeable to water, netifeft&g&ByWWQQfe&m lower beds have yielded water in any quantity to deep borings in the neighbourhood of m y-> ft Under the gault lies 30 HYGIENE AND PUBLIC HEALTH London. Their outcrop is very limited, with but a small ex- posure of catchment area for rain ; and these formations appear also to thin out considerably in their underground extensions towards the centre of the basin. Near their outcrops in many places the greensands furnish abundant supplies of water, which are, however, very frequently due to percolation from the over- lying chalk. Several borings made in or near London have passed through all the strata above mentioned into the primary rocks beneath. In making these borings it is usual to excavate a wide well-hole for some depth, from the bottom of which a bore tube of small diameter (6 to 15 inches) is sunk. The water should rise through the bore tube in sufficient volume to form a reservoir in the lower part of the well-hole, from which it can be pumped to the surface from considerable depths. Boring tools of large diameter have been recently introduced, and these are found less costly, whilst the borings are more easily made. At some new works in the chalk at Southampton, the bore tubes are 6 feet in diameter. It has been in many cases found that the driving of headings (" galleries ") and adits horizontally below the water-level, is more effective in increasing the yield of wells than deepening them, as the area of collection of water is thereby increased, and there is a greater likelihood of striking the fissures through which the largest volumes of water are moving. Artesian wells, so called from the province of Artois in France, where they have long been in use, are formed when a boring taps a subterranean reservoir confined in a permeable stratum by impermeable strata above and below, the permeable stratum having its outcrops on the surface at considerably higher levels than the surface of the ground where the boring is sunk. The subterranean reservoir is consequently basin-shaped ; and the water, when tapped at the lower part of the basin, strives to regain its level by flowing up the boring and spouting out at its mouth. The waters which feed these wells often come from a great distance, the outcrops of the permeable strata on each side of the basin being sometimes 60 or 70 miles from the well in a straight line. The best Artesian wells are found in the chalk. The water supplied ^tity *W& generally remarkably free from organic impurities, even when sunk in the midst of WATER 31 large cities. Nitrogen, as nitrates and nitrites, is usually present in deep well waters ; the other mineral constituents of the well water depend chiefly on &&§&& ^Mfff which the water has 32 HYGIENE AND PUBLIC HEALTH percolated, and on the solubility of the component elements of these strata by water charged with carbonic acid. In the near neighbourhood of the sea there is a danger of the infiltration of sea water into deep wells, especially when sunk in chalk formations. Such infiltration is recognized by an increase in the amount of chlorine in the well water, and is probably due in some cases to excessive pumping causing considerable depres- sion in the water-level of the well. It has happened that the brackishness so caused has rendered a town water supply quite unusable for domestic purposes, and has given rise to diarrhoea and other evidence of gastro-intestinal disturbance among some of those drinking it. The yield of water from a well can only be ascertained by pumping down to a certain level, and observing the length of time required for the water to regain its original level. In this country the largest supplies of deep well water are obtained from the chalk, the oolite, and the new red sandstone. Although deep wells, when protected from surface drainage in their upper parts, are but rarely polluted, even when situated in the centre of towns, it does occasionally happen that liquid soakage from sewers or cesspools finds its way into fissures in chalk or sandstone, which conduct it to the water of the well, unfiltered and therefore unpurified, and pregnant with danger to the consumers. Deep wells in Liverpool and other places have been closed for this reason. The following facts will be found of value in seeking for water. In comparatively flat districts, trials should be made by Norton's tube wells at the lowest sites on the survey. The part most covered by herbage is probably the site where the water reaches nearest to the surface. The same fact is sometimes denoted by localized early morning mists or swarms of insects. The nearer the sea, the more likely is water to be found, but if too near the sea the water may be brackish. In hilly country a search should be made in the deepest valleys, especially the side of the valley towards the highest hill, and at the junction of two long valleys. If there is any evidence of an original watercourse at this point, water is often found at no great depth. A knowledge of the dip of the strata in the district, and the situation and za^&edfcytteroapaicrop, is of the greatest value in such an investigation. WATER Pumps. 33 Suction pump. — Fig. 5 shows a section of a common suction pump, which works by the exhaustion of air inside a. cylinder, by means of the upward stroke of a piston ; the atmospheric pressure on the surface of the water forcing the water up through the suction pipe into the cylinder. The downward stroke of the piston forces the water through the piston I 3=lE^i-=^-3!t 3* Fig. 6. Single- Acting Suction and Force Pump. V V 1 , valves. Fig. 5. — Suction Pump. A, piston ; B, piston valve ; C, suction or clack valve; D, suction pipe ; E, water ; F, spout. Fig. 7. Double-Acting Suction and Force Pump. V, V 1 , V 2 , iV 3 , valves. valve, and the next upward stroke delivers it through the spout of the pump. Where water has to be delivered at a height above the pump, the spout is replaced by a pipe (the rising main) with a valve at the point of attachment to the cylinder, which permits water to enter the rising main, but prevents its reflux into the cylinder. In this class of pump the lift of water is effected by the u^war^d sjxoke^o^the piston, and the delivery roke of the piston the suction is in consequence intermitteni 34 HYGIENE AND PUBLIC HEALTH or clack valve C is opened and the piston valve B is closed ; at each down-stroke the action of the valves is reversed. The height of the clacK valve C above the lowest level of the water to be raised must not ^ more than 25 feet. Although theoretically atmospheric pressure -is capable of supporting a column of water 3 3"9 feet in height, Poetically the most perfect vacuum obtainable in a suction pump is only equivalent to 25 feet of head, and these pumps work best with heights of less than 15 feet. Force Pumps.— Sections of force pumps are shown in figs. 6-7- ^-^ pumps are used where water has to be raised to a height exceeding 25 feet, as from deep wells. In each case the water is raised by suction into the pump, but whilst in the single acting pump (fig. 6) the delivery is inter- mittent, in the double-acting pump (fig. 7) the flow of water is con- tinuous. . Semi-rotary Pumps.— -These are suction and lift pumps, in which the water is raised by the suction induced in a small disc-shaped cylinder by means of metal valves rotating in a half-circle at a considerable speed. These pumps are small, occupy little space, and are easily worked by a lever with vertical action. Centrifugal Pumps .—These are used (see fig. 8) where large quantities of water or sewage have to be raised through a moderate lift, not exceeding 25 feet. The apparatus is simple and compact, consisting of revolving fans, which by their rapid revolu- tion cause a vacuum, and draw water through a suction pipe into the centre of the rotary wheel. The centrifugal action set up by the fans causes the water to be ejected through the delivery pipe. The wheel is made to revolve by belting passing round the fly-wheel of a steam, gas, or oil engine. Chain Pumps. — In this pump, water is raised by means of a series of small buckets attached at equal distances to an endless chain, which passes round a vertical wheel above and dips into the water below. Instead of the buckets, the endless chain may be enclosed in a tube, and carry a number of equidistant diaphragms pro- vided with leather washers just large enough to work up and down inside the tube. The vertical wheel is made to revolve, and the little buckets, or the diaphragms, in their ascent lift the water, and discharge it into a spout at the top of the apparatus. These pumps are especially suitable for raising sewage or other water containing suspended 'matter, which is apt to clog and derange the action of ordinary pump valves. Pulsometers. — These are mostly used for temporary pumping purposes. The pump consists of two vessels with a ball valve at the top, steam from a boiler being admitted alternately into each vessel. The steam forces the water out of the vessel into the rising main or delivery pipe ; and the condensation of the steam, by contact with the cold sides of the vessel, causes a vacuum, the pump thus having a suction effect on the water over which it is suspended, which rises through a suction tube and suction valve into the pulsometer. Thus alternate condensation and discharge takes place in each of the two vessels composing the pulsometer and there is a continuous discharge of water so long as steam is supplied. Water-wheels. — By the use of water-wheels the motive power of a running stream can be utilized in raising water to a height. Vertical water-wheels are of three kinds : (1) Oi^^hd^Wi^Sm^ is delivered on the top of the wheel ; (2) Breast, when the water is delivered near the centre of the Fie. Centrifugal Pump. WATER 35 wheel ; and (3) Undershot, when the wheel is driven from the bottom by the impact of a strong current. For overshot and breast wheels the stream must be dammed, as seen in the common mill dam and wheel. By suitable gearing the circular motion of the wheel is transformed into the reciprocating motion of the piston rod of the pump used to lift the water of the well or reservoir. Hydraulic Ram. — When water flowing rapidly in a pipe is suddenly checked, there is an increase of pressure on the interior of the pipe. This Fig. 9. — Hydraulip Ram. V, self-acting pulsating discharge valve ; A, air vessel ; supply pipe ; E, delivery pipe. O, ball valve; S, increase of pressure is known as ramming, and is used to force a certain proportion of the water flowing down the pipe to a height above the point at which ramming takes place. The apparatus is shown diagrammatically in fig. 9. Water descends with considerable velocity down the supply pipe S from a stream or reservoir, and runs to waste through an opening at V, which is guarded by a valve. But the momentum of the water in its flow is sufficient to overcome the weight of the valve, which is raised and closes the orifice. The flow of water thus momentarily checked causes an increase of internal pressure in the apparatus, and the ball valve O is opened, allowing water to pass into the air-chamber A, where the cushion of compressed air drives the water steadily up the pipe E to the storage tank. As soon as the pressure is reduced by the opening of the ball valve O the discharge valve falls, and water again escapes at V, until the velocity of flow reaches the point at which the discharge valve is again raised, and the cycle of events is reproduced. A fall of 10 feet from a stream or reservoir to the ram is sufficient to raise water to a height 150 feet above the ram. Composition of Water from Various Sources. The nature and amount of the organic pollution to which water from various source^ is liable, is such a variable quantity that it is useless and misleading to attempt any classification under this head ; for it is local circumstances that will determine whether a shallow well water is polluted or a deep well water is pure. Generally speaking, however, the purest waters are derived from deep springs and wells and upland surfaces, while the waters from the subsoil, from cultivated surfaces, and from Digitized by Microsoft® rivers are especially liable to be organically polluted. But the 36 HYGIENE AND PUBLIC HEALTH character of the soil and subsoil from which the water is collected influences its composition to an extent which, though variable, may be approximately denned by chemical analysis. i. Surface Waters.— Those waters collected from the hard sur- faces of the practically impervious rocks which support little animal or vegetable life are very pure. They commonly contain less than 10 parts of total solids, 5 of total hardness, 1 of chlorine, and o«i of nitrogen as nitrates, in 100,000 parts of water. The mineral solids consist mainly of sodium carbonate and chloride, and a trace of lime or magnesia. The variable amount of organic matter, which is often exclusively of vegetable origin (peat), yields practically no free ammonia ; but the organic ammonia figure and that of the oxygen absorbed by organic matter may be high, in which case the water is often highly-coloured and acid in re- action. Such characters are presented by the waters collected from the surfaces of the igneous metamorphic (quartz, mica, granite, etc.), Cambrian, Silurian, and Devonian rocks. The waters from the surface of the non-calcareous carbonifer- ous rocks (Yoredale rocks, millstone grits, and coal measures) are very similar ; but those which have flowed over the surface of the calcareous carboniferous rocks — the mountain limestone and limestone shales — -differ from the former in possessing a moderate degree of hardness, higher total solids, and a neu- tral or faintly alkaline reaction. The mineral solids consist chiefly of sulphate and carbonate of calcium and magnesium. Surface waters from the lias, new red sandstone, magnesium limestone, and oolite may vary considerably in their composition. The total solids are generally between 10 and 20 parts per 100,000, the total hardness between 10 and 15 parts, the chlorine is below 2 parts per 100,000, and the nitrogen as nitrates below 0-2 of a part. Clay waters are, as a rule, opaque, from a variable quantity of suspended matter, but generally there are few dissolved solids, and the water is fairly soft. Tb.ey vary, however, greatly in their composition. The waters collected from cultivated land present great variations in composition, and the total hardness may range from 5 to 20 parts per 100,000, according as to whether the soil is non-calcareous or calcareous. Alluvium is generally a mixture of sand, clay, and organic matter ; and waters from such a source generally contain high mineral solids (50 to 100 parts), cofl^cfl^ y o¥ /c £S3cnfm and magnesium salts WATER 37 sodium chloride, iron, and silica, and also excess of organic matters. 2. Waters from a Depth. — Those collected from the chalk are generally clear, bright, and well charged with carbonic acid. The total solids are generally from 25 to 50 parts per 100,000, and the total hardness from 15 to 30 parts ; the hardness is mostly temporary, and calcium carbonate may vary from 10 to 30 parts. The chlorine is commonly from 2 to 3 parts, but it may reach a higher figure in some pure chalk waters. The nitrogen as nitrates is below 05 part per 100,000, and is commonly about 03. Sulphates are present in small quantity, and there is often a trace of phosphates and of iron. Although the carbonic acid present is often sufficient to turn blue litmus red, when this is driven off an alkaline reaction is invariably obtained. Some waters derived from the chalk are very soft and contain sodium carbonate. They are only found where the chalk lies buried beneath a thick mass of London clay (Thresh). Waters from the oolite present characters very similar to those from the chalk. Those derived from limestone and magnesium limestone formations only differ from the chalk waters in generally con- taining more total solids, far more calcium or magnesium sulphate (which may reach nearly 20 parts per 100,000), and less calcium or magnesium carbonate, and by consequence the hardness is generally higher and to a greater degree permanent. In dolomite districts the mineral solids contain much mag- nesium carbonate and sulphate, and a large proportion of the total hardness is permanent, dolomite being a double carbonate of lime and magnesia. The greensands are porous strata containing a reducing salt of iron, which by reducing oxidized nitrogen to ammonia often furnishes to the water a very high figure of free ammonia. The total solids vary considerably, but they sometimes approach 100 parts per 100,000 where the water is collected at great depths from greensand underlying the chalk ; the chlorine may reach a figure of from 4 to 14 parts ; the total hardness (much of which is permanent) is very variable — from a low to a high figure ; and the nitrogen as nitrates is generally from about 0-3 to o-6 part per 100,000. Waters from red sandstone strata vary considerably in their , . Digitized ±>y Microsoft® . - . ,, composition, according as the deposit is pure or impure, sott 38 HYGIENE AND PUBLIC HEALTH or hard. The total solids and total hardness are both some- times high, and the former may reach ioo parts per 100,000 ; the latter is mainly of a permanent nature, but the water may sometimes be soft and possess a total hardness figure not exceed- ing 10 parts per 100,000. The chlorine may vary from 2 to 6 parts per 100,000 ; and traces of phosphates are always to be detected in the mineral solids, which mainly consist of sodium chloride, carbonate and sulphate, calcium and magnesium carbonates and sulphates, and a trace of iron. Waters from selenitic deposits are often harmful to drink, on account of the large proportion of calcium sulphate (10 to 30, or more, parts per 100,000), which is taken up from the deposit — this consisting of calcium sulphate in clear crystals. Waters collected from loose sands are of variable composition. Some are soft, with total solids of from only 6 to 12 parts per 100,000, and others are rather hard (permanent) with mineral solids amounting to even 100 parts per 100,000. The chlorine figure is generally rather high, and may amount to a high figure in some cases. The mineral solids consist of sodium chloride, carbonate and sulphate, calcium and magnesium salts, and traces of iron and silica. Those from gravel are generally soft, but some are hard, with high total solids. Waters coming from a depth in the lias clays have generally very high mineral solids (often consisting largely of calcium and magnesium sulphate). There is, as a rule, considerable opacity, and the physical characters generally are not favourable to the water. The hardness, which is almost entirely permanent, is generally over 20, and the mineral solids may reach 300 parts per 100,000. Quantity. The water supplied to a community must be good in quality and abundant in quantity. Impure waters are liable to cause injury to the health of those who drink them ; whilst deficiency of water means want of cleanliness, with its ensuing discomforts and dangers. Water is required fo /fe the foUow^g purposes, the under- mentioned quantities representing average requirements : Household WATER Fluids as drink Cooking .... Personal ablution . Utensil and house washing Clothes washing (laundry) vWater closets Trade and Manufacturing . (Cleansing streets Public baths and fountains . Flushing and cleansing sewers Extinguishing fires Total 27-08 The quantities of water given above as required for the house- hold are those which are necessary to maintain a good condition of cleanliness. The 5 gallons for personal ablutions would allow a daily sponge bath for each person. If each person has also a weekly general bath of from 30 to 40 gallons, 5 gallons extra per head daily must be added. In towns, 5 gallons per head daily is found to be ordinarily sufficient for municipal purposes ; and the same amount is required, on the average, for manufacturing and trade purposes. Water is also required for animals — drinking, washing, and cleansing of stables. About 16 gallons daily for each horse, and 10 gallons for every cow, are average requirements. On the whole, it may be said that not less than 30 gallons per head daily of the population should be supplied to every town. There will always be some waste in households from leaky taps and fittings, and this must be provided for. The greater part of the waste, however, very often takes place from the mains, before the water reaches the consumer. In some towns it has been found that as much as one-half or two-thirds of the total water supply has leaked out of the mains into the soil. The supplies per head in the various towns in this country vary greatly. The amount of water actually utilized in the houses of a town varies enormously. In the houses of the poor it may be only 2 or 3 gallons per head daily ; whereas it should amount to at least 15. The adult human being consumes daily about i\ pints of water as drink, and about another 2 pints in his solid food. Digitized by Microsoft® 40 hygiene and public health Distribution. The system adopted by the ancient Romans for conducting the water collected at the gathering grounds into their cities was the construction of masonry aqueducts built on arches, with a gentle incline to allow of a steady flow of water from its source to its outflow in the city. The aqueducts usually crossed the valleys on raised arches, but the Romans also knew how to construct inverted siphons of lead piping for the passage of the water across valleys. The remains of the reservoirs with which the inverted siphons were connected on either side of a valley are still to be seen in the neighbourhood of Lyons. The water supplied by public companies to towns in this coun- try is now usually distributed from their reservoirs through iron pipes laid underground. These cast-iron mains are subject to much rusting and corrosion, especially when the water is soft. Many of these pipes have been found much weakened by corro- sion at some places, and nearly blocked with accumulated rnst at others, the water also having deteriorated in quality. It is now usual to coat these pipes with some material which is unacted on by water, such as Angus Smith's solution, 1 or with a vitreous glaze. The magnetic oxide of iron produced on the surface of the metal by Barff's process is also occasionally used. In this process the iron pipes are heated to a white heat, and then exposed to superheated steam for several hours. The practice of caulking the joints of iron pipes with tow or gaskin next the interior of the pipe, and then running the joint with molten lead, was strongly condemned by the Rivers Pollution Commissioners, as the water absorbs impurities from the tow and hemp. They recommended that the pipes should have turned and bored joints, or, in the case of mains large enough for a man to enter, that the inside of the joint should be pointed with Portland cement. The mains should have scouring valves at their dead ends, and should be placed at a minimum depth of 3 feet, so as to be protected from frost and sun. All the service pipes of the house must also be protected from extremes of temperature, but they should "always be left accessible ■ and if concealment is necessary, it should only be by a removable wooden casing. On freezing, water expands, and the pipe 1 Angus Smith's process consists in heating the pipes to a high tempera ture and then dipping them. into a hot varnish consisting of coal-tar ni+^h resin, and linseed oil. D/grf/zed by M/croscM) * coal tar pitch. WATER 41 may burst ; but as the fracture is not discovered until the thaw sets in, there is a popular impression that the thaw is the cause of the pipe bursting. An enormous amount of leakage takes place from water companies' mains in many towns, from slight settling of the ground after laying, or from the vibration of heavy traffic causing fracture of the pipes and joints. It has been estimated that in London at one time 15 gallons out of the 35 supplied per head daily ran to waste in the soil. The loss is especially great where the supply is constant and the mains always kept under pressure. If the spots at which leakage occurs could be known, the pipes could be easily taken up and repaired, but the difficulty is to find where the leaks are. This difficulty has been over- come by Mr. Deacon, who has invented a meter which can be used as a waste detecter. One of these meters is placed on each district main ; it registers the flow of water by day and night and therefore the waste, for the water flowing through the main during the dead of night is not used by the consumers, but is running to waste. Having localized the waste to the district supplied by a district main, the exact spots where the leakages are taking place can be determined by the vibrations thereby produced in the nearest house communication pipes, which can be distinctly heard on applying a stethoscope to the pipe. By this system, to take one example only, the Lambeth Water Companv has reduced its consumption from 34 gallons per head per day to 20 gallons, the quantity available to the consumer remaining the same. The temperature of the water in the underground mains of a town varies considerably with the season of the year. In Chelsea, where the temperature of the water in the mains has been tested daily since 1897, a minimum temperature of from 37° F. to 40 F. is usually recorded in January or February, whilst a maximum of from 68° F. to 74° F. is usually attained in July or August. The water temperature follows the mean air temperature, but the changes are of course far less in volume, and are effected more gradually. It would seem probable that the temperature of the water in cisterns exposed to the sun and atmosphere is likely to be considerably in excess of that drawn from the mains during the warm months of the year, so that temperatures of 8o° E. are .prahabhkJiot unusual under such conditions. 42 HYGIENE AND PUBLIC HEALTH The house communication pipes in nearly all towns are of lead, connected with the main by a brass screwed ferrule. Lead house service pipes are employed, because the ductile metal can be easily bent as occasion may require in carrying the pipes through a house, and they are easily jointed and rustless. If wrought-iron pipes are used, double screw joints should be provided at convenient points to admit of the clearing away of the rust, which often chokes an unprotected iron service pipe. Lead pipes may be acted on by water, especially soft water with an acid reaction, and in this way there may be danger to the consumers. Such has not been found generally to be the case, for although new lead pipes are undoubtedly acted on by soft water, an oxide of lead being formed which rapidly dis- solves again in the presence of faint acidity, the action is often very slight. The Loch Katrine water acts most powerfully on lead, and yet no symptoms of lead-poisoning have ever been observed amongst the population of Glasgow. It is now recognized that the degree of plumbo-solvency of a water is chiefly determined by the amount of its acidity. The hard waters, which contain salts of lime and magnesia, either have very little solvent action on lead, or they quickly coat the metal with the basic carbonate or sulphate of lead, which prevent further action. The soft, highly oxygenated waters containing organic matters, peaty acids, nitrites, nitrates, and chlorides, are those which have the most powerful action on lead, the oxide of lead which forms upon the surface of the metal being constantly dissolved and carried away in the water. Where lead-poisoning is feared, a block-tin pipe or a cast or wrought-iron pipe protected by a coating of Angus Smith's solution should be substituted for the lead pipe. Block-tin pipes enclosed in lead pipes are occasionally used ; it is impor- tant that there should be no crack or fracture of the tin lining, otherwise galvanic action will be set up when the pipe is full of water and large quantities of lead will be dissolved. Great care, moreover, is necessary in making the joints on this kind of piping, as the heat necessary for making a joint in the lead pipe is liable to melt the tin. To obviate this a layer of asbestos is sometimes introduced between the lead and tin this serving to keep the metals apart. Polluted shallow well waters have sometimes been known to have a verv rjowerfnl anrl . . , , ^.Digitized by Microsoft® , r y f UWCTlm ana persistent solvent action on lead, probably from their containing WATER 43 excess of carbonic acid, which tends to dissolve the coating of carbonate of lead formed in the pipe or cistern. It has been suggested that the varying powers of corroding lead, exhibited by soft waters of apparently identical chemical composition, are influenced by the presence or absence of silica in the water. When silica is present, even in the proportion of only half a grain per gallon, the action on lead is said to be very slight. There must be no excess of alkali in the water, or this inhibitive action of silica is not displayed. By passing distilled waters and other soft waters known to have a corrosive action on lead through a filter formed of layers of sand, broken flints, limestone and granite, enough silica is taken up to reduce the lead-corrosive power to one-thirtieth. Recent experi- ment, however, seems to show that the alkaline carbonate, which may be taken up from the limestone, may be an even more important factor than the silica. The waters of several large towns in Yorkshire, which have a considerable effect on new lead, have been rendered nearly inactive by neutralizing the acid present by a solution of sodium carbonate. The solvent properties of these waters are believed to be mainly due to the presence of peaty acids (humic, ulmic, etc.), and if the acidity is thus neutralized the plumbo-solvent action of the water is much reduced. After the prolonged drought of 1887, the waters in the Sheffield reservoirs ran very low, the peaty acids — derived from the gathering-grounds — were not diluted to the usual extent, and a severe outbreak of lead-poisoning occurred in the town. In other cases the acidity which gives the water its lead-dissolving powers may be due to the presence of free sulphuric acid formed by oxidation of iron pyrites, when the water drains off rocks rich in that substance. It has been suggested by Mr. Power, in a report to the Local Government Board, that the biological characteristics of a water — the pre- sence or absence of bacterial organisms — may exercise an influ- ence over its " plumbo-solvent " properties ; but this is probably true only in so far as the production of acidity in peaty matter is the result of micro-organic life. Having regard to the importance of acidity as affecting plumbo- solvency, on some gathering-grounds measures are taken to divert the most acid feeders of the general upland surface supply, and so avoid the inclusion of plumbo-solvent water in the general supply. There'%'Sso^ome s eviaence to show that leaden 44 HYGIENE AND PUBLIC HEALTH pipes are much more rapidly corroded when the mains are inter- mittently charged, than when kept under constant high pressure. Water companies supply water to their customers either on the constant or the intermittent system. Under the former, the aim is to keep the mains constantly charged with water under pressure, so that the house pipes being also always charged, no storage of water on the premises of the consumer is required. The only cisterns which should be required in a house supplied with a constant service of water are small cisterns or water-waste preventers for flushing water-closets, and a small cistern to supply water to the kitchen boiler. Under the intermittent system, the flow of water in the mains is stopped, except for a short period of every day, by the turncock. The house pipes are only charged when the water is flowing in the main, and consequently water must be stored for use on the premises when the pipes are empty. The great fault of the intermittent service is that water must be stored on the premises of the consumer. Water stored in small receptacles, even under the most favourable circumstances, deteriorates ; it loses its aerated character, becomes flat and insipid, and collects impurities from the air. In the houses of the poor, water is often stored in the most filthy receptacles — wooden butts and tubs rotten and decayed within, or in cisterns exposed to the air, which are the receptacles of all sorts of filth and rubbish. The situations in which cisterns are often found on such property are the immediate vicinity of the w.c, and beneath landing floors, staircases, or even bedroom floors. Even in the better-class houses cisterns are sometimes placed in the most improper places, as under stairs or floors, where dust and dirt fall into them, or inside water-closets, where the air is at times charged with foul gases. Another disadvantage of the intermittent service is that the capacity of the cistern is often utterly inadequate — especially in tenement houses, occupied by numerous poor families — for the wants of the people who depend upon it as their only source of supply. The same cistern is far too frequently used to flush water- closets as well as to supply the drinking water, which may become polluted in this way [see Chapter II). Another method, by which drinking water in cisterns be- comes liable to pollu^^^sT M^pfffctice— now, fortunately, WATER 45 but seldom seen — of connecting the " standing waste " or over- flow pipe of a cistern with a drain or soil pipe of the house, or with a D trap under a water-closet. It may be that the overflow pipe has a \j- bend on it before its junction with the drain, but as the water in such a trap quickly evaporates when not renewed — and the water in this trap can only be renewed if the ball-cock of the cistern leaks — little obstacle is presented to the passage of foul air from drain, soil pipe, or D trap, up the overflow pipe, where it escapes over the water of the cistern (see Chapter II). The overflow pipe from the cistern should discharge in the open air as a warning pipe — at some point where it is not exposed to polluted air. Besides the danger of pollution of water in cisterns by sewer air, dust, soot, and accidental contaminations such as dead mice, birds, or cockroaches, the material of which the cistern is composed is an important factor as regards the purity of the water stored in it. Iron cisterns rust and discolour the water ; zinc is occasionally dissolved in small quantities by water ; lead is dissolved at first when the cistern is new, but rapidly becomes coated with carbonate or sulphate of lead when the water is hard. The deposit forms a lining which protects the surface of the metal from further action, and it is for this reason that the inside of a leaden cistern should never be scraped when the cistern is being cleaned out. A lead cistern may be pro- tected against the action of soft water by coating it with lime from time to time. Galvanized iron is largely used for cisterns ; it is light, cheap, and durable, and generally perfectly safe, but has been known to give up a trace of zinc to the water. In galvanizing iron, the metal is first washed in a weak solution of vitriol and cleansed and dried ; it is then placed in a vessel containing molten zinc, which adheres to it and forms a coating. Wrought-iron cisterns covered with a vitreous enamel may also be safely used. Slate, though heavy, is a good material for cisterns, but the cemented joints of the five slabs must not be repaired with red lead when they leak, as they often do ; for both white lead (a mixture of carbonate and oxide) and red lead (an oxide) are soluble in water. Glazed or vitrified stone ware and fireclay cisterns, though heavy, are very valuable, as they give up nothing to water, and no joints are necessary. In selecting them, however, care should be taken that the enamelling or glazing i§Mf^oftgl! c 6¥°frIctured. Enamelled iron, 46 HYGIENE AND PUBLIC HEALTH glass lined iron, and tinned copper cisterns have been made. Water should never be left in contact with wood, as wood, when constantly wet, rapidly rots, and forms a breeding place for minute worms and other animal organisms and fungi. To indicate briefly the conditions under which water may be safely stored in houses :— (a) The cistern should be of stone- ware, slate, or galvanized iron ; (b) it should be placed in a light and well ventilated position and should be properly covered ; (c) it must not be used to flush water-closets, but may supply the " intercepting " or waste-preventing cisterns which should be used for this purpose ; (d) the overflow pipe must be carried out into the open air to terminate as a warning pipe ; (e) the cistern should be cleaned out at least once in every three months. Cisterns are occasionally used to supply water-closets which have regulator valves on the supply pipes near to the closet basin. Although there is but little danger by this arrange- ment of foul air finding its way into the drinking water of the cistern, as the supply pipe is always full of water unless the cistern is empty, still, it is better to break the connection alto- gether between drinking water cisterns and water-closets. The advantages of an intermittent over a constant service are that there is less waste inside houses, and that the service of pipes, taps and fittings, need not be so strong as for a constant service. This latter point has been disputed, as regards the pipes, on the ground that there is a greater strain on the pipes where the water is suddenly turned on or off with a common stop-cock, than where it is slowly turned on or off by the screw- down tap used with a constant service ; but it must be remem- bered that with a constant service the water in the house pipes is under a much higher pressure than where the pipes are con- nected with a cistern in the house. There is less danger, also, with an intermittent service, of the higher parts of the town being without water on account of great waste in the low-lying parts, as sometimes occurs with a constant service. A merit often claimed for the constant service is that no storage is required on the premises of the consumer. The water drawn from the taps on the house pipes is clear, cool, and sparkling, in the same condition as it leaves the street mains, and the supply is— or should be — abundant and never-failing. But experience has shown that it is %iM&my Microsoft® disease was then unknown. 60 HYGIENE AND PUBLIC HEALTH Diphtheria is not usually propagated through the medium of drinking water, but cases favouring such a view have been recorded. Urinary calculi were at one time supposed to arise from the use of hard water, but this view is now generally abandoned from want of any definite proof. Rickets has been ascribed to the use of soft water, but the contention is not warranted by facts. Goitre appears to be due, in many instances, to the water used for drinking, but the impurities in the water which favour hypertrophy of the thyroid gland in some districts are not those found in the water of other goitrous districts. For instance, the carbonates and sulphates of lime and magnesia, which are present in the waters of some districts, and have been credited with being the cause of goitre, are not found in the waters of other districts where goitre prevails. The presence of sulphides of iron or copper in water has been regarded by some observers as the cause of goitre, but not apparently with much reason. On the whole, then, we shall be justified in concluding that the quality of the drinking water, in districts where goitre and its allied disease, cretinism, exist, is only one — and perhaps not the most potent — factor out of many which, in combination, are productive of the disease. Further researches are required to elucidate this question, which is one of great interest. Entozoa. — The embryos or eggs of the following parasites have been found in water, and may be taken into the stomach of man when such water is used for drinking. They are : Ttenia solium, Tcenia echinococcus, Bothriocephalus latus, Ascaris lumbricoides (round worms), Oxyuris vermicularis (thread worms), Filaria sanguinis hominis (tropical endemic chyluria) — the embryos of which are sucked from the blood of infected persons by mosquitoes, and, after developing in the body of that insect, are then transferred to water by means of the \a.rv3e—Bilharzia harnatobia, Tricocephalus dispar, and Distoma hepaticum (liver fluke of sheep). Bilharzia hamatobia causes endemic hematuria in Egypt, Abyssinia, the Cape, etc. The ova are passed with the urine, find their way into water, and hatch into ciliated embryos. Anchylostoma duodenale causes anaemia, internal haemorrhages, etc., and occasions great mortality in Brazil, West Indies, and Egypt, where it is thought to be sometimes due to infected wate^Tte ^brv^ guinea worm, Filaria WATER 61 dracunculus, is aquatic and finds its way into the human body through the alimentary canal by means of drinking water, the adult worm being subsequently found in most cases in the sub- cutaneous tissue of the feet and legs of affected persons. Aquatic leeches may be swallowed in the act of drinking, and fixing them- selves in the pharynx may cause much haemorrhage. Anthrax, hog-cholera, and glanders may all be communicated to cattle through the agency of impure water ; and drinking water appears to be the principal medium by which the entozoa generally pass from one animal to another. Metallic poisoning may be caused by pollution of drinking water with refuse from trades and drainage from metalliferous mines, or from absorption by water of the metals used in the construction of distributing pipes, tanks, and cisterns. The amounts of copper, zinc, or arsenic, which must be present in the water to give rise to symptoms of poisoning have not been definitely ascertained ; as regards lead, as little as y^ grain per gallon may produce plumbism in predisposed persons. In the case of the poisoning of Louis Philippe's family at Claremont, Yo grain of lead was found in each gallon of water. The Collection of Samples of Water. The water should be sent to the analyst in a stoppered Winchester bottle of white or pale green glass. These bottles should be used only for water samples, and should be cleansed with strong acid, and subsequently well washed with clean water, before use. The bottle should be rinsed out twice with some of the water to be examined, and should not be entirely filled with the sample, a small amount of air being left in it. The bottle should then be stoppered and capped with clean wash- leather or linen, and dated and labelled to secure subsequent identification. Where the sample must be taken by immersing the bottle, as in ponds, reservoirs, rivers, and open wells, the bottle invented by Dr. Thresh, which contains a contrivance whereby water can be made to enter the bottle at any required depth from the surface, finds a useful application. The Opinion upon a Water Sample. Where the water is considerably polluted, no difficulty is experienced in detect^t^ ^ohuj^gn by chemical analysis, 62 HYGIENE AND PUBLIC HEALTH but, generally speaking, the slighter degrees of pollution are detected only with difficulty. The most a chemical analysis of a water can tell us is whether the figures of the analysis indicate little or much organic impurity as judged from certain arbitrary standards. Whether the slight contamination which is practically always discovered is harmful, or whether the particular water has recently received slight (but significant and maybe dangerous) pollution, can only be told with certainty by several analyses of the water at short intervals of time, and a careful comparison of the results obtained ; or by a comparison between the sample of water and others in the immediate neighbourhood, collected from similar sources from the same geological area, and which are known to be above suspicion. A chemical analysis, in short, cannot always guarantee absolute purity and safety, but it very frequently serves to reveal impurity- and danger. Nitrates and Nitrites. — These are the oxidized residues of organic matters, almost always derived from an animal source (sewage). Their determination is, therefore, a point of the greatest importance, for they indicate either a pollution of the water at some remote period with possibly dangerous ingredients, or the contamination of the water at the present time with partially or completely purified sewage. They are found, often in considerable quantities, in deep wells or spring waters, and in this case merely indicate the complete purification which the water has undergone in its passage from the surface to the subterranean reservoirs. In the case of shallow-well waters, nitrates and nitrites, if found in association with excess of chlorine and ammonia, indicate soakage of sewage or animal refuse into the well, more or less purified by its passage through the intervening layers of earth. At any time, however, the purifying power of the filtering earth may be exceeded or overcome, and then the liquid filth may pass into the well with its dangerous ingredients unchanged or unpurified. Nitrates and nitrites are not present in raw sewage, but they are found in polluted streams and watercourses, where a certain amount of oxidation is always in progress, and in the effluent subsoil waters from manured or sewaged land. Ammonia— The. urea of the urine, by a process of fermentative of ammonia in all sewage-polluted yr m jjja. waters, unless the sewage has been filtered through a sufficient thickness of soil to enable the bacteria to convert the ammonia by oxidation into nitrates and nitrites. A few pure deep-well waters from the greensand are found to contain excess of ammonia owing to the presence of a reducing salt of iron, which converts oxidized nitrogen into ammonia ; but these waters are remarkably free from organic matters. On the other hand, sewage polluted shallow-well waters, which contain excess of ammonia, often contain also an excessive amount of organic matters. Organic matters derived from an animal source are dangerous as well as disgusting ; the slightest trace of such matters in a water should suffice to condemn it. Organic matters derived from the vegetable world, though often quite harmless, as when they exist in the form of peat, should not be disregarded ; and their presence in considerable quantity should insure the rejection of the water for drinking purposes. The distinction between animal and vegetable organic matters in a water is often only made with difficulty, if at all. Generally it may be said that, when excess of organic matter in a water co-exists with excessive chlorine, oxidized nitrogen, and ammonia, the source of pollution is animal filth or sewage. When, on the other hand, excessive organic matter is not accompanied by excessive chlorine, oxidized nitrogen, and ammonia, the source of pollution is probably vegetable ; and this diagnosis may be con- firmed by the results of physical examination of the water, and by microscopic examination of the suspended matters and sediment. Inasmuch as the chemical methods of analysis can only determine the presence and amount of organic matters in water, and cannot determine their quality, nor separate living and possibly actively dangerous organisms from dead and inactive matter, it has been thought by many that a bacterioscopic examination would afford conclusive evidence of the possibly dangerous qualities of a water, and might come in time to super- sede chemical analysis altogether. But the characteristic micro-organisms of cholera and typhoid fever are only with great difficulty isolated and separated from the crowds of harmless species which are found in greater or less abundance in all natural waters. The finding of a greater or less number of non-pathogenic bacteria or fungi in a water gives evidence of the presence of a larger or smaller amount of organic pollution, wl^rffms^s^ij^le pabulum for bacteria ; 64 HYGIENE AND PUBLIC HEALTH for pure waters are found to contain very few bacteria or fungi, whilst impure waters often swarm with them. They increase in numbers if water is stored for any length of time. The detection of bacteria of intestinal type, which have their usual habitat in the intestines of man and animals, throws considerable light on the nature of the pollution, and if they are present in such amount as to point to recent contamination, should serve to secure the condemnation of the water. The more important of these intestinal organisms, .for which the tests have been most fully elaborated, are Bacillus coli communis and its congeners, Bacillus enieritidis sporogenes, and streptococci. A water which gives no indications of the presence of typical B. coli communis in 10 c.c. of the water examined, nor of strepto- cocci in 50 c.c.(?), nor of the spores of B. enieritidis sporogenes in 500 c.c. is, at the time of the examination, so free from sewage pollution that it may be certified as safe for all domestic purposes, providing its source is satisfactory (Thresh). By the typical B. coli communis is meant the organism found in animal excrement and in fresh sewage. It would appear that in water to which this organism has obtained access, the typical B. coli undergo after a time changes of a degenerative character, so that they no longer fulfil all the tests which are characteristic of the typical organism. There are also other organisms of intestinal type, such as B. acidi lactici and B. enteritidis (Gaertner), which give most of the reactions of B. coli, but not all. It is doubtful, at present, as to what is the precise significance of the presence of such organisms in water. Their presence certainly should lead to suspicion and to further inves- tigation, as they may indicate a recent previous sewage con- tamination, a contamination which may also be a recurring one. The mere presence of typical B. coli communis and of B. enteritidis sporogenes in a water would not justify, on this ground alone, the condemnation of the water ; for they do not necessarily indicate human contamination. It is only when the B. coli is appreciably present in 1 c.c. of the water that, in the opinion of many, the water should be regarded as definitely unsafe. The presence of streptococci is of considerable corroborative value, but B. enteritidis sporogenes affords little, if any, additional indication of recent or dangerous pollution. In the search for B. enteritidis sporogen S ^ e ^y Mlsm ^axgex quantity of water should be taken for examination, viz., 500 c.c. instead of 10 c.c, WATEK 65 for the reason that whereas B. toli communis is seldom present in crude sewage in fewer numbers than 100,000 per c.c., B. enterilidis sporbgenes may only exist to the extent of from 100 to 2,000 per c.c. The Bacillus Typhosus is exceedingly difficult to detect in sewage-polluted waters. It is very doubtful if this organism has ever been isolated from a natural water, even although such a water has been credited with the causation of enteric fever. In addition to a chemical and biological examination of a water sample, it is of great advantage to possess the fullest information as to the risks of pollution to which the water has been subjected, and this can only be obtained from a painstaking local investigation. Analytical Results of Certain Waters (Parts per 100,000). New River Company (Filtered). Polluted Well Water. Peaty Surface Water. Spring Water from Chalk. Rain Water. A Sus- picious Water. Total solids (a) Volatile . . (b) Non-volatile . 31-2 9-8 21-4 60 -O 25-0 3S-o IO-O 7-0 3-o 33-° IO-O 23-0 3-0 I'5 1-5 40'0 I5'0 25-0 Total hardness (a) Temporary. (b) Permanent 21-5 13-0 8-5 30-0 15-0 150 5-0 IO 4-0 26-0 20-0 6-o 0-5 o-o 0-5 25-0 14-5 10-5 Chlorine .... i-8 7-0 07 2-5 0-25 4-0 Oxidized nitrogen 0-18 o-8o O-OI 0-30 001 0-50 Free and saline NH 3 . Organic NH 3 . O-OOI 0-003 0-030 0-015 O-OOI 0-018 O-OOI 0-003 0-025 o-ooo 0-006 0-0I2 Oxygen absorbed in two hours at 80° F. 0-030 0-160 O-200 0-030 0-015 0-120 Digitized by Microsoft® CHAPTER II THE COLLECTION, REMOVAL, AND DISPOSAL OF EXCRETAL AND OTHER REFUSE In any community of persons, arrangements must be made for the collection and removal of their excretal refuse (faeces and urine), of the waste waters from houses, and of the dry refuse (ashes, dust, and refuse food). The solid and liquid refuse matters from stables, cowsheds and slaughter houses, street sweepings, and the waste waters from works and manufactories, must also be removed. In all towns the collection and removal of dung, ashes, dust, refuse food, and street sweepings, is performed by mechanical labour, the various processes above mentioned being included in the term scavenging ; whilst in some, human faeces and a certain amount of urine are also removed by this method, after being deposited in privies, cesspools or dry closets, on what is known as the conservancy system. In a large majority of the towns of this country, at the present time, human excrement is removed with the liquid refuse of dwellings on what is known as the water-carriage system — a system of drains and sewers for the passage of the refuse in a liquid condition to some spot outside the town. The public health largely depends on the efficiency with which refuse matters, and especially human excretal refuse, are re- moved from towns ; for the health of towns in this country and abroad has very much improved, and the death rates have been permanently lowered, as the result of works of sewerage. Removal of Domestic Dry Refuse. Domestic dry refuse consists partly of mineral matters, but to a considerable extent of organic substances derived from the waste scraps of food. These latter, being prone to undergo decomposition when *ty$jp$jll&®jfoOT other receptacles, are DISPOSAL OF REFUSE 67 very liable to become a source of nuisance. It is, therefore, very desirable that the quantity of organic refuse to be temporarily stored on the house premises should be reduced as far as possible ; and this may be accomplished by burning the more easily des- tructible matters, such as potato peelings and other food scraps, in the kitchen fire at the end of every day. The old-fashioned brick dust-bin is now being largely replaced by galvanized iron receptacles, with well-fitting metallic covers, to insure dryness of the contents and their protection from rain. This is an important point, as the presence of moisture hastens putrefaction and the formation of offensive gases in the refuse. The non-absorbent walls of iron pails, and the ease with which they can be moved and carried out to the dust-carts, constitute very great advantages over the brick dust-bins, of which the walls become saturated with decaying matters and the contents are often incompletely removed at each visit of the scavengers. The contents of the dust-bins or pails should b.e removed at least twice a week ; in summer a more frequent removal is desirable, but is not usually practicable. Specially constructed carts provided with covers should be employed to convey household refuse through the streets. There is an obvious advantage in keeping the refuse as dry as possible, and if such vans are not provided with sliding metal covers or covers of tarpaulin, the escape of dust in windy weather creates a great nuisance. Motor dust vehicles are to be recommended as effecting a great saving of time. Horse manure must also be frequently removed from stables, and the removal in urban districts is often attended with considerable nuisance, especially where peat moss litter is used as a bedding for the horses. The nuisance mainly arises at the time of loading the cart, in which the manure is removed, from the receptacle, the disturbance of the contents of the receptacle giving rise to very offensive gases ; and the recently disturbed manure is often highly offensive as it is carted along public thoroughfares. It is found in practice that the best remedy for the nuisance is to store the manure in the same cart in which it is to be removed. The disposal of house refuse has hitherto been mainly effected by depositing -it on waste ground, the site being commonly called a "shoot." These refuse heaps frequently constitute a serious nuisance in W /z nei^hbour8ood. Offensive gases are 68 HYGIENE AND PUBLIC HEALTH given off from the fermentation of the organic matters, and the liquids draining from the heap are of the most noxious character and occasionally cause serious pollution of neighbouring water- courses. In windy weather dust and the lighter particles are scattered around, whilst in summer the rotting refuse attracts large numbers of flies, which invade surrounding houses and settle on food exposed to the air. Rats, too, burrow in the heap in search of food, and are generally much complained of. The practice of shooting or tipping refuse cannot be defended, and it is slowly giving way to a more sanitary method, i.e., the destruction of refuse by fire. As the area of a town increases, these muck-heaps often become the sites for buildings long before natural agencies have succeeded in purifying the " made- soil " ; and, moreover, the difficulty of acquiring sites sufficiently near the area to be scavenged is growing greater year by year in our larger towns, and makes the adoption of some other method of house .refuse disposal imperative. The refuse, when deposited at the " shoot," is sometimes submitted to the process of hand-sorting. The paper and rags are removed for paper-making, the tins and iron for scrap, the bones for manure, the unbroken bottles for re-use, and the broken glass for re-melting. This sorting process is a degrading occupation ; the workers are of necessity in a filthy condition, and the air they breathe is constantly polluted with fine dust and foul odours. The best method of getting rid of dust-bin refuse is to burn it in a destructor furnace ; and offensive market refuse, fish offal, and even diseased carcases can also be disposed of by this method without creating a nuisance. The proportion of cinders in the refuse is always sufficient to insure complete combustion in a well constructed furnace. A small commercial value attaches to the residual clinker, either for making mortar, or mixed with granite chippings and cement to make paving slabs or concrete bricks. The temperature attained in the furnace, while destroying the refuse, can be utilized to generate steam for electric power, to pump water or sewage, or to drive mortar mills. The calorific value of the screened house refuse varies from -fa to I- that of coal. In summer the heat value of the refuse is less, owing to the smaller proportion of cinders and ashes and the greater quantity of garden refuse and vegetable matter. There are various ty'ptWrfc^structors, most of which DISPOSAL OF REFUSE 69 possess the following features in common : — The furnaces or cells are strongly built of brick with fire-brick lining, and the general building is also of brick. The destructor is approached by an inclined roadway to the top or tipping platform, which is well above the ground level. In the centre of this platform is a series of feeding holes or hoppers into which the refuse is shot, and allowed to fall into the cells below. The stokers rake the refuse forward on to the fire ; and after burning, the refuse is reduced to about one-third or one-fourth of its original weight, the residue consisting of fine ash, hard clinker, etc. By means of forced draught produced by a steam jet or fans, the com- bustion can be made so complete that temperatures of 1,500 to 2,000° F. are attainable merely from the burning of the refuse. Some destructors are known as " slow combustion " or " low tempsrature " destructors, and in these " fume cremators " should be provided at the foot of the chimney. In the fume cremator (which is a coke furnace) incompletely burned vapours and fine dust particles, which are liable to escape into the air from the destructor furnace, are completely burned up before they can enter the chimney-flue. In the " high temperature " destructors such cremators are unnecessary, and the expense of burning the coke or coke-breeze in the fume cremator is saved. The advantages of the " low temperature " destructors consist in the diminished wear and tear on the fire-brick sides of the cells, and the consequent saving in up-keep. On the other hand, the disadvantages are that both the inlet for refuse and the outlet for gases are, as a rule, at the rear of the cell, and therefore the empyreumatic and noxious vapours and fumes given off during the drying of the refuse, and before it is in active combustion, escape before being burnt, and a cremator is neces- sary. Further, more cells are required, because a smaller quantity of refuse per cell (from 6 to 8 tons) is burnt per day than with " high temperature " destructors. In the " high temperature " destructors (such as the Horsfall or the Beaman and Deas) the outlet for gases is at the front of the cell, and the vapours given off during the process of burning and drying pass over the hottest part of the fire to reach the exit. As the cell is raised to a very high temperature by forced draught (steam blast or fans), such gases are destroyed within the cell itself ; a larger quantit^'o^eM^fMnt per day per cell (i.e., JO HYGIENE AND PUBLIC HEALTH from io to 16 tons), and fewer cells are therefore required. On the other hand, they cost more for maintenance. The site on which the destructor is placed should be a central one for the district to be served, or the cost for cartage may considerably exceed that for burning ; and in some cases it would appear advisable to construct two destructors in different parts of a large town. The number of cells required will of course depend on the nature and amount of the refuse to be destroyed, and also upon the type of cell adopted. If a " high temperature " destructor is selected, about ten cells are necessary for a population of 100,000. These cells can be erected in a single row or " back to back." The cost of erection may be taken as about £500 per cell, including enclosing building ; and the burning will cost from gd. to 2s. 6d. per ton, according to the greater or less completeness of com- bustion required, and the number of tons to be burnt per cell per day. Human Excreta. An adult male, living on a mixed diet of animal and vegetable food, passes daily 4 ounces, by weight, of solid, and 50 fluid ounces of liquid excreta. The solid excreta of children under twelve years of age are in amount considerably less, probably on an average not much more than one-half the above quantities. If all ages and both sexes are considered, the daily amount of excreta per head of a mixed population may be taken at 2|- ounces of faeces, and 40 fluid ounces of urine. Fresh faeces contain on the average 23-4 per cent, of dry solids, and fresh urine contains 4-2 per cent, (of which 54 per cent, is urea). To find the amount of dry solid manure produced daily by a population of 10,000, where the pail system is in force, and all the faeces, but only one third of the urine, are collected in the pails. (10,000x2-5 x^~) = 5,850 ozs. of dry solids in fasces. (10,000 x — x 40 x -^L) = 5,600 oz. of dry solids in urine. 3 100 5,850 +5,600= 1 i,4So«*. = U*& ( = 7i5 . 6) lb. = gg ( = 0.32) ton. If this manure, instead of being dry, contains 25 per cent, of moisture, it will weigh A f 0-32 = 0-43 ton. 3 If it contains 50 per cerrWf e nT&sW¥§ , ^ fi w'ill weigh 2 x 0-32 = 0-64 ton ms.rusAL OF REFUSE yx • The quantity of nitrogen voided per head daily in the excreta of a mixed population as calculated from the above data is 189 grains. The other valuable constituents of the excreta are phosphates and potash. A given weight of faces is more valuable than the same weight of urine, in the proportion of about ten to six ; but the weight of urine passed daily (in a mixed population) is about sixteen times as great as that of the faeces, consequently the total urine is worth about ten times as much as the total faeces. The estimated or theoretical money value, then, of the excretal refuse of an individual of a mixed population for one year may be taken as being 6s. 8d. to js. It is very evident that it must be impossible to realize practically any such value, because it is impossible to colleGt the whole of the urine and faeces free from admixture with other substances, which greatly detract from the value because they are agriculturally worthless. fs Faeces and urine, especially when mixed, as in cesspools, privies, and sewers, rapidly undergo putrefactive changes, giving rise to the formation of foetid gases (organic vapours, sulphuretted hydrogen, ammonium sulphide, etc.). The urea — CO(NH 2 ) 2 — of the urine decomposes, giving rise to carbonate of ammonia — CO(NH 2 ) 2 + 2H 2 0= (NH 4 ) 2 C0 3 — and so rapid is the change that it is probable that, even in the best sewered town, all the urea of the urine in the sewage has been converted into ammonia before the arrival of the sewage at the outfall. House Waste Waters. In these are included the waste waters from kitchens, which are highly charged with decomposable organic matters and grease, and slop waters containing urine, soap, and the dirt from the surface of the body and from clothes. These waste waters, when mixed with the liquid refuse or drainage of stables, cow- sheds, and slaughter houses, with the washings from the street surfaces, with the urine from public urinals, and the waste liquors from manufactories, form the sewage of the non-water- closeted or midden towns. The drainage from stables is very rich in urine (one horse excretes about fifteen times as much urine as an adult man), and the waste liquors from manufactories are often excessively foul. It is not surprising, D t^^ c nd o/ ^at such sewage is often 72 HYGIENE AND PUBLIC HEALTH quite as foul as that of some water-closet towns, which con- tains the solid human excreta as well. The Rivers Pollution Commissioners stated in their First Report that, " for agri- cultural purposes, 10 tons of average water-closet sewage may, in round numbers, be taken to be equal to 12 tons of average privy sewage " — i.e., sewage of privy towns, where human faecal matters are kept out of the sewers. Such being the case, it is necessary to bear in mind that, in towns where there are middens or some form of dry closet for the collection of faecal matters, there is also a liquid sewage to be conveyed away from houses by drains and from the town by sewers, which is too impure to be admitted into a stream and which must therefore be purified before being discharged. Conservancy Systems. The Privy or Midden System. — The system which formerly prevailed in many towns in this country — where there was any system at all — was that of privies, midden pits, and cesspools, often open to the air and unprotected from rain, and situated in the yards and areas about houses. These receptacles were generally mere holes dug in the ground, and their contents over- flowed, saturating the air with noxious effluvia, or percolated into the soil around and under the houses and poisoned the water in the neighbouring wells. At the present time, in those towns which still retain con- servancy systems, the middens are required to be constructed according to certain definite rules. The model bye-laws of the Local Government Board with regard to the construction of privies and middens for new buildings require that the privy must be at least 6 feet away from any dwelling, and 40 or 50 feet away from any well, spring, or stream ; means of access must be provided for the scavenger, so that the filth need not be carried through a dwelling ; the privy must be roofed to keep out rain, and provided with ventilating openings as near the top as practicable ; that part of the floor of the privy which is not under the seat must be not less than 6 inches above the level of the adjoining ground, must be flagged or paved with hard tiles, and must have an inclination towards the door of the privy of \ inch to the foot ; the capacity of the receptacle under the seat of the Df8^ toMr°fi o remove all house refuse in Fig. 12. Privy constructed for Pail System. j6 HYGIENE AND PUBLIC HEALTH one receptacle ; but if it is intended to create a saleable manure from the excretal refuse, all garbage and kitchen refuse, and even all but the very finest ash (for this detracts from the value of the manure), should be kept out of the pails and removed separately. In such cases the pail contents can no longer be kept dry, and sanitary considerations are, to a certain extent, sacrificed to insure commercial ends. All slops should be kept out of the pails, and should be carried away from the houses in drains with the other waste waters. In some cases separation of the urine from the faeces has been attempted. Besides introducing a complication into a system whose chief merit, perhaps, is simplicity, this plan is open to the great objection of abstracting the most valuable fertilizing con- stituents of the manure in -posse. In the Goux system an attempt is made to dry the excreta by lining a wooden tub with a layer of refuse sawdust, shoddy, tan, or other absorbent material, to which is added a little soot, charcoal, gypsum, or other cheap deodorizer. This system was in use at Halifax, and on the whole has worked well. Wood charcoal and charcoal obtained from seaweed (Stan- ford's patent) have been used instead of ashes to aid in drying the pail contents. They act as absorbents, and to a certain extent as deodorizers. Manufacture of Manure. — In towns situated in agricultural districts, where there is a demand for the coarser sorts of manure, the pail contents need merely be mixed with a certain portion of fine ash. But in some of the large towns, where the pail systems are in vogue, it is now the practice to convert the pail contents into a dry manure of a more imperishable character, which can be packed and sold at a distance. The heat required for this purpose is generated by the combustion of house cinders and refuse in a destructor furnace, the invention of Mr. Fryer. The pail contents — urine and faeces without ashes — are mixed with a small portion of sulphuric acid, to fix the ammonia, in an air-tight store tank, where the thicker portion of the material settles at the bottom. The more fluid portion of the contents of the tank is drawn off into evaporators, which are tall cast- iron cylinders, each containing near its lower end a drum-shaped heater, precisely resembling a multitubular steam boiler. These cylinders are partially nlfecff anat!ie s neating drums are covered DISPOSAL OF REFUSE 77 with the thin liquid ; steam is then introduced within the heating drums, and the liquid becomes partially concentrated. When the contents of these cylinders have lost by evaporation the greater portion of their water, they are drawn off into a Firman's Dryer, into which the thick portion of the pail contents, which settled in the store tank, has also been admitted. This machine consists of a steam-jacketed horizontal cylinder, traversed by a steam-heated axis with steam-heated revolving arms, and furnished with scrapers to keep the inner surface of the cylinder free from accumulations of dried excreta. The pail contents are admitted into the dryer at a consistency of thin mud ; after treatment they emerge as a dry powder — • poudrette — resembling guano in appearance and quality. The odorous gases given off during the process are all passed through the destructor fire and burnt. From the time the liquid material enters the store tank until the end of the process when it emerges as a dry powder, no odorous gases should be permitted to escape into the outer air, and no nuisance ought to result. The Dry Earth System. — This system is the invention of the late Rev. Henry Moule, and consists in the application to the excreta, deposited in a pail or tub, of a certain quantity of dried and sifted earth. One and a half pounds of dry earth applied in detail, i.e., each particular stool being covered at once with this quantity, is found to be sufficient to remove odour and to form a compost which remains inoffensive as long as it is dry. A certain action takes place in the mixture of earth and excrement, which results in the complete disintegration of the faecal matters and paper, which after a time are found to have completely disappeared and are no longer recognizable. The compost after further drying may be used over again, and has the same action as the original dry earth. The best kinds of earth are loamy surface soils, and vegetable mould. Sand, gravel, and chalk are unsuitable and inefficient. The closet generally used with this system is almost identical with the cinder-sifting ash-closet previously mentioned. There is a hopper or metallic receptacle above and behind the seat, and the proper amount of dry earth is shot into the pail by a simple mechanical contrivance connected with a handle, or self-acting seat arrangement. The contents of the pail must be kept as dry as pcgsible,, ^fermentation results, with the disengagement of foul gases ; consequently slops must on no 78 HYGIENE AND PUBLIC HEALTH account be thrown into them, and even chamber urine must be kept out of them, unless a considerable extra quantity of dry earth is used. The earth must be dried before use, and then sifted by means of a sieve, the finer portions only being used. There can be but little doubt that the compost or manure produced by the passage of the earth even five or six times through the closet has but little agricultural value. The late Dr. Voelcker estimated its value as only js. 6d. per ton. It is probable that there is some escape or evolution of nitrogen in a free state from the manure when kept ; and this may partly account for its deficiency in fertilizing properties. But when we reflect on the large amount of valueless earth with which the compost is diluted, and the absence from it of a large pro- portion of the daily urine of each individual, the reasons for its low value are not far to seek. The Disposal of Slop Waters. We have already seen that the conservancy systems do not provide for the removal of the liquid refuse, domestic or muni- cipal ; and we have seen, too, that in the so-called midden towns this liquid refuse or sewage may be quite as impure as the ordinary sewage of some water-closet towns. In these towns, too, there is always a certain percentage of houses provided with water-closets, so that the crude matter passing into the sewers is inadmissible into a river or stream, and requires to be purified. A system of drains and sewers is necessary for its removal from the town ; and the principles on which such drains and sewers must be constructed do not differ from those which would be necessary if they were intended to carry water-closet sewage as well. In small villages and isolated houses provided with middens or some form of dry closet, the slop waters are usually carried by a drain from a sink or yard gully into " sumpt " holes in the ^garden, into an open ditch, into a cesspool, or into a stream ; if into a " sumpt " hole or open ditch, there to stagnate and generate offensive gases ; if into a cesspool, often to percolate through its porous walls and pollute the neighbouring wells ; and if into a stream, to foul it nearly as much as if they contained the solid excreta also. The slop waters may be retained in cesspools which are reM&^tfrWp^Hftl^able by brickwork set in DISPOSAL OF REFUSE 79 cement and well puddled with clay outside ; and they can then be utilized on garden ground by means of a pump and hose and jet. They may also be passed through a small coke or ash filter, which should be prepared on a specially selected area well away from the house ; or they may be disposed of by irrigation upon grass fields. Wherever the nature of the soil and the slope of the land will permit of it, recourse may be had to sub-irrigation to purify the dirty water and utilize it to the best advantage. A very small piece of ground is required for this purpose. The late Mr. Rogers Field considered 4 perches of land sufficient for an ordinary cottage. The drain conveying the slop waters from the house should be connected by a few lengths of impermeable piping with a system of 2-inch agricultural porous earthenware pipes, with- out joints, laid laterally about 5 or 6 feet apart, at a depth of about 8 to 12 inches in the soil, the whole having a slight fall or inclination, away from the house, of 6 or 8 inches in 100 feet. The ends of the pipes should rest upon cradles formed of larger half-pipes, and similar covers should be placed above, so as to prevent earth getting into the pipes, whilst allowing the water to escape. The lower end of the main outlet pipe should turn up into the air to allow air to escape. This is especially necessary when the slop waters are discharged into the sub-irrigation drains by a flush-tank. If the soil is very porous, no under-drainage is needed ; other- wise, porous drain pipes must be laid at a depth of about 3 feet from the surface, with an outlet into a stream or ditch. The slop waters escape through the open joints of the sub-irrigation pipes into the soil, where some of their fertilizing ingredients are absorbed by the roots of the grasses and vegetables grown on the plot, and the rest is purified by percolation through the soil ; so that the effluent water passes away in a purified condition into a stream or ditch, or helps to swell the volume of the subsoil water. The chief difficulty in connection with this method is that the flow of slop waters from a single house is so small that the liquid penetrates but a short way along the sub-irrigation pipes, which become in time choked with deposit ; and that portion of the sub-irrigation plot nearest the house receives an unduly large share of the irrigating Muid, ajid^ it| cleansing properties are speedily overtaxed. This difficulty? where the gradients admit 8o HYGIENE AND PUBLIC HEALTH of the necessary loss of head, has been overcome by pro- viding a flush tank which will discharge at intervals into the head of the system. The tank now in most general use for this purpose is fitted with the annular siphon arrangement invented by Mr. Rogers Field. In the annular siphon tank (fig. 13) the ascending arm of an ordinary siphon is represented by a short wide cylindrical pipe, closed at the top, which is placed over and encloses the descend- ing arm, a longer pipe of smaller diameter. The upper end of the descending arm is open, and in Field's tank is provided with a lip projecting inwards and downwards, which serves to direct the water, as it overflows, into the centre of the pipe. The lower end of the descending arm opens over a discharging trough below the body of the tank, and is trapped by the water which stands in this trough to the level of the top of a weir, over which the water flows into a pipe connected with the head of the sub-irrigation system. Only a very small dribble of water into the tank is necessary to put the siphon into action. This takes place as follows : As the tank fills, the water ascends between the inner and outer pipes Field's Annular Siphon Flush Tank const i tutin g t he siphon, until it for Flushing House Drains. ° r ' reaches the level of the top of the inner pipe, the air displaced finding an exit through this pipe into the discharging trough below. The water then trickles over the top of the inner pipe, and, thrown into its centre by the lip, falls clear of the sides, entangling and carrying air with it which cannot pass back, owing to the lower end of the pipe being trapped. This continues until the siphon is sufficiently exhausted of air to be brought into action, when the whole contents are discharged by siphonage. It is not necessary to strain the slop waters before they enter the tank, as they contain but few of the coarser suspended matters and solid particles found in water-closet sewage. The sub-irrigation drains require to be taken out of the ground, and the deposit removed l$S##e^f%<^ c '8f@fi?elaid, every few years, according to circumstances. \J ■\ ^=s=-^=~:: : :F=B=§ Zz^Er^r^EE^Z^CS-Z^ J8S8S: _-- -593Sf^ "^ Fig. 13. DISPOSAL OF REFUSE 8l Comparison of Methods. There can be no doubt that all conservancy systems proceed on a wrong principle, viz., that of keeping excremental matters within or near dwellings longer than is desirable from the point of view of health. In towns the expense of scavenging is directly proportional to the frequency of removal, so that there is always an inducement to the local authority to economize at the risk of the health of the inhabitants. The costs of this kind of scav- enging are high, and nowhere does the sale of the refuse cover the expense. Movable receptacles are far better than fixed ones for the collection of excremental matters. The pail system is undoubt- edly the best for towns which will not enforce the adoption of water-closets. In the case of Nottingham, where middens, pails, and water-closets are in use in different parts of the town, Dr. Boobbyer has shown that the greatest prevalence of enteric fever is to be found in the houses with middens, and the least in the water-closeted houses, those with pails occupying an intermediate position. In 1902 there were twice as many cases of enteric fever proportionally in " pail " houses as in " w.c." houses, and 14 times as many cases in " midden " houses as in " w.c." houses. However suitable the earth-closet system may be for country houses and villages in this country, and for villages and stations in India, and in cold countries, where the water supply is small and liable to interruptions, and where earth of suitable quality is easily procured and dried and the compost can be distributed over gardens and fields in the immediate vicinity, it is quite inapplicable to towns of any size, on account of the enormous quantities of earth that would have to be dried and brought into the town, the difficulties of storing the earth on the premises of houses and keeping it dry, and the still larger quantity of nearly worthless manure to be removed out of the town and finally disposed of. The Water-Carriage System. In this system the solid excreta together with all liquid refuse are conveyed away — borne along by flowing water — in drains and sewers from the fttjjfe^uijfcpo^ houses and towns. In G &2 HYGIENE AND PUBLIC HEALTH many towns, before any general introduction of water-closets, sewers existed for conveying away house waste waters, stable drainage, surface and storm waters, and in some cases waste liquors from manufactories. These sewers, which were made of brick, oval or circular in section, acted also as land drains ; for not being constructed of impermeable materials, they admitted subsoil water and had considerable effect in drying the soil. It became at one time also the practice to drain off the liquid contents of privies and middens, or to carry overflow pipes from cesspools into these sewers, which in consequence speedily became choked with sediment. This sediment rapidly putrefied, and the offensive gases given off created an abominable nuisance. It then became necessary for the sewers to be regularly cleansed, and the deposit had to be removed at great expense by hand labour. The drainage of privies and middens entered the sewers in a most foul and offensive condition, owing to the putrid state of the contents of these receptacles. Another result was that the streams and rivers into which this sewage was permitted to pass became highly polluted. In 'many towns these brick sewers still exist, and perform the double function of removing sewage and rain-water, and draining the subsoil ; whilst in others they are only permitted to perform their original function of carrying off rain and surface water and of draining the subsoil, impermeable sewers being laid to remove the sewage of the town on what is known as the separate system. House Drainage Arrangements. Water-closets. — A water-closet may be defined as an apparatus for the reception of excrement, which is connected with a sewer by a pipe, and in which water must be used to carry away the excrement deposited in it. It is therefore seen at once to differ in all essentials from a privy, which ought not to be connected in any way with a sewer, and in which water cannot properly be used. Water-closets may be classified under two heads : (a) those in which there is no movable apparatus for retaining water in the basin ; (b) those in which there is such a movable appara- tus. Under the first head are included the various types of hopper closets ; under the second head, pan, valve, and plug closets. The hopper closet (®§®^bpki&SkomveTte& stoneware cone, connected below with an \y\ or [f -shaped pipe, which retains DISPOSAL OF REFUSE 83 sufficient water to prevent the free passage of air, and is known as a trap. The old form of hopper closet, called the long hopper, from the length (about 18 inches) of the cone (fig. 14), is liable to fouling of the basin, and is difficult to flush, especially where the water is admitted by a side inlet, which has the effect of causing the water to whirl round and round, whereby the trap is not flushed out and excreta are left behind. A short hopper or Fig. 14. — Long Hopper Water- closet with Side-inlet for Flushing. Fig. 15. Wash-down Water-closet. wash-down (fig. 15) is constructed with a shorter (8 to 9 inches) cone of china or stoneware ; the back of the cone should be made nearly vertical, so that the excrement drops into the water of the Fig. 16. — Wash-out Water-closet. trap, and not upon the sides of the basin. The short hopper, especially when constructed with a " flushing rim," by which the sides of the basin are well washed, is found, under proper management, to be easily kept clean. It is a form of closet which is now largely in use, for it is simple in construction, inexpensive, has no confined air space where foul air could accumulate, and conveys slop waters a^ z |^n^ dr no^verflow pipe being neces- sary. 84 HYGIENE AND PUBLIC HEALTH For the out-door water-closets of the houses of the working classes the short hopper closet, made in stout glazed stoneware or fireclay, is far the best. The floor of the closet should not be of wood, but of cement-concrete sloped towards the door of the closet. The siphon trap under the closet basin should be fixed upon the cement floor by embedding it in cement so as to form a pedestal, thus rendering it and the basin very strong and perfectly secure. There should be no vertical wooden casing, and the seat should be hinged, so that every corner around the space beneath the seat can be got at for cleansing. The trap of the closet should be jointed at the back of the basin to a 4-inch stoneware drain pipe by a cemented joint. A closet fixed after this manner will stand a great deal of rough usage without getting broken or out of order. Nearly all closets of the wash-down type are now made in pedestal form, that is to say with a hinged, lifting seat, and with- out wooden casing or riser. The closet is then well adapted for use as a urinal and for the discharge of chamber slops. The space under the closet should be cemented or tiled, or lined with lead finished with a beaded border. In the bracket form of closets, the basin and trap are supported by galvanized cantilever brackets let into the wall, and do not rest on the floor, conse- quently all the space beneath the closet apparatus can be readily cleansed. Bracket closets are much used in hospitals. The wash-out closet (fig. 16) is constructed of stoneware or china, with the basin so shaped that a small quantity of water remains in it to receive the excreta, which are flushed out over the edge of the basin into a siphon trap below. This form of closet is difficult to flush with only 2 gallons of water, for the rush of the water from the flushing cistern is broken by the force necessary to clear out the contents of the basin ; and then the water falls into the trap, but often without sufficient impetus to propel the excreta through it. The basin, too, is very apt to become soiled by solid matters near the outlet. The basin — as in the case of every closet basin — should be provided with a flushing rim. These disadvantages have led to the disuse of wash-out closets. Various " siphonic " closets are now made by English manu- facturers, in which the contents of the basin are not only forced out by the water-flush, but are also sucked out by means of a temporarily induced UpWrntk^eMiffo^M^ trap. Not all of these closets are reliable, as in some cases it has been found that foul DISPOSAL OF REFUSE 85 water returns to the basin after flushing ; also in some forms of this closet, to prevent the siphon becoming " air bound," air- escape pipes have to be inserted — an undesirable complication of what should be a simple apparatus. Water-waste preventing cisterns should be used with each of these three forms of closet, both for economy of water and to break the connection between the house cistern, used for drink- ing water, and the water-closet basin. Where there is no house cistern, the water being supplied by constant service, the water- waste preventer is especially necessary. Numerous outbreaks of •i-SYPHOKIC JE* 6UPPUV TO BASH Fig. 17. — Century Siphonic Closet. enteric fever have been attributed to the ascent of foul air and liquid filth from water-closet basins up the supply pipes into the water-mains, with which they were directly connected. One of the simplest forms of water-waste preventer merely has a spindle valve in the cistern on the supply pipe of the closet, which can be raised by pulling a chain attached to a lever, when the water — -2 or 2J gallons — is discharged. When the lever is de- pressed by the chain, the ball valve is raised, and no more water can enter the waste preventer as long as the chain is held. The chain must be held until the waste preventer is empty. The best form of waij&?#fe*asi>0 ^Jteaaawter is that with a siphon 86 HYGIENE AND PUBLIC HEALTH action. A very short pull of the chain will put the siphon in action, when the whole contents of the cistern are discharged through the flush pipe of ij- to ij inches in diameter. No more water can then escape until the cistern is re-filled and the chain again pulled. There are numerous forms of siphon water-waste preventer.' The especial advantage of the siphon action is that the cistern is emptied by a very short pull of the chain — an im- portant factor in the proper flushing of closets used by careless persons. These cisterns should be fixed at a height of not less than 4 feet above the closet basin. If this " head " is not obtainable, a good flush can be secured, as in the "combination" closets, by using a cistern, fixed at the seat level, with a comparatively large outlet pipe, which is only narrowed just before it joins the basin. The joint between the china or stoneware trap and lead soil pipe is difficult to make perfectly secure with red lead as a joint- ing material. Therefore it is better for these closets, where they must be connected to a lead soil pipe, to have lead traps, as a wiped joint can be easily made between the closet trap and the soil pipe. The disadvantage of the lead trap is that it cannot be enamelled internally, and enamel paints soon wear off, giving a dirty appearance to the bottom of the closet. In most cases a good joint is made by wiping a brass collar on to the lead soil pipe, when the joint between the china trap and brass collar is made with Portland cement, a little asbestos packing being employed to prevent the cement finding its way into the interior of the pipe. Under the head of closets with a movable apparatus for retain- ing water in the basin, we have the pan, the valve, and the plug closets. The pan closet (fig. 18) has been, up to 20 years ago, more largely in use than any other form in the better class of houses ; and it is undoubtedly a very badly contrived closet, and one which is often productive of nuisance. The pan closet consists of a china basin, shaped like an in- verted cone, with its outlet guarded by a movable metal pan, which retains water in the basin ; and for this purpose the pan must be of considerable size. On raising the handle of the closet, the pan is swi^^^a/^ Afl*3s^4arge rounded cast iron receptacle called the " container," into which the excreta and DISPOSAL OF REFUSE 8 7 water fall. From the bottom of the container a short pipe leads to a trap— usually a D trap — designed to prevent the passage of ca Fig. 18. — Pan closet with D trap, supplied from drinking water cistern. Standing waste pipe directly connected with unventilated soil pipe. Waste pipe of safe tray enters the D trap. foul air from the soil pipe into the closet. The interior of the container becomes m 'ijfh rf/ ^glashjd /0 jy^ ) soiled by the excreta ; 88 HYGIENE AND PUBLIC HEALTH and the deposit thus formed putrefies, giving rise to foul gases which escape into the air of the closet apartment as soon as the pan is swung back. The D trap — so called from its resemblance to the letter placed sideways (Q) — is made of lead, and quickly becomes coated with a deposit of foul matter, for there are parts of the trap which cannot be flushed by the water passing through. This deposit, like that in the container, gives rise to the for- mation of foul gases. The walls of old D traps and containers IgCTlOH A ■ B Fig. 19. Era Valve Closet. are not uncommonly found perforated in places, owing to the chemical action of the deposited matter. Pan closets and D traps, wherever found, should be replaced by one of those forms of closet which are capable of being flushed in such a manner that no deposit of filth can take place in any part of the apparatus. The valve closet (fig. 19), which is now largely in use, con- sists of a semi-spherical basin of china or stoneware, with a circular outlet at its lowest part, 3 inches in diameter. This outlet is closed by a circular water-tight clack valve, hinged at one side where it is connected with the handle of the closet. On raising the handle, the free edge of the valve is depressed into a metal valve box? / f«(§! d lfegi' c g , r!8'u|h to allow the valve to assume a perpendicular position. The valve box is connected DISPOSAL OF REFUSE 89 at its lower part with a trap — preferably a siphon trap, or an anti-D trap formed of 4-inch lead pipe — and the outlet of this trap is connected with the soil pipe. The valve closet should be flushed from a small cistern holding 6 or 8 gallons of water, and not from a water-waste preventer, as it is necessary to pro- vide a considerable " after-flush " — that is to say, to allow a supply of water to enter the basin after the handle is released and the valve closed. To secure an after-flush, some form of " regulator " valve in the supply pipe from the cistern to the closet basin must be used. The " bellows regulator," which is commonly used, con- sists of a piston working in a cylinder, and connected with the handle of the closet and with the valve in the supply pipe. The cylinder is provided with an escape pipe for air, on which is a tap to regulate the speed with which the air escapes and the piston falls. When the handle is raised, the valve in the supply pipe is opened, and the piston also is raised ; but on letting go the handle — the clack valve to the closet basin being then closed — the valve on the supply pipe is kept open, admitting water to the basin, until the piston has completely fallen and thereby closed it. The amount of after-flush, which is directly pro- portional to the slowness with which the piston sinks in the cylinder, can be regulated to a nicety by the tap on the air- escape pipe. As the outlet to the closet basin is guarded by a water-tight valve, the basin may overflow from too much after-flush, or from the throwing in of slops. It is necessary, therefore, to provide an overflow pipe to the basin ; this is usually carried from near the top of the basin into the valve box below, after forming an \T) bend, which by holding water prevents the ascent of foul air from the valve box. But it is found in practice that foul matters may find their way into or accumulate in the over- flow pipe, and that the water in the bend is liable to be evapor- ated or drawn out by siphonage when the contents of the basin are discharged through the valve box. Two precautions are adopted to obviate this difficulty. The first is to carry the overflow pipe into that side of the valve box where its open end will be protected by the depressed valve ; and the second, which is most necessary, is to recharge the water in the overflow at each use of the closet. The basin of the JJigitjzea.by Microsoft® . ., closet should be provided with a flushing rim. Occasionally a go HYGIENE AND PUBLIC HEALTH ventilating or "puff" pipe is attached to the valve box, and carried up and out into the open air, being left with an open end away from any windows. When the contents of the basin are being discharged, the foul air in the valve box then escapes into the open air, instead of into the closet compartment, There is very little risk of the deposition of filth in any part of the apparatus, as the large volume of water which the basin can contain effectually flushes the small valve box and trap beneath. Occasionally the valve box is enamelled inside to prevent corrosion. The chief disadvantage of the closet is that the clack valve may become in time leaky, allowing the water in the basin to escape, and possibly foul air to ascend into the general air of the closet. Wherever a valve closet is used as a urinal or for the recep- tion of chamber slops, a white ware slop-top should be fitted, and the seat should be hinged for lifting. Valve closets are also now made in pedestal form, so as to obviate the wooden casing and riser. An advantage possessed by valve closets over the wash-down closets is that the flushing is comparatively noiseless ; and this fact accounts for their popularity in the best class of residential property. In the anti-D trap the calibre of the pipe is diminished in the bent portion which holds the trapping water, and the bend of the pipe beyond the trap instead of being circular is squared. These properties cause some resistance to the passage of water through the trap, and tend to prevent both siphonage by suction — i.e., the drawing of the water in the trap by the passage of water down the soil pipe from a higher level — and siphonage by momentum, which may occur in plain siphon traps by the water discharged from the water-closet sweeping through the trap, insufficient remaining behind to form the water-seal. The depth of the water-seal in water-closet traps should not be less than i inch, and not greater than if inches. If the depth of the water- seal is too small, there is a liability for the trap to be unsealed ; if the seal is too great, the trap and the closet above it are not self-cleansing with an ordinary flush of water. These remarks apply more especially to " wash-down " closets (short hoppers) with water-waste preventers. The Water-seal of Traps. — The water-seal of a trap is the vertical distance between the level at whid^SR#fej&flJG§°«fl$Il the trap is fixed in position, and the lowest point of the bend of the upper surface of the trap. Thus in DISPOSAL OF REFUSE gi figs. 20 and 2 1 , which are diagrammatic sections of a S trap and a P trap, in each case the water-seal is the same, namely the vertical distance AB in the case of the S trap, and the vertical distance A'B' in the case of the Ptrap. The water-seal is, in fact, the depth of water that opposes the passage of air or gases from one side of the trap to the other, from outlet to inlet or from inlet to outlet. In the figures, the upper dotted line represents the water - Fig. 20. — S trap, with Water Seal. Fig. 21. — P trap, with Water Seal. level in each trap, and the lower dotted line is parallel with the upper dotted line, and is tangential to the apices of the bends. In the plug closet the basin and trap are usually cast in one piece of china or stoneware, the basin above being shut off from the trap (siphon) below by a solid plug or plunger, by which water is retained in the basin. The cistern and flushing arrange- ments may be the same as those for the valve closet, an after- flush being necessary for both alike. The plug, which is con- nected directly with the handle, is usually perforated by a channel bent on itself so as to form a trap, and thus provides an overflow to the basin, permitting water to pass through the plug to the trap beneath. Sometimes these closets are used without the trap beneath, but in both plug and valve closets a siphon trap is necessary to prevent the passage of foul air from the soil pipe when the closet is discharging its contents. The plug or plunger is liable to become much soiled, and, being out of sight, escapes cleaning. When this is so, it may happen that excremental filth is forced up on the handle when the plug is suddenly plunged. This constitutes a great disadvantage in use, and has led to the practical abandonment of plug closets. The valve and plug closets are under the disadvantage of having a space between the water in the basin and the water in the trap, from which air — possibly foul — escapes into the general air of the closet when the contents of the basin are being dis- charged. But they have this advantage over those of the first class, that the larger quantity of water in the basin renders them more cleanly in use. On the floor beneath the closet basin is usually placed a lead sate-tyay^to catch an^vefnW' cre Pmf tray should be provided 9 2 HYGIENE AND PUBLIC HEALTH with a waste pipe, which must be carried through the wall into the outer air, its end being covered by a brass flapper to prevent cold currents of air passing into the house. It was formerly the custom to connect this waste pipe with the D trap (see fig. 18) under the closet basin, thereby permitting foul air to enter the house at all times. Water-closets should be placed against the outside wall of a building, in which is a window with an area of at least 2 square feet, made to open, and reaching to the ceiling. Where possible they should be separated from the house by a well-ventilated lobby ; for it is important that air from the closet should find an easy exit to the outer air, and not pass into the house, as so often happens when water-closets are placed in dark, unventilated corners. The water-closet must not open directly into any Fig. 22. — Trough Water-closet. living-room, factory, workshop or compartment in which food is stored. The division wall between the water-closet and a dwelling-room, or a factory, or workshop, or food store, should always be of brick, and not a porous lath and plaster structure. The trough closet is used in large establishments, as hospitals, schools, workhouses, and asylums. One apparatus serves for the use of several people at the same time, and the flushing can be rendered automatic. The old form of closet (fig. 22) con- sists of an open trough, usually of stoneware, with rounded bottom, of varying length according to the number of com- partments desired. The trough has a slight incline towards the drain ; and by means of a weir at its lower end it is able to retain sufficient water to cover the bottom for its whole length. It terminatesDitf/zad&pli/e«s<$fp protected by a grid, to keep back articles improperly thrown in, before joining the DISPOSAL OF REFUSE 93 drain. Each seat over the trough should be in a separate compartment. The closet may be flushed by means of a Field's annular siphon flush tank {see fig. 13) of capacity proportional to the length of the trough to be flushed. The more modern and approved type of trough w.c. or latrine, is a great improvement upon the old form. In this (fig. 23) the Fig. 23. — New form of Trough Closet or Latrine with isolated pans. trough is retained, but each closet is cut off from its neighbours by a separate basin, the outlet from which dips into the water in the trough. The trough, moreover, is kept filled with water, which also rises up for a few inches into each w.c. basin ; this is effected by doing away with the weir and substituting a high siphon trap at the ouflBPtfl WffBflfB. Each separate basin 94 HYGIENE AND PUBLIC HEALTH is flushed through its flushing rim every time the automatic flush tank discharges, this discharge causing the emptying of the basins and trough by siphonic action. On the whole, trough closets have not been found to be very satisfactory in practice, and in schools and institutions they are now being replaced by separate pedestal wash-down closets. Waste-water closets, in which the excreta are carried away by means of the house waste waters, and in which flushing cis- terns with separate water supply are not used, were originally introduced by Dr. Alfred Hill, and are now to be seen in many working-class houses in Midland towns. Fig. 24. — Day's Waste-Water Closet. The annexed figure (fig. 24) shows a section through Day's waste-water closet. In this pattern the excreta fall into a stoneware tipper, which also receives the waste water. This tipper is so balanced on its bearings that when full it automatic- ally tips over and discharges its contents (fseces, urine, paper, and waste water) into the siphon trap below, which leads to the drain. The entrance to the siphon trap is considerably nar- rowed transversely, so as to prevent bulky articles improperly introduced finding their way into and obstructing the drain. The upper part of th£'®I@§e'l^l#%eP s e8fi , structed as to prevent, as far as possible, fouling of the sides above the tipping basin ; DISPOSAL OF REFUSE 95 and this upper part can be taken down easily and removed for cleaning. In another pattern of waste-water closet the tipper is not placed under the seat, but in some position between the closet and the gulley into which the house waste water empties itself. The discharge of water from the tipper flushes the drain in which the excreta are deposited direct from the closet. The advantages of this system of waste-water closets are that clean water is not required for flushing, a head of water is not necessary, there is no delicate apparatus to be damaged and get out of order by rough usage, and both the primary cost and the outlay in keeping in repair are small. On the other hand, the economy of clean water and the absence of dilution cause the sewage passing from districts supplied with these forms of closets to be very strong and foul ; and the difficulty of satisfactory treatment of the sewage at the outfall is much enhanced. Economy of water is purchased at the expense of difficulties in the purification of the sewage. Moreover, waste- water closets are liable to get foul and to block up, for in the poorer class houses with no bathrooms the slop-waters may not be adequate to provide sufficient flushing. It should be stated that waste-water closets should only be fitted up outside dwel- ling houses. In the Midlands these closets are not now regarded with favour, and the system is not being extended. Urinals should be made of non-corrosive materials, such as china, slate, and stoneware ; all metal apparatus is liable to corrosion, and should not be used. The floor should be ce- mented, and should slope towards a channel which discharges into a siphon trap connected with a drain. Urinal basins may be made of china or stoneware, constructed so as to retain water, and their waste pipes should discharge over the channel in the floor. The best kind of flush is that from siphon-action flush tanks which discharge automatically at regular intervals. Unless urinals are regularly and freely flushed with water, there will be a deposit of urates in the attached lead waste pipe, soil pipe, or drain, which by continual accretion and hardening eventually leads to obstruction. Slop sinks should be used only where it is objectionable to discharge slops from bedrooms through the water-closets. They are usually short hopper china basins with a siphon trap below, protected by a grid to^e^^cftBl^rger foreign bodies which 96 HYGIENE AND PUBLIC HEALTH might obstruct the pipes. The trap should be connected with the soil pipe like a water-closet. They should be provided with a flushing rim, and flushed from a water-waste preventer. Soil pipes are used to receive the contents of water-closets, urinals, and slop sinks, which are above the basement or ground level. They should be circular in section, and 3| or 4 inches in diameter, these being the most convenient sizes for ordinary use. They should be of drawn, milled, or rolled lead, 8 pounds to the square foot, or 9 pounds to the square foot for very high buildings, without any longitudinal seam, and should be fixed outside the house, with wiped (soldered) joints between the different lengths of pipe, each pipe being 10 feet in length. Lead T pieces are used to receive the branches from the water- closets. The London County Council Byelaws require 3t-inch lead soil pipes to weigh not less than 65 lb. per 10 feet length, and 4-inch pipes not less than 74 lb. per 10 feet length. The thickness of metal of 3 J-inch and 4-inch iron soil pipes must be not less than J s inch ; and the weight of 4-inch iron pipes per 6 feet length (including socket and headed spigot or flanges, the socket not to be less than J-inch thick) must be not less than 54 lb. Soil pipes outside the house are often made of light cast iron or galvanized iron. They are inferior to lead pipes, as the internal surface of iron pipes is much rougher than that of lead, and the joints as usually made with red lead putty are insecure. Heavy cast-iron socketted soil pipes are in some cases insisted on by local drainage bye-laws, especial precautions being laid down for the construction of the joints between the different lengths. To prevent oxidation and the formation of rust, iron soil pipes should be coated inside and outside with the magnetic oxide of iron (Barff's process), with hot coal-tar pitch, or with Angus Smith's solution. All cast-iron pipes must be free from holes or other defects, and properly tested, and of a uniform tnickness of not less than t« inch. The joints between the different lengths must be caulked with oakum and molten lead ; and the joints between the iron pipe and the lead T pieces from the closets should be made with a brass ferrule, caulked x in with lead, the lead pipe being attached to the ferrule by a wiped joint. Heavy iron soil pipes are heavier than lead pipes in the proportion of about 9 to 7-4. 1 A caulked lead joint is a joint made by firmly packing lead into the socket of the iron pipe b-fiffltimi &f Mig s 9ftg) fits more or less firmly into the other, but allowing a certain amount of play for expansion. DISPOSAL OF REFUSE 99 are useless as aids to extraction of air ; and they very frequently lead to obstruction of the outlet, besides being perishable. Where one soil pipe receives the discharges of several water- closets on different floors, the passage of the contents of one of the upper closets down the soil pipe may cause the water in the trap of one of the lower closets to be drawn off, owing to the suctional force of the downward \ir current of air caused by the descent of the ~r liquid in the soil pipe. To prevent this siphon- E age by suction taking place, a 2-inch or 2j-inch lead ventilating pipe should be carried up from every branch soil pipe, a few inches beyond the trap (on its soil pipe side), and these anti- siphonage pipes should join with one another on their way up outside the house, the common pipe being carried up separately or connected with the ventilator to the soil pipe (fig. 27). By this means the water - closet traps will not be disturbed by the passage of liquid down the soil pipe, for air will be sucked down these anti- siphonage pipes to restore the disturbed equilibrium. Siphonage is most likely to occur in 3j-inch lead soil pipes where the branch pipes from the water-closet traps to the soil pipe are long and curved. If they are short and straight, there is less likelihood of siphonage occurring.. The long arms or branches from water-closets thus ventilated are relieved of foul air which otherwise accumulates in them, and eventually leads to erosion and perforation of the metal of which the pipes are made. A trap at the foot of the soil pipe immensely in- tensifies siphonage by suction. Fig. 27. ■ — Soil pipe and ventilator, with anti- siphon- Ram-water pipes from the root should not be a ge pipes from the water branches. closet used as soil pipes and ventilators, for during heavy rain, when it may be most necessary to give a safe exit for displaced drain air, they will be use- less as ventilators, and foul air from unventilated drains may be forced through w&tffl^ffiptymkfesktf® the houses. Moreover, rthe joints of rain-water pipes are frequently found to be defec- 100 HYGIENE AND PUBLIC HEALTH tive ; and if the pipe passed near to windows there would be a risk of drain gases finding an entrance into the house. House drains are usually constructed of circular glazed stone- ware socketed pipes, 2 feet in length, with cemented joints (Port- land cement). The pipes are also connected by Stanford's patent joints or Doulton's modification (which makes the pipes adjustable in any position), in which the spigot and socket ends of each pipe are provided with a mould of smooth plastic material, causing them to fit accurately into each other when in position ; a very perfect joint being formed by greasing the prepared ends with a little rosin and melted tallow. These patent joints, however, are inferior to cement, as they are liable to erosion and decay, and are usually found not to be watertight some years after laying. Stoneware pipes are less porous and more durable than earthen- ware pipes ; the former may be distinguished from the latter by their colour (generally pale buff), the ringing note which they give out on being struck with a hammer, and their comparatively slight increase in weight after twenty-four hours' immersion in water. Portland cement is a mixture of chalk and clay burnt at a high temperature and subsequently ground very fine. It is stronger and capable of bearing greater tensile strains than other cements (Roman and Medina), but does not set so rapidly. When cemented joints are made, neat Portland cement only should be used, and care must be taken to remove any cement projecting from the interior of the joint into the drain, which when hardened would form an obstruction to the flow of sewage through the drain. Portland cement should be spread out and exposed to the air for some time before it is used, otherwise the joints, when made, are apt to " blow," and the collars become fractured. Socketed cast-iron pipes coated inside and outside with some preservative material such as the magnetic oxide of iron (Barff process) or Angus Smith's solution, to prevent oxida- tion, are used when the drain is required to be of extra strength to withstand constant vibration, as when laid under roads or paths on which there is heavy traffic, and also in soft, swampy ground. The joints of an iron drain must be caulked with molten lead and gasket or hemp. Iron pipes have an advantage over stoneware as the^e^d^g^eet and 12-feet lengths, and consequently fewer joints are required, and they are capable DISPOSAL OF REFUSE IOI of resisting strains that would fracture stoneware pipes ; on the other hand the interior of even the best protected iron drains are liable to rusting and erosion in course of time, a defect which stoneware drains are free from. When it is necessary to connect a lead to a heavy iron pipe, a strong brass ferrule or thimble should be joined to the lead pipe by means of a wiped soldered joint ; the brass ferrule is then received into the socket of the iron pipe and the joint made with hemp and molten lead. For small and medium-sized houses a drain 4 inches in diameter is the proper size ; for large houses a 6-inch drain may be used, and for large institutions or establishments consisting of several buildings a 9-inch drain may rarely be required. The smaller the drain, the better the flushing and removal of deposit ; but the drain must in all cases be large enough to guard against blockage and to carry off at all times all the rainfall over the area drained, as well as the maximum flow of sewage proper of the house. A volume of water sufficient to make a 4-inch pipe run full causes a 6-inch pipe to run less than half full, and a 9-inch pipe only about a quarter full, when all three are laid at the same inclination, since the sectional areas of the three pipes are in the ratio of about 1, 2, and 5. Stoneware drains are made in 3-inch, 4-inch, 6-inch, 9-inch, 12-inch, 15-inch, and 18-inch sizes. Iron drains are made in these sizes, and in addition 5 inches in diameter — a size which is very frequently employed. The London County Council Bylaws require stoneware drains (4-inch and 6-inch) to be not less than f inch in thickness ; the depth of the socket to be 1 J inches for 4-inch, and 2 inches for 6-inch pipes ; and the annular space for the cement to be not less than T 5 S inch for both 4-inch and 6-inch drains. For iron drains (4-inch, 5 -inch, and 6-inch) the thickness of metal must be not less than £ inch ; and the weight per 9 feet length (including socket and beaded spigot or flanges, the socket not to be less than f inch thick) must be not less than 160 lb. for 4-inch drains, 190 lb. for 5-inch drains, and 230 lb. for 6-inch drains. The pipes must be laid (with the socket end pointing upwards towards the head or commencement of the drain) on a perfectly smooth incline of hard ground, or where passing under the basement of a house, on a bed of 6 inches of cement concrete, the drain being embedded to the extent of half its diameter. In London it is the practice in addition to cover stoneware drains with 6 inches of cernent concrete all round, the concrete 102 HYGIENE AND PUBLIC HEALTH projecting on each side of the drain to an extent equal to the external diameter of the drain. Concrete should be made of clean sharp sand, 2 parts ; clean ballast (gravel, or hard brick broken small), 6 parts ; Portland cement, i part. Each pipe should rest upon the concrete for its whole length, so that the drain may be truly laid, the lumen of each pipe being concentric with the next. The concrete should be hollowed out where the collar of the pipe rests, and the cement must be introduced all round the joint, below as well as above ; and the joint should be finished with the trowel. It is sometimes the practice to introduce a strand of spun yarn into the interior of the joint to prevent the cement passing into the drain, and to insure the thickness of cement being the same all round. It is often the custom now to lay the drain on bricks at the bottom of the trench, and when the joints have been made with cement, to fill in with concrete beneath the pipes. If this is done, a brick should be used to support each end of every pipe, so that the drain may be truly laid. Iron drains should be laid on 6 inches of concrete, where passing under a building, as above de- scribed for stoneware drains, but need not be embedded in concrete. The gradient of a 4-inch drain should, if possible, be not less than 1 in 40, of a 6-inch drain 1 in 60, and of a 9-inch drain 1 in 90; this will give in each case a velocity of flow of between 3 and 4 feet per second. The drain should not, wherever it can be avoided, be carried under the basement of a house. Where, however, this is unavoidable, the special precautions noticed above must be taken, and at the point where the drain leaves the premises the wall should be supported by a relieving arch to prevent settlement and fracture of the pipes. Drains should be laid as far as possible in straight lines. If a bend is necessary, it should be effected by means of a special pipe curved to the proper degree, and the radius of any curve should not be less than ten times the cross-sectional diameter of the drain or sewer. The bends most commonly used are known as \, \, and ^ bends, implying that if 4, 8, or 16 respectively of these pipes are placed together they will form a complete circle. A branch drain should be made to join the main drain by means of a V junction pipe, so that the branch current may be flowing nearly in $^n^£rfefiP s 8?®the main current, thus causing no obstruction at the point of union. In large houses DISPOSAL OF REFUSE 103 it is very often impossible to carry the drain in a straight line for its whole length. It is advisable in these cases, at every change of direction, to provide means of inspection by manhole chambers, the drain being continued through the floor of the chamber by a suitably curved channel pipe, i.e., a pipe divided longitudinally in half. Into these inspection-chambers the branch drains also should be made to discharge by means of short curved channel pipes emptying over the main channel, Winser's curved channel pipes, from which about a quarter section only of the circumference has been removed, should be used when connected with a high soil pipe, so as to avoid splashing of solid faecal matters over the floor of the chamber ; and where the drains are joined in a manhole, the invert or bottom of the smaller drain should be higher than that of the main by so much as the difference between the diameters of the two, so as to prevent the liquid flowing in the large or main drain from backing up into the smaller. By this system of manhole or inspection-chambers, the drain — which runs in a straight line from manhole to manhole — can be inspected, and cleared by rods of deposit or obstructions, without breaking into it. Where it is necessary to connect a small pipe with a larger pipe, the junction should always be effected by means of a taper or diminishing pipe. The disconnection of the house drain from the public sewer is generally provided for, although it is not now generally held that sewer air is more specially harmful than drain air. Siphon disconnecting traps, however, prevent the passage of sewer rats up the house drains ; and unless such traps are fixed, it would be impossible to provide for the ventilation of house drains by fresh air inlets as now practised. Disconnection is effected by interposing a siphon trap between the house drain and the sewer, and on the house side of the trap a means of inlet for fresh air into the house drain is provided. The point usually chosen for disconnection is immediately before the house drain leaves the premises in its course to the street sewer. If the house drain is provided with a ventilating pipe at the further end, air, ad- mitted on the house side of the disconnecting trap, will generally travel continuously from the lower opening to the higher, and a circulation will thus be established in the drain and soil pipe; preventing any accumulation of foul air. The simplest form c^ 'cfficoWecfmg apparatus consists of a io4 HYGIENE AND PUBLIC HEALTH siphon trap with fresh air inlet formed of stoneware pipes on the house side of the water seal. There are several varieties of this sort of trap sold, under the names of " sewer air inter- cepter," " sewer air trap," etc. The points to be observed in choosing a trap of this description are : (i) Where the drain is a 6-inch or a 9-inch pipe, the siphon should be a size smaller than the drain ; (2) there should be a fall of 2 inches or more from the level of the discharging end of the house drain to the surface of the trapping water ; (3) the siphon should provide Fig. 28. — Section of Disconnecting Chamber. A, junction 45 (4") ; B, junction 90° (4") ; C, junction 30 (4") ; D, main channel (4") ; E, intercepting trap (4" to 6") ; F, clearing eye ; G, drain to sewer (6") ; H, drain (4") ; I, fresh air inlet ; K, galvanized terminal ; L, air-tight cover ; M, condensing dome ; N, york stone ; 0, glazed bricks, or preferably brickwork rendered in Portland cement ; P, concrete ; Q, cement ramps ; R, cap to clearing eye ; S, water joint automatically sealed by condensation ; T, ordinary joint, tallow or soft soap. an adequate seal of 2 or 3 inches of water ; (4) the inlet to the siphon should be nearly vertical, whilst the outlet rises at an angle of not more than 45 °. These qualities, except (3), are necessary to insure efficient flushing of the trap ; and, to further attain this end, the drain should be laid with a slightly greater fall before its junction with the trap. The fresh air inlet to the siphon is continued up by a vertical pipe to a little above the surface of the ground, and there covered by an open iron grating, which maybe fS#?9e&'l^ c 't s ?fi1ca flap valve to prevent any escape of foul air. DISPOSAL OF REFUSE 105 In larger houses it is now usual to provide a disconnecting manhole chamber (fig. 28), instead of the simple trap above described. The chamber walls are built of brickwork rendered in cement, and the floor is made of concrete. Walls lined with glazed brick are not so good as rendered walls, as the joints in the brickwork are apt to become defective, and then the cham- ber is no longer water-tight. The drain is continued through the floor of the manhole in the form of a glazed channel pipe, from which the floor — made of cement — slopes up (ramps or benchings) at an angle of 30 to the brick walls of the manhole. The branch drains, in the form of suitably curved (J or f ) glazed channel pipes, are made to discharge over the main channel, which itself discharges into a trap. The siphon trap should be provided with a " raking " arm or clearing eye, one end of which opens into the manhole, the other end being connected with the drain beyond the trap. This arm is to permit of ob- structions being removed from the drain between the siphon trap and the sewer ; when not in use, the manhole end should be closed with a patent stopper or a tile or piece of slate set in cement. The manhole chamber may be closed above by an air- tight iron cover ; and the fresh air should then be admitted into the chamber by a 6-inch pipe, the manhole end of the pipe being opposite the entrance of the drain, whilst the end open to the air is covered by an iron grating and provided with mica flaps, which permit air to pass in but prevent the reflux of foul air. The double -seal condensing cover (fig 28) is frequently used where the manhole chamber must be built inside the walls of a house. Where the disconnecting chamber is some distance from the house and away from footpaths, fresh air may be admitted by perforations in the iron cover. The chief advant- age of the manhole chamber is the readiness with which the drain can be inspected and cleansed. Wherever possible, the plan of drainage should be so designed as to provide for all manhole chambers being situated in yards or open areas, and not actually within the walls of the house ; for there is generally some danger of escape of drain air through covers which are not perfectly air-tight. It is important also that the interiors of manholes should be rendered in cement, so as to be water-tight, as, if the disconnecting trap becomes choked, the chamber may become filled with sewage. For house drains witlFVniumcieriP'gradient, in which deposit 106 HYGIENE AND PUBLIC HEALTH is liable to occur, it is advisable to provide an automatic flush tank to discharge into a gulley at the head of the drain ; by this means the dangers arising from insufficient fall may be to a great extent ■ obviated. Automatic flush tanks should be fed with clean water and not with bath or other dirty waste waters. Flush tanks fed with dirty waste waters invariably become a nuisance. The frequency of discharge of the tank can be regulated by adjusting the tap through which the water enters ; the merest dribble is usually quite sufficient. These tanks in practice should work without " dribbling " or " continuous action," which can be secured by fixing them on a perfectly level surface with the discharge pipe quite plumb. Flush tanks are now usually fitted with a " reversed " ball-valve. When the ball is depressed in the tank very little water passes through the valve ; but when the tank is very nearly full the valve is fully opened, a rush of water enters the tank and siphonage at once takes place. Dribbling and continuous action, which are some- times due to smallness of flow into the tank, are thus avoided, whilst the time of filling the tank can still be regulated as desired. All waste pipes from baths, lavatories, sinks, and safe-trays under water-closets or baths must be disconnected from the drain or soil pipe by being made to discharge into the open air. The waste pipes from baths, lavatories, and sinks should be of a large diameter (i| or 2 inches) to insure rapid emptying of the baths, sinks, etc., and as short as possible, for they tend to become coated internally with a deposit of dirt and soap, which decomposes and may be productive of nuisance. To prevent foul air from these pipes entering the house, a cast- lead siphon trap should be fixed under every bath, lavatory, and sink ; and in the case of kitchen sinks this siphon trap should be provided at its lowest point with a screw cap, capable of removal, in order to clear the trap of sediment and grease. The waste pipes from the upper floors are often carried through the external walls to discharge into the open head of a rain-water pipe divided, if necessary, into lengths for this purpose ; but this is not a very good plan if the open heads are any- where near windows, for the iron pipes become in course of time much fouled from soap and dirt, and then are apt to smell offensively. In such QM^^^ifSmS^ lead waste pipe should be continued down to the gulley at the ground level, its upper DISPOSAL OF REFUSE 107 end being carried up to the roof and left open ; anti-siphonage pipes will usually be required in the case of bath and lavatory wash-hand basin waste pipes, to prevent siphonage of traps, especially where several waste pipes on different floors discharge DRAIN Fig. 29. — Flushing Grease Gulley. into a main waste pipe. Every rain-water or waste pipe must be disconnected from the drain at its foot by opening over or under the iron grating over a stoneware siphon yard gulley. The basement waste pipes may discharge into yard gulleys by side inlets. When it is irflj^gfrfcte M^SfSfrf having a long waste pipe, 108 HYGIENE AND PUBLIC HEALTH this must be ventilated by a pipe of its own diameter carried up outside the house to a convenient point. Whenever it is neces- sary to place waste or other pipes within partitions or recesses in walls, they should never be covered, except with woodwork, which should always be made readily removable. The surface water from yards and areas should, where possible, be carried off by those siphon gulleys which receive the waste waters from the house, because these gulleys are always efficiently trapped in dry weather. Yard gulleys used for sur- face water only become untrapped in dry weather, owing to the evaporation of the water in them. These gulleys for waste and surface water are connected with branch drains which join the main drain in the inspection or manhole chambers before referred to ; they require to be cleansed periodically of sand and dirt, which collect at the bottom of the trap. In large houses it is found that the sand and grease discharged through the kitchen or scullery sink are apt to lodge in the drain from the gradual solidification of the grease as the water cools, and so form an obstruction. It is usual in such cases to cause the waste pipe (2-inch pipe, trapped under the sink) to discharge into a grease gulley instead of into a yard gulley. This grease gulley is made of stoneware, and may with advantage be connected with an automatic siphon flush tank (fig. 29). The hot water from the sink is cooled on entering a large volume of cold water in the trap, the grease solidifies and rises to the top, whilst the sand sinks to the bottom of the trap. When the flush tank dis- charges, the grease is thoroughly broken up by the sudden inrush of the large volume of water, and is then carried along through the drain without any opportunity being given to it to deposit on the sides or floors of the pipes. The grease gulley should be covered above by a grating, and sunk a little beneath the surface of the adjoining ground to confine all splashings to the trap. To carry off the water used for washing down laundries, sculleries, and dairies, the floors should slope to a channel leading to a yard gulley outside the house. The house drainage arrangements described above have for their object : (1) The speediest possible removal from the house to the public sewer of excretal and other refuse by means of water ; (2) the prevention of deposit of foul matter in any part of the drainage system, SM^f j%Mm&M into the soil of polluting liquids ; (3) the establishment of a current of air through every DISPOSAL OF REFUSE iog part of the soil drains and pipes, in order to disperse any foul gases that may form, and allow them to escape with safety B Fig. 30. — Semi-detached houses. A, modern drainage ; B, old drainage system ; D.C., disconnecting chamber ; F.A.I., fresh air inlet ; I.C., inspection chamber; S.P., soil pipe; G., gulley; S., sink; R.W.P., rain-water pipe ; W.C., water-closet. into the open air ; (4) the prevention of any entry of gases ., . , . ^Digitized by Microsoft® . , . , / , > from soil pipes, drains, and waste pipes, into the house ; (5) HO HYGIENE AND PUBLIC HEALTH the exclusion of the air of the common sewer from the house drain and the house. Objects (4) and (5) are to a great extent attained, as we have seen, by means of traps or water seals, and the question arises, " How far do such traps carry out the objects for which they are designed ? " Siphon traps are the most cleanly of all traps, because they present no corners or angles where deposit can accumulate, and are most easily flushed clean. Their liability to siphonage we have considered, and we have endeavoured to show that it can be obviated by a sufficient depth of siphon,, providing an efficient seal of water, and by adequate ventilation.. There is, however, another disadvantage common to all water traps, which is that the water may absorb gases on one side of the trap, and give them off on the other, so that foul air from the drain or sewer may be given off — only, however, to an inconsiderable extent — into a house, notwithstanding the presence of the trap. The only remedy for such a state of things is the prevention of foul air accumulations by adequate ventilation. The proper ventilation of drains and soil pipes can only be effected where there is an inlet for fresh air at one end of the system, and an outlet for foul air at the other end. Where there is an outlet °but no inlet, the pipes must be always full of foul air, though not under pressure, for there can be then no renewal of the air in them by the passage of fresh air currents. The Testing of Drains and Soil Pipes and their Branches. Tests are employed for new sanitary work, during the progress of the work, to ascertain that it is being properly constructed, and also for sanitary works that have been in existence for some time, to ascertain if the work is still sound. The principal tests are the water or hydraulic test, the smoke test, the pneumatic or air test, and the chemical test.. The Water Test. — This test is now almost invariably employed for new drainage work, and is applied after the drains are laid and jointed, but before they are embedded in concrete, or before the drain trenches are- filled in. The lower end of the drain, as it enters the disconnecting cham- ber, is plugged by means of an expanding screw plug with rubber rim of the size appropriate to the drain, or by means of a strong canvas bag, which can be filled with air under pressure by means of an air force-pump. As- soon as the drain is securely plugged, and a cord has been attached to the; plug to prevent its being carried away when the water is released, water is'- allowed to flow into the upper portion of the system until it has risen to the- top of an inspection chamber or gulley at the head of the drain. If, after stopping the flow, the water-level remains stationary for some minutes, the drainage system under te£t/^/ie8*jt M/ferefeeft®uld the water-level fall, there- is a defect at some point, and the joints of the drain should be carefully DISPOSAL OF REFUSE III examined for evidence of leakage. It is important to remember that in thus applying the test to a system of drains, air will be imprisoned in the branch drains leading from gulleys or water-closets, if the latter are charged with water. This air is liable to become slowly absorbed by the water, when compressed, and thus lead to a fall in the general level of the water, although the drains may be sound. The imprisoned air should be allowed to escape by passing a bent pipe through the water of the trap that retains the air. In drains of considerable length with steep gradients the head of water pressure in the lowest section of the drain may be considerable ; but in testing house drains, at any rate, nothing approaching a bursting strain for well made and well jointed stoneware drains is liable to be reached. In testing the drains of very large establishments, however, the system should be tested in sections, and any general test which would place undue strains upon the pipes and joints should be avoided. In applying the water test to existing drainage, the same methods are applicable ; but should a general test show leakage, it will be necessary to test in sections until the leak is sectionally located. There is no difficulty in carrying this out, if there are the proper proportion of inspec- tion chambers, as branch drains can be plugged in the inspection chambers to which they are connected at one end, and tested with water up to the levels of the tops of the gulleys or water-closets with which they are connected at the other. Inspection chambers, which are very often found to be leaky from defective rendering with cement, can be tested separately by filling with water, after all drains entering or leaving them have been securely plugged. It sometimes happens that an old drain is found to be in a very dirty condition, but water-tight on testing. After the drain has been rodded and cleansed, on further testing, it may be found to be no longer water-tight, owing to the grease and filth which sealed the interiors of defective joints being washed away in the process of cleansing. In old drainage systems without any inspection chambers the water test cannot be applied unless the drain is exposed at some point (usually at or near its lower end), and a pipe removed in order that the plug may be inserted. Old drains of this description are very seldom found to be water-tight ; and it has been said that the application of the water test to an old drain is liable to damage it and open up the joints. It is very doubtful, however, if the water test carefully applied ever does any injury of this sort even to an old drain. Any soil drain passing under or quite near to a house should be sufficiently sound to pass a water test. Vertical soil pipes and their water-closet branches may be tested with water, before the w.c.'s are connected, by soldering over the apertures where the closet apparatus is connected, and then filling with water, after plugging the lower end of the soil pipe, or the branch drain from the soil pipe in the nearest inspection chamber. This is a severe test, if there is a great head of water, and one but rarely applied, yet it is withstood by a good lead soil pipe with strong wiped joints. The Ball Test. — This is applied to new drainage work, before the drains are covered in, to ascertain that there are no projections of cement from the joints into the interior of the drain, by passing a spherical wooden ball, i inch less in diameter than the drain, though the pipes from the upper to the lower end. The Smoke Test. — This test is applied either by means of a smoke rocket or by a smoke machine. The test is usuallyapplied to both underground drains and vertical soil prpW?fi4r?&#VeSeffeing pipes, at the same time. 112 HYGIENE AND PUBLIC HEALTH The disconnecting chamber, or inspection chamber at the lowest point of the drain, is uncovered, and the smoke rocket after ignition is inserted into the drain delivering into the chamber. The rush of smoke from the rocket forces the air upwards through the drain, and where there is a good upward draught, the smoke will shortly be observed issuing from the top of the soil pipe or the drain ventilator. As soon as the smoke issues freely from the outlet, this should be closed by means of a plug or by a wet cloth, and at the same time the drain should be plugged where the rocket is inserted, or the cover to the inspection chamber should be replaced to prevent reflux of smoke at this point. In this way the whole length of drain and soil pipe and soil-pipe ventilator can be charged with smoke confined under very slight pressure. If there are any defects in the pipes or in their joint- ing, smoke will escape at such points, and will generally make itself evident either to sight or smell, according as to whether the defect is exposed to view or concealed beneath the ground or in walls and casings. In carrying out the smoke test, particular care is necessary to ensure that all traps connected with the drain or soil pipe under test are properly charged with water, and that doors and windows facing the spot at which the test is being applied are carefully closed. In the smoke machine, air is forced by means of a bellows through a metal compartment containing smouldering paper or cotton waste well saturated with oil, and a flexible pipe from the machine leads the smoke into the drain or soil pipe. The machine is rather cumbersome to carry about, but has the advantage over smoke rockets that the test may be applied under a definite pressure of about I to 2 inches of water, and that the flexible pipe can be passed through gulleys or traps on the line of a drain, where inspection chambers do not exist, or the test can be applied from the top of the soil pipe ventilator in the reverse manner to that usually employed with rockets, where this method is more convenient. The test with the smoke machine is carried out in the same way as previously described for rockets. In either case, when there is no disconnecting chamber to the drain, the water seal in the gulley trap whichis nearest to the outlet of the drain is generally removed, and the smoke rocket, or the tube of the smoke machine, is inserted into the bend of the trap. The smoke test is better evidence of defects in vertical soil pipes and ventilating pipes than of defects in underground drains ; as, in the case of the latter, although defects may exist, the issuing smoke may not reach the surface of the ground or find its way to any point at which it could be detected either by sight or smell. Escapes from vertical pipes are usually readily detected. The Pneumatic or Air Test. — This is very similar to the smoke test as applied by a smoke machine, air being forced by means of an air pump into the drain or soil pipe after the top of the soil pipe or other drain ventilating pipes have been securely plugged. A water gauge attached to the pneu- matic machine shows the pressure in inches of water ; and if this pressure is maintained for a few minutes, it is evident that the system under test is air-tight. The nozzle of the machine passes through an expanding screw plug or pneumatic bag, which makes an air-tight joint with the drain or pipe into which the nozzle is inserted. The test is a severe one, as the very smallest pin-hole defect will present an aperture for the escape of air, sufficient to prevent a pressure of an inch of water being maintained with the pipes under test. It suffers also from the drawback that there is nothing to indicate the exact posirW'of d tftfe' ^iRMfince the escaping air is both colourless and odourless. DISPOSAL OF REFUSE 113 The Chemical Test. — This is usually applied by means of grenades or small glass capsules containing a composition of phosphorus and asafoetida. When the containing glass is broken and the composition comes into contact with water, a slight explosion takes place, and dense white fumes having the characteristic smell of asafoetida are evolved. These fumes escape through defects in the drain or pipes, and so give evidence of leakages, which are recognized by the sense of smell. In testing underground drains by this method a certain time (15 to 30 minutes) should be allowed to elapse before deciding that there is no evidence of defects, as the odour may take a considerable period to travel from the defective drain to any point at which its presence could be appreciable. In using the grenades, one or two may be wrapped up in blotting paper, broken by a sharp tap, and then thrown into the w.c. basin on the highest floor, the basin being imme- diately flushed, so as to carry the broken capsules to the drain side of the w.c. trap ; or the same result may be attained in Kempes apparatus, the grenade or capsule being floated through the trap of the w.c. and then broken by a sharp pull on a string which releases a spring. Stables. The proper paving and drainage of stables is important, as dampness and foul air are very injurious to the health of horses. The floors of stables should be paved with a small hard brick, such as that known as adamantine clinker, with chamfered edges set in cement, such bricks being impervious to water and small enough to give a foothold to the animals. The floor should have a gentle slope of about 1 inch in 10 feet, from the heads of the stalls to- wards a cement drainage channel constructed to convey liquids outside the stable to a gulley in the stable yard. These chan- nels should be covered with iron gratings flush with the floor, easily detachable for the purpose of cleansing. If horse and mare pots are considered preferable to channels, they should be con- nected to drains, which are led outside the stable to discharge into the back or side inlet of a deep gulley. Inasmuch as a good deal of straw or other material used for litter is apt to pass away with the stable drainage, the gulley receiving those liquids should be a Dean's silt gulley with removable bucket for collecting solid pa#frisJea>>{wi^bs6gt> 3 1 )- A Fig. 31. — Dean'sSilt Gulley. A, cast- iron receptacle to lift in and out. 114 HYGIENE AND PUBLIC HEALTH For storing stable manure, whilst awaiting removal, the best receptacle is an open wire cage, which allows the free play of air over the surface of the refuse, and thus prevents heating and fermentation in the interior. Sunken dung pits are generally a nuisance, as they favour fermentative changes ; they should be abolished in favour of open wire cages resting on a cemented surface in the stable yard. Peat moss, dried and compressed, is now largely used as litter instead of straw, especially in cab and omnibus yards. It is more absorbent than straw, and consequently keeps the stables where it is in use very dry. If used too long, it becomes highly impregnated with urine and gives off' most offensive effluvia. In cab and omnibus yards the peat moss manure is generally very rank and stale before it is removed from the stable, and when stacked in heaps and subsequently thrown up into carts, the nuisance is very great. It is in these cases especially that carts or vans should be used to receive the manure directly' as it issues from the stalls of the stables, so that when the van is filled it can be drawn away without further disturbance. Defective Sanitary Arrangements in Houses. In examining houses, all sorts of appliances and arrangements will be found departing more or less from the sound principles we have laid down, and we will now briefly describe a few of the sanitary defects still to be found in houses. Drains, rectangular, barrel, or oval in shape, constructed of bricks set in mortar without any cement, and of large size (18 inches or more in diameter), are not unusually found running under the basements of houses, and are sometimes connected with cesspools in these positions. These brick drains, although originally intended only to carry off surface and house waters, will sometimes be found to receive the water-closet discharges as well. They invariably leak, for the mortar becomes loosened from the bricks, and water finds its way out through these open spaces ; in some cases all the liquid leaks out of the drain to saturate the surrounding soil, whilst the solids accumulate in the drain until it is completely blocked. As the brick drain communicates directly with the sewer, rats find their way into it, and, pushing through the loosened bricks, form runs under the house and sometirnWmW'^Ta'f'efef, which become passages DISPOSAL OF REFUSE 115 for foul air. To ascertain if a brick drain exists under a house, the ground must be taken up ; or the sewer can be entered, if large enough, and the drain examined where it joins the sewer. Pipe drains are always preferable to leaky brick drains, but all sorts of mistakes are made in laying pipe drains, and the resulting evils are similar to those arising from brick drains. In the first place, the pipes may be of improper material, such as unglazed porous earthenware, and without proper sockets. If glazed stoneware socketed pipes are used, the drain may be laid for the whole or part of its length with insufficient fall, or with a fall the wrong way. Again, the pipes used may be, and often are, much too large — 9-inch pipes where 4-inch would be sufficient ; or the pipes may be laid the wrong way with the socket end downwards or towards the sewer. The pipes are sometimes laid dry, i.e., without any luting material in the joints, or the luting material used may be clay, which is soon washed out of the joints. Even where the joints are luted with cement, if the drain is laid on uneven ground settlement takes place and the cement joints become cracked and leaky. Bends in drains are often made by fitting straight pipes into one another, the result being an open joint on the side with the greater curvature. The junctions of branch drains are sometimes made by knocking a hole in one side of the main drain sufficiently large to receive the end of the branch, which projects more or less and constitutes an obstruction, the hole being filled in with clay or cement. Even where proper junction pipes are used, the junction may be made the reverse way, so that sewage from the branch enters the main drain in a direction opposed to the flow of sewage in it. Where a small pipe joins a larger pipe, the junction is often effected without a diminishing pipe by placing the socket end of the small pipe into the socket of the larger pipe, and the joint that results is most defective. In this case also, the smaller pipes will be all laid the wrong way (with the socket end downwards), and junctions will be wrongly connected in a direction opposed to the flow of sewage. The evils arising from such defects in drains are leakages of foul liquid into the soil, escape of foul a#i gi m$ bfysmtM) of foul de P osits in the drains, leading eventually to complete obstruction. n6 HYGIENE AND PUBLIC HEALTH House drains were, and are still, commonly connected directly with the common sewer, an iron flap trap only being placed over the opening of the drain into the sewer. This flap trap affords no protection against the passage of foul air or rats from the sewer into the drain. It was formerly the custom to place a dipstone trap (fig. 32) on the course of the drain to prevent the passage of foul air up it. It consisted of a brick chamber of some depth retaining liquid, into which dipped a stone fixed in the roof of the trap. This trap not being self cleansing, because the upper part of the trap, though soiled with splashings, is never flushed, becomes choked with deposit, which putrefies and causes a most offensive nuisance. Where disconnection is practised, it is not uncommon to find siphons too large, or of im- proper construction, and in- capable of complete flush- ing ; in some cases the siphon is so constructed that the outlet is higher than the inlet, with the result that the sewage is backed up in the drain. One of the worst forms is that in which a vertical access pipe rises from the dip of the trap, for in this pipe solid matters are bound to accumulate. Soil pipes are very commonly found fixed inside the house. If of lead, the pipe may be longitudinally seamed for its whole length, with perforations in the seam of solder, and the joints may be formed by slipping one length of pipe inside the other. Cast-iron pipes with loose packed joints occasionally do duty as soil pipes, and may perhaps take rain-water as well. Zinc is sometimes used for soil pipes ; where it has been long in use, it is sure to have numerous perforations. In old houses the soil pipe is almost invariably unventilated ; that is to say, it is not open, but closed at its highest point. The foul air in unventilated pipes acts on the lead (or zinc) walls, and gradually, , , , Digitized bv Micrtistft®. ' ' . , J by erosion, forms holes Through which foul air or liquids escape. Fig. 32. Sink with Double Trapped Waste Pipe. A, bell trap ; B, dipstone trap. DISPOSAL OF REFUSE II7 But such closed soil pipes are often in reality — though not so intended — ventilated into improper places, for the foul air in the drain and soil pipes is sure to find some way out. Where the waste pipes of baths, sinks, or lavatories are connected directly with the D trap under a water-closet, with the soil pipe, or with the drain, foul air will find its way out through these waste pipes, or through bell traps into the house. Another ready means of exit of foul gases is the waste pipe to the safe- tray under a bath or water-closet, when this is connected with the soil pipe or drain. Another sanitary defect sometimes found is the direct connec- tion of the overflow or standing waste pipe of a drinking water cistern with the drain or soil pipe (fig. 18). Other means by which foul air can escape from unventilated drains are bell traps (fig. 32) in the basement of the house (kitchen or scullery), or in yards and areas, and rain-water pipes directly connected with the drains. In this last case also, foul air will escape through any loose or open joints of these pipes, which may be in close proximity to bedroom windows. With an unventilated drain, water traps — even the best designed, as we have already seen — are not effectual safeguards against foul air entering the house. Bell traps, which present so small a seal of water and which are usually choked, with rubbish, are often incapable of preventing the passage of foul air. It is very usual, too, to find the bell removed and the trap consequently useless, because the obstruction to the flow of water through the trap is so great. The aspirating effect of fires inside a house must not be lost sight of ; the draught up the chimney tends to draw air towards it, from any opening, into the room ; and thus it often happens that drain or sewer air is drawn into the living rooms. Where some attempt has been made to ventilate the soil pipe, it is often either inadequate, as when a i-inch pipe is carried up as ventilator to a 4-inch soil pipe, or it is improperly carried out, as when a rain-water pipe is led into a soil pipe and also acts as ventilator. Besides the danger of foul air escaping into windows, especially attic windows under which the rain-water pipe often commences, it is obvious that during a storm of rain, when it is most necessary to provide a safe means of exit for displaced drain air, the ventilator may be running full of water D Ma e w^fl'i^ Wsl ) ess. 1 1 8 HYGIENE AND PUBLIC HEALTH The pan closet and D trap were perhaps the most common of all insanitary appliances, but of recent years it has become rarer to find examples of these defective contrivances. They should, wherever found, be replaced by improved forms of closet and trap. The pan closet is usually supplied with water from the same cistern that supplies drinking water, the supply pipe being connected with a small service box at the bottom of the cistern {vide fig. 18). Water is admitted into the service box by a spindle valve guarding an opening in the top of the box, this valve being connected with the handle of the water-closet by wires and cranks, and an air escape pipe rises from the service box to give exit to displaced air. When the handle of the closet is pulled up, the spindle valve is raised from its seat, water enters the service box, and air is forced up the escape pipe to be discharged over the surface of the water in the cistern. Now the supply pipe and service box are always full of air, which, ascending from the closet basin, is often befouled, and it is this air which escapes over the water of the cistern and may cause pollution. Hopper water-closets are often found to be supplied with water direct from the house main. During an intermission of the water service the tap may be left open, and foul air or liquid filth may at such times be sucked up from the closet basin into the water pipes. Several outbreaks of enteric fever have been attributed to this cause. Sewers. Sewers are underground channels designed to receive and convey away by gravitation the rainfall and waste waters of the town, and, where the water-carriage system has been adopted, excretal refuse as well. In former times, and in some towns at the present day, if a river or stream pass through or near a town, the sewers took the shortest available course to the banks of the stream, and there discharged — each sewer by its own outfall. When it became no longer possible for towns to discharge their crude sewage into streams in this manner, intercepting sewers of large size had to be constructed to receive the sewage of the tributary sewers and conduct it outside the town. As we have already seen, brick sewers, as originally constructed, perform a double fur&tffed &ttMey> s afg land drains as well as sewers. By permanently lowering the level of the subsoil DISPOSAL OF REFUSE IIQ water in towns, these sewers have had an important effect in improving the health of the inhabitants. But the beneficial influence of sewers acting as drains has an undoubted drawback, viz., that drain sewers will readily permit of foul liquids percolating out of them, through their walls, to pollute the surrounding soil and contaminate ground water and ground air in the neighbourhood. That such escape of foul water does take place is plainly shown by the fact that in London with its drain sewers, all shallow well waters have been found to be polluted with sewage, and the wells have in consequence been closed. It is now the practice of all engineers to construct sewers as far as possible water-tight, and to provide other means for draining the soil. The Combined System. — In this system the sewers are designed to receive the rain — or such part of it as does not evaporate or is not retained by the soil — falling over the area covered by the town, as well as the sewage proper. The amount of evapora- tion depends largely on the temperature of the air ; but even in summer it is found in towns, where a large part of the surface exposed to rainfall consists of roofs and paved surfaces of yards, courts, and streets (especially also where there are steep gradients), that from one-half to three-quarters of the rain falling reaches the sewers. It is therefore necessary to construct the sewers of sufficient size to take a large part of the rain falling during heavy storms, such as \ inch of rain in one hour in towns, and \ to \ inch in the suburbs ; otherwise, if no storm overflows are provided, the sewers in low-lying districts are overcharged, and cellars and basements are flooded. In London the inter- cepting sewers were constructed to receive \ inch of rain over the whole area sewered in twenty-four hours (including subsoil water) ; but storm overflows direct into the Thames relieve these sewers during heavy storms. When a storm occurs after a time of drought, the sewers are flushed of accumulated deposit, and the sewage which first escapes by the storm overflows is often very strong and foul, and productive of nuisance in the river. At high-water, too, the storm overflows are tide locked, and then low-lying districts may be flooded. This principle of the interception of sewage is also commonly practised in seaside towns where the original sewers have been given a direct course to the sea, and the escaping sewage gave rise to offence. The Werty Microsoft® . . towns, especially manufacturing towns, the air is often loaded 164 HYGIENE AND PUBLIC HEALTH with soot and dust of mineral origin. The dust in the atmo- sphere provides innumerable nuclei for the condensation of moisture or water vapour. In towns, the amount of organic and mineral dust in the air will depend greatly on the efficiency of the scavenging and watering of the streets. The wind raises minute particles from the surface of the ground, and carries them often great distances before they are deposited. In this way infectious particles from domestic dust heaps and dried excreta may be caught up and carried into the air. Air is vitiated by respiration of men and animals , by com- bustion of coal, gas, oil, etc. ; by fermentation and -putrefaction of animal and vegetable organic matters ; by various trade and manufacturing processes. Vitiation by Respiration. An adult individual at rest breathes at the rate of about seventeen respirations a minute. At each respiration about 500 c.c. (30 - 5 cubic inches) of air pass in and out of his lungs. The air in the lungs loses 4 per cent, of oxygen, which is absorbed by the blood in the pulmonary capillaries, and gains carbonic acid from the venous blood to the extent of 3 - 5 to 4 per cent. The nitrogen remains unchanged. In addition, the expired air is raised in temperature to nearly that of the blood, 98 "4° F. ; it contains 5 per cent, of aqueous vapour, and a larger proportion of putrefiable organic matters than the air which is inspired. The amount of carbonic acid which is given off by an adult male person at rest can be calculated from the above figures, 1 and will be found to be 072 cubic foot in one hour. From actual experiment it has been determined that an average adult gives off 0'9 of a cubic foot of C0 2 during gentle exertion, and possibly 'as much as i'8 during hard work. The adult female gives off about one-fifth less of each of these quantities under similar circumstances, and an infant is said to give off about o'5 cubic foot of C0 2 per hour. In a mixed assembly at rest, including male and female adults and children, the C0 2 given off per head is therefore taken as 0'6 of a cubic foot. 1 17 x 30 x 60 — D£rti?ap *jrtftMee*(«aathed per hour. 4 per cent, of 175 = 072 cub, foot per hour of CO s . AIR AND VENTILATION 165 The repeated inhalation of air fouled by human beings tends to the production of a lowered state of health and promotes the onset of disease. It is not definitely known what are the exact constituents injurious to health, of air vitiated by the presence of human beings. Increase of Carbon-dioxide gas. — In the air of an inhabited room the amount of C0 2 is always increased, as compared with pure air ; and this increase is directly proportional to the num- ber of persons present, and inversely proportioned to the volume of fresh air introduced by ventilation. But the increase of C0 2 , even in crowded and badly ventilated rooms, is compara- tively speaking a small matter. The amount of C0 3 by volume in pure air being from 3 to 4 parts per 10,000, in inhabited rooms, the proportion of C0 2 , even where there is excessive crowding and very defective ventilation, as in some elementary schools, seldom rises above 50 volumes per 10,000, and it requires about six times as much (300 volumes per 10,000) to produce an immediately perceptible effect on the respiration, as shown by increased depth and frequency of breathing (Haldane) ; whilst no poisonous effects appear to be produced until the proportion of C0 2 rises to 500 volumes per 10,000, or 10 times the amount ever likely to be found in inhabited rooms. There is always about 6 per cent, of C0 2 in the residual air of the pul- monary alveoli (Haldane and Priestley). An increase of C0 2 in the respired air stimulates the respiratory centre to induce increased pulmonary action, so that the percentage of C0 2 in the alveolar air remains constant. The alteration in the breath- ing induced by respiring air containing 50 volumes of C0 2 per ro,ooo is quite inappreciable. A slight muscular exertion, such as that of walking at the rate of 3 miles an hour, would pro- duce 30 times as much effect on the breathing. From these facts it may be inferred that the increased C0 2 in the air of inhabited rooms is not of itself productive of injury to health. Diminution of Oxygen. — The diminution of oxygen in air vitiated by respiration has been the subject of experiment, but in no case has the reduction been found to be more than trifling. The normal amount of oxygen in pure air being 20"94 per cent, by volume, instances have been recorded where the oxygen has been reduced to 20^65 ; but it can hardly be supposed that such a reduction can exerbp^m^n^flgp health, having regard to the fact that many mountain climates are notoriously healthy l66 HYGIENE AND PUBLIC HEALTH at altitudes where the diminution of atmospheric pressure cor- responds with a very much greater reduction in the percentage of oxygen. Ozone. — Formerly considerable importance was attributed to the alleged absence of ozone from the air of inhabited places. But owing to the unreliability of the methods for ascertaining the presence of this gas, doubt has arisen as to whether this supposed allotropic form of oxygen exists in the general atmosphere at all, and whether the supposed characteristics of ozone are not really due to the presence of nitrous acid. Organic Matter. — For many years it was believed that the injurious effects due to the breathing of air vitiated by human respiration were attributable to organic matters contained in expired air. It was supposed that these organic matters were partly suspended in the air, consisting of small particles of epi- thelium and fatty matters from the mouth, and in part were in the form of an organic vapour from the lungs and air-passages, which was held to be nitrogenous in character and poisonous when re-breathed. The experiments, however, of Berger, Weir Mitchell, and Billings in the United States, and of Haldane and Lorrain Smith in this country, tend to show that there is no volatile organic poison in expired air ; whilst there is no definite proof that the tests for the presence of organic matter in air vitiated by respiration are any indications that the source of such matters is the air expelled from the lungs. The reducing action of vitiated air upon permanganate of potash may be due to other constituents of such air than organic matters ; and the fact that the washings of such 'air with distilled water yield, on distillation, ammonia and albuminoid ammonia in excess of that present in pure air, does not necessarily mean that the organic matters, of which these ammonias may be taken as evidence, are invariably derived from the lungs. They may, in fact, be due to volatile products given off from the teeth and gums, from dirty skins, and from excretions adhering to foul clothing. More exact research is required to ascertain the organic constituents (if any) of expired air, and to differentiate them from the volatile products of decomposition arising from the general surface and other parts of the body. Personal Emanations. — These emanations are undoubtedly very largely responsilfl(9*feP' Wi*?'q(HfpJ^sant odours which are perceptible on passing from the outer air into a crowded, unven- AIR AND VENTILATION 167 tilated room, more particularly when the occupants are persons of uncleanly habit. No sufficient experiments have been made, nor are there perhaps any satisfactory tests known which could determine the nature and quantity of the volatile matters to which these odours are due. It is possible that the deleterious action of air vitiated by the presence of human beings is to some extent due to the presence of these odoriferous volatile substances, minute in amount though they be. The long con- tinued action of such substances on the olfactory nerves may ultimately induce through the central nervous system alterations in respiration, circulation and nutrition, which are inconsistent with the maintenance of good health. Heat and Moisture. — It is probable that the heightened tem- perature and the larger amount of watery vapour present in the air of places much vitiated by the presence of human beings are auxiliary factors of some importance in producing loss of health. The debilitating effects produced by respiring impure air are undoubtedly augmented when such air is much raised in temperature, and the tendency to an increased output of foul-smelling volatile products from the bodies of the occupants of a room is materially increased by a high temperature and an atmosphere approaching saturation from the presence of mois- ture given off in the breath. Unless the vitiation, however, is extreme, it is but seldom that the temperature of the air or its relative humidity are sufficiently raised by the presence of the occupants of a room to exert any noticeable effects, apart from the much greater effects produced in the same direction by the combustion of fires and gas. Micro-organisms. — It is now known that during ordinary quiet breathing micro-organisms are not given off from the air-pas- sages to the expired air ; but that the respiratory efforts associated with laboured respiration, such as coughing, sneezing, and loud talking, are characterized by the spraying of microbes present on the mucous membranes of the air-passages into the air. Most of the microbes so given off are harmless and incapable of affect- ing the health of those who breathe such air ; but at times the infective organisms of nasal and laryngeal catarrhs, of influenza, diphtheria, tuberculosis, and other diseases, are thus ejected from the air-passages, and may be the means of propagating these diseases. Apart, however, from the occasional presence of definite pathogenic baMFS', / %M /c fflfrrrfer of harmless organisms l68 MYGIENfi AMD PUJ5LIC HEALTIf in the air we breathe does not appear to be very material. A small number of germs per litre of air is more an indication of cleanliness of the apartment and the absence of dust, than of efficient ventilation and the avoidance of respiratory impurity. : The number of microbes present in air vitiated by respiration seems to bear no very definite relation to the amount of C0 2 gas present. This is not to be wondered at when we know that the greatest numbers of microbes are found in the air which contains the largest amount of dust, and that the air of inhabited places may be stagnant and therefore comparatively free from dust, although much polluted by respiration. It appears also that the microbes and dust particles in the air we breathe do not as a rule reach the lungs, but adhere to the moist membranes lining the mouth, nose, and throat, and are got rid of by the mucous excretions of these membranes. The air reaching the lungs is consequently, as a rule, sterile ; and the expired air in gentle breathing is also devoid of organisms. It is probable that the infective organisms present occasionally in the air are absorbed into the system, after being deposited on the mucous surfaces of the nose, tonsils, or palate, and only occasionally reach the air cells or bronchi of the lungs. On the whole, then, it would appear that there is some con- stituent of air vitiated by human respiration and transpiration, which is responsible for the injurious action of such air upon health, but that this constituent has not yet been certainly identified. Whether this unknown substance is present in the air from the lungs, or whether it is given off from other parts of the body, is uncertain. It hardly seems probable that excess of C0 2 , deficiency of oxygen, absence of ozone, a raised tem- perature, excess of moisture, or the presence in the air of non- pathogenic micro-organisms from the air-passages, taken either singly or in combination, would be able to give rise to those far- reaching effects that the continued respiration of foul atmospheres is known to produce. It may, however, be the fact that whilst nothing of any importance is given off to the air by human re- spiration and transpiration, yet the air by such means is deprived of some vital element, with which we are unacquainted, and with- out which the highest state of bodily health and efficiency cannot be maintained. The purity of the $i«W<4tt»nf ^f%oms depends upon the amount of cubic space for each individual and the facilities AIR AND VENTILATION 169 afforded for the entrance of fresh and the exit of foul air. Where these points are properly attended to, the air, although rather more impure than the external atmosphere, will not be productive of injury to health. In those extreme cases where many people are crowded together and the ventilation is totally inadequate, the air often becomes sufficiently impure to cause headache, lassitude, nausea, and fainting. In a schoolroom crowded with seventy girls Pettenkofer found the carbonic acid to exist in the air to the extent of 0723 per cent., or about twenty times the amount normally present in air ; whilst the organic matter, measured as albuminoid ammonia (usually present in pure air to the extent of o'o8 milligramme per cubic metre) has been found in the ward of a hospital to reach 1 3 milligrammes per cubic metre. The above figures represent in each case excessively foul atmospheres ; all intermediate conditions of air, vatying accord- ing to circumstance, may be found in the different kinds of inhabited rooms and dwellings; The long-continued breathing of even much less vitiated air than the above sample is, probably, one of the causes of rickets in children, and tends to produce a lower state of vitality, characterized by anasmia, dyspepsia, and lassitude, in older people. People in this lowered condition of health, which is very common amongst those who spend the greater portion of every day indoors, in offices, schools, work- rooms and factories, offer much less resistance to attacks of acute disease than do people who live out-of-door lives ; and they are greatly more subject to all chronic and wasting dis- eases. Dr. Ogle's researches have shown that, of all the indus- trial classes, those which are the healthiest and have the lowest death rates are the gardeners, farmers, agricultural labourers, and fishermen — those, namely, whose occupations are carried on in the open air. The death rate from phthisis in these classes is only half that of the male community generally, and they enjoy about the same amount of freedom from diseases of the respiratory organs. Differences in food or housing accommo- dation cannot account for the comparative freedom of these classes from pulmonary disease. The causal relation subsisting between foul air, produced by overcrowding and insufficient ventilation, and phthisis is now generally recognized. The most, convincing proofs of such a relation are to be found in the comparative immunity enjoyed 170 HYGIENE AND PUBLIC HEALTH by soldiers, sailors, and prisoners at the present time from this disease. Formerly, owing to the very limited amount of cubic space allotted per head, and the disregard paid to ventilation, phthisis was considerably more prevalent among soldiers, Royal Navy sailors and marines, and prisoners in His Majesty's gaols than amongst the males of the same age in the classes from which they were derived. At the present time, other conditions, such as food, exercise, etc., remaining much the same, but more air-space and better ventilation having since been provided, the death rate from phthisis is considerably less amongst these servants and prisoners of the State than amongst the civil population. The theory of the contagiousness of phthisis has received the strongest confirmation from the discovery by Koch of the tubercle bacillus, an organism invariably present in tubercular deposits, but not found in any other disease. The tubercle bacillus is present in the sputa, and may be thus transferred through the air, as dust from dried sputa, to the lungs of the healthy, under conditions of too close crowding and failure to observe other necessary precautions. The excessive incidence of disease on the inmates of back-to- back houses, in which there can be no through ventilation and circulation of air, has been well established. Acute diseases of the air-passages, especially catarrhs, bron- chitis, and pneumonia, are very prevalent amongst those who live in heated, overcrowded rooms. The zymotic diseases generally are more prevalent amongst overcrowded populations than amongst those who are better lodged ; but this may be accounted for by the ease with which contagion can pass from the sick to the healthy ; for air vitiated by the ordinary products of respiration of a healthy person may induce illness, but cannot be productive of a specific disease. There is, however, evidence that insufficient air-space and defective ventilation of school dormitories and classrooms tend to produce inflammatory conditions of the throat (follicular and ulcerative tonsilitis) which in some instances, as the outbreak progresses, may be indirectly responsible for attacks of true diphtheria. The defective ventilation induces the unhealthy throat conditions ; and the subsequent appearance of diphtheria may, as Thorne suppmU^d^n Mfax&tftP progressive development in type of the throat organisms, or, as is more probable, it AIR AND VENTILATION 17I may merely be due to the accidental introduction of the true bacillus diphtheria, which at once assumes virulence under the defective sanitary conditions prevailing. In the air of ill- ventilated sick-rooms and hospital wards the debris of dried epithelial scales and pus cells may often be found floating. These matters are especially frequent in wards where many of the patients have purulent discharges from suppurating wounds or copious expectoration from the lungs, and are usually accompanied by an abundance of spores of fungi and bacteria, and large excess of organic matters generally in the air. In many persons the breathing of such polluted air causes an imme- diate effect on the throat and tonsils, passing sometimes into acute tonsilitis or hospital sore throat. Its effect in increasing the severity of, and in retarding recovery and convalescence from acute disease, is now generally recognized. Patients suffering from erysipelas, ophthalmia, pyaemia, septicaemia, and hospital gangrene, are undoubtedly infectious to those who have open wounds. The contagious particles (pyogenic micro- organisms of various kinds) — contained in dried epithelial scales and pus cells — may be transferred through the air from patient to patient ; and often no measure short of emptying the ward appears to be of any avail to stop an epidemic once begun. In times not very far distant, these diseases were, in the surgical wards of many hospitals and infirmaries, almost constantly present. Freer ventilation, improved sanitary arrangements, and the aseptic treatment of wounds and injuries, have almost eradicated such calamities from modern hospital nractice. It is possible that parasitic skin diseases may spread through the air, for sporules and mycelia of Tricophyton tonsurans and Achorion Schonleinii have been found floating in the atmosphere of wards occupied by patients suffering from diseases of the skin. Vitiation by Combustion. There are three kinds of mineral coal — lignite, anthracite or smokeless coal, and bituminous coal. Lignite is a deposit intermediate in its characters between peat and coal. In some parts of Germany, considerable deposits occur ; and it is there often used both for domestic and manufacturing purposes. It is a poor fuel mmjffiS&MM'mtff® Bituminous coal is used Vj% HYGIENE AND PUBLIC HEALTH exclusively in the manufacture of illuminating gas. Anthracite is a sort of natural coke, most of its gases having been driven off during the process of formation. Bituminous coal is generally used for domestic fireplaces, although anthracite, being smoke- less (no soot), when used in properly constructed stoves, would be far preferable. Bituminous coal when burnt in an open fireplace gives off nearly three times its weight of carbonic acid, small quantities of carbonic oxide, sulphurous acid, bisul- phide of carbon, sulphuretted hydrogen, and steam. About i per cent, is given off as fine particles of carbon or soot and tarry matters. One pound of coal requires 240 cubic feet of air for complete combustion. Illuminating gas is obtained by the destructive distillation of coal in closed retorts, without access of air. The gas is subsequently purified by condensation to remove tar and water, and its temperature is reduced to about 60° F. If the tempera- ture of the gas is lowered below 58° F., naphthaline and other valuable illuminants are deposited, and the gas is impoverished. The crude gas is then passed through coke scrubbers, which are large chambers so arranged as to offer an extended surface, constantly sprayed with water, to the gas. The water absorbs from the gas nearly the whole of the ammonia and the remain- ing tarry matters, whilst a certain quantity of the ammoniacal and sulphur compounds are removed. This water impregnated with ammonia and its compounds forms the " gas liquor " or crude ammoniacal liquor of commerce, which is conducted to the tar well. The gas is then led on to the purifiers, formed of lime or sesquioxide of iron, or both, and here the carbonic acid, sulphuretted hydrogen, bisulphide of carbon, sulphocyanides, and other offensive sulphur compounds, are removed, or at least reduced in the gas to a practically unimportant quantity. The purified gas is stored in gasometers, which are sunk in the earth to a considerable depth, water being used as a seal to prevent the escape of the gas. The standard adopted by the Metropolitan Gas Referees requires all gas to be quite free from sulphuretted hydrogen ; the maximum of sulphur (in compounds other than H 2 S) must not exceed 17 grains per 100 cubic feet, nor the ammonia 4 grains per 100 cubic feet. When purified, coal gas contains, on an average : hydrogen, 47 per cent. ; marsh gas, 35 perMrr?? ^arferfS^xide, 6 per cent. ; illumin- ants (ethylene, acetylene), 6 per cent. ; carbonic acid, 1 per cent. ; AIR AND VENTILATION 173 nitrogen, sulphurous acid, etc., 5 per cent. The products of combustion of coal gas are nitrogen, 67 per cent. ; water, 16 per cent. ; carbonic acid, 7 per cent. ; carbonic oxide, variable — least when combustion is most perfect — sulphurous acid and ammonia. One cubic foot of average gas combines with the oxygen of from 5 to 8 cubic feet of air, and produces when burnt about \ cubic foot of C0 2 , and from o'2 to o - 5 grain of S0 2 ; and it is able to raise the temperature of 31,290 cubic feet of air i° F. A common gas burner consumes on an average about 4 cubic feet of gas per hour, and furnishes, therefore, about 2 cubic feet of C0 2 in that time. If this C0 2 is to be brought down to 0'6 per mille, 10,000 cubic feet of fresh air would have to be supplied per hour for each such burner. But this is not necessary, and indeed, when adequate measures are adopted for purifying coal gas, its products of combustion contain but little impurity besides C0 2 . It is therefore generally considered that about 1,200 cubic feet of fresh air supply is amply sufficient for every cubic foot of gas consumed. A " standard " sperm candle (six to the pound), and burning 120 grains per hour, gives off about 0'4 cubic foot of C0 3 per hour; and one cubic foot of C0 2 is produced by the combustion of about 300 grains of oil in a lamp. The sulphurous acid in the air of towns, where coal is largely consumed, may cause the rain to be acid, and has a very destructive effect on vegetation, mortar, and the softer kinds of building stone. The products of combustion of coal gas usually escape into the air of the rooms where the gas is burnt, and serve to intensify the ill-effects on health of air already vitiated by respiration. Carbonic acid when present in the air, even to the extent of 2 per cent., if unmixed with other impurities, appears to have little, if any, effect upon health ; but above this quantity it may produce headache and nausea, and if present to the extent of 10 per cent., or even less, it may produce rapidly fatal results. Carbonic oxide, on the other hand, is very poisonous. As little as o - 4 per cent, in the air may cause death from asphyxia, the gas uniting with the haemoglobin of the^ red corpuscles and displacing the oxygen, so that the red corpuscles can no longer act as carriers of oxygen to the tissues, and failure of the chief nervous centres results. It therefore acts as a powerful narcotic, and exerts its effects in a most insidious manner; for being destitute of odour £M tiz R^ y (M!&m^®any irritation of the air- 174 HYGIENE AND PUBLIC HEALTH passages when inhaled, it may be breathed unconsciously by the victim, who quickly experiences a loss of the power of move- ment, and even of any desire to make an effort to escape from the poisoned atmosphere. The sulphurous acid and soot in the general air of towns like Manchester, Liverpool, and London, appear to have no very marked effect on healthy people ; but they are undoubtedly injurious to many asthmatics and to people suffering from bronchitis. During dense fogs the mortality from lung diseases always increases. Yellow town fogs are due to the suspended particles of moisture in the air (which constitute a mist) be- coming enveloped in a greasy coat of mixed carbon and hydro- carbons. The mist is thus rendered yellow and opaque, the light of the sun cannot penetrate, whilst the sulphurous pro- ducts contained in the fog are extremely irritating to the re- spiratory mucous membranes. Corfield has called attention to cases of relaxed and ulcerated sore throat caused by slight escapes of coal gas into houses by defective pipes and burners. Coal gas also occasionally finds its way into houses from leaky or fractured mains in the street. The gas passes through the soil and escapes under the base- ment floor, or even finds its way up the walls behind panelling. When the escape is large in amount, the effects produced on persons inhaling the gas are of an asphyxial type due to the contained carbonic oxide ; but when the escape is small, but long continued, the sulphur compounds, and especially the bisulphide of carbon, appear to be the injurious factors affecting the throat. These effects of escape of gas would probably be most intense where the gas is insufficiently purified after manufacture. The method usually adopted for testing the soundness of gas pipes and fittings is to subject them to air pressure by means of a force pump. A pressure gauge is attached to one of the burners, and air is forced into some other connected pipe until a pressure of 5 or 6 inches of water is registered on the gauge, when the stopcock on the force pump is closed. If the pressure gauge reading is not maintained during a few minutes, the pipes or fittings are unsound. Foul smelling sulphur compounds may also gain access to the atmosphere of oCcupi€ , S ,/Y ¥S6m / s M »9ffi[ ft %efective chimney flues. A chimney flue may be tested very much as a drain ; the outlet AIR AND VENTILATION 175 should be sealed from the roof, and one or more smoke rockets discharged from the fire-place, the opening of which must be subsequently sealed with a large piece of gummed paper ; the smoke will- then escape at any defective parts of the flue. Vitiation of Air from Decomposition of Organic Matters. Animal and vegetable organic matters in cesspools and in badly constructed sewers and drains ferment and putrefy, disengaging gases, some of which are fcetid and highly complex bodies, probably carbo-ammoniacal and allied in chemical constitution to the compound ammonias (methylamine and ethylamine), whilst others are the simple gases, carbonic acid, sulphuretted hydrogen, ammonium sulphide, carbon bisulphide, carburetted hydrogen, nitrogen, etc. Recent research tends to show that the organic vapours arising from decomposition of animal substances may contain traces of the animal alkaloidal sub- stances — ptomaines and leucomaines — which are contained in the faecal and urinary excretions of the animal body, and which exert a directly poisonous action on the system. The carbo- ammoniacal vapours have a strongly offensive odour, and are found in the air of cesspools and sewers where fermentative pro- cesses are in action. The suspended particles in cesspool or sewer air are dead organic debris and living organized germs (bacteria, moulds and fungi, and their spores). The -micro-organisms — the bacteria and fungi — are constituents of sewer air to which attention has been lately most directed. The net result of these observations goes to show that, contrary to what might have been expected, sewer air is under ordinary conditions remarkably free from the microbes which are capable of cultivation on solid nutrient media at ordinary temperatures. By ordinary conditions are meant sewers of modern construction, well laid with good gradients, and therefore comparatively free from deposits. Several observers have shown that sewer air generally possesses a relatively less number of microbes, capable of forming colonies on cultivation, than the atmospheric air outside ; and Mr. Parry Laws' investigations tend to prove that the microbes in sewer air are derived from the organisms usually present in atmospheric air, and are not identical with those found in sewage. The microbes in sewer 7 ' air are cmeny moulds, whilst those in 176 HYGIENE AND PUBLIC HEALTH sewage belong to the class of bacilli. The explanation appears to be that the internal walls of sewers are more or less wet or moist, and it is assumed, probably with reason, that the microbes in the sewer air adhere to the damp surfaces, and are thus prevented from floating in the air. This reasoning is strengthened by what is already known of the presence of microbes in atmospheric air generally ; for in dry dusty weather they are found in far larger numbers than in damp weather or after rainfall. In well-made sewers the sewage is borne away from the houses in a fresh and undecomposed condition ; but in old and defective sewers, and even in moderately good ones when the temperature of the air is high, and the amount of diluting water is small — as during hot and dry summers — putrefactive bacteria undergo enormous multiplication, fer- mentative changes are set up in the sewage, and gases are formed which bubble up and break upon the surface of the liquid. It was demonstrated as long ago as 1871 by Professor Frank- land, that liquids flowing smoothly in channels give off no solid particles to the air, and that even considerable agitation re- sulting in frothing may not cause any perceptible increase of the solid particles in the superincumbent air, but that the burst- ing of bubbles of gas in a liquid had a marked effect in disseminat- ing solid particles. The experiments of Haldane and Camelry, which have been more recently made, also show that splashing in a sewer, which may be caused by branch drains entering near the crown of the sewer, is productive of dissemination of micro-organisms in the air. The investigations of Mr. Parry Laws and Dr. Andrewes on the micro-organisms of sewage and sewer air tend to show that sewer air has no power of taking up bacteria from the sewage with which it is in contact. They found that the micro-organisms present in sewer air are much more nearly related to those found in the outer atmosphere than to those existing in sewage. In the course of their experiments, the nature of the organisms in some 1,200 litres of sewer air was determined. Not once was the Bacillus coli communis found in such air, though the former is present in sewage in numbers varying from 20,000 to 200,000 per cubic centimetre. The authors conclude that the possibility of the existence of the bacillus of typhoid in the air of our sewers is infinitely remote. Ttf&ffiaW fflge?^xf erimented on the vitality of the bacillus of typhoid in sewage. They conclude, as the AIR AND VENTILATION 177 result of their investigations, that sewage does not form a medium in which much, if any, growth of the bacilli is possible under natural conditions. The death of the bacilli in sewage is probably only a matter of a few days, or at most one or two weeks. But this degree of resistance may, nevertheless, be sufficient to allow of their being carried in sewage to remote distances, and of their being able to produce disastrous results should they gain access to any water supply. Recent experiments by Horrocks, at Gibraltar, gave results rather at variance with those obtained by Laws and Andrewes. He found that specific bacteria present in sewage may be re- covered from the air of drains and sewers, even when the sewage is flowing smoothly and without splashing. In one experiment, the B. typhosus was found in the air of a drain through which the stools of an enteric fever patient had been slowly passed. He also recovered B. coli from the air of one of the main sewers of the town, about 10 feet above the flowing sewage. The ex- perimental results obtained by Horrocks will tend to revive the opinion, formerly held, that sewer and drain air may be the means of spreading infective diseases, such as enteric fever, and diarrhoea. They also showed that the disconnecting trap on a house drain prevents the passage of bacteria present in sewer air into the house drains. Horrocks concludes that specific bacteria present in sewage may be ejected into the air and carried by air currents through drains, sewers, and ventilation pipes by (a) the bursting of bubbles at the surface of the sewage, (b) the separation of dried particles from the walls of the sewers and pipes, and probably (c) by the ejection of minute droplets from flowing sewage. Chemical examination shows that sewer air is subject to wide variations. A sample of air taken from a choked sewer in Paris was found by Parent Duchatelet to contain only 13 '79 per cent, of oxygen, and as much as 2 -99 per cent, of sulphuretted hydrogen. The air of closed cesspools in Paris must often have been very polluted to have caused those symptoms of partial asphyxia from which the workmen employed to empty them occasionally suffered. Where the quantity of sulphuretted hydrogen has been re- latively great, sudden death has in some instances resulted amongst those who have opened cesspools. The same results have followed when QMS e MiQl§pefM\ly bones, hoofs, horns, and 190 HYGIENE AND PUBLIC HEALTH skin trimmings. The raw material is first limed, and then washed and well boiled for some hours. After the glue has been allowed to cool and set, it is cut into slices and dried. The chief sources of nuisance are : (1) Unsuitability and general filthiness of premises ; (2) the storage of material, especially when old and foul ; (3) vapours arising from the conduct of the process, which are especially offensive when old material is used ; (4) the accumulation and improper storage of the residue (" scrutch "). The fat is usually skimmed off the surface of the hot water, and the " scrutch " is used for manure making. The various nuisances in the trades above referred to may be prevented or abated by the adoption and enforcement of sufficient bye-laws. Such bye-laws should secure : — 1 . Free access to the premises by any officer of the sanitary authority. 2. The restriction of such trades to suitable premises. Gut scraping, for instance, cannot be carried on, as it sometimes is, in small houses, without giving rise to offence. 3. The maintenance in good order of the drainage, lighting, and ventila- tion of such premises, and the proper cleansing of them. The floors or pavements should be kept in good repair so as to prevent absorption of any liquid filth, and should be swept or washed at the close of every day, and all splashings should'be removed. The walls and ceilings should be hot limewashed twice a year at specified periods (say the first weeks of April and October), after all splashings have been wiped off; and the walls must be rendered non-absorbent of any liquid filth or refuse to at least the height to which such splashings may reach. 4. The proper conveyance to the premises, and storage on the premises, of the material used, so as to prevent the escape of noxious and offensive emanations. In some cases the material should be brought to the premises in non-absorbent covered receptacles, and stored in special closed compart- ments ventilated into a tall chimney flue, by means of an air shaft provided, if necessary, with a gas jet or fan. Sometimes the materials to be stored should be dried, or treated with milk of lime, or even sprinkled with a little carbolic acid solution (1 in 40). Stored fat should be dried and laid out on racks in a cool room ; and the materials used for glue making should be stored as dry as practicable, or treated with a sufficient quantity of milk of lime and closely stacked. 5. The best practical means of rendering inert the vapours emitted during the carrying on of the process. Where melting and boiling is performed, this should be done in steam jacketed pans, so as to guard against the higher temperatures which burn the fat, etc., and give rise to the formation of most offensive empyreumatic odours. Large hoods communicating by pipes with the furnace flue should be used to collect the vapours given off from the contents of the pans during the boiling ; and the chimney by which these fumes escape should either be carried up to a considerable height, or the vapours should be condensed in a suitable condensing appara- tus, 1 or conducted into the furnace fire and cremated. This cremation may also be effected by means of a small " cremator " placed in the chimney. 1 A cheap and satisfactory condenser can be made by taking ordinary drain pipes and packing them with pieces of coke, over which water is allowe'd to trickle in a corg^^sytgea^^^r^ie vapours may be absorbed in a water spray, or by being brought in contact with trays of water, as in a " scrubber." AIR AND VENTILATION igi The fumes arising from steaming bones, meat, etc., can be prevented by applying cold water, directly after their removal from the boiler. 6. All fifth and refuse matter to be collected in a sufficient number of non-absorbent vessels with close-fitting covers, and removed from the premises forthwith. Fellmongers and others must not keep uselessly decomposed skins, etc., on the premises. 7. All water used for soaking skins, etc., to be renewed sufficiently often (at least once a day) to prevent effluvia arising therefrom, and all pits used for holding such water to be rendered water-tight. This bye-law will apply to the trades of a fellmonger, gut scraper, and leather dresser. 8. All waste lime to be removed with reasonable dispatch in covered receptacles, as also all other waste or useless material. 9. All implements and receptacles to be kept sweet and clean. The floors and receptacles in some cases to be sprinkled or washed with some deodorant, as in gut scraping. 10. Penalties for offending. The discharge of waste liquor into drains at a temperature exceeding 110 F. has often given rise to great offence from the sewer ventilators adjoining the premises on which some of the above trades are conducted. This is now provided for by statute (The Public Health Act Amendment Act, 1890), and all hot liquid refuse must be allowed to cool before it is discharged into a drain. It will be well to next consider a few of the more common trade nuisances. Fish Frying. — Nuisances arise from the neglect to adopt proper means of collecting the effluvia and dealing efficiently with them. The effluvia are increased by (1) the prolonged use of the same oil for cooking purposes, (2) the burning of the oil and consequent production of empyreumatic odours, when the heating is done over an open fire. These nuisances are best prevented by using the best dripping instead of oil, and by supplying a large deep hood to collect the effluvia arising from the frying. The hood should lead by a shaft into a fairly high chimney, and it is often necessary to provide a gas jet at the mouth of the shaft leading from the hood, so as to promote draught. To obviate the burning of the oil, the frying should be done in a deep vessel containing from 6 to 10 inches in depth of oil, or preferably steam jacketed cylinders should be employed. It is rarely, if ever, necessary to cremate the effluvia in the fire, or to absorb them in the water of a " washer " or condenser. Knackeries. — A knacker is properly a horse slaughterer, but he also slaughters other old and diseased animals, and receives the carcases of those which have died of disease or accident. Nuisances arise from the cries of the animals prior to their slaughter, for they are commonly kept several days ; the filthy way in which they are sometimes kept ; the undue and improper storage of material on the premises ; the general unsuitability and filthiness of the premises ; and the processes of bone boiling, flesh boiling (for cats' meat or fat extraction), or gut scraping, etc., which are sometimes carried on in the same premises. Pig Keeping. — This trade may become a nuisance from the improper storage of sour, malodorous food, with which the pigs are frequently fed, and from the effluvia from the sties. The sties should always be placed at a considerable distance from houses — at least 100 feet in urban districts. They should be floored with hard, impervious, and jointless material (e.g. concrete), laid to a good fall towards a channel leading to a gulley which discharges into a drain or covered cesspool. The feeding material should be kept in impervious ve^g$ z wi(rfc''tKa?r o f ! o ? o^ubic feet in capacity nor a fore-cabin less than 80. AIR AND VENTILATION 211 In the large public schools of this country the amount of super- ficial area and cubic space varies according to the ages of the boys and other circumstances. Average requirements for boys of 12-18 years of age are 70-80 square feet of floor space and 700 to 900 cubic feet of air space ; but, as previously pointed out, ample floor and cubic space will not compensate for defective ventilation. Unhealthy conditions of atmosphere are sometimes found to prevail in large and lofty dormitories, where defective ventilation leads to stagnation of air. Natural Ventilation. — During the colder months of the year in this country three complete changes per hour of the air in an inhabited room is. all that can be borne when the entering air is not artificially warmed. Hence the importance of an allowance for each individual of cubic space not much less than 1,000 cubic feet. The area of the inlet opening should be sufficiently large to allow the required volume of air (3,000 cubic feet) to enter at no greater speed than 5 feet per second. This speed could be attained where the inlet opening for each individual was 24 square inches. During cold weather this velocity could not be borne ; and it may be said generally that efficient ventilation is difficult to procure in cold weather, unless the entering air is artificially warmed. A velocity of the entering air of 2 to 3 feet per second is far more agreeable to the senses than a velocity of 5 feet. If the entering air is artificially warmed, the size of the inlet opening may even be increased up to 70 or 80 square inches per head, and the amount of cubic space may be diminished, for it would be possible then to change the air of the apartment more frequently than three times per hour without creating a draught. Of the forces which act in natural ventilation, diffusion causes the gaseous impurities of respired air to mix with the fresh air in a room until homogeneity is established. Diffusion, however, does not affect the suspended matters, which tend to fall towards the earth in a still atmosphere. The perflating action of the wind may be utilized by opening windows facing the wind, and the action is increased when windows, or a window and door on opposite sides of a room, are left open. The room is rapidly and continuously flushed with air, an enormous effect being produced, for it is possible to renew the air of a room in this manner over a hundred times an hour, even when the moveir?eM z 8i %e*wincfoutside is only 3 feet per 212 HYGIENE AND PUBLIC HEALTH second, equivalent to a very gentle breeze. Such a method is of unquestionable utility for rapidly changing the air of an unoccu- pied room — especially school and work rooms — and may be generally put in operation in inhabited rooms in summer when the temperatures outside and inside the house approximate. In any system of ventilation, however, that depends entirely on the wind, there is always the difficulty of regulating the velocity of the current, and during complete calms the action is of course nil. The wind, too, often impedes ventilation by obstructing the passage of vitiated air from an exit shaft into whose mouth it blows ; and this is not to be wondered at, for when blowing at the rate of 10 miles an hour the pressure of the wind is \ pound on each square foot of surface. For ventilating the holds and cabins of ships at sea, the wind may be most advantageously utilized, because the ships' motion is almost always producing a breeze. A large cowl, placed so as to face to the wind, conducts the air below by means of a pipe, whilst another cowl, reversed so as to back to the wind, allows the used air to escape. By this exit shaft the aspirating force of the wind is utilized. Sylvester's system of house ventilation proceeds on these principles. A large cowl facing the wind is placed outside the house, and conducts the air to an under- ground chamber, where it can be warmed if necessary by passing over hot water or steam pipes ; it is then conducted to the rooms above by means of tubes, and finally escapes above the roof through tubes surmounted by cowls backed to the wind. The aspirating action of the wind is constantly being used to ventilate rooms by means of the chimney. With a fire burning in the grate, the draught up the chimney is increased by the aspiration of the wind when the top of the chimney is above surrounding buildings. Even when there is no fire in the grate, it will usually be found that there is a current setting up the chimney. Should the top of the chimney be lower than sur- rounding structures, the wind striking these and then descending will often cause a back-draught and a smoky chimney. The remedy is evidently to carry up the chimney to at least the height of the surrounding buildings. A suitable cowl surmounting the chimney may prevent or mitigate back draught. From experi- ments carried out by the Royal Sanitary Institute it appears that certain forms of cowls or terminals have the effect of increasing , , .... Digitized by Microsoft® ° the up draught in air shafts, but that some 30 per cent, of those AIR AND VENTILATION 213 forms experimented with were valueless for that purpose. It is evident that on dull days, when the atmosphere is still, ventila- tion is most required, and that then such air shafts surmounted by cowls or terminals are of little value. Another cause of smoky chimneys is an insufficient supply of air to the room. To feed the fire, air is drawn down the chimney, and coming down in puffs, it causes an escape of smoke. The remedy is obtained by making a suitable inlet for fresh air into the apartment. Sometimes it is found that the smoke escaping from one chimney is drawn down another opening close by and on the same level. In such a case one of the chimneys should be raised. The movement produced by inequality in density or weight of contiguous masses of air at different temperatures is the natural force chiefly relied on for ventilating the interior of houses in this climate. This force is naturally chiefly called into action in cold weather, when the difference between the internal and external temperature is considerable, and is more or less in abey- ance in summer, when the temperature outside is often equal to, or even higher than, that of the house. The greater this difference of temperature and the difference of level between the aperture for the entrance of cold air and the aperture for the , exit of heated air, the greater will be the velocity of the entering air. We are enabled to calculate the theoretical velocity by means of Montgolfier's formula, which is founded on the dyna- mical law that the velocity in feet per second of falling bodies is equal to eight times the square root of the height through which they have fallen. In this case the height fallen is repre- sented by the difference in pressure of the air inside and outside the house, which is equal to the difference of level between the apertures of entrance and exit multiplied by the expansion of air caused by the difference in temperature inside and outside. v = 8 'Y ^ LS ) = velocity in feet per second, 491 where h = height in feet of aperture of exit from ground ; ,, /&'= ,, ,, entrance from ground; t = temperature of air inside in degrees Fahr. ; ^'= ,, ,, outside in degrees Fahr. In practice an allowance for friction of \ or \ must often be made. As it is impossible to tell, with any degree of accuracy, , , ,, , -Digitized byMicrpsofjt® . , ' what allowance must be made for friction in any given instance 214 HYGIENE AND PUBLIC HEALTH the formula is little employed in actual practice, and the anemo- meter (v. page 228) is preferred. If the area of the inlet open- ing is known, the amount of air entering the room in a minute or hour can easily be calculated by multiplying the velocity of the entering air by the area of the inlet expressed as square feet, the result being the number of cubic feet entering. In a room as usually constructed with sash windows and with a fire-place and chimney, but without any special means of ventila- tion, when a fire is burning in the grate the fresh air entering the room gets warmed as it approaches the fire, and part ascends the chimney flue while part rises to the ceiling. Cold air from outside will then enter — if the windows are closed — under the door, under the skirting boards, between the sashes of the window, and through any other chinks or apertures due to loose fittings. The bricks and plaster of the walls are also porous to a certain extent, and if uncovered by paint or wall-paper will admit a small quantity of air. Thus a large volume of air may be entering a room in cold weather when the fire is burning, although there are no visible inlets ; and the amount of air thus supplied may be sufficient for the needs of two or three persons if it were pro- perly distributed. But such is not the case. The cold air, which enters chiefly near the floor, takes as straight a course as possible to the fire-place, often producing a disagreeable draught to the feet of the occupants, whilst the heated and vitiated air near the ceiling is left undisturbed. In this country, to prevent draughts and to insure a thorough distribution, fresh air not previously warmed should be admitted into the room slightly above the heads of the occupants, an upward direction being given to it so that it may rise a little towards the ceiling, mix with and be warmed by the heated air in this situation, fall gently into all parts of the room, and be gradually removed by means of the chimney flue, or other outlet — which should preferably be at the highest part of the room. Amongst simple contrivances for windows by which these objects may be attained may be mentioned Hinckes-Bird's method (fig. 33), now so well known, of placing a solid block of wood under the entire length of the lower sash frame of a window, so as to raise the top rail of the lower sash above the bottom rail of the upper sash. By this means the air is admitted between the two sashes above the h^§tf# y 1|fa«ragfl9tpants of the room, and is given an upward direction towards the ceiling. The same AIR AND VENTILATION 215 result may be more conveniently obtained by the use of a deep sill, which permits the lower sash to be raised without any passage of air under it, at the same time allowing air to enter between the two sashes. Holes bored in a perpendicular direction in the bottom rail of the upper sash, louvred panes to replace one of the squares of glass, an arrangement for allowing one of the squares of glass, provided with . side checks, to fall inwards upon its lower border, or a double pane of glass in one square, open at the bottom outside and at the Fig. 33. — Diagrammatic sketch of various provisions for ventilation. A, Sash window with Hinckes-Bird's arrangement. B, Hopper sash-light falling inwards. C, Louvred outlets. D, McKinnell's ventilator. E, Sher- ingham's Valve. F, Tobin's Tube (showing valve open). G, Ellison's Conical Bricks. H and I, Grid ventilators below floor joists. top inside, all effect the same purpose and are simple and inex- pensive contrivances. Cooper's ventilator, which consists of a series of apertures in the glass of a window pane, arranged in a circle and capable of being more or less completely closed by a circular glass disc, also with apertures, and movable on a central pivot, does not admit the air in an upward direction, but breaks it up into a nulSrWre6(fbjdiWicted«airrents, and thus lessens 2l6 HYGIENE AND PUBLIC HEALTH the tendency to draught. The same object can be obtained by placing wire gauze or muslin over any inlet opening. The most generally used wall inlet ventilators are Sheringham's valve, Tobin's tube, and Ellison's conical bricks. In the Sheringham valve (fig. 33) air passes through the wall by means of a perforated iron plate, and is then directed upwards by a valved plate with side checks, which projects into the room, and, being hinged at its lower border, is capable of being more or less completely closed by a balance weight. The usual size of the inlet opening in these ventilators is 9 inches by 3, giving an area of 27 square inches. In Tobin's tube (fig. 33) air is introduced from the outside at the floor level through a perforated plate, and then passes up a vertical tube to a height of from 4 to 6 feet above the floor. After escaping from the tube, the current of air ascends more or less vertically for a short distance, before it begins to spread out and mix with the air of the room. In these two contrivances (Tobin's tube and the Sheringham valve) the entering air may be filtered through muslin or cotton wool, or made to impinge upon a tray containing water, and so deposit its sooty particles — a procedure often advisable in smoky towns. Tobin's tubes and other inlet and outlet ventilators should be made accessible in all their parts for cleansing, as they quickly become lined internally with dirt and adherent filth. Tobin's tubes should be made detachable from the external wall opening for this purpose. Ellison's bricks (fig. 33) are pierced with conical holes, the small opening, \ inch in diameter, being placed outside the building, whilst the larger opening, 1 J inches in diameter, is placed inside. The thickness of the brick is 4| inches. The air passing through these conical apertures becomes distributed over a gradually increasing area, and in this way its slow entrance is rendered im- perceptible and unproductive of draught. These bricks are mostly used for ventilating drill halls, gymnasia, stables, and cowsheds. All the inlet ventilators described are intended to utilize the movements produced by contiguous masses of air at unequal tem- peratures. For this reason they should be protected as far as pos- sible from the perflating action of the wind. This cannot, how- ever, always be done ; and when a strong cold wind is blowing into a ventilator, even of the most approved sort, a most unbearable draught may be the resuTtf e< To / obviate "this, there should be some AIR AND- VENTILATION 217 means of controlling the amount of entering air by partially clos- ing the ventilator, and in many cases the ventilator must be closed altogether. Sheringham's valve, Tobin's tube, and louvred inlets, fulfil these requirements very satisfactorily. It is often found that inlet ventilators are acting as outlets for the escape of air, when fresh air is entering a room from other sources. This can- not be obviated, nor, indeed, is it necessary. All that can be done is to place the inlets in the best possible position for distributing the entering air throughout the apartment without causing a draught, and to close up all such sources of entering air as are productive of draughts. The usual outlet for the vitiated air of a room is the chimney flue ; and this, for an ordinary medium sized sitting-room, with a fire burning in the grate, is sufficient for three or four people provided no gas is alight, or the gas lamp has its own special ventilating arrangement. With an ordinary fire, from 10,000 to 15,000 cubic feet of air are drawn up the chimney in an hour, the current being generally from 3 to 6 feet per second ; but a large fire will often induce a current of 8 or 9 feet per second. Heated air rises to the top of a room ; therefore the proper place to admit of the vitiated air escaping is in or near the ceiling. Neil Arnott's or Boyle's valves, in which a metal frame supports small talc plates, which open into the chimney flue near the ceiling, are sometimes used as outlets for foul air. They permit air to pass from the room into the flue, but the talc plates prevent its return ; the objections to their use are that they occasionally permit the reflux of smoke into the room, and the movements of the plates produce a slight clicking noise. If exit shafts other than the chimney flue are provided, they should be short and straight, and capable of being readily cleansed ; otherwise friction, and loss of heat by passage of the air through an exposed tube, will stop the current altogether, or reverse it, causing a back-draught. The escaping air must have its temperature kept up, or it cannot escape. One of the best methods of attaining this object, which might be put into practice in all new buildings, is to construct a shaft at one side of or surrounding the chimney flue, with an inlet near the ceiling of the room, and the outlet at the level of the chimney top. The air escaping from the room will then have its temperature kept Bg/fed^/^so^* 1 the chimne Y fiue - thus aiding the up draught, whilst the risk of reflux of smoke will be 2l8 . HYGIENE AND PUBLIC HEALTH avoided. The air flues may be moulded in the same piece of fire clay as the smoke flue ; but those from different rooms should not be connected in any way, or foul air from one room might pass into another. The combustion of gas may be made a very effective means of getting rid of foul air. It has been found by experiment that the combustion of i cubic foot of coal gas causes the discharge of 1,000 cubic feet of air. An extraction shaft may be placed over a gas lamp or chandelier ; and by means of a Benham's ventilat- ing globe light, or a Mackinnel's ventilator, slightly warmed fresh air may be admitted at the same time as foul air is extracted. Mackinnel's ventilator (fig. 33), is very useful for a room which has no other apartment over it. Two tubes, one inside the other, are carried through the ceiling or roof of the building. The inner one, which is for the extraction of foul heated air, projects outside above the outer, and inside also below it. At its lower end a broad circular horizontal rim is attached to the inner tube which deflects the air entering by the outer tube, and causes it to pass for a short distance parallel to the ceiling before falling into the room, as otherwise the fresh air would be drawn round into the inner or exit shaft. The gas burners or lamps used to light the room are placed immediately under the inner tube of this ventilator. The inner or extraction tube should have its top protected by a cover or cowl, to prevent the wind blowing down and the entrance of rain, which by evaporation might so cool the escaping air as to cause it to be heavier than the air of the apartment. The entering air will be slightly warmed by its passage over the heated extraction shaft. The area of the outer tube for the passage of fresh air should be equal to, or slightly larger (for there is more friction to overcome) than the area of the inner tube for exit of foul air. Mackinnel's ventilator is well adapted for large buildings, as schools, churches, halls, etc., which have no upper floors or stories. Benham's ventilating globe light, as its name expresses, combines ventilation and lighting ; slightly warmed fresh air is admitted, and foul air is extracted along with the products of combustion. In theatres sunlight burners are largely used ; they aid the extraction of foul air, but do not admit fresh air. In Pott's method okpnjfla^^j^low metallic perforated cornice is divided into an upper and lower half by means of a AIR AND VENTILATION 210. horizontal plate. Pure air enters the room through the lower half, which communicates with the outside air, and foul air is ex- tracted through the upper half, which opens into the chimney. Extraction shafts, like inlet openings, are liable to have their action reversed under certain circumstances. When the wind is blowing down upon them, when rain gets in, when the escaping air is subject to much cooling in an exposed shaft, or when there are more outlets than one in a room, one predominating over the others, down draughts are likely to occur. This most frequently happens when the draught up the chimney is very great from there being a large fire burning ; then there is a tendency for every other opening into a room to become an inlet. Also, when the wind is blowing down an exist shaft or chimney flue, the win- dows or inlet ventilators may become outlets. These matters can, however, generally be regulated by attention to the facts and principles which have been already laid down as a guide to proper ventilation. • It will be convenient to mention in this place some facts with regard to loss of velocity in air shafts by friction. The actual loss can in some cases be determined by calculating the theor- etical velocity in an air shaft by Montgolfier's formula, and then ascertaining practically by means of a current meter or anemome- ter the actual rate at which the air is issuing or escaping. The dif- ference represents the loss due to friction ; but allowance must of course be made for disturbing forces, such as the perflating or aspi- rating action of the wind. Contrasting two similar tubes of equal sectional area, the loss by friction will be directly as the length of the tube. If the two similar tubes are of unequal size, the loss by friction is inversely as the diameter of the cross section in each. When two tubes are dissimilar in shape, the loss by friction is inversely as the square roots of the sectional areas. A circle is a figure which includes the greatest area within the smallest periphery ; thus, if there are two tubes, one of which is circular in section and the other square, but having the same area (i square foot), the loss by friction is directly as the periphery 3i and in this case is as — , the periphery of the square being 4 4 feet and of the circle j,\ feet. Every right angle in a bent shaft diminishes the velocity of the current one-half. It will thus be seen that air shaf^^gu^, /g/Brfej^bly be circular in section, short and. straight, so as to diminish the loss by friction as 220 HYGIENE AND PUBLIC HEALTH far as possible. The absurdity of ventilating soil pipes and drains by narrow pipes, i or 2 inches in diameter, of great length, and bent on themselves often to a right angle, is apparent from the above statements. The ventilation of drains is always difficult to establish ; carried out by such methods it becomes an impossibility. Ventilating appliances whose object is the supply of artificially warmed air will be considered separately in the chapter on Heating and Warming. Artificial Ventilation. — Under this heading are usually described methods of extraction of air from inhabited buildings by means of heat, steam, or fans ; and methods of propulsion of air into buildings by mechanical means. It has been found convenient to describe under natural ventilation of rooms the ventilating effects produced by fires and chimneys in ordinary rooms ; and the extractive properties of gas lights have been also alluded to, although, properly speaking, fires and gas are artificial means of ventilation. The fire and chimney of an ordinary sitting-room are types of the methods used on a larger scale for extraction by heat. The principle is the same in all, and depends on the heating of a column of air in an extraction shaft, which being thus made lighter ascends ; as long as the heat is applied, a continuous current of air towards the shaft is produced, which, in its turn being heated, ascends and escapes, to be replaced by more from below. It is in this way that some mines are ventilated. The under- ground workings and galleries of the mine are connected with two large shafts — an upcast shaft and a downcast shaft, usually from 8 to 12 feet in diameter, leading to the open air — when air is made to pass down the downcast or intake shaft, it has to travel through all the workings of the mine before it can escape by the upcast or return shaft. The power which produces this continued movement of air may be supplied by a furnace at the bottom of the upcast shaft exerting an extractive force by the heated column of air, as previously described. But in many mines the extractive force is exerted by means of a powerful rotary exhaust fan placed at the top of the upcast shaft ; such fans can be made to propel some 12,000 cubic feet of air per minute. Numerous doors , .... Digitized by Microsoft® ,. . . and partitions are necessary in the galleries and workings m AIR AND VENTILATION 221 order to make the air traverse the whole length of these, and prevent it taking short cuts. An enormous volume of fresh air must be passed through a mine in the course of every hour in order to supply the quantity necessary for the respiration of the men and ponies employed underground, and to withdraw the products of combustion of lights (lamps and candles) and agents used for blasting, and to replace these injurious gases by pure air. Where fire damp (CH 4 ) is evolved from the strata cut through, the ventilation must be exceptionally good, in order to dilute this gas sufficiently to prevent its forming an explosive mixture with atmospheric oxygen. The same may be said with regard to the evolution of carbonic acid from the rocks underground, which so frequently takes place. This gas must not be allowed to form much over i per cent, of the underground air, or its asphyxiating properties will be exerted on all animal life within its influence. The injurious effects produced by gunpowder blast- ing are no longer necessary evils in the life of the collier or coal miner since the introduction of cartridges made of quicklime, which swell up from slaking when water is run over them, and exert their action without producing any gas at all. By the use of such cartridges there is, besides, no risk of explosion from ignition of fire damp or of coal dust. Other substitutes for explosives in fire damp collieries are plugs of dry wood, which swell when wetted, wedges worked by hydraulic pressure, and cartridges containing compressed air at extremely high pressures. Dynamite is now largely used instead of gunpowder, as it is more powerful, may be used under water, and requires no hard tamping. It is a mixture of nitro-glycerine C 3 H 6 3(N0 3 ) and infusorial earth or kieselguhr. Carbonic oxide is not one of the products of its explosion under pressure ; and hence its superiority to gunpowder, in which carbonic oxide forms 7J per cent, of the explosive gases. There is besides no forma- tion of sulphuretted hydrogen and marsh gas when dynamite is exploded, whereas these gases form respectively about 2 per cent, of the total gases resulting from gunpowder explosion. Carbonic acid and nitrogen form nearly the entire bulk of the gases result- ing from nitro-glycerine explosion in closed vessels. Nitrated gun-cotton and blasting gelatine (nitro-cotton and nitro-glycerine) are also superior to gunpowder for the same reasons, carbonic acid and nitrogen fornMg^MRPftfe® entire bulk of the gases 222 HYGIENE AND PUBLIC HEALTH generated when these substances are exploded under pressure. 1 Notwithstanding the importance of an abundant supply of pure air to all the workings of a mine, it has been found impos- sible by the Government inspectors to insist even on so low a standard of purity as that indicated by o - 25 per cent, of C0 2 in 'the air. It is maintained that in every mine at least 6,000 cubic feet of fresh air per hour should be supplied for every man employed below, for if this quantity is much reduced there is a serious diminution in the amount of work performed by the men, so that even commercially it pays employers to have adequate ventilation. In mines where fire damp or choke damp is evolved, the amount of fresh air supplied should exceed this figure. The furnace at the bottom of the upcast shaft, or the speed at which the fan is driven, must be regulated according to the number of men employed and the amount of work that is going on at any time below ground. Public halls, hospitals, and other large buildings, are some- times ventilated on the extraction principle. Shafts for the escape of vitiated air lead from the different rooms and open into the chimney just over the furnace. The air from these shafts should not be used to supply the fire or furnace, but should always open into the flue just above it, where the draught is greatest. The column of air in an extraction shaft may be heated by steam or hot water pipes, instead of by a fire. This is the plan adopted at the Hopital Lariboisiere in Paris. The extraction shaft is heated throughout the greater part of its length by spiral hot water pipes coming from a boiler in the basement. These hot water pipes are also carried into the wards, where they are coiled so as to warm the fresh air entering from with- out ; they then return to the boiler, and thus complete the circuit. The tubes from the wards for the escape of foul air open into the bottom of the extraction shaft. In summer the circulation of hot water in the pipes in the wards is stopped, the circuit being completed by return pipes from the top of the extraction shaft, so that the ventilation continues, but the air entering the wards is not artificially warmed. The column of air in an extraction shaft may be heated by gas instead of by fire ; but this method is more suitable for the smaller tubes used as exit shafts in ordinary sized dwelling-rooms. 1 Encyclopedia Britanmca, arucreon '"Mining," by C. Le Neve Foster D.Sc, F.R.S. AIR AND VENTILATION 223 Foul air may also be extracted by passing a steam jet into a chimney or upcast shaft. The shafts for the escape of foul air must open into the extraction shaft below the steam jet. The cone of steam emitted from a boiler is said to set in motion and drive before it a body of air equal to 217 times its own bulk. On board steamships and men-of-war it has been found that very effective ventilation can be obtained by causing the furnaces to extract the air from all parts of the ship through special shafts. By this means also, if the boilers and steam apparatus are enclosed in iron casings, as far as possible, within which the air shafts open, the temperature of the stokehole is greatly reduced. Some of the chief objections to the method of extraction by heat are : (1) Where the heat is produced by a furnace, it is most difficult to keep this at a constant temperature, conse- quently the draught is often very irregular. This difficulty is not encountered where the extraction shaft is heated by steam, gas, or hot water pipes, or where the air in it is forced upwards by steam. (2) In all cases where a number of air conduits from rooms at different distances open into an extraction shaft, there is a great tendency to create powerful currents from rooms that are near, and have short conduits leading from them ; whilst Irom the distant apartments with long and perhaps much curved con- duits the current may be very slight, or even nil. This difficulty may to a certain extent be overcome by increasing the diameter of the longer pipes so as to reduce the friction, and by bending the shorter pipes so as to increase it ; but in practice it is a rather serious drawback. (3) When air is drawn out of a room it is somewhat difficult to control the entrance of fresh air to supply its place, especially with regard to its points of entry, and its exclusion from places such as water-closets, from which it is most desirable that no air should be taken. In the ventilation of factories, steam may often be economically and usefully applied as the extraction force, but extraction by fans has also been largely used, and presents considerable advan- tages, as the amount of draught can be nicely regulated by altering the speed (the number of revolutions per minute) at which the fan is driven. It is especially in the textile trades — in the cotton, woollen, silk, worsted, and flax factories — that ventilation is most urgently needed. In many of the processes of these manufactures the work is not only carried on in clouds of dust, but also in grej/^^e^t^c^aitspheres which are satur- 324 HYGIENE AND PUBLIC HEALTH ated with moisture, this being necessary in some instances to the proper performance of the work. To carry off the floating particles of dust it is necessary to induce a powerful current in the exit shaft, so that the air may be drawn in as if to a vortex. In some cases the opening into the exit shaft may be in the centre of the room ; but it is more often advisable to carry the dust away as soon as it originates, and before it can mix with the general air of the apartment. Thus, in the wool sorting trade, each bench on which the wool is sorted has an opening leading by means of a pipe into the extraction shaft, at the extremity of which the exhaust fan is working. When the wool is being shaken, the dust, amongst which may be the spores of Bacillus anthracis, is drawn into the tube, and does not mix with the air which is inhaled by the workmen. The dust is then driven into settling chambers, where it is damped by steam jets, and so deposited can be col- lected and burnt. In silk dressing processes, air tubes are placed above the machinery with dependent hooded openings, which cover the area of dust production and quickly remove the dust ; such flues either lead into the chimney flue, or have a powerful draught created in them by means of fans placed towards the end of the shaft which leads from them to the out- side air. In the dry grinding processes of the metal trades, the air tubes are placed level with the grindstones and have openings opposite each stone, in such positions as to catch the dust, as it is driven off, and carry it away at once. The best material for the exit shafts and tubes is galvanized sheet iron, as it can be made into smooth circular pipes. Arrangements must be made to provide that the draught from the benches, or the workrooms nearest the fan, is not so great as to prevent the shafts at a dis- tance from working properly. A very convenient form of fan is that known as the Blackman Air Propeller ; it can be used for exhaustion (vacuum ventilation) or for propulsion (plenum ventilation), and is very powerful in its action, its vanes being large and curved. Another good form of fan, which is noiseless in its working, is that known as the Sturtevant " blower." They can be driven by a gas or steam engine, by water or electricity, and are employed for removing dust, foul air, or fumes and steam. When used for propelling air into a building, tffe^a^offi^elWt in the main conduit should not exceed 5 feet per second, and, where delivered into Air and ventilation 225 the rooms, not more than 1^ or 2 feet per second. The sectional area of the air shafts should be at least equal to that of the fan, so as to reduce resistance by friction. The warmed fresh air should be delivered by the pipes into the rooms near the ceilings. As it cools, it descends, and becomes equally distributed over every part. Special exit shafts are not always necessary, and those existing near the ceiling should be closed. The air finds its way out through fire-places, doors, windows, or the innumer- able minute apertures by which every room communicates with the exterior. Where special exit shafts are provided the openings should be low down in the rooms or workshops, and principally on the same side of the room as the inlets, so as to cause the in- coming air to circulate thoroughly before it escapes. Mechanical ventilation by means of fans is now much used in public halls and restaurants, and is advocated for school class-rooms. The objections to the propulsion or " plenum " system of ventilating buildings is that experience shows that air which has travelled through lengthy shafts and special air chambers has lost its freshness and is liable to cause lassitude and a feeling of depression amongst those who habitually come under its influ- ence. Chemical and bacterioscopic examination may demon- strate the purity of such ai r , but none the less there is reason to believe that in such air the vitalizing principle characteristic of really fresh air is diminished. The essential distinction be- tween town and country air is likewise probably due to a diminu- tion or deterioration of the unknown vitalizing principle present in a purely natural atmosphere. The very artificiality of the plenum system, which permits of the air supply being regulated with great nicety as to volume, temperature, moisture, etc., robs it at the same time of the refreshing qualities so important for the maintenance of a good standard of health. Open windows and direct ventilation through the external walls of a building may cause draughts and irregularities of temperature, but it is at least doubtful if such methods are not really more healthful for hospitals and buildings of the factory and domestic class, which are more or less continuously occupied, than such artificial systems of ventilation. For theatres, churches, concert halls, etc., where large numbers are collected for limited periods only, artificial systems of ventilation find their best application. But ventilation by propulsion (plenum method) presents several advantages. °Mi? f &tobMift°?ff t fir delivered and the rate 9 226 HYGIENE AND PUBLIC HEALTH of movement can be regulated with nicety, and the entering air can be taken from the most desirable point, can be warmed or cooled by a spray of water, and filtered in special chambers through cocoa-nut fibre screens, kept moist by water, or, what is better, through a very fine mesh work of copper wire continu- ously sprayed by water ; and all this can be done at one spot for a number of rooms or buildings. In the Houses of Parliament at Westminster a combined method of ventilation by propulsion and extraction by heat is in operation. Air is propelled by rotary fans along conduits to the basement, where it is filtered through cotton-wool and warmed in winter by passing over steam pipes, and then passes upward through shafts into the space beneath the grated floor of the House. The heat can be regulated by covering the steam pipes with woollen cloths, and in summer the entering air can be sprayed with water or cooled by passing over ice. The vitiated air in the House passes through a perforated glass ceiling in the roof, and is then conducted by a shaft to the basement of the clock tower, where it passes into a flue from which the air is extracted by a rotary fan. In Verity's system, air is set in motion by a spray of water from a number of very fine jets. The rate of motion can be regu- lated by the tap which supplies the jet. The method is useful for houses where it is not desired to go to the expense of fans driven by machinery. In addition to hot water pipes, the incoming air may be warmed by passing it into firebrick chambers, or through air ducts, placed behind and at the sides of a fire grate or stove ; or the air may be warmed by conducting it through a tube which passes through the centre of a gas stove (George's Calorigen and Bond's Eu thermic (fig. 35). The Manchester stove is largely used for schools, hospitals, etc. In this stove the cold air is carried along a shaft placed between the joists of the flooring, and enters a firebrick chamber built into the back of the grate. It then passes through tubes leading from the top of this chamber, and, travelling round the hottest part of the smoke flue, enters the room through openings at the top of the stove. The smoke flue is bent back and carried down the back of the stove, passing under the flooring to the outside, where it is dSJaMe&i topW&pi&f®iimriey. In all systems of ventilation it is important to remember AIR AND VENTILATION 227 that air ducts of all kinds should be made easily accessible for cleaning. This principle has been too often neglected in the past, with the result that air fouled by contact with dirt is very fre- quently used to supply buildings whilst outlet pipes and shafts are found choked with accumulations and practically valueless. Practical Examination of the Ventilation of Inhabited Rooms. In the first place it is necessary to determine the amount of cubic space. In rooms of regular shape this may be done by multiplying together the three dimensions of height, length, and breadth. If the room is irregular in form, containing recesses and projections, or with a raised ceiling, it is usually most con- venient to divide it up into a number of simpler parts, whose cubic contents can be determined by some one or more of the following rules : Area of circle = square of diameter (D 2 ) x 07854. Circumference of circle = D x 3 '1416. Area of ellipse = the product of the two diameters x 07854. Circumference of ellipse =half the sum of the two diameters x 3-1416. Area of square = square of one of the sides. Area of rectangle = the product of two adjacent sides. Area of triangle = base x \ height. Area of a parallelogram = divide into two triangles by a diagonal, and take the sum of the areas of the two triangles. Area of trapezoid = half the sum of the parallel sides x the perpendicular distance between them. A trapezoid is a plane four-sided figure having two of its opposite sides parallel. H 3 Area of segment of circle = (Ch x H x f) -\ 2 Ch (Ch = chord, H= height). Cubic capacity of cube or solid rectangle = length x height x breadth. Cubic capacity of solid triangle = area of triangle x height. Cubic capacity of cylinder = area of base (circle) x height. Cubic capacity of cone or pyramid = area of base (circle) x£ height. Cubic capacity of^^^a^gf^ase (circle) x f height. Cubic capacity of sphere = D 3 x C5236. 228 HYGIENE AND PUBLIC HEALTH Thus, supposing it was required to determine the cubic capacity of a circular hospital ward 30 leet in diameter, with walls 10 feet high, and a dome-shaped roof 5 feet high. The area of the base or floor space is 706-86 square feet. The cubic capacity of the cylin- der below the dome is 706-86 x 10 =7,068 M 6 cubic feet, to which must be added the cubic capacity of the dome = 2,356-2 cubic feet. So that the cubic capacity of the ward is 9,424-8 cubic feet. Having determined the gross cubic space, the next point is to determine the available cubic space, i.e., the gross cubic space less the space occupied by solid objects in the room. Any bulky furniture must of course be measured, and it is usual to deduct 3 cubic feet as the space occupied by each individual, and 10 cubic feet for each bed and occupant. Having made these deductions, the available space for ventilation is arrived at. Next, the various openings acting as inlets and outlets respectively must be determined, and thus the area of inlet and outlet provision per head can be ascertained. To distinguish inlets from outlets, observe the direction given to the smoke evolved from smoulder- ing brown paper or cotton velvet, when held close to the aper- tures, some of which will be found to act as inlets and others as outlets. The rate of movement of air through these apertures may be approximately ascertained by placing in them an anemo- meter, which is an instrument consisting of four little revolving sails driven by the wind or current of air. The sails turn an axis with an endless screw running on small toothed wheels, which, by means of a plate and dial, indicate the number of revolutions of the axis and the space traversed by the sails. By experiment with air moving at a known rate of speed, the anemometer may be graduated. It appears, however, that even tested anemometers are subject to variations, and too much reliance must not be placed on their indications. When the instrument is placed in a ventilating shaft or opening, it should be at about two-fifths of the distance from the centre to the margin of the opening, that being the situation where the mean velocity is obtained with the greatest degree of approximation. A modification of the water manometer, or pressure gauge, is occasionally used. The current of air impinges on the surface of the water in one arm of a bent tube, and in proportion to its strength drives the water up the other arm, which is inclined at a certain angle. The 1 i . • j ■ xi.- Digitized by Microsoft® , . , , records obtained m this mannercan be compared with the theor- etical velocities arrived at by the use of Montgolfier's formula, AIR AND VENTILATION 229 allowances being of course made for friction and wind. When the wind is at all strong and is blowing directly into inlet ventila- tors, or is exerting a powerful aspirating action on chimneys or exit shafts, calculation is useless. As air enters a room by every crack and crevice, and may even do so through the brickwork of the wall, it is practically impossible to gauge the amount of the incoming air. The best plan is to deduce it from the amount which is leaving the room, as the out- going air will only leave the room by well-defined channels or out- lets. In an ordinary room practically the whole of such air tends to escape by the fire-place, the entrance to the flue of which has generally a transverse section of about 126 square inches. If the rate at which the air is travelling up the chimney is ascertained by an anemometer, the amount of air leaving the room is easily cal- culated. Thus, assuming the velocity to be 7 feet p?r second, then the quantity of air escaping will equal this velocity x the sectional 126 area of the opening (in feet) = 7 x = 6'i cubic feet per second, 144 or 21,960 cubic feet per hour. If samples of the air are to be taken for an estimation of the C0 2 , any gas burners, lamps, etc., which may be alight at the time must be carefully noted, together with the temperature at the time the sample is taken. In any scheme of ventilation, regard must be had to the follow- ing practical points : — 1. When air is heated it expands and tends to rise ; when air is cooled it contracts and tends to fall. 2. Cold air tends to enter a room and to move about very much as water would ; and this holds true so long as the tempera- ture of the fresh air remains lower than that in the room. 3. The extent of inlet provision, for fresh air is not quite of the same importance as that for the exit of foul air ; for if foul air is extracted in sufficient quantities, fresh air will enter somehow to replace it, as by skirtings, crevices in doors and windows, or even through the brickwork of the walls; 4. The inlet provision for fresh air should average 24 square inches for each individual ; the provision of inlet areas somewhat larger than those of exit tends to minimize draughts. 5. Inlets should generally be as low in the room as possible, viz., just above the floor (so as not to raise the dust) if the outside air is warm or has be&Mgma3itrti$d/iipm£aft l &o entry, but at a height of about 5 feet if the outside air is cold ; otherwise unpleasant 23O HYGIENE AND PUBLIC HEALTH draughts are experienced. As a further protection against unpleasant draughts when cold air is admitted, the incoming air should be directed upwards ; while hot air, since it tends to rise, should be directed downwards. 6. Outlets should in every case be as high as possible, and preferably close to or in the ceiling ; and they should have their extractive powers maintained by means of heat or an exhaust fan, or they are liable to act as inlets. 7. Where practicable, an effort should be made to so place out- lets that the vitiated air is drawn towards them before mixing with the general air of the apartment. 8. There is a tendency for fresh air to take a direct course to the outlets, and this must be counterbalanced by a judicious selection of the relative positions of inlets and outlets. 9. Methods of ventilation devised to ventilate crowded premises are generally inefficient, unless the incoming air can be warmed in winter to about 6o° F. ; for then efficient ventilation by cold air cannot be tolerated, and there is a great tendency among workers to close all ventilating inlets. 10. With less than 250 cubic feet of space per head, no ventila- tion can be satisfactory which is not aided by mechanical force. 11. The source of the incoming air should be considered. It should not be borrowed from adjoining rooms, but taken direct from the outside. One great advantage of the more expensive mechanical system of plenum ventilation is the fact that sufficient air can always be obtained from a source which is known and selected. 12. Ventilation dependent on the extraction of foul air is often more convenient than that in which propulsion is mainly relied upon ; but the purity of the air is not so easily provided for or guaranteed. 13. If warmed air is forced into a room, it should only be raised to a temperature sufficient to prevent a feeling of cold (about 6o° F.). More highly heated air is often felt to be overdry and unpleasant. 14. The heating of the room should be effected by fires, stoves, or pipes in the room itself, and should not be made to depend upon the warmth of the incoming air. 15. It is difficult ancfcpgsB&iyM&appiy methods of mechanical ventilation to old premises. c CHAPTER IV WARMING AND LIGHTING Warming. Individual susceptibilities to heat and cold are various, depend- . ing as they do upon age, robustness of constitution, and previous habitude. It may, however, be stated that, as a general rule, the temperature of a sitting-room or workroom should be about 6o D F. to 65 ° F. Radiation. In this country houses are generally warmed by radiant heat from open fire-places. By radiation is meant the direct passage of heat from warm bodies to colder ones, the rays of heat passing through the intervening air. This form of heat is no doubt the most healthy, for whilst objects within the range of the fire are warmed, no impurities are added to the air of the room. Moreover, the column of air in the chimney flue is heated, and, becoming lighter, escapes at the roof of the house, to be replaced by colder and denser air from below, and thus an open fire-place is a great factor in ventilation. It is, however, extremely wasteful, for the greater part of the heat escapes up the chimney. The intensity of radiant heat is inversely as the square of the distance of the heated object from the source of heat. Thus, if there are two objects, 1 foot and 3 feet distant (respectively) from an open fire-place, the more distant object only receives one-ninth the amount of heat received by the nearer object. This fact shows the impossibility of warming equally all parts of a room, when the source of heat is an open fire-place. Of late much has been done to improve open fire-places by securing the greatest amount of heating effect with the least consumption of fuel. Some of these improvements have been made at the suggestion of Mr. Pridgm Teale. They may be thus 232 HYGIENE AND PUBLIC HEALTH summarized : The width of the grate at the back should be about one-third the width in front facing the room, the sides of the grate being splayed out at the necessary angle. The back and sides of the grate should be formed of fireclay, and the back, instead of rising perpendicularly, should be "rifle-backed," i.e., curved forward so that the flames may play upon it (fig. 34)'. The curved portion becomes heated by some of the upward rays, which would otherwise be lost up the chimney, and radiates this heat into the room. Verti- cal fire bars are said to allow more heat to radiate into the room than horizontal bars. The floor of the grate should be formed of a solid slab of fire- clay as in slow combustion grates ; or if the lower fire bars are retained, a shield should be placed on the hearth, rising as high as the bottom bar of the grate, so as to form a hot air chamber under the grate com- pletely cutting off the air of the room (fig. 34) ; or an iron plate may be laid upon the bars form- ing the bottom of the grate. The object of this arrangement is to prevent a draught under a fire, which hastens combustion and wastes fuel. The whole fire-place should be brought well forward into the room, the grate being placed low down near the floor ; and to reduce draught the chimney throat should be narrowed as much as possible. A movable hinged canopy, to regulate the draught up the chimney, is a desirable arrangement. Open grates of this description create much smoke, as the combustion of the fuel is by no means complete. Attempts have been made to construct a smokeless open grate ; and the. plan' which has been found on the whole to answer the best is to " underfeed " the fire, by which is meant that the supply Fig. 34. — Economizer. B, flue. Rifle back Stove with A, hot air chamber ; WARMING AND LIGHTING 233 of fresh fuel is introduced beneath the incandescent coal which forms the top of the fire, and through which the smoke arising from the fresh coal must pass, thus securing complete combustion. In one of the best of these smokeless fire-places a curved ledge projects from the bottom of the grate. The fresh fuel is placed on this ledge and forced under the blazing coal above by means of a special kind of shovel. These " underfed " grates are found to be very efficient heaters for the amount of coal con- sumed, and they continuously expose a clear fire free from smoke, but they require more care in stoking and management than ordinary grates. Wherever possible, fire-places and chimney flues should be built in one of the inner walls of a house. The waste heat of the flue will then help to warm the upper rooms. It is evident that, as open fire-places act as ventilators for extraction of air, to carry on this function the column of air in the flue must be kept continuously heated ; otherwise the chimney will not " draw," and back currents of smoke enter the room. In an ideal stove, the heat escaping up the chimney should be not more than sufficient to maintain a good draught, the rest being radiated into the room. There are several forms of " slow combustion " grates now upon the market, the principle of which is to reduce the draught through the fire to its smallest possible dimensions. One of these, the " Well Fire," consists of a fireclay trough, inside which is placed a cast-iron grate whereon the fire rests. The space between the iron and the fireclay constitutes a hot air chamber to which a continuous current of air at a raised temperature is admitted by side tubes. With a reduction in the price of coal gas, open gas fires have come more largely into use. As usually constructed, the flames from a row of Bunsen burners play upon asbestos, in lumps or fibre, which is heated to a red heat. A gas fire consumes from 10 to 20 or more cubic feet of gas per hour. Until gas is supplied at is. or is. 6d. per 1,000 cubic feet, which could easily be done if it were freed from illuminants, or until a public supply of water gas is made safe and available, gas fires must be more expensive than coal. But they have the advantage of being very cleanly- there is no soot in the- chimney flue and no dust or ashes — very convenient, and of causjjn&gg ^b^^s regards the prevention of smoke, the more extended use in our large towns of coal gas 234 HYGIENE AND PUBLIC HEALTH for heating and cooking would undoubtedly tend to free the air from much of the soot and smoke that now pollute it. Fogs, which depend so largely upon climate and site, would be just as frequent, though less sooty and yellow. They would also be less sulphurous, for the sulphur compounds produced by gas combustion are less than those produced by coal. It is probable that water-gas would come largely into use for heating and illuminating purposes — for gas fires and gas cooking stoves, and for incandescent burners — were it not dangerous, from containing such a large percentage of carbonic oxide. Water gas is produced by blowing steam through incandescent coke or other carbonaceous matter, raised to a high temperature in a " generator " furnace by the aid of an air blast. The in- candescent coke gives off what is known as " producer gas," and this is led away from the generator before the steam is introduced. The introduction of the steam is only continued for about four minutes, after which time it is necessary to turn on the air blast again to reheat the coke. The " producer gas," consisting largely of carbonic oxide, is used for heating the boilers which generate the steam. It will thus be seen that the process consists of alternately blowing the generator hot (for ten minutes), when producer gas is formed and led away, and of making water gas by introducing steam over the hot fuel (for four minutes). In this way the water is split up into hy- drogen and oxygen ; the hydrogen remains free, and the oxygen with most of the carbon forms carbon monoxide, the mixture being " water gas." The water gas, as formed, is passed over scrubbers and purified over oxide of iron, in much the same way as coal gas, before being stored in gas holders ; it then consists of hydrogen gas (about 35 per cent.) and of carbonic oxide (25 to 35 per cent.), marsh gas 20 per cent., and 10 per cent, of ethylene, etc. In heating power water gas is far superior to coal gas ; and as the only products of combustion are H 2 vapour and C0 2 , the sulphur products of combustion of coal gas are avoided. Water gas, too, can be produced very cheaply, viz., at about 40!. per 1,000 cubic feet. But the large quantity of CO in water gas causes it to act as a powerful poison, and yet, from being odourless, escapes, if they occur, are not at once detected. For lighting purposes the gas is " carburetted " — that is, enriched by hydrocarbons derived from oil. This car- buretted water gas snIMW&lMSB&Q&l gas ; its candle power WARMING AND LIGHTING 235 is greater, and it is, on the whole, cheaper to make. It has been adopted for lighting purposes in many towns in America, and it is often used, mixed with coal gas, in this country. A recent Departmental Committee recommended a statutory limit of 12 per cent, of CO in any illuminating gas ; for an escape leading to the presence of o - 4 per cent, of CO in the general atmosphere may prove fatal. It is perhaps needless to point out that plumbers should never be allowed to fix a gas fire, or, in fact, any gas consuming appliance (such as a bath heater or "geyser"), which burns more than 12 feet of gas per hour, without providing a chimney flue to carry off the products of combustion to the outer air. Ventilating grates may be combined with open fireplaces. The usual method is to construct a chamber lined with fireclay at the back and sides of the fire-place, and extending up around the lower part of the chimney flue. An opening below admits fresh air from outside the house into the chamber, where it is warmed and escapes by an opening into the room above the chimney piece. Galton's Grate and the Manchester School Grate act upon this principle. Conduction and Convection. By conduction heat passes from one molecule of air to another in contact with it ; but, as air is a very bad conductor of heat, the process is very slow. The conveyance of heat by means of the movements of masses of heated air (convection) is the most effectual agent for heating. Air when heated expands, and becomes lighter bulk for bulk than colder air, so it rises up- wards, its place being taken by the colder, denser air. Houses may be heated by means of stoves in which coal, coke, gas, or oil is burnt, by hot water and steam pipes, or by ra- diators. The air coming in contact with the heated surfaces is warmed, and therefore expands and rises, and is replaced by colder air. In this way currents of air are maintained which circulating about a room tend to heat every part of it. The most satisfactory way of uniformly heating the whole house is by warming the air of the entrance hall by means of hot water pipes, a hot water radiator D ^gftpfi^ c ^fe the kitchen boiler, or a ventilating stove placed in the hall. The warm air which ascends 236 HYGIENE AND PUBLIC HEALTH ■H gnnnnnnnwfr V \ can then be admitted to all the rooms above the ground floor by openings over the doors, which openings may be fitted with valves. The great distinction between stoves and open fire-places is that, whilst in the latter the heated air escapes up the chimney, in the former the heated air circulates through the room. There is a great variety of heating stoves, but they may all be classified as either close or ventilating stoves. In the former kind no arrangements exist for providing fresh warmed air ; whilst in the latter fresh air from outside the house is made to circulate through the stove, with- out coming into contact with the products of com- bustion, and is, when warmed, allowed to enter the room. Bond's Eu- thermic Stove is one of the best forms of ventil- ating stove. In this the fresh air from the out- side is conveyed to and warmed in a central up- right tube, which com- municates with the room at the top of the stove. The space between this tube and the outer case of the stove is open below, where a circle of gas jets burn, and above it communicates with a flue. Thus, not only is warmed fresh air supplied to the room, but also foul air is removed along with the products of combustion be- tween the inner tube and the outer case. In all stoves economy of fuel is aimed at, by providing doors and dampers to shut off the draught and make the combustion as slow as possible ; and the flues are sometimes carried horizontally for some distance, in order that extra heat may be obtained. It is evident that the slower the combustion and the more complete the utilization of the heat of the burning fuel in warming the room, the less does a close stove actas an exhaust ventilator ; Fig. 35. Euthermic Ventilating Gas Stove. A, fresh air chamber ; B, ring of Bunsen gas burners ; C, to foul air flus. WARMING AND LIGHTING 237 and economy of fuel and utilization of heat may be procured at the expense of healthiness. The ventilating stoves which introduce a supply of fresh warmed air are decidedly more healthy ; but there are certain disadvantages which require consideration in the use of stoves of all kinds. In the first place, they are apt to render the air of a room too dry, and therefore unpleasant to the nose, eyes, and skin. There may be the same amount of moisture in a cubic foot of heated air as in a similar bulk of cold air before it is warmed ; but the relative humidity of the air when heated would be greatly diminished, as hot air is capable of holding more moisture, before saturation is reached, than cold air ; and it is upon relative humidity that health and comfort depend. This drawback may, to a certain extent, be overcome by placing vessels of water in the room or on the stove. Secondly, if the stove becomes overheated, the organic matters in the air become charred by contact with the heated surface, and a disagreeable close smell is perceived. Lastly, the presence of carbonic oxide has been detected in the air of stove-heated rooms, more especially when the stove is of cast iron. Either this gas passes out of the furnace through invisible fissures in the cast iron, or it traverses the walls of the stove when at a red heat. Others suppose that the gas may be formed by incomplete combustion of particles of carbon or organic matter floating in the air, when brought into contact with the hot metal. Cast-iron stoves are very liable to become overheated, as, being good conductors, they rapidly heat and cool. In such stoves, therefore, the heating surface should be increased by ver- tical flanges projecting from the top and sides, by which means the heat, being conveyed to a larger surface, is less intense, be- cause cooling is more rapid. It is safer not to use cast-iron stoves at all, unless lined inside with fireclay ; this, being a good non-conductor, prevents the over rapid heating of the iron walls, and the warming of the room is altogether more equable. There are many ornamental stoves now made entirely of fireclay and china, with arrangements for the supply of warmed fresh air at an agreeable temperature of about 65 ° to 70 F. They are especially valuable for heating halls and public buildings. Digitized by Microsoft® 238 HYGIENE AND PUBLIC HEALTH No ill effects appear to follow upon the use of oil stoves in living rooms, if the combustion of the oil is complete and there is efficient air renewal in the room, despite the general absence of flues to convey away the products of combustion. Steam pipes are largely used for heating factories and work- shops and public buildings where steam power and waste steam are at hand. Two kinds of hot water pipes for heating purposes are in use. In the low pressure system, 2 or 3 inch cast-iron pipes are con- nected with a boiler so as to provide a complete circulation. The water is heated in the boiler, circulates through the pipes, parting with some of its heat to the air in contact with them, and on cooling returns again to the boiler, the circulation being due to the difference between the specific gravities of the water in the flow and return pipes. From the highest part of the system, a small escape pipe, to give vent to steam and hot air, must be carried into the outer air. The water circulating in such a system never acquires a temperature exceeding 200 ° F. or thereabouts. In the high pressure system (Perkins') the pipes are of welded iron with thick walls and J-inch internal diameter. A coil of the pipe, of about one-sixth of the total length, passes through the furnace, no boiler being required. The expansion of the water is provided for by a small cistern fitted with a weighted valve, or by a larger pipe, capable of holding from 10 to 15 per cent, of the water, fixed at the highest point in the system. The water, being under pressure, can be heated to 300° or 350 F. It is estimated that 12 feet of low pressure piping is equivalent for heating purposes to 8 or 9 feet of the high pressure piping. Heat radiators heated by steam, hot water, or even electricity, are also used for warming purposes. Ventilating heat radiators are now being made. They are fixed against an outer wall, so that fresh air can be conducted into the base of the radiator, and thence pass over the heating surface to escape into the room through a grating at the top of the radiator. By means of a valve, the communication with the outer air can be closed if desired. Electric radiators possess the advantages of yielding no products of combustion, and the heat is available immedi- ately the current is turned on. Soft water is far preferable to hard water for use in boilers and hot water pipes. WM^MpoMipnai^B^e salts from hard water WARMING AND LIGHTING 239 gradually narrows the calibre of the pipes, which in time may become completely blocked. In boilers, the deposit forms a non-conducting lining, which obstructs the passage of heat to the water. When the fur lining is thick it may lead to an explosion, for the iron boiler plates become red hot from the heat of the fire. Should a crack in the fur suddenly form, the water, coming in contact with the red hot metal, is converted into steam with explosive violence. Another cause of explosion in kitchen boilers which are^not connected with a hot water cistern, or are unprovided with*' a steam escape pipe, is the blocking of the pipe which supplies cold water to the boiler. This occasionally happens after a hard frost, if the pipe is unprotected. Lighting. The illumination of a room is a matter greatly affecting the comfort and, indirectly, the health of the occupants, and is of especial importance to eyesight in the case of factories, work- shops and schools, where the eyes are concentrated on small objects for many hours at a time. Artificial Lighting. The most commonly employed method of obtaining an artificial illumination is the combustion of inflammable material pro- ducing a flame. Coal gas, petroleum and colza oils, and candles, are well known examples of this form of illumination. In the electric light, on the other hand, there is no combustion, or only to a trifling extent ; but light is emitted from a substance raised to a high temperature and a state of incandescence by the passage through it of an electric current. The inflammable gases and vapours are chiefly compounds of carbon and hydrogen. When these inflammable vapours are heated to a sufficient temperature, the hydrogen combines with oxygen to form water vapour, and an intensely hot flame with- out luminosity is produced ; the carbon particles, which are liberated in a state of very fine subdivision, are rendered incan- descent by the heat of the hydrogen flame, and they combine with oxygen to form C0 2 and traces of CO. The luminosity, which is situated in the outer portion of the flame, is due to the incandescent carbon, whilst the inner portion — the hydrogen flame— is very hot, M z i1M cr n1?Muminous. The products 240 HYGIENE AND PUBLIC HEALTH of combustion are chiefly water vapour and carbonic acid. The light is very deficient in the blue and violet rays of the solar spectrum, and has therefore a yellow or orange colour. Hence the true colours of objects illuminated by a flame are not perceptible. Coal Gas. — The principal illuminant of coal gas is heavy carburetted hydrogen or olefiant gas (C 2 HJ. There are also present other hydro-carbons — i.e., benzene, propylene, naphtha- lene — which are illuminants. The heavy hydro-carbons, if burned by themselves, would yield a smoky flame ; but these are suitably diluted in coal gas by hydrogen, marsh gas or methane, and carbonic oxide, which together form some 90 per cent, of the coal gas. When the gas is burnt, the hydrogen or hydro- carbons are almost destroyed, and the products are approxi- mately : Nitrogen, 67 per cent. ; water, 16 per cent. : carbonic acid, 7 per cent. ; carbon monoxide, variable (traces), and traces of sulphurous acid and ammonia. Coal gas illumination was a great advance on the candle illumination of a former period, but it has certain drawbacks. There is the danger of escape of gas in the houses from mains and pipes, forming, if the escape is large, explosive mixtures with the oxygen of the air ; or if small, causing a serious pollu- tion of the atmosphere. The products of combustion are injurious to health, and the sulphurous acid from the sulphur compounds in coal gas is destructive to books, furniture, and pictures. The combustion also heats the air and dries it ; for although watery vapour is one of the products, the relative humidity of the air at the higher temperature is lowered. Finally, when the supply of gas and air is not regulated during combustion, the gas is wasted, the light is lessened, and un- consumed particles of carbon are given off which deposit as soot on adjacent cold surfaces. The burners in common use are : (1) The fish tail or union jet, which has a flat steatite top, slightly depressed in the centre, through which two small holes are bored in directions inclining towards one another from below upwards. The two streams of gas meet and produce the flat flame usually seen. (2) The batwing has a hemispherical steatite top, through which a vertical slit is cut for the gas to issue. The flame is flat and semicir- cular. The flames from these two burners require no chimneys, but are usually enclos3&'Wg&fW°f8 fi foften the light. (3) The warming And Lighting 241 Argand burner is a small ring or double-walled cylinder, pierced at the top with fine holes lor the issue of the gas. The flame thus forms a hollow cylinder, and the air has free access both to its interior and exterior. The flame must be enclosed in a chimney, in order that the supply of air to it may be regulated. The Argand burner has been improved by Silber, Sugg, and other manufacturers. These improvements are directed, first, to cause the issue of the gas at the lowest possible velocity, and, secondly, to divide and regulate the air supply both to the outside and inside of the flame, and to direct a part of it to the higher portions of the flame, where perfect oxidation of the carbon is most required. These improved Argands give a far better and steadier light for the same consumption of gas than the flat flame burners. There are several ventilating burners in which the products of combustion of the flame are conducted through a flue to the external air, the heated and vitiated air from the top of the room or hall being also removed by ducts surrounding the flue. The sunlight burners used in theatres, and the globe light are examples of these. The Welsbach incandescent gas burner now has a very ex- tended use. It consists of a Bunsen burner, with a cap (mantle) of asbestos gauze material (rendered non-inflammable by chemical treatment with sulphate of zirconium) suspended in the non- luminous flame ; the gauze mantle becomes incandescent and gives a brilliant light, far whiter and steadier than the ordinary gas flame. The flame should be enclosed in a chimney. The illuminating power is very high for the amount of gas consumed, and the heat given off is far less than with an ordinary gas flame. If such burners came into general use, a cheap form of gas containing no illuminants could be supplied ; for heat and not light is required in the flame. The cheap gas would also lead to a more general adoption of gas-heating and gas-cooking, and thus to the partial solution of the smoke question. The Welsbach incandescent gas burner is, hygienically, by far the best form of lighting by coal gas. In the albo-carbon light, the vapour of naphthalene is burnt in the coal gas, and a brilliant white light is produced. The naphthalene, which is solid at ordinary temperatures, is placed in a reservoir connected with the gas burner, and this reservoir must be heated by a smM^gas^efcOis&^strips of metal extending 242 HYGIENE AND PUBLIC HEALTH from the flame. The vapour of naphthalene must not be allowed to escape into the air, as its odour is most offensive. One cause of waste and imperfect combustion with flat flame burners is the constant alterations of pressure in the gas pipes and mains. At one period of the day the pressure may be less than one inch of water, whilst at another it may be 3 inches or more. Consequently the flat flame, which is steadily burning under the low pressure, at the high pressure is flaring and singing ; more gas is issuing from the burner than can be perfectly burnt, and unconsumed carbon is given off from the flame to pollute the air and blacken everything around. To control these varia- tions in pressure, gas governors or regulators are employed. In the larger form, the governor is fixed close to the meter, and controls the pressure throughout the house pipes ; whilst a small form is made as part of each individual burner. The best kind of governor acts automatically ; by the action of valves an increased pressure narrows the lumen of the channel through which gas passes, and a diminished pressure widens it. Single burner governors are also found to answer fairly well. Acetylene gas (C 2 H 2 ), generated by the action of carbide of calcium on water (CaC 2 -|-H 2 = CaO +C 2 H 2 ), furnishes a powerful white light ; but its use is not unattended with danger, unless great care is exercised. Petroleum Oils. — By the distillation of crude petroleum oil an oil suitable for burning in lamps — commonly called crystal oil or kerosene — is obtained. In the distillation, a volatile spirit (benzoline) and heavy oils, some of which are solid from containing paraffin, are also obtained, and are separated from the lamp oil. Lamp oil contains the hydro-carbons previously mentioned, and gives off an inflammable vapour which at a certain temper- ature takes fire. This temperature varies for different specimens of oil, and is called the " flashing point." A select Committee appointed by Parliament attributed the chief danger from lamp explosions to cheap lamps of de- fective design, and they recommended that the flash point (Abel close test) should be raised from 73 F. (the limit defined by the Petroleum Act, 1879) to ioo° F. ; that statutory powers should be created to enable the Secretary of State to issue orders affecting the manufacflSS^StfAr ¥a?£ s eff®lamps ; and that infor- WARMING AND LIGHTING 243 mation should be spread among the public as to the nature of petroleum and the management of lamps. In the suggestions issued by the London County Council, it is pointed out that the flashing point of ordinary petroleum oil is a little above 73° F., that the oil in the reservoirs of lamps is rarely heated above 100° F., and that the best safeguard against accident is therefore never to burn oil which has a flashing point of less than 100° F., which oil should be sold as cheaply as low flash oil. Lamps, too, should be strongly made, and kept thoroughly clean ; especially should the reservoir and burner be strong ; the latter should screw into the collar, and the base of the lamp should be broad and heavy. The wick should be soft, and should reach to the bottom of the reservoir, and just fill the wick tube ; it should be frequently renewed, and before being put into a lamp it should be dried at a fire, and immediately soaked with oil. The reservoir should be filled with oil before the lamp is lit, and the burner made clean before lighting ; the wick when lit should be partially turned down, and then gradually raised ; the wick should not, however, be left turned down ; lamps that have no extinguishing apparatus should be put out by turning down the wick until there is only a small flickering flame, and a flat piece of metal should then be placed on the top of the chimney, so as to close it entirely ; finally, cans or bottles used for oil should be free from water and dirt, and kept closed. Owing to improvements in lamps, and to the prohibition of the sale of highly inflammable oils, the danger of explosion is now slight. Lamp explosions may occur when, from any cause, the vapour over the oil in the reservoir comes in contact with the flame of the lamp, as through defects in the lamp or by blowing down the chimney past an ill-fitting wick, etc. But the best duplex lamps (the Defries and other safety lamps) are now sold with extinguishers, and with an ingenious arrange- ment by which, if the lamp is overturned, the flame is immedi- ately extinguished. Lamp accidents generally appear to arise from the use of cheap lamps of defective design, leading to a leakage of oil through imperfect connections and fittings. The oil may thus become ignited. Sometimes the lamp is upset from its instability, or broken owing to the fragile character of the reservoirs. The " Petrolite " lafl^?S d l^ie~°ESn?b of high candle-power. 244 HYGIENE AND PUBLIC HEALTH In this lamp the petrol is absorbed by a block of highly ab- sorbent stone, and the petrol vapour, being made to mix with air, furnishes a hot flame, which, playing upon a mantle, produces a brilliant incandescent light. In the event of the lamp being upset the flame is immediately extinguished. The Kitson light has been used successfully for the pur- pose of public street lighting. This light is obtained by the automatic vaporization of petroleum oil, the mixture of air with this oil by injection, and the impingement of the flame upon a specially made mantle. The diffusive power of this light exceeds both the electric arc light and the in- candescent gaslight, it is cheaper than either, and the roads, have not to be taken up — as when electric light or gaslight are employed. Colza oil does not give off any inflammable vapour, but it is much dearer than kerosene, and the illuminating power is less. Colza oil lamps require more care in trimming than kerosene lamps. Kerosene, like coal gas, gives off sulphurous acid when burned, but colza oil does not. Candles, especially the cheaper kinds, give off much uncon- sumed carbon, by reason of their low melting point admitting of volatile products being given off before the fats reach the flame and are properly consumed. Electric Light. — The electric light presents the following advantages over coal gas, oil, and candles. There is no con- sumption of oxygen, there are no products of combustion to pollute the air, and the heat produced is relatively slight. The light of the arc light is not yellow, but white. It precisely resembles solar light in being rich in the violet and the ultra- violet rays. Plants grow and flower, and fruit ripens, when exposed to this light, just as they do in the sunlight ; whilst photographs can be taken as easily by the arc electric light as by daylight. The electric current can be produced by batteries, accumu- lators and dynamo machines, and is conveyed in copper wires to the spots where illumination is required. In the arc light, which is suitable for lighting streets, squares, and large halls and buildings, the illumination is produced by the passage of the current through two carbon tods brought into close apposition.O'Sf^MsTgfft^ offered to the passage of the current across the space intervening between the points WARMING AND LIGHTING 245 of the carbon rods creates sufficient heat to cause the carbon points to become brilliantly incandescent. The light is ex- tremely dazzling, and is productive of injurious effects on the eyes of those who are much exposed to its influence. The incandescent lamps are best suited for domestic use. In these the current is passed through a loop of filamentous carbon enclosed in a small glass globe exhausted of air, or filled with some gas (such as nitrogen) which does not support com- bustion. The resistance offered by the carbon to the passage of the current raises it to a white heat. The extent to which different modes of lighting affect the atmosphere may be thus represented : — Amount Candle Oxygen CO2 pro- Heat calories pioduced. consumed. power. removed. duced. Tallow candles 2,200 grs. 16 107 C ft. 7-3 1,400 Sperm candles 1,740 ,, 16 9-6 „ 6-s 1. 137 Paraffin oil lamp 992 „ 16 6-2 ,, 4-5 1,030 Kerosene oil lamp 9°9 ,. 16 5-9 „ 4-1 1,030 Coal gas, No. 5 bat- wing burner 5-5 eft. 16 6-5 „ 2-8 1,194 Electric incandescent — 16 o-o ,, o-o 37 Digitized by Microsoft® CHAPTER V SCHOOL HYGIENE Notes upon the School Premises. In selecting the site for a school, regard should be paid to a central position and the facilities of access by the scholars. A noisy site is very undesirable, and if a quiet site cannot be obtained the building should be set back at least 60 feet from the street. In planning a school building the schoolrooms must be the prime consideration ; the building should be a number of school- rooms properly disposed, and not a whole cut up into school- rooms, whose size and arrangement are dependent upon the size and shape of the building (E. R. Shaw). If possible the rule should be observed that lines drawn from the bottom of the walls of the building to the tops of the nearest adjacent buildings should not make a greater angle than 30 with the horizon. It is desirable that the building should not exceed two stories in height, and the main corridors or halls should be at least 10 feet in width and well lighted. The best shape for a schoolroom is an oblong, with the windows in one of the longer sides only. A suitable size is 30 feet long, 25 feet broad, and 13 feet high ; such a room would seat 48 pupils. There should be no windows on the opposite side, for cross lights are better avoided, although some authorities think a cross light is not a drawback if it does not overpower the light admitted on the left of the scholar. The area of the windows, clear of sash frames, should be from one-fourth to one-sixth of the floor space of the room. The windows should reach as high as the ceiling of the room, and open directly into the ex- ternal air, and the intervals between them should be as small as possible. The minimum light for each desk should be 50 candle metres (i.e., i^JS^^MI^S^ h ? $° stan dard candles at one metre distance). Double windows economize heat, SCHOOL HYGIENE 247 keep out noise, and may be made to help ventilation. The height of the sills from the floor should never be less than 4 feet. The defective lighting in schoolrooms is one of the chief causes of short sight. The child, not being able to read its book when placed at the proper distance (at least 12 inches) from its face, stoops over the desk to lessen the distance ; the eyes converge when brought too near the object, and the mus- cular strain thus induced leads to a gradual elongation of the antero-posterior axis of the eyeball, with the production of myopia; i.e., the image of the object seen forms in front of the retina, unless the object itself is very close to the eyes, and is blurred and indistinct. Imperfect lighting leads to the use of artificial light, with its attendant vitiation of the atmosphere. Daylight reflectors sometimes serve to reduce the evil. Seats and Desks should be arranged parallel with one another, but at right angles with the windows ; and wherever possible the desks should be placed in the space intermediate between two windows. To avoid shadows when writing, the scholars should sit with the left hand nearest the windows, so that the illumination of books and lessons may be from the left front. There is then plenty of light on the objects on the desk, but the rays are not reflected directly into the eyes of the scholars, as they are in front illumination with desks facing the windows. If the predominant light comes from the scholar's right, then the shadow of his hand, while writing, falls upon the paper. Desks should be from 15 to 18 inches broad, and should slope at an angle of about 15° for writing and 45 for reading. Height of seat from ground should equal length of scholar's legs from sole of foot to knee. Distance of front of seat from a perpendicular line let fall from edge of desk should not exceed one inch. Perpendicular distance of seat from edge of desk should be one-sixth of scholar's height. Front to back measurement of seat should be two-thirds of upper leg. Seats and desks should be adjusted to the scholars twice yearly. The heights of scholars of the same age often vary as much as 10 inches. Girls grow most between 12 and 14 ; boys, between 14 and 16. Straight back to seat, with a curved pad or cushion to fit into and support the small of back and loins to the level of $| /f/ §h£u^£ r ^^s. Space, on a common seat, for each pupil, should equal 20 to 24 inches ; there should 248 HYGIENE AND PUBLIC HEALTH be 10 inches between the rows of seats, and the rows should not extend to within 24 inches of the wall. From each seat one should be able to see the sky. There should be a small raised platform for the teacher. For young children the lesson hours should be broken by frequent short intervals for play, and the proper ventilation, warming, and artificial lighting of the room demand every atten- tion. Every classroom should have a thermometer, placed away from fire, etc., and at breathing level. The thermometer should be read frequently, and the temperature should always register from 55°-65°. The rooms should be warmed before scholars enter. The warming must not be at the expense of fresh air (stuffiness is more harmful than draughts) . * Except in very small class-rooms fires must be supplemented by some other heating agency. Hot water pipes should always be made to assist ventilation. All stoves should be ventilating-stoves and should be provided with chimneys. The warming of corridors and lobbies is of great importance. Some system of artificial ventilation with a supply of warmed fresh air is especially necessary for schoolrooms where the amount of cubic space per head is often very limited. The English Educa- tion Department requirements are only 100 cubic feet of space per scholar, and 10 square feet of floor space. These are the minimum requirements ; but even with double these amounts, adequate ventilation by natural means in cold weather would be productive of draught and great lowering of tempeature in the room. Dr. Newsholme is of opinion that good average requirements for schools are, for each scholar, 150 cubic feet of space, 15 square feet of floor space and 1,500 to 1,800 cubic feet of fresh air per hour. The walls of a schoolroom should preferably be painted or tiled, so that they can be washed, and any colouring should be pale and subdued (a soft greenish-grey is recommended) ; un- necessary projections (cornices, etc.) which can harbour dust should be avoided. The best floors are made of hard wood in narrow planks, with dovetailed or matched joints ; these may be beeswaxed and polished at intervals, and should always be swept daily. All staircases should be at least 5 feet wide and fireproof and , j , , , j digitized by Microsoft®. . r ' faced at the ground floor hy'a wide door, opening outwards SCHOOL HYGIENE 249 towards the street. The cloakrooms must be capacious, specially heated and ventilated, and the numbered pegs for hanging clothes should be at intervals of at least 12 inches to allow of the clothes hanging without touching each other. If pegs are arranged on both sides of a stand, a thin partition should be provided, so as to keep the articles on the two sides from touching. It is desirable to have a separate cloakroom for each class-room. Covered sheds should be provided for recreation when it rains ; and if space is unprocurable on the adjoining ground, a basement or a flat roof may be designed to meet the purposes of a covered playground. It is essential that the scholars should receive plenty of physical drill and exercise in the open air. The school hours should not be unduly prolonged, and in all intervals of work the rooms should be thoroughly flushed with air. Under a proper system of medical inspection, com- mencing physical defects can be promptly detected and remedied by appropriate exercises. No home work should be required before the tenth year of age. Urinal accommodation to the extent of at least five places for every 100 children should be provided, and at least one water-closet seat for every fifteen girls or twenty-five boys. One of the modern types of trough water-closet or latrine {vide page 93) is sometimes used for schools, but the flushing provision must be adequate and systematically regulated. Many author- ities now prefer separate closets for use in schools. All dormitories must be well lighted and ventilated, and at least 400 to 500 cubic feet of space should be allowed for each scholar under 12 years of age {see p. 211). The drinking cups used in common by most scholars may be a means of communicating disease, such as diphtheria. Many cups should, therefore, be supplied in the place of the one or two only which are generally provided. Arrangements should also be made so that the cups, after use, are continually exposed to flowing water during play hours ; and the cups should be well cleansed with wet sand at least twice a week. In the " Crystal Stream " drinking fountain no cups are necessary, the scholars directly taking the water as it issues in weak upward jets from the fountain. * The school premises^u^^v^gie best possible hygienic environment for the scholars, and should present an object- 250 HYGIENE AND PUBLIC HEALTH lesson of cleanliness, brightness, good taste, and of scrupulous regard for all sanitary demands. The teacher is not concerned with such matters as the selection of site and the planning and construction of premises, but can always secure the best sanitary circumstances under the existing conditions, and often an improvement in respect of matters of hygienic importance. School Cleaning. Dust and dirt are dangerous to health. They are only removable by damp cleaning, and when collected should be burnt or removed at once. Dirt should be reduced to a minimum — clean boots, clean scholars, clean clothes ; chalk-troughs to blackboards. All dirt-harbouring arrangements in classrooms should be reduced to a minimum, viz., cupboards, shelves, projections (cornices, etc.), platforms, hangings. All decorations on walls should be easily cleanable — floors and walls washable. Daily Cleansing. — The most important. At end of school-day doors and windows should be opened and floors swept with damp broom, or after application of wet sawdust — cloak-rooms, corridors, etc., included. Weekly Cleaning. — On Saturdays all horizontal surfaces scrubbed with soap and water and windows cleaned if necessary ; ventilators dusted. All accessible woodwork on walls should be scrubbed once a month. Vacation Cleaning. — Thorough scrubbing of all horizontal surfaces. Walls washed and the insides of desks, lockers, cupboards, etc. Slates washed ; books dusted. AH waste-matters upon school premises should be burnt when possible ; and failing this, promptly deposited in covered, movable, metal dust- bins, placed out of reach of scholars. Disinfection oj School Premises — Generally by the Sanitary authority, or under their directions. For disinfecting purposes, solutions of izal or cyllin, one tablespoonful to a pint of water ; Calvert's No. 5 Carbolic, two tablespoonful to a pint of water, may be used. All horizontal surfaces (floors, seats, desks, etc.) to be also scrubbed with hot water (with a little soda) and soap. Notes upon the Scholar. The Nervous System contains the machine of the Mind ; it receives and interprets various sense-impressions, regulates all the vital functions of the body, and controls or commands the muscular system. It should be the cardinal study and concern of the teacher. Wrong or slovenly acts, at first under conscious control, may in time develop into sub-conscious or unconscious habits. Hence the necessity for a careful attention to the formation of good habits of thought and of action, and for the correction of bad habits or tendencies. Even in health, children differ greatly ; and in mental education the special needs of the individual must be studied. Permanent injury results from premature or excessive stimulation of the brain faculties, by impairing the whole nervous system, and the general health and development of the brain and body suffer as £>igHr88$bprMterfl9&ft§> therefore opposed to all the objects of education. SCHOOL HYGIENE The Symptoms of Brain Fatigue and " Over-pressure ' 251 (a) Normal and Transient. — Yawning, lassitude, wandering eyes and inattention, drowsiness, fidgetiness, slow or faulty response to words of command and questions, head balance impaired, little or purposeless movement. (b) Continued and Abnormal (over-pressure). — Nerve-signs : — Irregular muscular movements — chiefly of fingers, eyes and mouth ; knitting of eyebrows and overaction of frontal muscles ; defective muscular balance of the body (especially of the head) ; the abnormal position of the hand when held out in front at word of command ; stuttering ; restlessness and frequent twisting of body and neck. Impairment of the delicacy of touch perception. Irritability, grumbling, and excessive sensitiveness to reproof. Facial expression of exhaustion or anxiety ; open mouth ; lower eyelid baggy and relaxed. Langour, listlessness, headache, speedy fatigue, dulness or apparent stupidity ; slow or inaccurate response to questions or commands ; excessive drowsiness or wakefulness ; night terrors ; walk- ing in sleep ; poor bodily development and impaired health (pallor, failure of appetite, poor digestion, feeble circulation, etc.). A predisposing factor to chorea, hysteria and epilepsy. Apparent Dulness may be due to defects of hearing or vision ; poor nutrition or injudicious teaching ; illness; bad air ; insufficient recreation and sleep (child-labour). Mentally Defective children make poor progress in studies and show unusual peculiarities of temperament and of moral perception. Chorea (St. Vitus's Dance). — Occurs chiefly in girls between 7 and 14. Onset gradual. Constant twitchings of body, face, limbs or hands. Things are dropped because of impaired control and power of muscles. Child generally below normal weight. Hysteria. — Especially in emotional girls at age of puberty. Emotional outbursts ; morbid sensations (ball in throat, etc. ) ; paralytic symptoms, etc. Fits are of gradual onset, with sobs, laughter or other emotional display, then with a scream the girl falls violently convulsed and apparently insensible ; she rarely injures herself and never bites the tongue. Epilepsy. — Momentary palsy of face, then sudden unconsciousness, stiffening of body, biting of tongue, hands clenched, and convulsive move- ments of limbs and muscles of face (face distorted and blue from congestion). Fit followed by drowsiness. Scholars especially liable to suffer from over-pressure. — Delicate nervous children (apt to be irritable, passionate and emotional) ; constitutionally weak children ; anaemic, badly fed, rapidly growing, excit- able and mentally precocious children ; those exposed to bad air or bad conditions of study ; bad teaching and unhealthy home conditions ; too little sleep and recreation ; defects of sight, hearing, etc. ; excessive strain of vision, etc. ; the period of puberty. The Prevention of Brain Fatigue. A Hygienic Time Table of prime importance — one which economizes the brain energy and directs it aright : — Short lessons, but length varying with the subject ; a proper sequence and variation of subjects ; proper regard to stage of development of the scholars and the immaturity and instability of the nervous^gsiern. K,%S~S^StW eals OI school life ; sufficient intervals for rest, recreation, physical exercise and food. 252 HYGIENE AND PUBLIC HEALTH Fresh air ; quiet class-rooms ; strict limitation of the subjects selected for, and the duration of, home lessons. An observant teacher will see first signs before exhaustion results, and will discover when imperfections of vision and hearing are causing strain and brain fatigue. The physiological needs for adequate rest and recreation and good physical training must not be ignored. These reduce the number of cases with signs of brain disorderliness and the number of dull children. Sleep. — The importance of quality and quantity as affecting the working capacity of the brain. The quantity of sleep which is desirable during school ages is as follows : — Years of Age. Hours of Sleep. 4-8 12. 9-12 ri. 12-14 9-10. 14-21 9. The quality of the sleep is also important, and a well- ventilated room (open windows), absolute quiet, darkness, and a warm bed, favour sound and refreshing sleep. Vision. — The rays of light stimulate the sensitive nerve-endings (retina) on the back of the eye, and these visual impulses are carried by the two optic nerves to the brain, and conscious vision results. If anything prevents the eye from properly focussing a clear image of external objects upon these nerve-endings (retina) ; then vision is defective. Distant vision is rest to the eye, near vision is exertion. In children the eye is relatively short from before backwards, and the child has to compensate for this by muscular effort, which involves eye- fatigue and nervous strain ; moreover, the still developing nerves of the retina are easily tired. In early life the eyes are soft and plastic, and readily yield to conditions favouring defective vision. The eyesight of at least 20 per cent, of scholars is defective, and in 10 per cent, it is seriously defective. Affections of vision are, therefore, among the most common hindrances to school work. Causes of Eye-strain. — Too continuous eye-work, and a bad time-table ; fine and indistinct work, and work brought too near the eyes ; bad or faulty lighting of room; bad posture in reading and writing. Predis- posing causes are foul air and over-heated room, debility and poor nutrition of scholar. N.B. — The printing, etc., of school books is of great importance. " Double pica" f ° r kfe*s, ^ «■ pica leaded " for other school children. The lighting arrangements in school class-rooms are very important. Symptoms of 'Defective Vision. — Headache, generally frontal.worse at night and relieved by sleep ; a sense of fulness in head ; redness of eyeballs and eyelids ; watering of eyes ; blinking ; partial closing of eyes when looking at distant objects ; frequent rubbing of eyes ; heat and pain in eyes ; dizziness and sometimes nausea or even vomiting ; squint ; irritability, neuralgia, and impaired general health ; books held within twelve inches of the eyes ; confusion of letters — especially h and b, e and c ; inattention and apparent stupidity. Defects 'of Vision. Short-sight (myopia). — ^g^ e b^fi r /&/ ( SJ^fe(^ ears of a § e > and increases greatly as we pass from lower to higher grades at school ; hence an illustra- SCHOOL HYGIENE 253 tion of the injurious effect of school-life upon the scholars' eyesight. This condition is due to the " long eye ' ' with the too distant retina ; and hence concave lenses are needed. Most liable to develop in delicate children with poor muscular and nervous tone, and especially when parents myopic. Bad posture during reading and writing may cause myopia, and myopia may cause bad posture. Long-sight (hypermetropia).— This condition is due to the " short eye " with the too near retina ; and hence convex lenses are needed. Astigmatism.— Blurred images and indistinct vision at any distance, due to eyeball being irregularly shaped. Squint.— Generally due to the focussing power of the two eyes being unequal. Glasses do not weaken the eyes, but strengthen them ; they conserve the sight ; prevent headache, etc. ; and prevent squints— or may even cure them. Colour-blindness. — Most colour-blind people cannot tell red from green, and call them shades of the same colour. Ophthalmia and Conjunctivitis. — Redness of eyes, crusts on margins of lids with loss of eyelashes ; extreme sensitiveness to light ; excessive watering of eyes ; formation and discharge of yellow matter. Hearing. — Generally from 12 to 20 per cent, of scholars are defective in their hearing. Signs of Defective Hearing and Ear Disease. — Inattention and apparent stupidity ; early exhaustion from lessons ; mouth-breathing ; earache ; headache ; discharges from ears ; giddiness ; impaired general health. Causes of Defective Hearing. — Adenoids ; inflammation or abscess in the middle ear from inflammation or disease of nose or throat ; wax in ears. N.B. — Early attention to defects of sight and hearing will either lead to a cure or will prevent matters going from bad to worse, and thus save the scholars from grave educational losses and disabilities in after-life. The Bones and Muscles. — Posture. — Physical Exercise. The muscles contain in their substance about one quarter of the blood of the whole body ; their action promotes the circulation of the blood, and hence plays an important part in promoting the general nutrition. During muscular exercise the force and frequency of the heart's action are increased ; the respirations are more frequent and deep ; and the func- tional activity of the organs of digestion and excretion (skin, kidneys and bowels) is increased. Since the functional activity of the tissues and organs of the body is the source of body heat, the muscles are the chief producers of this heat. The development of the nervous and muscular systems are inter-dependent, and both are promoted by muscular activity. Hence muscular exercise promotes an active circulation of the blood generally throughout the body ; develops the muscles and improves the carriage and symmetry of the body ;. trains, through the nervous system, the action of the muscles and the "muscular sense"; promotes the symmetrical development of the brain, healthy and vigorous brain power ; and generally improves body nutrition and maintains the body functions in health. Furthermore, physical exercises at school counteract the harmful tendencies of bad postur$'a£gc£cfefejdMe''fM'6P ; i < 3®%=86-9 grains only. 276 HYGIENE AND PUBLIC HEALTH Although the weight of oxygen in a cubic foot of air is decreased at high altitudes, the oxygenation of the blood is increased, for the respirations are more frequent and have greater depth ; and after a period of residence the capacity of the chest is found to be increased in all its measurements, together with increased power of expansion and contraction. The action of the heart is also increased, and tissue change is stimulated by the low tem- perature and the dryness of the air, leading to improved digestion, assimilation and excretion, with increased bodily activity. These effects of residence at a high altitude, together with the freedom of the air from dust and germs, and its impregnation with ozone, have led to the treatment of cases of phthisis at mountain resorts, with often the most beneficial results. The cases most benefited are those in an early stage without much congestion or bronchitis, which might be aggravated by the cold dry air. It is advisable that spots should be chosen which are sheltered from cold winds ; and those popular resorts, where many phthisical persons are crowded together in hotels and boarding houses without proper precautions being taken, should be avoided. As much time as possible should be spent in the open air. A mountainous district in proximity to the sea is liable to ex- cessive rainfall. The moist currents of air blowing in from the sea are chilled by striking against the mountain chain ; clouds are formed, and some of the moisture, no longer able to be held as invisible vapour at the lower temperature, is deposited as rain, snow, or sleet, according to the temperature and season of the year. If the mountains are in the centre of a continent far removed from the sea, the rainfall may not be great. The excess of moisture in the ocean currents will already have been deposited before reaching the hills ; and in these situations a mountain climate without the drawback of excessive rainfall may be obtained, suitable for the requirements of consumptives and invalids. The westerly winds which blow over the Rocky Mountains deposit most of their moisture on the western sides of the range, and on the eastern slopes the climate is comparatively dry and cold. Increased pressure of the atmosphere produces effects very much of an opposite nature to those just considered. It is found, however, thatD/gaft e 83^*fl»o^B®kly accustoms itself to increased atmospheric pressure, and that men can work vigor- CLIMATE AND METEOROLOGY 277 ously in diving bells, in the compressed air chambers necessary to lay the foundations of bridges and aqueducts under water, and in the very deepest mines. The painful effects of exposure to high atmospheric pressure are generally referred to as " caisson disease." A caisson is a cylinder of iron plates rivetted together, which is sunk on the bed of a river so as to form a shaft. Into this, when closed at the top, air is pumped under sufficient pressure to force the water out of the lower part of the shaft, and to keep it our while men excavate the bed of the river, for the purpose of obtain- ing a suitable foundation for the piers of bridges. There is at the top part- of the cylinder, near to the closing diaphragm, a chamber or " air lock," in which the pressure of the air can be gradually increased or diminished. By this means the men, before entering the compressed air in the shaft, are subjected to a pressure which is gradually increased, until it equals that within the shaft. Similarly, on leaving the shaft the men are gradually " decompressed " in this lock before emerging into the outside air. The workers are liable to suffer from the altered conditions of atmospheric pressure to which they are daily subjected, and they are affected far more by the consequences of decompression and returning to the outside air, than from compression and continu- ance of exposure to the high pressure in the caisson. The leading symptoms of caisson disease are : (i) Unpleasant sensations or severe pains in the ears, doubtless the result of the tympanum being driven in by the compressed air. The drum of the ear is said to have been even ruptured, and sometimes deafness results. These ear symptoms are materially aggravated if the person happens to be suffering from a cold in the head or sore throat, when pain in the forehead is often marked. (2) Neuralgic pains. (3) A feeling of giddiness, with a tendency to fall. (4) Loss of power in the legs, amounting at times to par- alysis. (5) Slight to severe pains in legs, arms, and shoulders. (6) Epistaxis. (7) Itching of skin. (8) Haemoptysis. (9) Epi- gastric pain, and sometimes nausea and vomiting. (10) Occasion- ally unconsciousness. There is, of course, a physiological rise in the blood pressure. Three theories have been adduced to explain compressed air illness. It has been held to be due to C0 2 poisoning ; to the mechanical congestio# / ^ e iW 3 6eM*afl >s eft|ans ; and to increased 273 HYGIENE AND PUBLIC HEALTH solution by the blood of the gases in the compressed air, and the liberation of these gases (probably forming gas emboli) during decompression. The last theory is most generally accepted. If the first were correct, the illness should occur while the men are in the caisson, and not after they emerge from it. In support of the second theory, it may be said that in several necropsies the membranes of the brain, etc., have been found deeply congested. The symptons mostly yield to recompression, followed by slow decompression lasting some forty-five minutes. The favouring causes are : Too long stay in the compressed air ; insufficient ventilation of the compressed air space — the amount of illness varies inversely with the extent of the provision for ventilation (Snell ) ; too rapid decompression ; fulness of habit ; advancing age ; over-indulgence in alcohol ; and organic disease. New hands suffer more than the old. The preventive measures to be adopted include : Working during short shifts — if the pressure exceeds 35 pounds, the shifts should probably not exceed four hours, and if the pressure reaches 50 pounds, two hours ; an abundant supply of fresh air ; electric lighting to be employed, so as to insure the continued purity of the air ; the rate of decompression certainly not to exceed one minute to every 3 pounds of pressure ; the systematic examination of all hands, and the selection of those who are physically sound ; advice to be given as to how to inflate the middle ear by swallow- ing air when uneasiness first appears, as to the importance of rest for a short period after leaving the compressed air, and as to the necessity for extreme temperance with alcohol. It is desirable to temporarily exclude those with a cold in the head or sore throat. The climate of small islands and of places on the seashore differs from that of the interior of continents chiefly in its greater equability. The variations in temperature between day and night and between summer and winter are much less marked, whilst the winds blowing in from the sea bring a moist but pure air, comparatively rich in ozone and free from dust and germs. The specific heat of water is far greater than that of land ; hence water heats slowly, and parts with its heat slowly. The land heats quickly and radiates quickly ; but on the land it is the surface alone which is affected by the change of seasons. At Greenwich the variations between summer and winter tempera- tures at a depth of 25 f?ei e are' only "about 2 F. In winter the CLIMATE AND METEOROLOGY 279 ocean acts as a storehouse for the heat absorbed from the summer sun, and slowly parts with it to warm the superincumbent air. In summer the land is heated by the sun more rapidly than the water ; consequently, the air over the land is heated and rises, and a cool breeze blows in from the sea during the day. During the night the earth is rapidly cooled by radiation, if the sky is clear ; the air over the sea is then warmer than the air over the land, i 1- rises, and a land breeze sets out to -sea. On a summer's day at the seashore the air is constantly in motion, and is cool and moist, whilst in the interior it may be insufferably hot, close and dry. Marshes, by the evaporation from the shallow water, help to lower the summer temperature ; but the influence of large lakes, as in North America, is to bring about an almost insular climate in summer, and a continental one in winter, for the frozen lakes then exert a similar influence to land. Ocean climates are of the greatest benefit to certain cases of lung disease, where a pure air, free from dust, but moist and of equable temperature is desired ; but ocean voyages should be recommended with extreme caution to phthisical patients. The confinement and over-crowding in cabins and state rooms, the want of exercise, and the costive habit thus produced (tending to excite haemoptysis), are all grave disadvantages, and may counteract any benefit to be derived from the sea air. The effect of vegetation on climate must not be lost sight of. In cold climates trees and shrubs obstruct the passage of the sun's rays to the soil, which is therefore liable to be cold and moist ; on the other hand, they may protect against cold winds. In hot climates the evaporation of water from the leaves tends to dry the soil and to lower the temperature, and the ground is sheltered from the direct rays of the sun and kept cool. Thus, the heat of summer is lowered and the cold of winter tempered by the presence of trees, and, having a lower temperature than the neighbouring earth's surface, high forests increase the rain- fall. In very dense forests the air is generally stagnant. Pro- bably in all climates a due admixture of herbage, shrubs and trees, without dense undergrowth, but admitting the passage of free currents of air in every direction, is the most conducive to health. Large tracts of country destitute of trees and vegeta- tion are in hot climates unbearably warm and dry, and in cold climates are exposed to every chilling wind. In such districts, too, rainfall is often arJMf f&tyelr^ r gfigFl in amount, the influence 280 HYGIENE AND PUBLIC HEALTH exerted by trees upon water-charged clouds being wanting. For these reasons the Desert of Sahara gives to the south of Europe a much higher temperature than would otherwise be the case. The mean temperature of the air of any place is dependent on the latitude, the altitude, the relative proportions of land and water, the aspect, and the nature of the soil ; and the extent of the diurnal variations in temperature is largely determined by the proximity to the coast and the height above sea level. The " amplitude of the yearly fluctuations " in temperature is not more than about 4 F. in some tropical places at sea level, while it may be as much as no° F., or even more, in the heart of large : continents situated near the poles. The principal factors, therefore, wh'ch determine the climate of a district are : (1) Distance from the equator ; (2) distance from the sea ; (3) altitude ; and (4) prevailing winds. Of the many separate elements that go to make up the climate of a place, temperature is the most important, and the mean annual temperature depends primarily upon the amount of radiant heat received from the sun. The heat received from the sun, however, in one place may be carried by winds and ocean currents to another. The mean temperature of the tropics is about 8o°F., and that of the arctic circle in latitude 6o° is 25 F., the difference of some 55 F. being due to the fact that the heat received from the sun is concentrated upon a small surface when the sun's rays fall near the equator, and is spread over a large surface when they fall near the poles. The differ- ence would be far greater were it not for the heat carried away from the tropics to the temperate and arctic regions by ocean currents, and to a less extent by winds. The difference between summer and winter temperatures is also important, but little variation being shown in places within the tropics, or on islands in the middle of large oceans, either in tropical or temperate latitudes. The heating of the air in the tropics, the cooling around the poles, and the deflective action of the earth's rotation, produce all the prevailing winds of the globe. The colder air of the northern and southern regions of the globe is constantly flowing towards the warmer and more rarefied air over the open seas on both sides of the equg^g zed T^iB?/<£<0&wte of the earth's rotation on the flow of the warm water from the equator towards the CLIMATE AND METEOROLOGY 28l poles in the North Atlantic Ocean is the large circular swirl, the northern and eastern sides of which produce the well known current of the Gulf Stream. This current, together with the circumstance that the prevailing winds have a westerly direction, accounts for the British Isles possessing such a mild climate ; whilst countries with the same latitude as England — such as Labrador and Eastern Asia, in which the prevailing winds are from the land instead of from the sea — have a mean winter temperature below zero. Weather Observations. Under the modern system, a number of barometrical readings taken at the same time over an extended area, such as the greater part of Western Europe, are telegraphed to a central station, where they are laid down upon a map. On this map lines are drawn connecting the places showing equal barometrical pressure ; these lines are termed " isobars." This weather map will show the cyclonic or anticyclonic systems, as the case may be, their position, and their extent. A cyclonic system is a sys- tem having at its centre the lowest barometrical pressure, and surrounded by isobars of gradually increasing pressure. The isobars will be near or far apart according to the amount of depression in the centre. If this depression is great, then the isobars are generally close together, and the " gradients " are said to be " steep." If, on the other hand, the depression in the centre is shallow, the isobars are further apart, and the gradients are " shallow." An anticyclonic system is the reverse of this, for its centre is the highest barometrical reading, and it is surrounded by isobars of gradually decreasing pressure. In order to restore atmospheric equilibrium, the air tends to move from a region where the barometer is high and pressure greatest, towards one where it is low and the pressure is least. Consequently, currents of air set in from all sides towards the centre of a cyclonic system, and flow out in all directions from the centre of an anticyclonic system. These currents of air do not, however, as a matter of fact, flow straight to or from the centre, but have a gyratory movement imparted to them, owing to the rotation of the earth on its own axis. The equatorial circujgfe&r^MTirt&SKSarth being 24,900 miles, 282 HYGIENE AND PUBLIC HEALTH and the earth rotating on its axis once in twenty-four hours, it follows that a point on the earth's crust at the equator must be carried round at the rate of 1,040 miles an hour. In latitude 30 , however, the point would only move at the rate of 900 miles an hour, owing to the lesser circumference of the earth at this distance from the equator. In latitude 6o° the rate will be only 520 miles an hour, and at the poles it will be nil. Now, the atmosphere is carried round, from west to east, at the same rate as the earth's crust ; consequently winds or currents of air travelling from the equator towards the poles, or from low lati- tudes into high, tend to keep the higher rate of rotatory motion imparted to them when nearer the equator, and become westerly — that is, come from the south-west (in the northern hemi- sphere) as they progress towards high latitudes. In the same way, winds travelling from high latitudes to low ones meet an atmosphere which is rotating at a greater rate than they are, and consequently appear 1 to come out of the north-east (in the northern hemisphere). This is the reason why the trade winds which blow towards the equator appear as north-east winds in the northern hemisphere, and south-east winds in the southern hemisphere. This direction of the trade winds is constant over all open seas to about 30 north and south of the equator, but land changes their course. The position of the sun has an influence on the strength and direction of these trade winds ; when the sun is near the Tropic of Cancer the south-east wind is more southerly and strong, and the north-east wind is weaker and more easterly ; and the reverse happens when the sun approaches the Tropic of Capricorn. The same forces apply to the currents of air moving towards the centre of a cyclonic system, or away from the centre of an anticyclonic system. In the case of a cyclonic system (in the northern hemisphere), a current setting towards its centre from the north appears to come from north-east. A current setting towards the centre from the south of the system is deflected to the east, or comes from south-west. In this way a gyratory or spiral movement is imparted, which causes the wind to travel round the centre of a cyclonic depression, in a direction against the hands of a watch ; or supposing a person to be travel- 1 As when a steamship is rapidly passing- through the air from west to east a wind coming i-RM'lm ^nWfyf'pears to come from the north- east. CLIMATE AND METEOROLOGY ' 283 ling with his face towards the direction the wind is taking, he will always keep the centre of the system, i.e., the point of lowest pressure, on his left hand side. The central space of the cyclone is occupied by a vast ascending current, which after rising to a considerable height flows away as upper currents into surrounding regions. The direction of the wind round an anticyclonic centre is exactly the reverse. The air flows away from the centre of greatest pressure in all directions. The current flowing south- wards is deflected to the west, and appears to come from north- east. The current flowing northward is deflected to the east, and comes from south- west. Consequently the currents revolve with the hands of a watch, and the person travelling with the wind keeps the centre of the system — the point of highest pres- sure — always on the right hand. From this it follows that having a weather (synoptic) chart be- fore us, and knowing the distribution of pressure over the area included in the chart, we can generally tell the direction of the wind at any particular spot ; and if we know what course the system is taking, i.e., the direction in which it is travelling, we can predict what changes will subsequently take place in that direction, so long as it remains included in the system. Cyclonic systems are never stationary. They move over the earth's surface, usually 'from weM c Twu or C002 inch). In order to take an accurate observation, the eye, the zero edge of the vernier, and the top of the mercury, should all be in the same horizontal plane ; hence the necessity of fixing the barometer at a height convenient to the observer. The tem- perature of the attached thermometer (c) is first noted ; then the level of the mercury in the cistern is so adjusted that the ivory point (d) projecting downward from the roof of the cistern just touches the surface of the mercury. This little ivory point indicates the zero of the scale ; and since the level of the mercurial surface in the cistern varies with every change of atmospheric pressure, the level of the mercury must be adjusted, prior to each observation, to the zero of the scale. Next read off on the barometer scale the division immediately below the top of the column of mercury. Then adjust the vernier (fig. 40) so that its lowest line is level with the top of the column of mer- cury, and the light is just excluded between the lower end of the vernier and the top of the mercury, and count the number of divisions on the vernier from below upwards, until a line on the vernier is exactly continuous with one on the barometer scale. Multiply the number of the divisions on the vernier so obtained by 0'002, and add the result to the already observed height on the barometer scale. 1 Corrections, by Glaisher's tables, must then be made for temperature above 32 F. — for mercury, like all other metals, expands with a rise of temperature. The mercury falls about -j-J- ^ inch for every foot ascent above sea- level, and allowance must be made for this if the observation is made at an altitude. The barometer must always be carefully and truly fixed by means of a plumb line, in a good light and protected from sunshine, rain, and winds. Before fixing, it should always be ascertained if the vacuum above the mercury is true. To do this, unscrew the bottom of the cistern until the mercury is 2 or 3 inches from the top, and then rather suddenly incline the instrument. If 1 For instance, in fig. 40 the mercury is shown to reach to a little above 29/55 inches on the barometric scale; taking the seventh line on the vernier as the line which is exactly continuous with one of the baro- metric scale, then 7 x -oog =.^4 : ami tte^rometric reading is 29-55 + •014=29-564 inches of mercury. 288 HYGIENE AND PUBLIC HEALTH the vacuum is true, the mercury strikes against the top of the tube with a sharp click, but a dull sound results if air is present. In the latter case, screw up the bottom tightly, turn the instru- ment upside down, and tap the side forcibly until a bubble of air is seen to pass through the mercury column into the cistern. Barometric observations are always expressed to the third place of decimals ; and isobarometric lines, as shown on charts, in- dicate areas over which the barometric pressures are identical. If the isobars, which are drawn for each y-y inch, are close to- gether, the " barometric gradient " is said to be steep, and the wind velocity will be high. The aneroid barometer is a small watch-shaped metal box from which the air has been exhausted, and in which the two flat surfaces of the box are kept apart by a powerful but sensitive spring. The atmospheric pressure acts upon the spring, and is recorded on a dial. This instrument is chiefly used for taking altitudes. The practice is to read the aneroid to the nearest T J-q- inch both at the commencement and at the termination of an ascent, and then to subtract one reading from the other (ignoring decimal points), and multiply the difference by 9, this giving the height of the ascent in feet. Example. — Reading at start— 30-00 inches. Reading at end —29-00 ,, 100 9 900 feet ascended. The weight of a cubic foot of dry air at 32 F. and 30 inches of mercury is 566-85 grains. As air expands wt of its volume for every degree rise Fahrenheit, the volume at 6o°F., for instance, is i + iihrx (60— 32) =1-057 curj ic feet. The weight is inversely as volume ; consequently the weight of a cubic foot of dry air at 6o° F. = = 536-28 grains. i'057 The weight of a cubic foot of water vapour at 6o° F. is 5-77 grains. Therefore, the added weights of a cubic foot of dry air at 6o° and of a cubic foot of vapour at 6o° are 536-28 + 5-77 = 542-05 grains. But dry air expands on taking up moisture, and the actual weight^^^bj^cfeg^f saturated air at 6o° is 532-84 grains, or 3-44 grains less than the weight of an equal CLIMATE AND METEOROLOGY 289 volume of dry air at that temperature, because the cubic foot of originally dry air is now more than a cubic foot. This fact explains the fall of the barometer when the moisture in the air is increasing and a fall of rain is imminent. Robinson's Wind Anemometer is an instrument which records the velocity of the wind. The figure (41) sufficiently explains the construction of the instrument. The revolving cups set in action a train of clockwork, and the velocity of the wind is recorded on a series of dials. The cups travel at a rate equal to only one-third that of the wind, and allowance is made for this fact in graduating the instrument. The square of the velocity in miles per hour, multiplied by o - oo5, gives the wind pres- sure in pounds per square foot ; and on the other hand, the square root of 200 times the wind's pressure gives the velocity. The instrument must be kept clean and well oiled, and should be fixed at least 20 feet from the ground, and away from build- ings. The average velocity of the wind is from six to eight miles per hour. On the Beaufort scale, in a light wind, the air travels at a rate of 13 miles per hour ; in a moderate breeze, 23 ; in a strong breeze, 34 ; and in a gale, 65. All wind direction observations by vanes, etc., should be recorded to the nearest point of the compass. The instruments which register the moisture in the atmosphere are known as hygrometers. Of these there are two distinct classes, i.e., those which indicate the dew point directly, and those from which the dew point is indirectly determined. In the former class the air is cooled until the moisture is de- posited on a bright surface to which a thermometer is attached , the latter indicating tb®ittampfiMttmbftid the dew point. Robinson's Anemometer, 290 HYGIENE AND PUBLIC HEALTH In Daniell's hygrometer (fig. 42) ether is placed in the lower bulb, and the other bulb (which contains nothing but ether vapour) is covered with muslin moistened with ether. This ether on the muslin evaporates into the air, and the loss of heat so occasioned condenses the ether vapour inside the bulb, causing evaporation from the ether inside the other (lower) bulb. The lower bulb thus becomes gradually colder, and chills the air sur- rounding it, until a temperature is reached at which the air is compelled to part with some of its moisture, which condenses upon the bright metal band surrounding the bulb. Directly this takes place the temperature of the dew point is read off from the attached thermometer. The temperature at which the dew disappears is next ob- served, and the mean between these two temperatures is taken as the dew point. In Regnault's instrument (fig. 43) one cylinder is half filled with ether, and the other is left empty, thermometers being inserted in both cylinders. An aspirator communicates, by means of the hollow upright, with both cylinders, and when this is put in action air is drawn through them. The passage of the air through the evaporating ether soon cools it down to the dew point, and then the bright metal surface surrounding the lower part of the cylinder becomes dulled with moisture. The temperature recorded at that instant by the thermometer in the ether is the temperature of the dew point, the second thermometer simply showing the temperature of the air at the time of observation. In Dines' instrument, a vessel which holds ice water has a bright metal plate with an attached thermometer in its roof. As the cold water is made to flow under the plate, the outside air in contact with it be- comes chilled ; and when the dew point, as shown by the deposition of dew, is reached, it can be read off from the attached thermometer. Wet and Dry Bulb Hygrometer. — This instrument consists of two absolutely identical thermometers mounted on a stand. In the wet bulb thermometer the bulb is kept moist by being covered with muslin, ofl&^ff^ WBKMgps into a small vessel of distilled or rain-water, so that moisture ascends by capillary Fig. 42. Daniell's Hygrometer. CLIMATE AND METEOROLOGY 29I attraction. The evaporation of moisture from the wet bulb, which takes place so long as the surrounding air is not saturated, causes loss of heat, and the wet bulb reads lower than the dry bulb. Both the vessel containing water and the wet bulb must be sufficiently far from the dry bulb to insure that the readings of the latter are not affected by the evaporation. The instrument must be exposed in the shade and protected from air currents and Fig. 43. — Regnault's Hygrometer. direct sunshine, both of which, by increasing evaporation, would cause the wet bulb thermometer to indicate a temperature not strictly due to the hygrometric state of the atmosphere. If the muslin becomes frozen in the winter, the two thermometers will read the same ; then the wet bulb should be brushed over with cold water, and the evaporation which will go on from the frozen surface will enable a proper reading to be taken. From the readings of the dry and wet bulbs can be ascertained — the relative humidity of the air, i.e., the amount of moisture present in air, expressed as a percentage of the amount just necessary to cause saturation ; the dew point, i.e., the temperature at which the amount of moisture actually present in the air causes saturation ; and the weight of vapour in a cubic foot of air, from which can l>e deduced the additional weight 2Q2 HYGIENE AND PUBLIC HEALTH of vapour necessary to cause saturation, or the drying power of the air. The relative humidity is found from tables. The greater the difference between the dry and wet bulbs, the lower is the relative humidity. If the dry and wet bulbs record the same temperature, the air is completely saturated with moisture. The dew point can be determined by the equation : Dew point -TJ ; where T d is the dry bulb temperature, T w is the wet bulb temperature, and F the factor opposite the dry bulb temperature found in Glaisher's tables. In De Sassure's instrument (the hair hygrometer), a hair freed from fat by ether is fixed at one end, and this hair contracts with lesser and expands with higher degrees of humidity. The hair is kept stretched by a small weight, the connecting cord of which is led round a pulley ; and an index needle attached to the pulley indicates the relative humidity on an empirically grad- uated scale of relative humidities. The instrument is standardized by first wetting the hair and noting whether it accurately registers saturation on the scale (i.e., ioo) ; but it is necessary to frequently verify the readings by other methods. The " elastic force of vapour," or " the tension of aqueous vapour," is the amount of the barometric pressure which is due to the aqueous vapour in the atmosphere. If the temperature of the air is lowered, and with it the tension of aqueous vapour, a temperature will sooner or later be reached at which the air is saturated with moisture ; and then the slightest further reduction in temperature will cause a deposition of dew (" dew point "). The tension of aqueouS/^ftpdtijr Mscasogftained from tables or by formula. The relative humidity can be calculated by dividing Fig. 44. Wet and Dry Bulb Hygrometer. CLIMATE AND METEOROLOGY 293 the elastic force of aqueous vapour at the temperature of the dew point by the elastic force of the aqueous vapour at the temperature of the air, and then multiplying by 100. Example. — The dry bulk temperature is 62° F., and that of the wet bulb is 56 F. The dew point is therefore 62 - \ {62 - 56) X 1 -86 y — 50-84° F. The aqueous tension at 62° F. is (from Glaisher's tables) 0-556 of an inch of mercury, and that at 50-84° F. is 0-372 of an inch. The relative humidity 0*372 is, therefore, — - — X 100 =66-0 per cent, of saturation. 0-556 If the relative humidity at 6i° F. is 70, the amount of vapour in a cubic foot is 70 per cent, of saturation, or y^Q of 6 = 4 "2 grains ; and the drying power of a cubic foot of the air is 6 — 4'2 = i"8 grains. Atmometers, for determining the amount and rate of evapora- tion, have been devised. In these instruments a known volume and weight of water is exposed in a receptacle, so as to present a known surface area to the atmosphere ; and the evaporation in a given time is determined by the loss either in volume or in weight of the orginal water. The weight of moisture which a cubic foot of dry air can take up, before it is saturated, varies with the temperature. The higher the temperature, the larger is the amount of vapour which can' be held, as the following table shows : — Grains of Vapour to saturate a Cubic Foot of Dry Air (Approximate). 30° F. 2 grains 66° F. 7 grains 8o° F. 1 1 grains 41° F- 3 70° F. 8 83° F. 12 49° F. 4 ,, 74° F. 9 .. 86° F. 13 56° F. 5 ,, 77° F. 10 88° F. 14 „ 6i° F. 6 » Hence, when warmer air, already moisture laden, is chilled, the moisture representing the difference between what it orginally held and what it is capable of holding at the reduced temperature is deposited in the form of dew or rain. Rain Gauge. — This instrument consists of a vessel supporting at its top a circular funnel which collects the rainfall. The vessel must be sunk in level ground, away from shrubs and build- ings, to such a depth that the collecting surface is one foot from the ground. A measu^ffgzgfefesflgeaslGffied according to the area 2 9 4 HYGIENE AND PUBLIC HEALTH of the funnel, so as to indicate the fall of rain as decimals of an inch, is required. The area of the top of the circular funnel (the receiving surface for the rain) is usually 50 square inches. To graduate the measuring glass for a funnel of this area, 50 cubic inches of water are poured into it, and a mark placed at the level the fluid stands at. Then if the rainfall collected on 50 square inches should measure the 50 cubic inches, each square inch of surface has collected one cubic inch of water, and the rainfall is " one inch." But the glass below the mark is divided into 100 equal parts, so that each division indicates a fall of too or o'oi inch of rain. The readings are generally taken daily at 9 a.m. In time of snow, the collected snow should be melted by adding a measured quantity of warm water to it, the extra water derived from the snow being recorded as rain-water. The average depth of the adjacent snow should also be noted. In Crosley's self-registering rain guage every j Jo inch of rainfall is recorded on a dial. The rain- fall collected gradually fills one compartment of a small bucket divided into two compartments, and balanced on a pivot. When one compartment is full, the bucket tips and causes an index to record, and the second com- partment then commences to fill. Aqueous vapour requires free surfaces for its condensation. When air is filtered, no cloud of condensed vapour can be formed. " Wet fogs " result when the particles of suspended matter are relatively few and the condensed moisture excessive, whereas " dry fogs " occur when the smoke and dust are relatively abundant. When the films of moisture are discoloured by the products of coal combustion, a yellow or "pea soup" fog will result. The death-rate gengrajl^^inc^ase^^ a result of town fogs, and the increase is ascribed to the irritating effects of the im- Fig. 45. — Rain Gauge. climate And Meteorology" 295 purities in the atmosphere upon the lungs, and to the sudden fall of temperature which takes place on the occurrence of the fog. Fogs lead to a considerable loss of that important element, sunshine, in our great towns : for, as a rule, when the town is enveloped in fog there is a cloudless sky above. Clouds consist of collections of condensed aqueous vapour. The principal forms which they assume are : (i) The cirrus, con- sisting of separate fine feathery formations, generally white in colour; (2) the stratus, consisting of a smooth horizontal stratum of cloud ; (3) the nimbus, constituting the raining clouds, of dark coloured, irregular forms ; and (4) the cumulus, or heavy, thick, well defined clouds, generally rounded off in shape. Two or more of these four principal forms may be mixed together, giving rise to appearances which are defined as " cirro-stratus," " cirro- cumulus," " strato-cumulus,'' " cumulo-nimbus," etc. Thermometers measure the temperature by the amounts of expansion and contraction of certain bodies when these are exposed to varying degrees of heat and cold. Mercury is com- monly employed, because of its very low freezing point ( — 38 F. ) and its high boiling point (675 F.) ; but alcohol is preferred when very low temperatures may have to be recorded, because it does not freeze at the greatest known degree of cold. The instruments are graduated from the fixed points of freezing and boiling water, by plunging them into melting ice and boiling water, respectively, at the standard pressure. On the Centigrade scale the freezing and boiling points are o° and ioo° respectively, while on the Fahrenheit scale the freezing point is 32 and the boiling point 21 2° ; therefore, to convert Centigrade to Fahren- heit, multiply the former figure by ?- and add 32, while to convert Fahrenheit to Centigrade subtract 32 and then multiply by f r Maximum thermometers are instruments designed to register the highest temperature reached during the period of exposure of the instrument ; in these the temperature is registered by mercury. The registration is effected by either breaking the column of mercury by an air bubble, or by a slight narrowing of the tube near the bulb. In either case the natural cohesion of the metal when contracting is overcome, and the mercury always remains at the highest point reached. Another method is to insert a small piece of solid glass enamel in the bend near the bulb ; this, acting as a valve, allows the mercury to pass on one side of it as it expands,°Mf <$d&= l V!i8?'&ffikf it to return on cooling. 296 HYGIENE AND PUBLIC HEALTH In hanging a maximum thermometer, it is necessary to see that the end of the tube furthest from the bulb is slightly inclined downwards, to assist in preventing the return of any portion of the column of mercury into the bulb on a decrease of temperature. Before reading the instrument, the end furthest from the bulb should be gently elevated to an angle of about 45°. Minimum thermometers record the lowest temperature reached. They are alcohol instruments, with an index in the alcohol (Rutherford's) which moves with the spirit on contraction by cold, owing to capillary attraction, but not on expansion, and is therefore left registering the lowest temper- ature. The end of the index furthest from the bulb indicates the minimum temperature. Occasionally air bubbles appear in the alcohol and fix the index. They can be removed by holding the thermometer with the bulb down- wards, and swinging it round rapidly at arm's length. These instruments should be hung so that the bulb end is 1 inch lower than the other end, because then the index is less likely to be affected by a rise in temperature. The so-called " earth " thermometer is a maxi- mum thermometer which is suspended by a chain in a stout iron tube, 5 feet long, which is provided with a pointed metal cap. By this means the temperature of the earth at depths up to nearly 5 feet can be ascertained. In taking an observation the thermometer must be quickly drawn up and read. In Six's thermometer (fig. 46) there is a U tube, the middle part of which is oc- cupied by mercury. The bulb (a) and both tubes above the mercury contain alcohol, in which are two steel indices, which are brought, by means of a magnet, to rest upon either column of mercury ; and b is a small chamber containing air. On a rise of temperature, the alcohol, expanding in the bulb {a), depresses the mercury level in one arm, and therefore raises it in the other, the maximum temperature being indicated by the position reached by the lower end of the index. Con- versely, as the tempera t^ z klky1to