,transcriber's ,notes3 ,the spelling1 hyphenation1 punctuation and accentuation are as the original1 except for apparent typographical errors which have been corrected4 ,italic text is denoted thus4 ,bold text is denoted thus4 ,see further notes at the end of the book4 ,illustration3 ,,general ,,view ,,of ,,filters ,,at ,,hamburg4 ,frontispiece4 ,,the ,,filtration ,,of ,,public ,,water-,,supplies4 ,,by ,,allen ,,hazen1 ,,member ,,of ,,the ,,american ,,society ,,of ,,civil ,,engineers1 ,,the ,,boston ,,society ,,of ,,civil ,,engineers1 ,,the ,,american ,,water-,,works ,,association1 ,,the ,,new ,,england ,,water-,,works ,,association1 ,,the ,,american ,,chemical ,,society1 ,,the ,,american ,,public ,,health ,,association1 ,,etc4 ,,third ,,edition1 ,,revised ,,and ,,enlarged4 ,,second ,,thousand4 ,,new ,,york3 ,,john ,,wiley ,,sons4 ,,london3 ,,chapman ,,hall1 ,,limited4 #aije4 ,copyright1 #aijj1 ,,by ,,allen ,,hazen4 ,,robert ,,drummond1 ,,electrotyper ,,and ,,printer1 ,,new ,,york4 ,,preface ,,to ,,first ,,edition4 ,the subject of water-filtration is commencing to receive a great deal of attention in the ,united ,states4 ,the more densely populated ,european countries were forced to adopt filtration many years ago1 to prevent the evils arising from the unavoidable contaminations of the rivers and lakes which were the only available sources for their public water-supplies2 and it has been found to answer its purpose so well that at the present time cities in ,europe nearly if not quite equal in population to all the cities of the ,united ,states are supplied with filtered water4 ,many years ago1 when the whole subject of water-supply was still comparatively new in this country1 filtration was considered as a means for rendering the waters of our rivers suitable for the purpose of domestic water-supply4 ,st4 ,louis investigated this subject in #ahff1 and the engineer of the ,st4 ,louis ,water ,board1 the late ,mr4 ,j4 ,p4 ,kirkwood1 made an investigation and report upon ,european methods of filtration which was published in #ahfi1 and was such a model of full and accurate statement combined with clearly-drawn conclusions that1 up to the present time1 it has remained the only treatise upon the subject in ,english1 notwithstanding the great advances which have been made1 particularly in the last ten years1 with the aid of knowledge of the bacteria and the germs of certain diseases in water4 ,unfortunately the interest in the subject was not maintained in ,america1 but was allowed to lag for many years2 it was cheaper to use the water in its raw state than it was to purify it2 the people became indifferent to the danger of such use1 and the disastrous epidemics of cholera and typhoid fever1 as well as of minor diseases1 which so often resulted from the use of polluted water1 were attributed to other causes4 ,with increasing study and diffusion of knowledge the relations of water and disease are becoming better known1 and the present state of things will not be allowed to continue2 indeed at present there is inquiry at every hand as to the methods of improving waters4 ,the one unfortunate feature is the question of cost4 ,not that the cost of filtration is excessive or beyond the means of ,american communities2 in point of fact1 exactly the reverse is the case2 but we have been so long accustomed to obtain drinking-water without expense other than pumping that any cost tending to improved quality seems excessive1 thus affording a chance for the installation of inferior filters1 which by failing to produce the promised results tend to bring the whole process into disrepute1 since few people can distinguish between an adequate filtration and a poor substitute for it4 ,it is undoubtedly true that improvements are made1 and will continue to be made1 in processes of filtration2 so it will often be possible to reduce the expense of the process without decreasing the efficiency1 but great care must be exercised in such cases to maintain the conditions really essential to success4 ,in the present volume ,i have endeavored to explain briefly the nature of filtration and the conditions which1 in half a century of ,european practice1 have been found essential for successful practice1 with a view of stimulating interest in the subject1 and of preventing the unfortunate and disappointing results which so easily result from the construction of inferior filters4 ,the economies which may possibly result by the use of an inferior filtration are comparatively small1 and it is believed that in those ,american cities where filtration is necessary or desirable it will be found best in every case to furnish filters of the best construction1 fully able to do what is required of them with ease and certainty4 ,,preface ,,to ,,third ,,edition4 ,there have been several distinct epochs in the development of water purification in the ,united ,states4 ,the first may be said to date from ,kirkwood's report on the 8,filtration of ,river ,waters10 and the second from the inauguration of the ,lawrence ,experiment ,station by the ,massachusetts ,state ,board of ,health1 and the construction of the ,lawrence city filter1 with the demonstration of the wonderful biological action of filters upon highly polluted waters4 ,the third epoch is marked by the experiments at ,louisville1 ,pittsburg and ,cincinnati1 which have greatly increased our knowledge of the treatment of waters containing enormous quantities of suspended matter1 and have reduced to something like order the previously existing confused mass of data regarding coagulation and rapid filtration4 ,the first edition of this book represented the earlier epochs before the opening of the third4 ,in the five years since it was written1 progress in the art of water purification has been rapid and substantial4 ,no apology is needed for the very complete revision required to treat these newly investigated subjects as fully as were other matters in the earlier editions4 ,in the present edition the first seven chapters remain with but few additions4 ,experience has strengthened the propositions contained in them4 ,new data might have been added1 but in few cases would the conclusions have been altered4 ,the remaining chapters of the book have been entirely rewritten and enlarged to represent the added information now available1 so that the present edition is nearly twice as large as the earlier ones4 ,in the appendices1 also1 much matter has been added relating to works in operation1 particularly to those in ,america4 ,,new ,,york ,january1 #aijj4 ,,contents4 ,,page ,chapter ,i4 ,,introduction4 #a ,,ii4 ,,continuous ,,filters ,,and ,,their ,,construction #e ,sedimentation-basins #h ,size of ,filter-beds #aj ,form of ,filter-beds #aa ,covers for ,filters #ab ,,iii4 ,,filtering-,,materials #bj ,sand #bj ,sands ,used in ,european ,filters #bd ,effect of ,size of ,grain ,upon ,efficiency of ,filtration #cj ,effect of ,grain ,size ,upon ,frequency of ,scraping #cb ,selection of ,sand #cc ,thickness of the ,sand ,layer #cd ,underdraining #ce ,gravel ,layers #ce ,underdrains #ci ,depth of ,water on ,filters #de ,,iv4 ,,rate ,,of ,,filtration ,,and ,,loss ,,of ,,head #dg ,effect of ,rate ,upon ,cost of ,filtration #dh ,effect of ,rate ,upon ,efficiency of ,filtration #ej ,the ,loss of ,head #eb ,regulation of the ,rate and ,loss of ,head in the ,older ,filters #eb ,apparatus ,for ,regulating the ,rate and ,loss of ,head #ee ,apparatus ,for ,regulating the ,rate ,directly #eg ,apparatus ,for ,regulating the ,height of ,water ,upon ,filters #ei ,limit to the ,loss of ,head #fj ,v4 ,,cleaning ,,filters #fh ,frequency of ,scraping #gb ,quantity of ,sand to ,be ,removed #gd ,wasting the ,effluents ,after ,scraping #gd ,sand-washing #gf ,,vi4 ,,theory ,,and ,,efficiency ,,of ,,filtration #hc ,bacterial ,examination of ,waters #ic ,,vii4 ,,intermittent ,,filtration #ig ,the ,lawrence ,filter #ajj ,chemnitz ,water-,works #ajg ,application of ,intermittent ,filtration #aaa ,,viii4 ,,turbidity ,,and ,,color1 ,,and ,,the ,,effect ,,of ,,mud ,,upon ,,sand ,,filters #aac ,the ,measurement of ,color #aad ,amount of ,color in ,american ,waters #aae ,removal of ,color #aag ,measurement of ,turbidity #aag ,relation of ,platinum-wire ,turbidities to ,suspended ,matters #abb ,source of ,turbidity #abc ,the ,amounts of ,suspended ,matters in ,water #abi ,preliminary ,processes to remove ,mud #acc ,effect of ,mud upon ,sand ,filters #acg ,effect of ,turbidity ,upon the ,length of ,period #acg ,power of ,sand ,filters to ,produce ,clear ,effluents from ,muddy ,water #aci ,effect of ,mud ,upon ,bacterial ,efficiency of ,filters #ada ,limits to the ,use of ,subsidence for the ,preliminary ,treatment of ,muddy ,waters #adb ,,ix4 ,,coagulation ,,of ,,waters #add ,substances used for ,coagulation #ade ,coagulants ,which ,have ,been ,used #aej ,amount of ,coagulant required to remove ,turbidity #aej ,amount of ,coagulant required to remove ,color #aec ,successive ,applications of ,coagulant #aed ,the ,amount of ,coagulant which ,various ,waters will receive #aee ,x4 ,,mechanical ,,filters #aei ,providence ,experiments #aei ,louisville,experiments #afa ,lorain ,tests #afa ,pittsburg ,experiments #afb ,wasting ,effluent ,after ,washing ,filters #afc ,influence of ,amount of ,sulphate of ,alumina on ,bacterial ,efficiency of ,mechanical ,filters #afe ,influence of ,degree of ,turbidity upon ,bacterial ,efficiency of ,mechanical ,filters #afg ,average ,results ,obtained with ,various ,quantities of ,sulphate of ,alumina #aga ,types of ,mechanical ,filters #agb ,efficiency of ,mechanical ,filters #agi ,pressure ,filters #ahj ,,xi4 ,,other ,,methods ,,of ,,filtration #aha ,worms ,tile ,system #aha ,the ,use of ,asbestos #aha ,filters ,using ,high ,rates of ,filtration ,without ,coagulants #ahb ,household ,filters #ahc ,,xii4 ,,removal ,,of ,,iron ,,from ,,ground-,,waters #ahf ,amount of ,iron ,required to ,render ,water ,objectionable #ahf ,cause of ,iron in ,ground-waters #ahg ,treatment of ,iron-containing ,waters #ahi ,iron-removal ,plants in ,operation #aib ,,xiii4 ,,treatment ,,of ,,waters #aig ,cost of ,filtration #bjj ,what ,waters ,require ,filtration #bjg ,,xiv4 ,,water-,,supply ,,and ,,disease--,,conclusions #baj ,appendix ,i4 ,,rules ,,of ,,the ,,german ,,government ,,in ,,regard ,,to ,,the ,,filtration ,,of ,,surface-,,waters ,,used ,,for ,,public ,,water-,,supplies #bba ,,ii4 ,,extracts ,,from 8,,bericht ,,des ,,medicinal-,,inspectorats ,,des ,,hamburgischen ,,staates ,f,r ,,das ,,jahr #ahib0 #bbf ,,iii4 ,,methods ,,of ,,sand-,,analysis #bcc ,,iv4 ,,filter ,,statistics #bda ,statistics of ,operation of ,sand ,filters #bda ,partial ,list of ,cities ,using ,sand ,filters #bdd ,list of ,cities and ,towns ,using ,mechanical ,filters #bdg ,notes ,regarding ,sand ,filters in the ,united ,states #bea ,capacity of ,filters #bed ,v4 ,,london',s ,,water-,,supply #bee ,,vi4 ,,the ,,berlin ,,water-,,works #bfa ,,vii4 ,,altona ,,water-,,works #bfe ,,viii4 ,,hamburg ,,water-,,works #bfi ,,ix4 ,,notes ,,on ,,some ,,other ,,european ,,water-,,supplies #bgb ,the ,use of ,unfiltered ,surface-waters4 #bge ,the ,use of ,ground-water4 #bgf ,x4 ,,literature ,,of ,,filtration #bgg ,,xi4 ,,the ,,albany ,,water-,,filtration ,,plant #bhh ,description of ,plant4 #bhi ,capacity of ,plant and ,means of ,regulation4 #cjh ,results of ,operation4 #cad ,cost of ,construction4 #cad ,,index #cag ,,units ,,employed4 ,the units used in this work are uniformly those in common use in ,america1 with the single exception of data in regard to sand-grain sizes1 which are given in millimeters4 ,the ,american units were not selected because the author prefers them or considers them particularly well suited to filtration1 but because he feared that the use of the more convenient metric units in which the very comprehensive records of ,continental filter plants are kept would add to the difficulty of a clear comprehension of the subject by those not familiar with those units1 and so in a measure defeat the object of the book4 ,,table ,,of ,,equivalents4 ,unit4 ,metric ,equivalent4 ,reciprocal4 ,foot #j4cjdh meter #c4bhjh ,mile #afji4cd meters #j4jjjfbad ,acre #djdg square meters #j4jjjbdga ,gallon#a #c4ghe liters #j4bfdag #a million gallons #cghe cubic meters #j4jjjbfdag ,cubic yard #j4gfde cubic meters #a4cjh #a million gallons per meter in depth acre daily #j4iced of water daily #a4jgj ,,acknowledgment4 ,i wish to acknowledge my deep obligation to the large number of ,european engineers1 directors1 and superintendents of water-works1 and to the health officers1 chemists1 bacteriologists1 and other officials who have kindly aided me in studying the filtration-works in their respective cities1 and who have repeatedly furnished me with valuable information1 statistics1 plans1 and reports4 ,to mention all of them would be impossible1 but ,i wish particularly to mention ,major-,general ,scott1 ,water-examiner of ,london2 ,mr4 ,mansergh1 ,member of the ,royal ,commission on the ,water-supply of the ,metropolis2 ,mr4 ,bryan1 ,engineer of the ,east ,london ,water ,company2 and ,mr4 ,wilson1 ,manager of the ,middlesborough ,water-works1 who have favored me with much valuable information4 ,in ,holland and ,belgium ,i am under special obligations to ,messrs4 ,van ,hasselt and ,kemna1 ,directors of the water companies at ,amsterdam and ,antwerp respectively2 to ,director ,stang of the ,hague ,water-works2 to ,dr4 ,van't ,hoff1 ,superintendent of the ,rotterdam filters2 and to my friend ,h4 ,p4 ,n4 ,halbertsma1 who1 as consulting engineer1 has built many of the ,dutch water-works4 ,in ,germany ,i must mention ,profs4 ,frhling1 at ,dresden1 and ,flgge1 at ,breslau2 ,andreas ,meyer1 ,city ,engineer of ,hamburg2 and the ,directors of water-works1 ,beer at ,berlin1 ,dieckmann at ,magdeburg1 ,nau at ,chemnitz1 and ,jockmann at ,liegnitz1 as well as the ,superintendent ,engineers ,schroeder at ,hamburg1 ,debusmann at ,breslau1 and ,anklamm and ,piefke at ,berlin1 the latter the distinguished head of the ,stralau works1 the first and most widely known upon the ,continent of ,europe4 ,i have to acknowledge my obligation to ,city ,engineer ,sechner at ,budapest1 and to the ,assistant ,engineer in charge of water-works1 ,kajlinger2 to ,city ,engineer ,peters and ,city ,chemist ,bertschinger at ,zrich2 and to ,assistant ,engineer ,regnard of the ,compagnie ,gnrale des ,eaux at ,paris4 ,on this side of the ,atlantic also ,i am indebted to ,hiram ,f4 ,mills1 ,c4,e41 under whose direction ,i had the privilege of conducting for nearly five years the ,lawrence experiments on filtration2 to ,profs4 ,sedgwick and ,drown for the numerous suggestions and friendly criticisms1 and to the latter for kindly reading the proof of this volume2 to ,mr4 ,g4 ,w4 ,fuller for full information in regard to the more recent ,lawrence results2 to ,mr4 ,h4 ,w4 ,clark for the laborious examination of the large number of samples of sands used in actual filters and mentioned in this volume2 and to ,mr4 ,desmond ,fitz,gerald for unpublished information in regard to the results of his valuable experiments on filtration at the ,chestnut ,hill ,reservoir1 ,boston4 ,,allen ,,hazen4 ,,boston1 ,april1 #ahie4 ,,filtration ,,of ,,public ,,water-,,supplies4 ,,chapter ,i4 ,,introduction4 ,the rapid and enormous development and extension of water-works in every civilized country during the past forty years is a matter which deserves our most careful consideration1 as there is hardly a subject which more directly affects the health and happiness of almost every single inhabitant of all cities and large towns4 ,considering the modern methods of communication1 and the free exchange of ideas between nations1 it is really marvellous how each country has met its problems of water-supply from its own resources1 and often without much regard to the methods which had been found most useful elsewhere4 ,england has secured a whole series of magnificent supplies by impounding the waters of small streams in reservoirs holding enough water to last through dry periods1 while on ,continental ,europe such supplies are hardly known4 ,germany has spent millions upon millions in purifying turbid and polluted river-waters1 while ,france and ,austria have striven for mountain-spring waters and have built hundreds of miles of costly aqueducts to secure them4 ,in the ,united ,states an abundant supply of some liquid has too often been the objective point1 and the efforts have been most successful1 the ,american works being entirely unrivalled in the volumes of their supplies4 ,i do not wish to imply that quality has been entirely neglected in our country1 for many cities and towns have seriously and successfully studied their problems1 with the result that there are hundreds of water-supplies in the ,united ,states which will compare favorably upon any basis with supplies in any part of the world2 but on the other hand it is equally true that there are hundreds of other cities1 including some among the largest in the country1 which supply their citizens with turbid and unhealthy waters which cannot be regarded as anything else than a national disgrace and a menace to our prosperity4 ,one can travel through ,england1 ,belgium1 ,holland1 ,germany1 and large portions of other ,european countries and drink the water at every city visited without anxiety as to its effect upon his health4 ,it has not always been so4 ,formerly ,european capitals drank water no better than that so often dispensed now in ,america4 ,as recently as #ahib ,germany's great commercial centre1 ,hamburg1 having a water-supply essentially like those of ,philadelphia1 ,pittsburg1 ,cincinnati1 ,st4 ,louis1 ,new ,orleans1 and a hundred other ,american cities1 paid a penalty in one month of eight thousand lives for its carelessness4 ,the lesson was a dear one1 but it was not wasted4 ,hamburg now has a new and wholesome supply1 and other ,german cities the qualities of whose waters were open to question have been forced to take active measures to better their conditions4 ,we also can learn something from their experience4 ,there are three principal methods of securing a good water-supply for a large city4 ,the first consists of damming a stream from an uninhabited or but sparsely inhabited watershed1 thus forming an impounding reservoir4 ,this method is extensively used in ,england and in the ,united ,states4 ,in the latter most of the really good and large supplies are so obtained4 ,it is only applicable to places having suitable watersheds within a reasonable distance1 and there are large regions where1 owing to geological and other conditions1 it cannot be applied4 ,it is most useful in hilly and poor farming countries1 as in parts of ,england and ,wales1 in the ,atlantic ,states1 and in ,california4 ,it cannot be used to any considerable extent in level and fertile countries which are sure to be or to become densely populated1 as is the case with large parts of ,france and ,germany and in the ,middle ,states4 ,the second method is to secure ground-water1 that is1 spring or well water1 which by its passage through the ground has become thoroughly purified from any impurities which it may have contained4 ,this was the earliest and is the most widely used method of securing good water4 ,it is specially adapted to small supplies4 ,under favorable geological conditions very large supplies have been obtained in this manner4 ,in ,europe ,paris1 ,vienna1 ,budapest1 ,munich1 ,cologne1 ,leipzig1 ,dresden1 a part of ,london1 and very many smaller places are so supplied4 ,this method is also extensively used in the ,united ,states for small and medium-sized places1 and deserves to be most carefully studied1 and used whenever possible1 but is unfortunately limited by geological conditions and cannot be used except in a fraction of the cases where supplies are required4 ,no ground-water supplies yet developed in the ,united ,states are comparable in size to those used in ,europe4 ,the third process of securing a good water-supply is by means of filtration of surface waters which would otherwise be unsuitable for domestic purposes4 ,the methods of filtration1 which it is the purpose of this volume to explain1 are beyond the experimental stage2 they are now applied to the purification of the water-supplies of ,european cities with an aggregate population of at least #bj1jjj1jjj people4 ,in the ,united ,states the use of filters is much less common1 and most of the filters in use are of comparatively recent installation4 ,great interest has been shown in the subject during the last few years1 and the peculiar character of some ,american waters1 which differ widely in their properties from those of many ,european streams1 has received careful and exhaustive consideration4 ,in ,europe filtration has been practised with continually improving methods since #ahbi1 and the process has steadily received wider and wider application4 ,it has been most searchingly investigated in its hygienic relations1 and has been repeatedly found to be a most valuable aid in reducing mortality4 ,the conditions under which satisfactory results can be obtained are now tolerably well known1 so that filters can be built in the ,united ,states with the utmost confidence that the result will not be disappointing4 ,the cost of filtration1 although considerable1 is not so great as to put it beyond the reach of ,american cities4 ,it may be roughly estimated that the cost of filtration1 with all necessary interest and sinking funds1 will add #aj per cent to the average cost of water as at present supplied4 ,it may be confidently expected that when the facts are better understood and realized by the ,american public1 we shall abandon the present filthy and unhealthy habit of drinking polluted river and lake waters1 and shall put the quality as well as the quantity of our supplies upon a level not exceeded by those of any country4 ,,chapter ,,ii4 ,,continuous ,,filters ,,and ,,their ,,construction4 ,filtration of water consists in passing it through some substance which retains or removes some of its impurities4 ,in its simplest form filtration is a straining process1 and the results obtained depend upon the fineness of the strainer1 and this in turn is regulated by the character of the water and the uses to which it is to be put4 ,thus in the manufacture of paper an enormous volume of water is required free from particles which1 if they should become imbedded in the paper1 would injure its appearance or texture4 ,obviously for this purpose the removal of the smaller particles separately invisible to the unaided eye1 and thus not affecting the appearance of the paper1 and the removal of which would require the use of a finer filter at increased expense1 would be a simple waste of money4 ,when1 however1 a water is to be used for a domestic water supply and transparency is an object1 the still finer particles which would not show themselves in paper1 but which are still able1 in bulk1 to render a water turbid1 should be as far as possible removed1 thus necessitating a finer filter2 and1 when there is reason to think that the water contains the germs of disease1 the filter must be fine enough to remove with certainty those organisms so extraordinarily small that millions of them may exist in a glass of water without imparting a visible turbidity4 ,it is now something over half a century since the first successful attempts were made to filter public water-supplies1 and there are now hundreds of cities supplied with clear1 healthy1 filtered water4 7,appendix ,,iv47 ,while the details of the filters used in different places present considerable variations1 the general form is1 in ,europe at least1 everywhere the same4 ,the most important parts of a filter are shown by the accompanying sketch1 in which the dimensions are much exaggerated4 ,the raw water is taken from the river into a settling-basin1 where the heaviest mud is allowed to settle4 ,in the case of lake and pond waters the settling-tank is dispensed with1 but it is essential for turbid river-water1 as otherwise the mud clogs the filter too rapidly4 ,the partially clarified water then passes to the filter1 which consists of a horizontal layer of rather fine sand supported by gravel and underdrained1 the whole being enclosed in a suitable basin or tank4 ,the water in passing through the sand leaves behind upon the sand grains the extremely small particles which were too fine to settle out in the settling-basin1 and is quite clear as it goes from the gravel to the drains and the pumps1 which forward it to the reservoir or city4 ,illustration3 ,,fig4 #a4--,,sketch ,,showing ,,general ,,arrangement ,,of ,,filter ,,plants4 ,the passages between the grains of sand through which the water must pass are extremely small4 ,if the sand grains were spherical and #a_/ej of an inch in diameter1 the openings would only allow the passage of other spheres #a_/cbj of an inch in diameter1 and with actual irregular sands much finer particles are held back4 ,as a result the coarser matters in the water are retained on the surface of the sand1 where they quickly form a layer of sediment1 which itself becomes a filter much finer than the sand alone1 and which is capable of holding back under suitable conditions even the bacteria of the passing water4 ,the water which passes before this takes place may be less perfectly filtered1 but even then1 the filter may be so operated that nearly all of the bacteria will be deposited in the sand and not allowed to pass through into the effluent4 ,as the sediment layer increases in thickness with continued filtration1 increased pressure is required to drive the desired volume of water through its pores1 which are ever becoming smaller and reduced in number4 ,when the required quantity of water will no longer pass with the maximum pressure allowed1 it is necessary to remove1 by scraping1 the sediment layer1 which should not be more than an inch deep4 ,this layer contains most of the sediment1 and the remaining sand will then act almost as new sand would do4 ,the sand removed may be washed for use again1 and eventually replaced when the sand layer becomes too thin by repeated scrapings4 ,these operations require that the filter shall be temporarily out of use1 and as water must in general be supplied without intermission1 a number of filters are built together1 so that any of them can be shut out without interfering with the action of the others4 ,the arrangement of filters in relation to the pumps varies with local conditions4 ,with gravity supplies the filters are usually located below the storage reservoir1 and1 properly placed1 involve only a few feet loss of head4 ,in the case of tidal rivers1 as at ,antwerp and ,rotterdam1 the quality of the raw water varies with the tide1 and there is a great advantage in having the settling-basins low enough so that a whole day's supply can be rapidly let in when the water is at its best1 without pumping4 ,at ,antwerp the filters are higher1 and the water is pumped from the settling basins to them1 and again from the reservoir receiving the effluents from the filters to the city4 ,in several of the ,london works 7,east ,london1 ,grand ,junction1 ,southwark and ,vauxhall1 etc47 the settling-basins are lower than the river1 and the filters are still lower1 so that a single pumping suffices1 that coming between the filter and the city1 or elevated distributing reservoir4 ,in many other ,english filters and in most ,german works the settling-basins and filters are placed together a little higher than the river1 thus avoiding at once trouble from floods and cost for excavation4 ,the water requires to be pumped twice1 once before and once after filtration4 ,at ,altona the settling-basins and filters are placed upon a hill1 to which the raw ,elbe water is pumped1 and from which it is supplied to the city after filtration by gravity without further pumping4 ,the location of the works in this case is said to have been determined by the location of a bed of sand suitable for filtration on the spot where the filters were built4 ,when two pumpings are required they are frequently done1 especially in the smaller places1 in the same pumping-station1 with but one set of boilers and engines1 the two pumps being connected to the same engine4 ,the cost is said to be only slightly greater than that of a single lift of the same total height4 ,in very large works1 as at ,berlin and ,hamburg and some of the ,london companies1 two separate sets of pumping machinery involve less extra cost relatively than would be the case with smaller works4 ,,sedimentation-,,basins4 ,kirkwood#b found in #ahff that sedimentation-basins were essential to the successful treatment of turbid river-waters1 and subsequent experience has not in any way shaken his conclusion4 ,the ,german works visited by him1 ,berlin 7,stralau7 and ,altona1 were both built by ,english engineers1 and their settling-basins did not differ materially from those of corresponding works in ,england4 ,since that time1 however1 there has been a well-marked tendency on the part of the ,german engineers to use smaller1 while the ,english engineers have used much larger sedimentation-basins1 so that the practices of the two countries are now widely separated1 the difference no doubt being in part at least due to local causes4 ,kirkwood found sedimentation-basins at ,altona with a capacity of #b-a_/d times the daily supply4 ,in #ahid the same basins were in use1 although the filtering area had been increased from #j4hb acre to #b4bj acres1 and still more filters were in course of construction1 and the average daily quantity of water had increased from #fjj1jjj to #d1aej1jjj gallons in #ahia-b1 or more than three times the capacity of the sedimentation-basins4 ,in #ahij the depth of mud deposited in these basins was reported to be two feet deep in three months4 ,at ,stralau in ,berlin1 also1 in the same time the filtering area was nearly doubled without increasing the size of the sedimentation-basins1 but the ,spree at this point has such a slow current that it forms itself a natural sedimentation-basin4 ,at ,magdeburg on the ,elbe works were built in #ahgf with a filtering area of #a4ib acres1 and a sedimentation-basin capacity of #aa1cjj1jjj gallons1 but in #ahid half of the latter had been built over into filters1 which with two other filters gave a total filtering surface of #c4ij acres1 with a sedimentation-basin capacity of only #e1fej1jjj gallons4 ,the daily quantity of water pumped for #ahia-b was #e1jjj1jjj gallons1 so that the present sedimentation-basin capacity is about equal to one day's supply1 or relatively less than a third of the original provision4 ,the idea followed is that most of the particles which will settle at all will do so within twenty-four hours1 and that a greater storage capacity may allow the growth of alg1 and that the water may deteriorate rather than improve in larger tanks4 ,illustration3 ,,paved ,,embankment ,,between ,,two ,,filters1 ,,east ,,london4 ,illustration3 ,,filters ,,and ,,channels ,,for ,,raw ,,water1 ,,antwerp4 ,to face page #aj4 ,at ,london1 on the other hand1 the authorities consider a large storage capacity for unfiltered water as one of the most important conditions of successful filtration1 the object however1 being perhaps as much to secure storage as to allow sedimentation4 ,in #ahic thirty-nine places were reported upon the ,thames and the ,lea which were giving their sewage systematic treatment before discharging it into the streams from which ,london's water is drawn4 ,these sewage treatments are1 with hardly an exception1 dry-weather treatments1 and as soon as there is a considerable storm crude sewage is discharged into the rivers at every point4 ,the rivers are both short1 and are quickly flooded1 and afterwards are soon back in their usual condition4 ,at these times of flood1 the raw water is both very turbid and more polluted by sewage than at other times1 and it is the aim of the authorities to have the water companies provide reservoir capacity enough to carry them through times of flood without drawing any water whatever from the rivers4 ,this obviously involves much more extensive reservoirs than those used in ,germany1 and the companies actually have large basins and are still adding to them4 ,the storage capacities of the various companies vary from #c to #ah times the respective average daily supplies1 and together equal #i times the total supply4 ,in case the raw water is taken from a lake or a river at a point where there is but little current1 as in a natural or artificial pond1 sedimentation-basins are unnecessary4 ,this is the case at ,zrich 7lake water71 at ,berlin when the rivers ,havel and ,spree spread into lakes1 at ,tegel and ,mggel1 and at numerous other works4 ,,size ,,of ,,filter-,,beds4 ,the total area of filters required in any case is calculated from the quantity of water required1 the rate of filtration1 and an allowance for filters out of use while being cleaned4 ,to prevent interruptions of the supply at times of cleaning1 the filtering area is divided into beds which are operated separately1 the number and size of the beds depending upon local conditions4 ,the cost per acre is decreased with large beds on account of there being less wall or embankment required1 while1 on the other hand1 the convenience of operation may suffer1 especially in small works4 ,it is also frequently urged that with large filters it is difficult or impossible to get an even rate of filtration over the entire area owing to the frictional resistance of the underdrains for the more distant parts of the filter4 ,a discussion of this point is given in ,chapter ,,iii1 page #da4 ,at ,hamburg1 where the size of the single beds1 #a4hh acres each1 is larger than at any other place1 it is shown that there is no serious cause for anxiety2 and even if there were1 the objectionable resistance could be still farther reduced by a few changes in the under-drains4 ,the sizes of filter-beds used at a large number of places are given in ,appendix ,,iv4 ,at a number of places having severe winters1 filters are vaulted over as a protection from cold1 and in the most important of these1 ,berlin1 ,warsaw1 and ,st4 ,petersburg1 the areas of the single beds are nearly the same1 namely1 from #j4eb to #j4ei acre4 ,the works with open filters at ,london 7seven companies71 ,amsterdam1 and ,breslau have filter-beds from #j4hb to #a4ej acres each4 ,liverpool and ,hamburg alone use filters with somewhat larger areas4 ,large numbers of works with both covered and open filters have much smaller beds than these sizes1 but generally this is to avoid too small a number of divisions in a small total area1 although such works have sometimes been extended with the growth of the cities until they now have a considerable number of very small basins4 ,,form ,,of ,,filter-,,beds4 ,the form and construction of the filter-beds depend upon local conditions1 the foundations1 and building materials available1 the principles governing these points being in general the same as for the construction of ordinary reservoirs4 ,the bottoms require to be made water-tight1 either by a thin layer of concrete or by a pavement upon a puddle layer4 ,for the sides either masonry walls or embankments are used1 the former saving space1 but being in general more expensive in construction4 ,embankments must1 of course1 be substantially paved near the water-line to withstand the action of ice1 and must not be injured by rapid fluctuations in the water-levels in the filters4 ,failure to make the bottoms water-tight has perhaps caused more annoyance than any other single point4 ,with a leaky bottom there is either a loss of water when the water in the filters is higher than the ground-water1 or under reverse conditions1 the ground-water comes in and mixes with the filtered water1 and the latter is rarely improved and may be seriously damaged by the admixture4 ,and with very bad conditions water may pass from one filter to another1 with the differences in pressure always existing in neighboring filters1 with most unsatisfactory results4 ,,covers ,,for ,,filters4 ,the filters in ,england and ,holland are built open1 without protection from the weather4 ,in ,germany the filters first built were also open1 but in the colder climates more or less difficulty was experienced in keeping the filters in operation in cold weather4 ,an addition to the ,berlin filters1 built in #ahgd1 was covered with masonry vaulting1 over which several feet of earth were placed1 affording a complete protection against frost4 ,the filters at ,magdeburg built two years later were covered in the same way1 and since that time covered filters have been built at perhaps a dozen different places4 ,illustration3 ,,interior ,,view ,,of ,,covered ,,filter1 ,,ashland1 ,,wis4 ,when in use the water rises nearly to the springing line of the arches4 ,illustration3 ,,covered ,,filter ,,in ,,course ,,of ,,construction1 ,,showing ,,wooden ,,centers ,,for ,,masonry ,,vaulting1 ,,somersworth1 ,n4 ,h4 ,to face page #ab4 ,it was found at ,berlin that1 owing to the difficulty of properly cleaning the open filters in winter1 it was impossible to keep the usual proportion of the area in effective service1 and as a result portions of the filters were greatly overtaxed during prolonged periods of cold weather4 ,this resulted in greatly decreased bacterial efficiency1 the bacteria in ,march1 #ahhi1 reaching #cjjj to #djjj per cc4 7with #ajj1jjj in the raw water71 although ordinarily the effluent contained less than #ajj4 ,an epidemic of typhoid fever followed1 and was confined to that part of the city supplied from the ,stralau works1 the wards supplied from the covered ,tegel filters remaining free from fever4 ,open filters have since been abandoned in ,berlin4 ,at ,altona also1 where the water is taken from an excessively polluted source1 decreased bacterial efficiency has repeatedly resulted in winter1 and the occasional epidemics of typhoid fever in that city1 which have invariably come in winter1 appear to have been directly due to the effect of cold upon the open filters4 ,the city has just extended the open filters1 and hopes with an increased reserve area to avoid the difficulty in future without resource to covered filters4 7,see ,appendices ,,ii and ,,vii47 ,brunswick1 ,lbeck1 and ,frankfort on ,oder with cold winters have open filters1 but draw their water-supplies from less polluted sources1 and have thus far escaped the fate of ,berlin and ,altona4 ,the new filters at ,hamburg also are open4 ,at ,zrich1 where open and covered filters were long used side by side1 the covered filters were much more satisfactory1 and the old open filters have recently been vaulted over4 ,knigsberg originally built open filters1 but was afterward obliged to cover them1 on account of the severe winters2 and at ,breslau1 where open filters have long been used1 the recent additions are vaulted over4 ,the fact that inferior efficiency of filtration results with open filters during prolonged and severe winter weather is generally admitted1 although there is some doubt as to the exact way in which the disturbance is caused4 ,in some works ,i am informed that in cutting the ice around the edges of the filter and repeatedly piling the loose pieces upon the floating cake1 the latter eventually becomes so thickened at the sides that the projecting lower corners actually touch the sand1 with the fluctuating levels which often prevail in these works1 and that in this way the sediment layer upon the top of the sand is broken and the water rapidly passes without adequate purification at the points of disturbance4 ,this theory is1 however1 inadequate to account for many cases where such an accumulation of ice is not allowed4 ,in these cases the poor work is not obtained until after the filters have been scraped4 ,the sand apparently freezes slightly while the water is off1 and when water is brought back and filtration resumed1 normal results are for some reason not again obtained for a time4 ,in addition to the poorer work from open filters in cold weather1 the cost of removing the ice adds materially to the operating expenses1 and in very cold climates would in itself make covers advisable4 ,i have arranged the ,european filter plants1 in regard to which ,i have sufficient information1 in the table on page #ae1 in the order of the normal mean ,january temperatures of the respective places4 ,this may not be an ideal criterion of the necessity of covering filters1 but it is at least approximate1 and in the absence of more detailed comparisons it will serve to give a good general idea of the case4 ,i have not found a single case where covered filters are used where the ,january temperature is #cb ,f4 or above4 ,in some of these places some trouble is experienced in unusually cold weather1 but ,i have not heard of any very serious difficulty or of any talk of covering filters at these places except at ,rotterdam1 where a project for covering was being discussed4 ,those places having ,january temperatures below #cj experience a great deal of difficulty with open filters2 so much so1 that covered filters may be regarded as necessary for them1 although it is possible to keep open filters running with decreased efficiency and increased expense by freely removing the ice1 with ,january temperatures some degrees lower4 ,where the mean ,january temperature is #cj to #cb ,f4 there is room for doubt as to the necessity of covering filters1 but1 judging from the experience of ,berlin and ,altona1 the covered filters are much safer at this temperature4 ,,table ,,of ,,places ,,having ,,open ,,and ,,covered ,,filters4 ,,arranged ,,according ,,to ,,the ,,mean ,,january ,,temperatures4 ---------------------------------------- ---------------------------- ,normal ,mean ,january ,place4 ,kind of ,filters and ,results4 ,temperature4 ,degrees ,f4 ---------------------------------------- ---------------------------- #cg-dj ,all ,english cities,open filters only are used1 and no great difficulty with ice is experienced4 #cc-ce ,cities in ,holland ,all filters are open1 and there is little serious trouble with ice2 but at ,amsterdam and ,rotterdam the bacteria in effluents are said to be higher in winter than at other times4 #cb ,bremen ,open filters4 #ca ,altona ,much difficulty with ice in open filters 7see ,appendices ,,ii and ,,vii74 #ca ,brunswick ,open filters4 #ca ,hamburg ,open filters4 #ca ,lbeck ,open filters4 #ca ,berlin ,open filters were formerly used1 but owing to decreased efficiency in cold weather they have been abandoned for covered ones4 #ca ,magdeburg ,covered filters1 but a recent addition is not covered4 #cj ,frankfort on ,oder ,open filters4 #cj ,stuttgart ,part of the filters are covered4 #cj ,stettin ,part of the filters are covered4 #bi ,zrich ,covered filters were much the most satisfactory1 and the open ones were covered in #ahid4 ,the raw water has a temperature of #ce4 #bi ,liegnitz ,open filters4 #bi ,breslau ,open filters have been used1 but recent additions are covered4 #bi ,budapest ,covered filters only4 #bi ,posen ,covered filters only4 #bf ,knigsberg ,the original filters were open1 but it was found necessary to cover them4 #bd ,warsaw ,covered filters only4 #af ,st4 ,petersburg ,covered filters only4 ---------------------------------------- ---------------------------- ,in case the raw water was drawn from a lake at a depth where its minimum temperature was above #cb1 which is the temperature which must ordinarily be expected in surface-waters in winter1 open filters might be successfully used in slightly colder places4 ,the covers are usually of brick or concrete vaulting supported by pillars at distances of #aa to #ae feet in each direction1 the whole being covered by #b or #c feet of earth2 and the top can be laid out as a garden if desired4 ,small holes for the admission of air and light are usually left at intervals4 ,the thickness of the masonry and the sizes of the pillars used in some of the earlier ,german vaultings are unnecessarily great1 and some of the newer works are much lighter4 ,for ,american use1 vaulting like that used for the ,newton1 ,mass41 covered reservoir#c should be amply strong4 ,roofs have been used at ,knigsberg1 ,posen1 and ,budapest instead of the masonry vaulting4 ,they are cheaper1 but do not afford as good protection against frost1 and even with great care some ice will form under them4 ,provision must be made for entering the filters freely to introduce and remove sand4 ,this is usually accomplished by raising one section of vaulting and building a permanent incline under it from the sand line to a door above the high-water line in the filter4 ,the cost of building covered filters is said to average fully one half more than open filters4 ,among the incidental advantages of covered filters is that with the comparative darkness there is no tendency to alg growths on the filters in summer1 and the frequency of scraping is therefore somewhat reduced4 ,at ,zrich1 in #ahib1 where both covered and open filters were in use side by side1 the periods between scrapings averaged a third longer in the covered than in the open filters4 ,it has been supposed that covered filters kept the water cool in summer and warm in winter1 but owing to the large volume of water passing1 the change in temperature in any case is very slight2 ,frhling found that even in extreme cases a change of over #c ,f4 in either direction is rarely observed4 ,illustration3 ,,removing ,,ice ,,from ,a ,,filter1 ,,east ,,london4 ,this represents the greatest accumulation of ice in the history of the works4 ,to face page #af4 ,at ,berlin1 where open and covered filters were used side by side at ,stralau for twenty years1 it was found that1 bacterially1 the open filters were1 except in severe winter weather1 more efficient4 ,it was long supposed that this was caused by the sterilizing action of the sunlight upon the water in the open filters4 ,this result1 however1 was not confirmed elsewhere1 and it was finally discovered1 in #ahic1 that the higher numbers were due to the existence of passages in corners on the columns of the vaulted roof and around the ventilators for the underdrains1 through which1 practically1 unfiltered water found its way into the effluent4 ,this at once removes the evidence in favor of the superior bacterial efficiency of open filters and suggests the necessity of preventing such passages4 ,the construction of a ledge all around the walls and pillars four inches wide and a little above the gravel1 as shown in the sketch1 might be useful in this way1 and the slight lateral movement of the water in the sand above would be of no consequence4 ,the sand would evidently make a closer joint with the horizontal ledge than with the vertical wall4 ,illustration3 ,,fig4 #b4 ,in regard to the probable requirement or advisability of covers for filters in the ,united ,states1 ,i judge1 from the ,european experience1 that places having ,january temperatures below the freezing-point will have considerable trouble from open filters1 and would best have covered filters4 ,places having higher winter temperatures will be able to get along with the ice which may form on open filters1 and the construction of covers would hardly be advisable except under exceptional local conditions1 as1 for instance1 with a water with an unusual tendency to alg growths4 ,i have drawn a line across a map of the ,united ,states on this basis 7shown by the accompanying plate7 and it would appear that places far north of the line would require covered filters1 and that those south of it would not1 while for the places in the immediate vicinity of the line 7comparable to ,hamburg and ,altona7 there is room for discussion4 ,in the ,united ,states covered filters have been constructed at ,st4 ,johnsbury1 ,vt41 ,somersworth1 ,n4 ,h41 ,albany1 ,n4 ,y41 ,ashland1 ,wis41 and ,grand ,forks1 ,n4 ,dak41 all of these places being considerably north of the above-mentioned line4 ,the filter at ,lawrence1 ,mass41 with a mean ,january temperature of about #be1 is not covered1 but serious difficulty and expense have been experienced at times from the ice1 so much so that it has been repeatedly recommended to cover it4 ,open filters have also been in use for many years at ,hudson and ,poughkeepsie1 ,n4 ,y41 with mean ,january temperatures about #bd2 and although considerable difficulty has been experienced from ice at times1 these filters1 particularly the ones at ,poughkeepsie1 have been kept in very serviceable condition at all times1 notwithstanding the ice4 ,at ,mount ,vernon1 ,n4 ,y41 with a mean ,january temperature of about #ca1 and with a reservoir water1 no serious difficulty has been experienced with ice2 and at ,far ,rockaway1 ,l4 ,i41 with a slightly higher temperature and well-water1 no difficulty whatever has been experienced with open filters4 ,filters at ,ilion1 ,n4 ,y41 with a mean ,january temperature of about #bc1 are not covered1 and are fed from a reservoir4 ,no serious difficulty has been experienced with ice1 which is probably due to the fact that the water applied to them is taken from near the bottom of the reservoir1 and ordinarily has a temperature somewhat above the freezing-point throughout the winter4 ,illustration3 ,map showing ,normal ,mean ,january ,temperatures ,,in ,,the ,,united ,,states and the ,area in which ,filters should be covered ,the cost of removing ice from filters depends1 among other things1 upon the amount of reserve filter area4 ,when this reserve is small the filters must be kept constantly at work nearly up to their rated capacity2 the ice must be removed promptly whenever the filters require cleaning1 and under some conditions the expense of doing this may be considerable4 ,if1 on the other hand1 there is a considerable reserve area1 so that when a filter becomes clogged in severe weather1 the work can be turned upon other filters and the clogged filter allowed to remain until more moderate weather1 or until a thaw1 the expense of ice removal may be kept at a materially lower figure4 ,in case open filters are built near or north of this line1 ,i would suggest that plenty of space between and around the filters for piling up ice in case of necessity may be found advantageous1 and that a greater reserve of filtering area for use in emergencies should be provided than would be considered necessary with vaulted filters or with open filters in a warmer climate4 ,,chapter ,,iii4 ,,filtering ,,materials4 ,,sand4 ,the sand used for filtration may be obtained from the sea-shore1 from river-beds or from sand-banks4 ,it consists mainly of sharp quartz grains1 but may also contain hard silicates4 ,as it occurs in nature it is frequently mixed with clayey or other fine particles1 which must be removed from it by washing before it is used4 ,some of the ,new ,england sands1 however1 as that used for the ,lawrence ,city filter1 are so clean that washing would be superfluous4 ,the grain size of the sand best adapted to filtration has been variously stated at from #a_/h to #a mm41 or from #j4jac to #j4jdj inch4 ,the variations in the figures1 however1 are due more to the way that the same sand appears to different observers than to actual variations in the size of sands used1 which are but a small fraction of those indicated by these figures4 ,as a result of experiments made at the ,lawrence ,experiment ,station#d we have a standard by which we can definitely compare various sands4 ,the size of a sand-grain is uniformly taken as the diameter of a sphere of equal volume1 regardless of its shape4 ,as a result of numerous measurements of grains of ,lawrence sands1 it is found that when the diameter1 as given above1 is #a1 the three axes of the grain1 selecting the longest possible and taking the other two at right angles to it1 are1 on an average1 #a4ch1 #a4je1 and #j4fi1 respectively and the mean diameter is equal to the cube root of their product4 ,it was also found that in mixed materials containing particles of various sizes the water is forced to go around the larger particles and through the finer portions which occupy the intervening spaces1 so that it is the finest portion which mainly determines the character of the sand for filtration4 ,as a provisional basis which best accounts for the known facts1 the size of grain such that #aj per cent by weight of the particles are smaller and #ij per cent larger than itself1 is considered to be the effective size4 ,the size so calculated is uniformly referred to in speaking of the size of grain in this work4 ,illustration3 ,,fig4 #c4--;,,apparatus ,,used ,,for ,,measuring ,,the ,,friction ,,of ,,water ,,in ,,sands4 ,another important point in regard to a material is its degree of uniformity--whether the particles are mainly of the same size or whether there is a great range in their diameters4 ,this is shown by the uniformity coefficient1 a term used to designate the ratio of the size of the grain which has #fj per cent of the sample finer than itself to the size which has #aj per cent finer than itself4 ,the frictional resistance of sand to water when closely packed1 with the pores completely filled with water and in the entire absence of clogging1 was found to be expressed by the formula v cd#b7;h_/l77t ,fah4 #aj7_/fj1 where v is the velocity of the water in meters daily in a solid column of the same area as that of the sand1 or approximately in million gallons per acre daily2 c is an approximately constant factor2 d is the effective size of sand grain in millimeters2 h is the loss of head 7,fig4 #c72 l is the thickness of sand through which the water passes2 t is the temperature 7,fahr474 ,,table ,,showing ,,rate ,,at ,,which ,,water ,,will ,,pass ,,through ,,even-,,grained ,,and ,,clean ,,sands ,,of ,,the ,,stated ,,grain ,,sizes ,,and ,,with ,,various ,,heads ,,at ,a ,,temperature ,,of #ej4 ---------------------------------------- ----------------------------- ,effective ,size in ,millimeters #aj per cent finer than3 h_/l------------------------------------ ------------------- #j4aj #j4bj #j4cj #j4ce #j4dj #j4ej #a4jj #c4jj ---------------------------------------- ---------------------- ,million ,gallons per ,acre daily4 4#jja 4#ja 4#jd 4#aj 4#ac 4#ag 4#bg #a4jg #i4fc 4#jje 4#je 4#ba 4#dh 4#fe 4#he #a4cd #e4ce #dh4ae 4#jaj 4#aa 4#dc 4#if #a4ca #a4ga #b4fg #aj4gj #if4cj 4#jej 4#ed #b4ad #d4hb #f4ee #h4ee #ac4dj #ec4ej 4#ajj #a4jg #d4bh #i4fc #ac4aj #ag4aj #bf4gj #ajg4jj #a4jjj #aj4gj #db4hj #if4cj #aca4jj #aga4jj #bfg4jj ---------------------------------------- ---------------------- ,the above table is computed with the value c taken as #ajjj1 this being approximately the values deduced from the earliest experiments4 ,more recent and extended data have shown that the value of c is not entirely constant1 but depends upon the uniformity coefficient1 upon the shape of the sand grains1 upon their chemical composition1 and upon the cleanliness and closeness of packing of the sand4 ,the value may be as high as #abjj for very uniform1 and perfectly clean sand1 and maybe as low as #djj for very closely packed sands containing a good deal of alumina or iron1 and especially if they are not quite clean4 ,the friction is usually less in new sand than in sand which has been in use for some years4 ,in making computations of the frictional resistance of filters1 the average value of c may be taken at from #gjj to #ajjj for new sand1 and from #ejj to #gjj for sand which has been in use for a number of years4 ,the value of c decreases as the uniformity coefficient increases4 ,with ordinary filter sands with uniformity coefficients of #c or less the differences are not great4 ,with mixed sands having much higher uniformity coefficients1 lower and less constant values of c are obtained1 and the arrangement of the particles becomes a controlling factor in the increase in friction4 ,the friction of the surface layer of a filter is often greater than that of all the sand below the surface4 ,it must be separately computed and added to the resistances computed by the formula1 as it depends largely upon other conditions than those controlling the resistance of the sand4 ,while the value of c is thus not entirely constant1 it can be estimated with approximate accuracy for various conditions1 from a knowledge of the composition1 condition1 and cleanliness of the sand1 and closeness of packing4 ,the following table shows the quantity of water passing sands at different temperatures4 ,this table was computed with temperature factors as given above1 which were based upon experiments upon the flow of water through sands1 checked by the coefficients obtained from experiments with long capillary tubes entirely submerged in water of the required temperature4 ,,relative ,,quantities ,,of ,,water ,,passing ,,at ,,different ,,temperatures4 #cb #j4gj #ce #j4ge #ch #j4hj #da #j4he #dd #j4ij #dg #j4ie #ej #a4jj #ec #a4je #ef #a4aj #ei #a4ae #fb #a4bj #fe #a4be #fh #a4cj #ga #a4ce #gd #a4dj #gg #a4de ,the effect of temperature upon the passage of water through sands and soils has been further discussed by ,prof4 ,l4 ,g4 ,carpenter1 ,engineering ,news1 ,vol4 ,,xxxix1 p4 #dbb4 ,this article reviews briefly the literature of the subject1 and refers at length to the formula of ,poiseuille1 published in the ,memoires des ,savants ,etrangers1 ,vol4 ,,xi1 p4 #dcc 7#ahdf74 ,this formula1 in which the quantity of water passing at #j4j ,cent41 is taken as unity1 is as follows3 ,temperature factor #a #j4jccfgit #j4jjjbbat#b4 ,the results obtained by this formula agree very closely with those given in the above table throughout the temperature range for which computations are most frequently required4 ,at the higher and lower temperatures the divergencies are greater1 as is shown in a communication in the ,engineering ,news1 ,vol4 ,,xl1 p4 #bf4 ,the quantity of water passing at a temperature of #ej ,fahr4 is in many respects more convenient as a standard than the quantity passing at the freezing-point4 ,near the freezing-point1 owing to molecular changes in the water1 the changes in its action are rapid1 and the results are less certain1 and also #ej ,fahr4 is a much more convenient temperature for precise experiments than is the freezing point4 ,,sands ,,used ,,in ,,european ,,filters4 ,to secure definite information in regard to the qualities of the sands actually used in filtration1 a large number of ,european works were visited in #ahid1 and samples of sand were collected for analysis4 ,these samples were examined at the ,lawrence ,experiment ,station by ,mr4 ,h4 ,w4 ,clark1 the author's method of analysis described in ,appendix ,,iii being used4 ,in the following table1 for the sake of compactness1 only the leading points of the analyses1 namely1 effective size1 uniformity coefficient1 and albuminoid ammonia1 are given4 ,on page #bh full analyses of some samples from a few of the leading works are given4 ,,analyses ,,of ,,sands ,,used ,,in ,,water ,,filtration4 ---------------------------------------- -------------------------- ,effective ,albu- ,size2 #aj ,uni- minoid ,finer formity ,ammo- ,source4 than ,coeffi- nia4 ,remarks4 7,milli- cient4 ,parts in meters74 #ajj1jjj4 ---------------------------------------- -------------------------- ,london1 ,e4 ,london ,co4 #j4dd #a4h #j4de ,new sand1 never used or washed4 ,london1 ,e4 ,london ,co4 #j4ci #b4a #bf4bj ,dirty sand1 very old4 ,london1 ,e4 ,london ,co4 #j4cg #b4j #h4fj ,same1 washed by hand4 ,london1 ,grand ,junc4 #j4bf #a4i #a4ij ,sand from rough filter4 ,london1 ,grand ,junc4 #j4dj #c4e #aj4jj ,old sand in final filter4 ,london1 ,grand ,junc4 #j4da #c4g #b4gj ,freshly washed old sand4 ,london1 ,southw'k ,v4 #j4ch #c4e #e4jj ,freshly washed old sand4 ,london1 ,southw'k ,v4 #j4cj #a4h #b4hj ,freshly washed new sand4 ,london1 ,lambeth #j4cf #b4c #b4fj ,freshly washed old sand4 ,london1 ,lambeth #j4cf #b4d #j4ce ,new unused sand1 washed4 ,london1 ,lambeth #j4be #a4g #j4gj ,new extremely fine sand4 ,london1 ,chelsea #j4cf #b4d #b4aj ,freshly washed old sand4 ,middlesborough #j4db #a4f #ag4fj ,dirty sand1 ordinary scraping4 ,middlesborough #j4dc #a4f #g4cj ,same1 after washing4 ,birmingham #j4bi #a4i #cc4bj ,dirty sand4 ,birmingham #j4bi #a4i #g4bj ,sand below surface of filter4 ,reading #j4cj #b4e #d4jj ,dirty sand4 ,reading #j4bb #b4j #a4ej ,same1 after washing4 ,antwerp #j4ch #a4f #g4hj ,dirty sand4 ,antwerp #j4ci #a4f #c4dj ,same1 after washing4 ,hamburg #j4bh #b4e #h4ej ,dirty sand4 ,hamburg #j4ca #b4c #j4hj ,same1 after washing4 ,hamburg #j4cd #b4b #g4ij ,dirty sand1 another sample4 ,hamburg #j4cj #b4j #j4ij ,same1 after washing drums4 ,hamburg #j4cd #b4c #a4ej ,same1 after washing ejectors4 ,altona #j4cb #b4j #i4jj ,dirty sand1 old filters4 ,altona #j4cg #b4j #a4ej ,same1 after washing4 ,altona #j4cc #b4h #j4ej ,washed sand for new filters4 ,berlin1 ,stralau #j4cc #a4i #ab4bj ,dirty sand-pile4 ,berlin1 ,stralau #j4ce #a4g #d4ej ,filter ,no4 #f1 #c below surface4 ,berlin1 ,stralau #j4cd #a4g #f4cj ,filter ,no4 #g1 #c below surface4 ,berlin1 ,stralau #j4ce #a4g #d4jj ,filter ,no4 #aj1 #c below surface4 ,berlin1 ,tegel #j4ch #a4f #aa4jj ,dirty sand1 old filters4 ,berlin1 ,tegel #j4ch #a4e #b4hj ,same1 after washing1 old filters4 ,berlin1 ,tegel #j4ce #a4f #c4bj ,same1 after washing1 new filters4 ,berlin1 ,mggel #j4ce #a4h #j4hj ,sand from filters below surface4 ,berlin1 ,mggel #j4cc #b4j #f4cj ,dirty sand1 ordinary scraping4 ,berlin1 ,mggel #j4cd #b4j #ae4cj ,dirty sand1 another sample4 ,charlottenburg #j4dj #b4c #g4bj ,dirty sand4 ,chemnitz #j4ce #b4f #j4bj ,new sand not yet used4 ,magdeburg #j4ci #b4j #i4ej ,dirty sand4 ,magdeburg #j4dj #b4j #b4hj ,same1 after washing4 ,breslau #j4ci #a4h #a4dj ,normal new sand4 ,budapest #j4bj #b4j #j4hj ,new washed ,danube sand4 ,zrich #j4bh #c4b #f4bj ,dirty sand4 ,zrich #j4cj #c4a #a4ej ,same1 after washing4 ,hague #j4ai #a4f #j4gj ,dune-sand used for filtration4 ,schiedam #j4ah #a4f #e4fj ,dune-sand used for filtration2 dirty4 ,schiedam #j4ca #a4e #ac4ej ,river-sand2 dirty4 ,amsterdam #j4ag #a4f #b4dj ,dune-sand4 ,rotterdam #j4cd #a4e #b4cj ,river-sand2 new4 ,liverpool1 ,rivington #j4dc #b4j #j4gf ,sand from bottom of filter4 ,liverpool1 ,rivington #j4cb #b4e #a4jj ,new sand unwashed and unscreened4 ,liverpool1 ,rivington #j4dc #b4g #d4aj ,washed sand which has been in use #cj to #dj years4 ,liverpool1 ,oswestry #j4cj #b4f #i4dj ,dirty sand4 ,liverpool1 ,oswestry #j4ca #d4g #b4bj ,same1 after washing4 ---------------------------------------- -------------------------- ,,note4--,it is obvious that in case the sands used at any place are not always of the same character1 as is shown to be the case by different samples from some of the works1 the examination of such a limited number of samples as the above from each place is entirely inadequate to establish accurately the sizes of sand used at that particular place1 or to allow close comparisons between the different works1 and for this reason no such comparisons will be made4 ,the object of these investigations was to determine the sizes of the sands commonly used in ,europe1 and1 considering the number and character of the different works represented1 it is believed that the results are ample for this purpose4 ,the ,english and most of the ,german sands are washed1 even when entirely new1 before being used1 to remove fine particles4 ,at ,breslau1 however1 sand dredged from the river ,oder is used in its natural state1 and new sand is used for replacing that removed by scraping4 ,at ,budapest1 ,danube sand is used in the same way1 but with a very crude washing1 and it is said that only new unwashed sand is used at ,warsaw4 ,in ,holland1 so far as ,i learned1 no sand is washed1 but new sand is always used for refilling4 ,at most of the works visited dune-sand with an effective size of only #j4ag to #j4ai mm4 is used1 and this is the finest sand which ,i have ever found used for water filtration on a large scale4 ,it should be said1 however1 that the waters filtered through these fine sands are fairly clear before filtration1 and are not comparable to the turbid river-waters often filtered elsewhere1 and their tendency to choke the filters is consequently much less4 ,at ,rotterdam and ,schiedam1 where the raw water is drawn from the ,maas1 as the principal stream of the ,rhine is called in ,holland1 river-sand of much larger grain size is employed4 ,it is obtained by dredging in the river and is never washed1 new sand always being employed for refilling4 ,the average results of the complete analyses of sands from ten leading works are shown in the table on page #bh4 ,these figures are the average of all the analyses for the respective places1 except that one sample from the ,lambeth ,co41 which was not a representative one1 was omitted4 ,the ,london companies were selected for this comparison both on account of their long and favorable records in filtering the polluted waters of the ,thames and ,lea1 and because they are subject to close inspection2 and there is ample evidence that the filtration obtained is good--evidence which is often lacking in the smaller and less closely watched works4 ,for the ,german works ,altona was selected because of its escape from cholera in #ahib1 due to the efficient action of its filters1 and ,stralau because of its long and favorable record when filtering the much-polluted ,spree water4 ,these two works also have perhaps contributed more to the modern theories of filtration than all the other works in existence4 ,the remaining works are included because they are comparatively new1 and have been constructed with the greatest care and attention to details throughout1 and the results obtained are most carefully recorded4 ,some of the most interesting of these results are shown graphically on page #bi4 ,the method of plotting is that described in ,appendix ,,iii4 ,,table ,,showing ,,the ,,average ,,per ,,cent ,,of ,,the ,,grains ,,finer ,,than ,,various ,,sizes ,,in ,,sands ,,from ,,leading ,,works4 ---------------------------------------- -------------------------- ,per ,cent by ,weight ,finer than ---------------------------------------- ----- #j4ajf #j4ahf #j4caf #j4df #j4ic #b4jd #c4hi #e4hi mm4 mm4 mm4 mm4 mm4 mm4 mm4 mm4 ---------------------------------------- ------------------- ,east ,london #j4b #j4e #c4f #bb4b #fi4g #hi4h #ie4j #ii4j ,grand ,junction #j #j4b #c4a #ag4d #dg4a #fh4b #hd4g #ic4f ,southwark and ,vauxhall #j4g #h4j #cd4a #fi4g #hc4e #ij4j #id4j ,lambeth #j #j4e #e4e #bf4f #fc4j #gi4b #hh4j #id4c ,chelsea #j #j4a #e4j #bh4f #fc4j #gf4g #hf4j #ic4f ,hamburg #j4b #a4e #aj4i #cc4b #gd4d #ie4g #ii4e ,altona #j4a #a4a #g4h #bh4g #gb4a #ib4a #ie4h ,stralau #j4c #g4j #cg4c #hf4i #ie4d #ig4f ,tegel #j4b #d4e #ce4d #id4c #ih4e #ii4a ,mggel #j4a #j4e #g4i #cc4f #gi4g #id4c #ih4e ---------------------------------------- ----- ,average of all #j4jf #j4ef #f4cc #bi4gaga4iihg4cdic4db7ig4de7 ---------------------------------------- ------------------- ,,average ,,effective ,,size1 ,,uniformity ,,coefficient1 ,,and ,,albuminoid ,,ammonia ,,in ,,sands ,,from ,,ten ,,leading ,,works4 ,i4 ,,london ,,filters4 ---------------------------------------- --------------------------- ,effective ,uniformity ,albuminoid ,ammonia4 ,size2 #aj ,coefficient4------------------ ,finer than ,dirty ,sand4,washed 7,millimeters74 ,sand4 ---------------------------------------- -------------------------- ,east ,london #j4dj #b4j #bf4jj #h4fj ,grand ,junction #j4dj #c4f #aj4jj #b4gj ,southwark and ,vauxhall #j4cd #b4e #c4ij ,lambeth #j4cf #b4d #b4fj ,chelsea #j4cf #b4d #b4aj ---------------------------------------- ---- ,average #j4cg #b4f #ah4jj #c4ih ---------------------------------------- -------------------------- ,,ii4 ,,german ,,works4 ---------------------------------------- -------------------------- ,stralau #j4cd #a4g #ab4bj #d4jj ,tegel #j4cg #a4f #aa4jj #c4jj ,mggel #j4cd #b4j #aj4hj #j4hj ,altona #j4cd #b4c #i4jj #a4ej ,hamburg #j4ca #b4c #h4bj #a4jg ---------------------------------------- ---- ,average #j4cd #b4j #aj4be #b4jg ---------------------------------------- -------------------------- ,illustration3 ,,placing ,,sand ,,in ,a ,,filter1 ,,hamburg4 ,to face page #bh4 ,the averages show the effective size of the ,english sands to be slightly greater than that of the ,german sands--#j4cg instead of #j4cd mm4--but the difference is very small4 ,the entire range for the ten works is only from #j4ca to #j4dj mm41 and these may be taken as the ordinary limits of effective size of the sands employed in the best ,european works4 ,the average for the other sixteen works given above1 including dune-sands1 is #j4ca mm41 or1 omitting the dune-sands1 #j4cd mm4 ,illustration3 ,,fig4 #c;a4--,,sand ,,analysis ,,sheet1 ,,with ,,analyses ,,of ,,several ,,european ,,filter ,,sands4 ,it is important that filter sands should be free from lime4 ,when water is filtered through such sands1 no increase in hardness results4 ,when1 however1 water is filtered through sand containing lime1 some of it is usually dissolved and the water is made harder4 ,the amount of lime taken up in this way depends both upon the character of the sand1 and upon the solvent power of the water2 and it does not necessarily follow that a sand containing lime cannot be used for filtration1 but a sand nearly free from lime is to be preferred4 ,the presence of lime in sand can usually be detected by moistening it with hydrochloric acid4 ,the evolution of gas shows the presence of lime4 ,some idea of the amount of lime can be obtained from the amount of gas given off1 and the appearance of the sample after the treatment1 but chemical analysis is necessary to determine correctly the amount4 ,experiments with filters at ,pittsburg were made with sand containing #a4c per cent of lime1 the result being that the hardness of the water was increased about one part in #ajj1jjj2 but the amount of lime in the sand was so small that it would be washed out after a time1 and then the hardening effect would cease4 ,larger amounts of lime would continue their action for a number of years and would be more objectionable4 ,turning to the circumstances which influence the selection of the sand size1 we find that both the quality of the effluent obtained by filtration and the cost of filtration depend upon the size of the sand-grains4 ,with a fine sand the sediment layer forms more quickly and the removal of bacteria is more complete1 but1 on the other hand1 the filter clogs quicker and the dirty sand is more difficult to wash1 so that the expense is increased4 ,,effect ,,of ,,size ,,of ,,grain ,,upon ,,efficiency ,,of ,,filtration4 ,it is frequently stated that it is only the sediment layer which performs the work of filtration1 and that the sand which supports it plays hardly a larger part than does the gravel which carries the sand1 and under some circumstances this is undoubtedly the case4 ,nevertheless sand in itself1 without any sediment layer1 especially when not too coarse and not in too thin layers1 has very great purifying powers1 and1 in addition1 acts as a safeguard by positively preventing excessive rates of filtration on account of its frictional resistance4 ,as an illustration take the case of a filter of sand with an effective size of #j4ce mm4 and the minimum thickness of sand allowed by the ,german ,board of ,health1 namely1 one foot1 and let us suppose that with clogging the loss of head has reached two feet to produce the desired velocity of #b4eg million gallons per acre daily4 ,suppose now that by some accident the sediment layer is suddenly broken or removed from a small area1 the water will rush through this area1 until a new sediment layer is formed1 at a rate corresponding to the size1 pressure1 and depth of the sand1 or #bfj million gallons per acre daily--a hundred times the standard rate4 ,under these conditions the passing water will not be purified1 but will pollute the entire effluent from the filter4 ,under corresponding conditions1 with a deep filter of fine sand1 say with an effective size of #j4bj mm4 and #e feet deep1 the resulting rate would be only #ag million gallons per acre daily1 or less than seven times the normal1 and with the water passing through the full depth of fine sand1 the resulting deterioration in the effluent before the sand again became so clogged as to reduce the rate to nearly the normal1 would be hardly appreciable4 ,the results at ,lawrence have shown that with very fine sands #j4ji and #j4ad mm41 and #d to #e feet deep1 with the quantity of water which can practically be made to pass through them1 it is almost impossible to drive more than an insignificant fraction of the bacteria into the effluent4 ,even when the sands are entirely new1 or have been scraped or disturbed in the most violent way1 the first effluent passing1 before the sediment layer could have been formed1 is of good quality4 ,still finer materials1 #j4jd to #j4jf mm41 as far as could be determined1 secured the absolute removal of all bacteria1 but the rates of filtration which were possible were so low as to preclude their practical application4 ,with coarser sands1 as long as the filter is kept at a steady rate of filtration1 without interruptions of any kind1 entirely satisfactory results are often obtained1 although never quite so good as with the finer sands4 ,thus at ,lawrence the percentages of bacteria 7,b4 prodigiosus7 appearing in the effluents under comparable conditions were as follows3 #ahib #ahic ,with effective grain size #j4ch mm 4444 #j4af ,with effective grain size #j4bi mm 4444 #j4af ,with effective grain size #j4bf mm 4444 #j4aj ,with effective grain size #j4bj mm #j4ac #j4ja ,with effective grain size #j4ad mm #j4jd #j4jc ,with effective grain size #j4ji mm #j4jb #j4jb ,we may thus conclude that fine sands give normally somewhat better effluents than coarser ones1 and that they are much more likely to give at least a tolerably good purification under unusual or improper conditions4 ,,effect ,,of ,,grain ,,size ,,upon ,,frequency ,,of ,,scraping4 ,the practical objection to the use of fine sand is that it becomes rapidly clogged1 so that filters require to be scraped at shorter intervals1 and the sand washing is much more difficult and expensive4 ,the quantities of water filtered between successive scrapings at ,lawrence in millions of gallons per acre under comparable conditions have been as follows3 #ahib #ahic ,effective size of sand grain #j4ch mm 4444 #gi ,effective size of sand grain #j4bi mm 4444 #gj ,effective size of sand grain #j4bf mm 4444 #eg ,effective size of sand grain #j4bj mm #eh 4444 ,effective size of sand grain #j4ad mm #de #di ,effective size of sand grain #j4ji mm #bd #ad ,the increase in the quantities passed between scrapings with increasing grain size is very marked4 ,with the fine sands1 the depth to which the sand becomes dirty is much less than with the coarse sands1 but as it is not generally practicable to remove a layer of sand less than about #j4f inch thick1 even when the actual clogged layer is thinner than this1 the full quantity of sand has to be removed2 and the quantities of sand to be removed and washed are inversely proportional to the quantities of water filtered between scrapings4 ,on the other hand1 with very coarse sands the sediment penetrates the sand to a greater depth than the #j4f inch necessarily removed1 so that a thicker layer of sand has to be removed1 which may more than offset the longer interval4 ,this happens occasionally in water-works1 and a sand coarse enough to allow it occur is always disliked by superintendents1 and is replaced with finer sand as soon as possible4 ,it is obvious that the minimum expense for cleaning will be secured with a sand which just does not allow this deep penetration1 and ,i am inclined to think that the sizes of the sands in use have actually been determined more often than otherwise in this way1 and that the coarsest samples found1 having effective sizes of about #j4dj mm41 represent the practical limit to the coarseness of the sand1 and that any increase above this size would be followed by increased expense for cleaning as well as by decreased efficiency4 ,,selection ,,of ,,sand4 ,in selecting a sand for filtration1 when it is considered that repeated washings will remove some of the finest particles1 and so increase slightly the effective size1 a new sand coarser than #j4ce mm4 would hardly be selected4 ,perhaps #j4bj might be given as a suitable lower limit4 ,for comparatively clear lake- or reservoir-waters a finer sand could probably be used than would be the case with a turbid river-water4 ,a mixed sand having a uniformity coefficient above #c4j would be difficult to wash without separating it into portions of different sizes1 and1 in general1 the lower the coefficient1 that is1 the more uniform the grain sizes1 the better4 ,great pains should be taken to have the sand of the same quality throughout1 especially in the same filter1 as any variations in the grain sizes would lead to important variations in the velocity of filtration1 the coarser sands passing more than their share of water 7in proportion to the square of the effective sizes7 and with reduced efficiency4 ,at ,lawrence a sufficient quantity of natural sand was found of the grade required2 but where suitable material cannot be so obtained it is necessary to use other methods4 ,a mixed material can be screened from particles which are too large1 and can be washed to free it from its finer portions1 and in this way a good sand can be prepared1 if necessary1 from what might seem to be quite unpromising material4 ,the methods of sand-washing will be described in ,chapter ,v4 ,,thickness ,,of ,,the ,,sand ,,layer4 ,the thickness of the sand layer is made so great that when it is repeatedly scraped in cleaning the sand will not become too thin for good filtration for a considerable time4 ,when this occurs the removed sand must be replaced with clean sand4 ,the original thickness of the sand in ,european filters is usually from #bd to #dh inches1 thicknesses between #cj and #dj inches being extremely common1 and this is reduced before refilling to from #ab to #bd inches4 ,the ,imperial ,board of ,health of ,germany has fixed #ab inches as a limit below which the sand should never be scraped1 and a higher limit is recommended wherever possible4 ,a thick sand layer has the same steadying action as a fine sand1 and tends to prevent irregularities in the rate of filtration in proportion to its frictional resistance1 and that without increasing the frequency of cleaning2 but1 on the other hand1 it increases the necessary height of the filter1 throughout1 and consequently the cost of construction4 ,in addition to the steadying effect of a deep sand layer1 some purification takes place in the lower part of the sand even with a good sediment layer on the surface1 and the efficiency of deep filters is greater than that of shallow ones4 ,layers of finer materials1 as fine sand or loam1 in the lower part of a filter1 which would otherwise give increased efficiency without increasing the operating expenses1 cannot be used4 ,their presence invariably gives rise sooner or later to sub-surface clogging at the point of junction with the coarser sand1 as has been found by repeated tests at ,lawrence as well as in some of the ,dutch filters where such layers were tried2 and as there is no object in putting a coarser sand under a finer1 the filter sand is best all of the same size and quality from top to bottom4 ,,underdraining4 ,the underdrains of a filter are simply useful for collecting the filtered water2 they play no part in the purification4 ,one of the first requirements of successful filtration is that the rate of filtration shall be practically the same in all parts of the filter4 ,this is most difficult to secure when the filter has just been cleaned and the friction of the sand layer is at a minimum4 ,if the friction of the water in entering and passing through the underdrains is considerable1 the more remote parts of the filters will work under less pressure1 and will thus do less than their share of the work1 while the parts near the outlet will be overtaxed1 and filtering at too high rates will yield poor effluents4 ,to avoid this condition the underdrains must have such a capacity that their frictional resistance will be only a small fraction of the friction in the sand itself just after cleaning4 ,,gravel ,,layers4 ,the early filters contained an enormous quantity of gravel1 but the quantity has been steadily reduced in successive plants4 ,thus in #ahff ,kirkwood1 as a result of his observations1 recommended the use of a layer four feet thick1 and in addition a foot of coarse sand1 while at the present time new filters rarely have more than two feet of gravel4 ,even this quantity seems quite superfluous1 when calculations of its frictional resistance are made4 ,thus a layer of gravel with an effective size of #bj mm4#e 7which is much finer than that generally employed7 only #f inches thick will carry the effluent from a filter working at a rate of #b4eg million gallons per acre daily for a distance of #h feet 7that is1 with underdrains #af feet apart71 with a loss of head of only #j4jja foot1 and for longer distances tile drains are cheaper than gravel4 ,to prevent the sand from sinking into the coarse gravel1 intermediate sizes of gravel must be placed between1 each grade being coarse enough so that there is no possibility of its sinking into the layer below4 ,the necessary thickness of these intermediate layers is very small1 the principal point being to have a layer of each grade at every point4 ,thus on the #f inches of #bj mm4 gravel mentioned above1 three layers of two inches each1 of #h and #c mm4 gravel and coarse sand1 with a total height of six inches1 or other corresponding and convenient depths and sizes1 would1 if carefully placed1 as effectually prevent the sinking of the filter sand into the coarse gravel as the much thicker layers used in the older plants4 ,the gravel around the drains should receive special attention4 ,larger stones can be here used with advantage1 taking care that adequate spaces are left for the entrance of the water into the drains at a low velocity1 and to make everything so solid in this neighborhood that there will be no chance for the stones to settle which might allow the sand to reach the drains4 ,illustration3 ,,reconstructing ,,the ,,underdrainage ,,system ,,of ,a ,,filter ,,after #be ,,years ,,of ,,use1 ,,bremen4 ,illustration3 ,,placing ,,sand ,,in ,a ,,filter1 ,,choisy ,,le ,,roi 7,,paris74 ,to face page #cf4 ,at the ,lawrence filter1 at ,knigsberg in ,prussia1 at ,amsterdam and other places1 the quantity of gravel is reduced by putting the drains in trenches1 so that the gravel is reduced from a maximum thickness at the drain to nothing half way between drains4 ,the economy of the arrangement1 however1 as far as friction is concerned is not so great as would appear at first sight1 and the cost of the bottom may be increased2 but on the other hand it gives a greater depth of gravel for covering the drains with a small total amount of gravel4 ,as even a very small percentage of fine material is capable of getting in the narrow places and reducing the carrying power of the gravel1 it is important that all such matters should be carefully removed by washing before putting the gravel in place4 ,in ,england and ,germany gravel is commonly screened for use in revolving cylinders of wire-cloth of the desired sizes1 on which water is freely played from numerous jets1 thus securing perfectly clean gravel4 ,in getting gravel for the ,lawrence filter1 an apparatus was used1 in which advantage was taken of the natural slope of the gravel bank to do the work1 and the use of power was avoided4 ,the respective grades of gravel obtained were even in size1 and reasonably free from fine material1 but it was deemed best to wash them with a hose before putting them in the filter4 ,to calculate the frictional resistance of water in passing gravel1 we may assume that for the very low velocities which are actually found in filters the quantity of water passing varies directly with the head1 which for these velocities is substantially correct1 although it would not be true for higher rates1 especially with the coarser gravels4#f ,in the case of parallel underdrains the friction from the middle point between drains to the drains may be calculated by the formula3 ,total head 7#a_/b77,rate of filtration 7#a_/b distance between drains7#b7_/7;,average depth of gravel discharge coefficient74 ,the discharge coefficient for any gravel is #ajjj times the quantity of water which will pass when h_/l is #a_/ajjj expressed in million gallons per acre daily4 ,the approximate values of this coefficient for different-sized gravels are as follows3 ,,values ,,of ,,discharge ,,coefficient4 ,for gravel with effective size #e mm c #bc1jjj ,for gravel with effective size#aj mm c #fe1jjj ,for gravel with effective size#ae mm c #aaj1jjj ,for gravel with effective size#bj mm c #afj1jjj ,for gravel with effective size#be mm c #bcj1jjj ,for gravel with effective size#cj mm c #cjj1jjj ,for gravel with effective size#ce mm c #cij1jjj ,for gravel with effective size#dj mm c #dhj1jjj ,example3 ,what is the loss of head in the gravel at a rate of filtration of #b million gallons per acre daily1 with underdrains #bj feet apart1 where the supporting gravel has an effective size of #ce millimeters1 and is uniformly #a ft4 deep8 ,total head 7#a_/b77b #ajb7_/7a #cij1jjj7 4#jjjbef ft4 ,the total friction would be the same with the same average depth of gravel whether it was uniformly #a foot deep1 or decreasing from #a4e at the drains to #j4e in the middle1 or from #b4j to #j4 ,the reverse case with the gravel layer thicker in the middle than at the drains does not occur and need not be discussed4 ,the depth of gravel likely to be adopted as a result of this calculation1 when the drains are not too far apart1 will be much less than that actually used in most ,european works1 but as the two feet or more there employed are1 ,i believe1 simply the result of speculation1 there is no reason for following the precedent where calculations show that a smaller quantity is adequate4 ,the reason for recommending a thin lower layer of coarse gravel1 which alone is assumed to provide for the lateral movement of the water1 is that if more than about six inches of gravel is required to give a satisfactory resistance1 it will almost always be cheaper to use more drains instead of more gravel2 and the reason for recommending thinner upper layers for preventing the sand from settling into the coarse gravel is that no failures of this portion of filters are on record1 and in the few instances where really thin layers have been used the results have been entirely satisfactory4 ,in ,knigsberg filters were built by ,frhling1#g in which the sand was supported by five layers of gravel of increasing sizes1 respectively #a4b1 #a4b1 #a4f1 #b4j1 #c4b1 or1 together1 #i4b inches thick1 below which there were an average of five inches of coarse gravel4 ,these were examined after eight years of operation and found to be in perfect order4 ,at the ,lawrence ,experiment ,station filters have been repeatedly constructed with a total depth of supporting gravel layers not exceeding six inches1 and among the scores of such filters there has not been a single failure1 and so far as they have been dug up there has never been found to have been any movement whatever of the sand into the gravel4 ,the ,lawrence city filter1 built with corresponding layers1 has shown no signs of being inadequately supported4 ,in arranging the ,lawrence gravel layers care has always been taken that no material should rest on another material more than three or four times as coarse as itself1 and that each layer should be complete at every point1 so that by no possibility could two layers of greater difference in size come together4 ,and it is believed that if this is carefully attended to1 no trouble need be anticipated1 however thin the single layers may be4 ,,underdrains4 ,the most common arrangement1 in other than very small filters1 is to have a main drain through the middle of the filter1 with lateral drains at regular intervals from it to the sides4 ,the sides of the main drain are of brick1 laid with open joints to admit water freely1 and the top is usually covered with stone slabs4 ,the lateral drains may be built in the same way1 but tile drains are also used and are cheaper4 ,care must be taken with the latter that ample openings are left for the admission of water at very low velocities4 ,it is considered desirable to have these drains go no higher than the top of the coarsest gravel2 and this will often control the depth of gravel used4 ,if they go higher1 the top must be made tight to prevent the entrance of the fine gravels or sand4 ,sometimes they are sunk in part or wholly 7especially the main drain7 below the floor of the filter4 ,with gravel placed in waves1 that is1 thicker over the drains than elsewhere1 as mentioned above1 the drains are covered more easily than with an entirely horizontal arrangement4 ,when this is done1 the floor of the filter is trenched to meet the varying thickness of gravel1 so that the top of the latter is level1 and the sand has a uniform thickness4 ,many filters 7,lambeth1 ,brunswick1 etc47 are built with a double bottom of brick1 the upper layer of which1 with open joints1 supports the gravel and sand1 and is itself supported by numerous small arches or other arrangements of brick1 which serve to carry the water to the outlet without other drains4 ,this arrangement allows the use of a minimum quantity of gravel1 but is undoubtedly more expensive than the usual form1 with only the necessary quantity of gravel2 and ,i am unable to find that it has any corresponding advantages4 ,the frictional resistance of underdrains requires to be carefully calculated2 and in doing this quite different standards must be followed from those usually employed in determining the sizes of water-pipes1 as a total frictional resistance of only a few hundredths of a foot1 including the velocity head1 may cause serious irregularities in the rate of filtration in different parts of the filter4 ,the sizes of the underdrains differ very widely in proportion to the sizes of the filters in ,european works1 some of them being excessively large1 while in other cases they are so small as to suggest a doubt as to their allowing uniform rates of filtration1 especially just after cleaning4 ,i would suggest the following rules as reasonably sure to lead to satisfactory results without making an altogether too lavish provision3 ,in the absence of a definite determination to run filters at some other rate1 calculate the drains for the ,german standard rate of a daily column of #b4dj meters1 equal to #b4eg million gallons per acre daily4 ,this will insure satisfactory work at all lower rates1 and no difficulty on account of the capacity of the underdrains need be then anticipated if the rate is somewhat exceeded4 ,the area for a certain distance from the main drain depending upon the gravel may be calculated as draining directly into it1 provided there are suitable openings1 and the rest of the area is supposed to drain to the nearest lateral drain4 ,in case the laterals are round-tile drains ,i would suggest the following limits to the areas which they should be allowed to drain3 ,diameter of ,drain4 ,to ,drain an ,area not ,corresponding ,velocity of ,exceeding ,water in ,drain4 #d inches #bij square feet4 #j4cj foot4 #f inches #gej square feet4 #j4ce foot4 #h inches #aecj square feet4 #j4dj foot4 #aj inches #bghj square feet4 #j4df foot4 #ab inches #ddjj square feet4 #j4ea foot4 ,and for larger drains1 including the main drains1 their cross-sections at any point should be at least #a_/fjjj of the area drained1 giving a velocity of #j4ee foot per second with the rate of filtration mentioned above4 ,the total friction of the underdrains from the most remote points to the outlet will be friction in the gravel1 plus friction in the lateral drains1 plus the friction in main drain1 plus the velocity head4 ,illustration3 ,,fig4 #d4--,,plan ,,of ,,one ,,of ,,the ,,hamburg ,,filters1 ,,showing ,,frictional ,,resistance ,,of ,,the ,,underdrains4 ,i have calculated in this way the friction of one of the ,hamburg filters for the rate of #a1fjj1jjj gallons per acre daily at which it is used4 ,the friction was calculated for each section of the drains separately1 so that the friction from intermediate points was also known4 ,kutter's formula was used throughout with n #j4jac4 ,on the accompanying plan of the filter ,i have drawn the lines of equal frictional resistance from the junction of the main drain with the last laterals4 ,my information was incomplete in regard to one or two points1 so that the calculation may not be strictly accurate1 but it is nearly so and will illustrate the principles involved4 ,illustration3 ,,constructing ,,the ,,underdrainage ,,system ,,of ,a ,,filter1 ,,hamburg4 ,to face page #db4 ,the extreme friction of the underdrains is #aa millimeters #j4jcf foot4 ,the frictional resistance of the sand #ci inches thick1 effective size #j4cb mm4 and rate #a4fj million gallons per acre daily1 when absolutely free from clogging1 is by the formula1 page #ba1 #aemm41 or 4#jdij foot1 when the temperature is #ej4 ,practically there is some matter deposited upon the surface of the sand before filtration starts1 and further1 after the first scraping1 there is some slight clogging in the sand below the layer removed by scraping4 ,we can thus safely take the minimum frictional resistance of the sand including the surface layer at 4#jg foot4 ,the average friction of the underdrains for all points is about 4#jbc foot and the friction at starting will be 4#jg 4#jbc 4#jic foot 7including the friction in the last section to the effluent well where the head is measured1 4#ajj foot1 but the friction beyond the last lateral does not affect the uniformity of filtration74 ,the actual head on the sand close to the outlet will be 4#jic and the rate of filtration 4#jic_/4jgj #a4fj #b4ab4 ,the actual head at the most remote point will be 4#jic - 4#jcf 4#jeg1 and the rate of filtration will there be 4#jeg_/4jgj #afj #a4cj million gallons per acre daily4 ,the extreme rates of filtration are thus #b4ab and #a4cj1 instead of the average rate of #a4fj4 ,as can be seen from the diagram1 only very small areas work at these extreme rates1 the great bulk of the area working at rates much nearer the average4 ,actually the filter is started at a rate below #a4fj1 and the nearest portion never filters so rapidly as #b4ab1 for when the rate is increased to the standard1 the sand has become so far clogged that the loss of head is more than the 4#jg foot assumed1 and the differences in the rates are correspondingly reduced4 ,taking this into account1 it would not seem that the irregularities in the rate of filtration are sufficient to affect seriously the action of the filter4 ,they could evidently have been largely reduced by moderately increasing the sizes of the lower ends of the underdrains1 where most of the friction occurs with the high velocities 7up to 4#ig foot7 which there result4 ,the underdrains of the ,warsaw filters were designed by ,lindley to have a maximum loss of head of only 4#jafd foot when filtering at a rate of #b4eg1 which gives a variation of only #aj per cent in the rates with the minimum loss of head of 4#afi foot in the entire filter assumed by him4 ,the underdrains of the ,berlin filters1 according to my calculations1 have 4#jbj to 4#jcj foot friction1 of which an unusually large proportion is in the gravel1 owing to the excessive distances1 in some cases over #hj feet1 which the gravel is required to carry the water4 ,in this case1 using less or finer gravel would obviously have been fatal1 but the friction as well as the expense of construction would be much reduced by using more drains and less gravel4 ,the underdrains might appropriately be made slightly smaller1 with a deep layer of fine sand1 than under opposite conditions1 as in this case the increased friction in the drains would be no greater in proportion to the increased friction in the sand itself4 ,the underdrains of a majority of ,european filters have water-tight pipes connecting with them at intervals1 and going up through the sand and above the water1 where they are open to the air4 ,these pipes were intended to ventilate the underdrains and allow the escape of air when the filter is filled with water introduced from below4 ,it may be said1 however1 that in case the drains are surrounded by gravel and there is an opportunity for the air to pass from the top of the drain into the gravel1 it will so escape without special provision being made for it1 and go up through the sand with the much larger quantity of air in the upper part of the gravel which is incapable of being removed by pipes connecting with the drains4 ,these ventilator pipes where they are used are a source of much trouble1 as unfiltered water is apt to run down through cracks in the sand beside them1 and1 under bad management1 unfiltered water may even go down through the pipes themselves4 ,i am unable to find that they are necessary1 except with underdrains so constructed that there is no other chance for the escape of air from the tops of them1 or that they serve any useful purpose1 while there are positive objections to their use4 ,in some of the newer filters they have been omitted with satisfactory results4 ,,depth ,,of ,,water ,,on ,,the ,,filters4 ,in the older works with but crude appliances for regulating the rate of filtration and admission of raw water1 a considerable depth of water was necessary upon the filter to balance irregularities in the rates of filtration2 the filter was made to be1 to a certain extent1 its own storage reservoir4 ,when1 however1 appliances of the character to be described in ,chapter ,,iv are used for the regulation of the incoming water1 and with a steady rate of filtration1 this provision becomes quite superfluous4 ,with open filters a depth of water in excess of the thickness of any ice likely to be formed is required to prevent disturbance or freezing of the sand in winter4 ,it is also frequently urged that with a deep water layer on the filter the water does not become so much heated in summer1 but this point is not believed to be well taken1 for in any given case the total amount of heat coming from the sun to a given area is constant1 and the quantity of water heated in the whole day--that is1 the amount filtered--is constant1 and variations in the quantity exposed at one time will not affect the average resulting increase in temperature4 ,if the same water remained upon the filter without change it would of course be true that a thin layer would be heated more than a deep one1 but this is not the case4 ,it is also sometimes recommended that the depth of water should be sufficient to form a sediment layer before filtration starts1 but this point would seem to be of doubtful value1 especially where the filter is not allowed to stand a considerable time with the raw water upon it before starting filtration4 ,it is also customary to have a depth of water on the filter in excess of the maximum loss of head1 so that there can never be a suction in the sand just below the sediment layer4 ,it may be said in regard to this1 however1 that a suction below is just as effective in making the water pass the sand as an equal head above4 ,at the ,lawrence ,experiment ,station filters have been repeatedly used with a water depth of only from #f to #ab inches1 with losses of head reaching #f feet1 without the slightest inconvenience4 ,the suction only commences to exist as the increasing head becomes greater than the depth of water1 and there is no way in which air from outside can get in to relieve it4 ,in these experimental filters in winter1 when the water is completely saturated with air1 a small part of the air comes out of the water just as it passes the sediment layer and gets into reduced pressure1 and this air prevents the satisfactory operation of the filters4 ,but this is believed to be due more to the warming and consequent supersaturation of the water in the comparatively warm places in which the filters stand than to the lack of pressure1 and as not the slightest trouble is experienced at other seasons of the year1 it may be questioned whether there would be any disadvantage at any time in a corresponding arrangement on a large scale where warming could not occur4 ,the depths of water actually used in ,european filters with the full depth of sand are usually from #cf to #eb inches4 ,in only a very few unimportant cases is less than the above used1 and only a few of the older works use a greater depth1 which is not followed in any of the modern plants4 ,as the sand becomes reduced in thickness by scraping1 the depth of water is correspondingly increased above the figures given until the sand is replaced4 ,the depth of water on the ,german covered filters is quite as great as upon corresponding open filters4 ,thus the ,berlin covered filters have #ea1 while the new open filters at ,hamburg have only #dc inches4 ,,chapter ,,iv4 ,,rate ,,of ,,filtration ,,and ,,loss ,,of ,,head4 ,the rate of filtration recommended and used has been gradually reduced during the past thirty years4 ,in #ahff ,kirkwood found that #ab vertical feet per day1 or #c4ij million gallons per acre daily1 was recommended by the best engineers1 and was commonly followed as an average rate4 ,in #ahfh the ,london filters averaged a yield of #b4ah million gallons#h per acre daily1 including areas temporarily out of use1 while in #ahhe the quantity had been reduced to #a4fa4 ,since that time the rate has apparently been slightly increased4 ,the ,berlin filters at ,stralau constructed in #ahgd were built to filter at a rate of #c4ba million gallons per acre daily4 ,the first filters at ,tegel were built for a corresponding rate1 but have been used only at a rate of #b4eg1 while the more recent filters were calculated for this rate4 ,the new ,hamburg filters1 #ahib-c1 were only intended to filter at a rate of #a4fj million gallons per acre daily4 ,these in each case 7except the ,london figures7 are the standard rates for the filter-beds actually in service4 ,in practice the area of filters is larger than is calculated from these figures1 as filters must be built to meet maximum instead of average daily consumptions1 and a portion of the filtering area usually estimated at from #e to #ae per cent1 but in extreme cases reaching #ej per cent1 is usually being cleaned1 and so is for the time out of service4 ,in some works also the rate of filtration on starting a filter is kept lower than the standard rate for a day or two1 or the first portion of the effluent1 supposed to be of inferior quality1 is wasted1 the amount so lost reaching in an extreme case #i to #ad per cent of the total quantity of water filtered4#i ,in many of the older works also1 there is not storage capacity enough for filtered water to balance the hourly fluctuations in consumption1 and the filters must be large enough to meet the maximum hourly as well as the maximum daily requirements4 ,for these reasons the actual quantity of water filtered in a year is only from #ej to #ge per cent of what would be the case if the entire area of the filters worked constantly at the full rate4 ,a statement of the actual yields of a number of filter plants is given in ,appendix ,,iv4 ,the figures for the average annual yields can be taken as quite reliable4 ,the figures given for rate1 in many cases1 have little value1 owing to the different ways in which they are calculated at different places4 ,in addition most of the old works have no adequate means of determining what the rate at any particular time and for a single filter really is1 and statements of average rates have only limited value4 ,the filters at ,hamburg are not allowed to filter faster than #a4fj or those at ,berlin faster than #b4eg million gallons per acre daily1 and adequate means are provided to secure this condition4 ,other ,german works aim to keep within the latter limit4 ,beyond this1 unless detailed information in regard to methods is presented1 statements of rate must be taken with some allowance4 ,,effect ,,of ,,rate ,,upon ,,cost ,,of ,,filtration4 ,the size of the filters required1 and consequently the first cost1 depends upon the rate of filtration1 but with increasing rates the cost is not reduced in the same proportion as the increase in rate1 since the allowance for area out of use is sensibly the same for high and low rates1 and in addition the operating expenses depend upon the quantity filtered and not upon the filtering area4 ,thus1 to supply #aj million gallons at a maximum rate of #b million gallons per acre daily we should require #aj #b #e acres #a acre reserve for cleaning #f acres1 while with a rate twice as great1 and with the same reserve 7since the same amount of cleaning must be done1 as will be shown below71 we should require #aj #d #a #c4e acres1 or #eh per cent of the area required for the lower rate4 ,thus beyond a certain point increasing the rate does not effect a corresponding reduction in the first cost4 ,the operating cost for the same quantity of water filtered does not appear to be appreciably affected by the rate4 ,it is obvious that at high rates filters will became clogged more rapidly1 and will so require to be scraped oftener than at low rates1 and it might naturally be supposed that the clogging would increase more rapidly than the rates1 but this does not seem to be the case4 ,at the ,lawrence ,experiment ,station1 under strictly parallel conditions and with identically the same water1 filters running at various rates became clogged with a rapidity directly proportional to the rates1 so that the quantities of water filtered between scrapings under any given conditions are the same whether the rate is high or low4 ,the statistics bearing upon this point are interesting1 if not entirely conclusive4 ,there were eleven places in ,germany filtering river waters1 from which statistics were available for the year #ahia-ib4 ,of these there were four places with high rates1 ,lbeck1 ,stettin1 ,stuttgart1 and ,magdeburg1 yielding #c4gj million gallons per acre daily1 which filtered on an average #ei million gallons per acre between scrapings4 ,three other places1 ,breslau1 ,altona1 and ,frankfurt1 yielding #a4he1 passed on an average #ee million gallons per acre between scrapings1 and four other places1 ,bremen1 ,knigsberg1 ,brunswick and ,posen1 yielding #a4cd million gallons per acre daily1 passed only #dj million gallons per acre between scrapings4 ,the works filtering at the highest rates thus filtered more water in proportion to the sand clogged than did those filtering more slowly1 but ,i cannot think that this was the result of the rate4 ,it is more likely that some of the places have clearer waters than others1 and that this both allows the higher rate and causes less clogging than the more turbid waters4 ,,effect ,,of ,,rate ,,upon ,,efficiency ,,of ,,filtration4 ,the effect of the rate of filtration upon the quality of the effluent has been repeatedly investigated4 ,the efficiency almost uniformly decreases rapidly with increasing rate4 ,frnkel and ,piefke#aj first found that with the high rates the number of bacteria passing some experimental filters was greatly increased4 ,piefke#aa afterward repeated these experiments1 eliminating some of the features of the first series to which objection was made1 and confirmed the first results4 ,the results were so marked that ,piefke was led to recommend the extremely low limit of #a4bh million gallons per acre daily as the safe maximum rate of filtration1 but he has since repeatedly used #b4eg million gallons4 ,kmmel1#ab on the other hand1 in a somewhat limited series of experiments1 was unable to find any marked connection between the rate and the efficiency1 a rate of #b4eg giving slightly better results than rates of either #a4bh or #e4ad4 ,the admirably executed experiments made at ,zrich in #ahhf-h upon this point1 which gave throughout negative results1 have but little value in this connection1 owing to the extremely low number of bacteria in the original water4 ,at ,lawrence in #ahib the following percentages of bacteria 7,b4 prodigiosus7 passed at the respective rates3 ---------------------------------------- -------------------------- ,no4 of ,depth4 ,effective ,rate4 ,millions gallons per acre daily4 ,filter4 ,size of ----------------------------------- ,sand4 #j4e #a4j #a4e #b4j #c4j ---------------------------------------- ---------------------- #cc;,a #fj #j4ad #j4jjb #j4jdj #cd;,a #fj #j4ji #j4jja #j4jje #j4jbj #cf;,a #fj #j4bj #j4jej #j4jej #cg #fj #j4bj #j4jaj #j4acj #ch #bd #j4bj #j4jah #j4adj #j4aaj #j4caj #ci #ab #j4bj #j4jad #j4jgj #j4jhj #j4ebj #dj #ab #j4bj #j4jgj #j4jij #db #ab #j4bj #j4jaf #j4aej #j4eej ---------------------------------------- ---------------------- ,average #j4jaj #j4jdh #j4jfg #j4jhh #j4cef ---------------------------------------- ------------------------ ,these results show a very marked decrease in efficiency with increasing rates1 the number of bacteria passing increasing in general as rapidly as the square of the rate4 ,the #ahic results also showed decreased efficiency with high rates1 but the range in the rates under comparable conditions was less than in #ahib1 and the bacterial differences were less sharply marked4 ,while the average results at ,lawrence1 as well as most of the ,european experiments1 show greatly decreased efficiency with high rates1 there are many single cases1 particularly with deep layers of not too coarse sand1 where1 as in ,kmmel's experiments1 there seems to be little connection between the rate and efficiency4 ,an explanation of these apparently abnormal results will be given in ,chapter ,,vi4 ,it is commonly stated#ac that every water has its own special rate of filtration1 which must be determined by local experiments1 and that this rate may vary widely in different cases4 ,thus it is possible that the rate of #a4fj adopted at ,hamburg for the turbid ,elbe water1 the rate of #b4eg used at ,berlin1 and about the same at ,london for much clearer river-waters1 and the rate of #g4ej used at ,zrich for the almost perfectly clear lake-water are in each case the most suitable for the respective waters4 ,in other cases however1 where rates much above #b4eg are used for river-waters1 as at ,lbeck and ,stettin1 there is a decided opinion that these rates are excessive1 and in these instances steps are now being taken to so increase the filtering areas as to bring the rates within the limit of #b4eg million gallons per acre daily4 ,from the trend of ,european practice it would seem that for ,american river-waters the rate of filtration should not exceed #b4eg in place of the #c4ij million gallons per acre daily recommended by ,kirkwood1 or even that a somewhat lower rate might be desirable in some cases4 ,of course1 in addition to the area necessary to give this rate1 a reserve for fluctuating rates and for cleaning should be provided1 reducing the average yield to #b4jj1 #a4ej1 or even less4 ,in the case of water from clear lakes1 ponds1 or storage reservoirs1 especially when they are not subject to excessive sewage pollution or to strong alg growths1 it would seem that rates somewhat and perhaps in some cases very much higher 7as at ,zrich7 could be satisfactorily used4 ,,the ,,loss ,,of ,,head4 ,the loss of head is the difference between the heads of the waters above and below the sand layer1 and represents the frictional resistance of that layer4 ,when a filter is quite free from clogging this frictional resistance is small1 but gradually increases with the deposit of a sediment layer from the water filtered until it becomes so great that the clogging must be removed by scraping before the process can be continued4 ,after scraping the loss of head is reduced to1 or nearly to1 its original amount4 ,with any given amount of clogging the loss of head is directly proportional to the rate of filtration2 that is1 if a filter partially clogged1 filtering at a rate of #a4j1 has a frictional resistance of #j4e ft41 the resistance will be doubled by increasing the rate to #b4jj million gallons per acre daily1 provided no disturbance of the sediment layer is allowed4 ,this law for the frictional resistance of water in sand alone also applies to the sediment layer1 as ,i have found by repeated tests1 although in so violent a change as that mentioned above1 the utmost care is required to make the change gradually and prevent compression or breaking of the sediment layer4 ,from this relation between the rate of filtration and the loss of head it is seen that the regulation of either involves the regulation of the other1 and it is a matter of indifference which is directly and which indirectly controlled4 ,,regulation ,,of ,,the ,,rate ,,and ,,loss ,,of ,,head ,,in ,,the ,,older ,,filters4 ,in the older works1 and in fact in all but a few of the newest works1 the underdrains of the filters connect directly through a pipe with a single gate with the pure-water reservoir or pump-well1 which is so built that the water in it may rise nearly or quite as high as that standing upon the filter4 ,illustration3 ,,fig4 #e4--,,simplest ,,form ,,of ,,regulation3 ,,stralau ,,filters ,,at ,,berlin4 ,a typical arrangement of this sort was used at the ,stralau works at ,berlin 7now discontinued71 ,fig4 #e4 ,with this arrangement the rate of filtration is dependent upon the height of water in the reservoir or pump-well1 and so upon the varying consumption4 ,when the water in the receptacle falls with increasing consumption the head is increased1 and with it the rate of filtration1 while1 on the other hand1 with decreasing draft and rising water in the reservoir1 the rate of filtration decreases and would eventually be stopped if no water were used4 ,this very simple arrangement thus automatically1 within limits1 adjusts the rate of filtration to the consumption1 and at the same time always gives the highest possible level of water in the pump-well1 thus also economizing the coal required for pumping4 ,in plants of this type the loss of head may be measured by floats on little reservoirs built for that purpose1 connected with the underdrains2 but more often there is no means of determining it1 although the maximum loss of head at any time is the difference between the levels of the water on the filter and in the reservoir1 or the outlet of the drain-pipe1 in case the latter is above the water-line in the reservoir4 ,the rate of filtration can only be measured with this arrangement by shutting off the incoming water for a definite interval1 and observing the distance that the water on the filter sinks4 ,the incoming water is regulated simply by a gate1 which a workman opens or closes from time to time to hold the required height of water on the filter4 ,the only possible regulation of the rate and loss of head is effected by a partial closing of the gate on the outlet-pipe1 by which the freshly-cleaned filters with nearly-closed gates are kept from filtering more rapidly than the clogged filters1 the gates of which are opened wide4 ,often1 however1 this is not done1 and then the fresh filters filter many times as rapidly as those which are partially clogged4 ,a majority of the filters now in use are built more or less upon this plan1 including most of those in ,london and also the ,altona works1 which had such a favorable record with cholera in #ahib4 ,the invention and application of methods of bacterial examination in the last years have led to different ideas of filtration from those which influenced the construction of the earlier plants4 ,as a result it is now regarded as essential by most ,german engineers#ad that each filter shall be provided with devices for measuring accurately and at any time both the rate of filtration and the loss of head1 and for controlling them1 and also for making the rate independent of consumption by reservoirs for filtered water large enough to balance hourly variations 7capacity #a_/d to #a_/c maximum daily quantity7 and low enough so that they can never limit the rate of filtration by causing back-water on the filters4 ,these points are now insisted upon by the ,german ,imperial ,board of ,health1#ae and all new filters are built in accordance with them1 while most of the old works are being built over to conform to the requirements4 ,,apparatus ,,for ,,regulating ,,the ,,rate ,,and ,,loss of ,,head4 ,many appliances have been invented for the regulation of the rate and loss of head4 ,in the apparatus designed by ,gill and used at both ,tegel and ,mggel at ,berlin the regulation is effected by partially closing a gate through which the effluent passes into a chamber in which the water-level is practically constant 7,fig4 #f74 ,the rate is measured by the height of water on the weir which serves as the outlet for this second chamber into a third connecting with the main reservoir1 while the loss of head is shown by the difference in height of floats upon water in the first chamber1 representing the pressure in the underdrains1 and upon water in connection with the raw water on the filter4 ,from the respective heights of the three floats the attendant can at any time see the rate of filtration and the loss of head1 and when a change is required it is effected by moving the gate4 ,illustration3 ,,fig4 #f4--,,regulation ,,apparatus ,,at ,,berlin 7,,tegel74 ,in the apparatus designed in #ahff by ,kirkwood for ,st4 ,louis and never built 7,fig4 #g7 the loss of head was directly1 and the rate indirectly1 regulated by a movable weir1 which was to have been lowered from time to time by the attendant to secure the required results4 ,this plan is especially remarkable as it meets the modern requirements of a regular rate independent of rate of consumption and of the water-level in the reservoir1 and also allows continual measurements of both rate 7height of water on the weir7 and head 7difference in water-levels on filter and in effluent chamber7 to be made1 and control of the same by the position of the weir4 ,mr4 ,kirkwood found no filters in ,europe with such appliances1 and it was many years after his report was published before similar devices were used1 but they are now regarded as essential4 ,illustration3 ,,fig4 #g4--,,regulation ,,apparatus ,,and ,,section ,,of ,,filter ,,recommended ,,for ,,st4 ,,louis ,,by ,,kirkwood ,,in #ahff4 ,illustration3 ,,fig4 #h4--,,regulation ,,apparatus ,,used ,,at ,,hamburg4 ,the regulators for new filters at ,hamburg 7,fig4 #h7 are built upon the principle of ,kirkwood's device1 but provision is made for a second measurement of the water if desired by the loss of head in passing a submerged orifice4 ,both the rate and loss of head are indicated by a float on the first chamber connecting directly with the underdrain1 which at the same time indicates the head on a fixed scale1 the zero of which corresponds to the height of the water above the filter1 and the rate upon a scale moving with the weir1 the zero of which corresponds with the edge of the weir4 ,the water on the filter is held at a perfectly constant level4 ,the regulators in use at ,worms and those recently introduced at ,magdeburg act upon the same principle1 but the levels of the water on the filters are allowed to fluctuate1 and the weirs and in fact1 the whole regulating appliances are mounted on big floats in surrounding chambers of water connecting with the unfiltered water on the filters4 ,i am unable to find any advantages in these appliances1 and they are much more complicated than the forms shown by the cuts4 ,,apparatus ,,for ,,regulating ,,the ,,rate ,,directly4 ,illustration3 ,,fig4 #i4--,,lindley',s ,,regulation ,,apparatus ,,at ,,warsaw1 ,,russia4 ,the above-mentioned regulators control directly the loss of head1 and only indirectly the rate of filtration4 ,the regulators at ,warsaw were designed by ,lindley to regulate the rate directly and make it independent of the loss of head4 ,the quantity of water flowing away is regulated by a float upon the water in the effluent chamber1 which holds the top of the telescope outlet-pipe a constant distance below the surface and so secures a constant rate4 ,as the friction of the filter increases the float sinks with the water until it reaches bottom1 when the filter must be scraped4 ,a counter-weight reduces the weight on the float1 and at the same time allows a change in the rate when desired4 ,this apparatus is automatic4 ,all of the other forms described require to be occasionally adjusted by the attendant1 but the attention they require is very slight1 and watchmen are always on duty at large plants1 who can easily watch the regulators4 ,the ,warsaw apparatus is reported to work very satisfactorily1 no trouble being experienced either by leaking or sticking of the telescope-joint1 which is obviously the weakest point of the device1 but fortunately a perfectly tight joint is not essential to the success of the apparatus4 ,regulators acting upon the same principle have recently been installed at ,zrich1 where they are operating successfully4 ,burton#af has described an ingenious device designed by him for the filters at ,tokyo1 ,japan4 ,it consists of a double acting valve of gun metal 7similar to that shown by ,fig4 #aa71 through which the effluent must pass4 ,this valve is opened and closed by a rod connecting with a piston in a cylinder1 the opposite sides of which connect with the effluent pipe above and below a point where the latter is partially closed1 so that the valve is opened and closed according as the loss of head in passing this obstruction is below or above the amount corresponding to the desired rate of filtration4 ,the use of the ,venturi meter in connection with the regulation of filters would make an interesting study1 and has1 ,i believe1 never been considered4 ,illustration3 ,,regulator-,,house1 ,,showing ,,rate ,,of ,,filtration ,,and ,,loss ,,of ,,head ,,on ,,the ,,outside1 ,,bremen4 ,illustration3 ,,inlet ,,for ,,admission ,,of ,,raw ,,water ,,to ,a ,,filter1 ,,east ,,london4 ,to face page #eh4 ,,apparatus ,,for ,,regulating ,,the ,,height ,,of ,,water ,,upon ,,filters4 ,it will be seen by reference to the diagrams of the ,berlin and ,hamburg effluent regulators 7,figs4 #f and #h7 that their perfect operation is dependent upon the maintenance of a constant water-level upon the filters4 ,the old-fashioned adjustment of the inlet-gate by the attendant is hardly accurate enough4 ,the first apparatus for accurately and automatically regulating the level of the water upon the filters was constructed at ,leeuwarden1 ,holland1 by the engineer1 ,mr4 ,halbertsma1 who has since used a similar device at other places1 and improved forms of which are now used at ,berlin and at ,hamburg4 ,at ,berlin 7,mggel7 the water-level is regulated by a float upon the water in the filter which opens or shuts a balanced double valve on the inlet-pipe directly beneath1 as shown in ,fig4 #aj4 ,it is not at all necessary that this valve should shut water-tight2 it is only necessary that it should prevent the continuous inflow from becoming so great as to raise the water-level1 and for this reason loose1 easily-working joints are employed4 ,the apparatus is placed in a little pit next to the side of the filter1 and the overflowing water is prevented from washing the sand by paving the sand around it for a few feet4 ,illustration3 ,,fig4 #aj4--,,regulation ,,of ,,inflow ,,used ,,at ,m,,ggel1 ,,berlin4 ,at ,hamburg the same result is obtained by putting the valve in a special chamber outside of the filter and connected with the float by a walking-beam 7,fig4 #aa74 ,illustration3 ,,fig4 #aa4--,,regulation ,,of ,,inflow ,,used ,,at ,,hamburg4 ,the various regulators require to be protected from cold and ice by special houses1 except in the case of covered filters1 where they can usually be arranged with advantage in the filter itself4 ,in regard to the choice of the form of regulator for both the inlets and outlets of filters1 so far as ,i have been able to ascertain1 each of the modern forms described as in use performs its functions satisfactorily1 and in special cases any of them could properly be selected which would in the local conditions be the simplest in construction and operation4 ,,limit ,,to ,,the ,,loss ,,of ,,head4 ,the extent to which the loss of head is allowed to go before filters are cleaned differs widely in the different works1 some of the newer works limiting it sharply because it is believed that low bacterial efficiency results when the pressure is too great1 although the frequency of cleaning and consequently the cost of operation are thereby increased4 ,at ,darlington1 ,england1 ,i believe as a result of the ,german theories1 the loss of head is limited to about #ah inches by a masonry weir built within the last few years4 ,at ,berlin1 both at ,tegel and ,mggel1 the limit is #bd inches1 while at the new ,hamburg works #bh inches are allowed4 ,at ,stralau in #ahic an effort was made to not exceed a limit of #dj inches1 but previously heads up to #fj inches were used1 which corresponds with the #ef inches used at ,altona2 and1 in the other old works1 while exact information is not easily obtained because of imperfect records1 ,i am convinced that heads of #fj or even #hj inches are not uncommon4 ,at the ,lawrence ,experiment ,station heads of #gj inches have generally been used1 although some filters have been limited to #cf and #bd inches4 ,in #ahff ,kirkwood became convinced that the loss of head should not go much above #cj inches1 first1 because high heads would1 by bringing extra weight upon the sand1 make it too compact1 and1 second1 because when the pressure became too great the sediment layer on the surface of the sand1 in which most of the loss of head occurs1 would no longer be able to support the weight and1 becoming broken1 would allow the water to pour through the comparatively large resulting openings at greatly increased rates and with reduced efficiency4 ,in regard to the first point1 a straight1 even pressure many times that of the water on the filter is incapable of compressing the sand4 ,it is much more the effect of the boots of the workmen when scraping that makes the sand compact4 ,i have found sand in natural banks at ,lawrence #gj or #hj feet below the surface1 where it had been subjected to corresponding pressure for thousands of years1 to be quite as porous as when packed in water in experimental filters in the usual way4 ,the second reason mentioned1 or1 as ,i may call it1 the breaking-through theory1 is very generally if not universally accepted by ,german engineers1 and this is the reason for the low limit commonly adopted by them4 ,a careful study of the results at ,lawrence fails to show the slightest deterioration of the effluents up to the limit used1 #gb inches4 ,thus in #ahib1 taking only the results of the continuous filters of full height 7,nos4 #cc;,a1 #cd;,a1 #cf;,a1 and #cg71 we find that for the three days before scraping1 when the head was nearly #gb inches1 the average number of bacteria in the effluents was #ca per cc41 while for the three days after scraping1 with very low heads1 the number was #dg4 ,the corresponding numbers of ,b4 prodigiosus#ag were #a4a and #b4g4 ,this shows better work with the highest heads1 but is open to the objection that the period just after scraping1 owing to the disturbance of the surface1 is commonly supposed to be a period of low efficiency4 ,to avoid this criticism in calculating the corresponding results for #ahic1 the numbers of the bacteria for the intermediate days which could not have been influenced either by scraping or by excessive head are put side by side with the others4 ,taking these results as before for continuous filters #gb inches high1 and excluding those with extremely fine sands and a filter which was only in operation a short time toward the end of the year1 we obtain the following results3 ,water ,b4 ,bacteria ,prodigiosus per cc4 per cc4 ,average #ast day after scraping1 low heads #gi #f4a ,average #b;d day after scraping1 low heads #dd #d4a ,average #c;d day after scraping1 low heads #de #c4f ,intermediate days1 medium heads #ei #d4e ,second from last day1 heads of nearly #gb inches #ff #b4g ,next to the last day1 heads of nearly #gb inches #ef #c4b ,last day1 heads of nearly #gb inches #hc #b4e ,these figures show a very slight increase of the water bacteria in the effluent as the head approaches the limit1 but no such increase as might be expected from a breaking through of the sediment layer1 and the ,b4 prodigiosus which is believed to better indicate the removal of the bacteria of the original water1 actually shows a decrease1 the last day being the best day of the whole period4 ,the ,lawrence results1 then1 uniformly and clearly point to a conclusion directly opposite to the commonly accepted view1 and ,i have thus been led to examine somewhat closely the grounds upon which the breaking-through theory rests4 ,the two works which have perhaps contributed most to the theories of filtration are the ,stralau and ,altona works4 ,after examining the available records of these works1 ,i am quite convinced that at these places there has been1 at times at least1 decreased efficiency with high heads4 ,for the ,stralau works this is well shown by ,piefke's plates in the ,zeitschrift fr ,hygiene1 #ahid1 after page #ahh4 ,in both of these works1 however1 the apparatus 7or lack of apparatus7 for regulating the rate is that shown by ,fig4 #e1 page #di1 and the rate of filtration is thus dependent upon the rate of consumption and the height of water in the reservoir4 ,at the ,stralau works1 at the time covered by the above-mentioned diagrams1 the daily quantity of water filtered was #bg times the capacity of the reservoir1 and the rate of filtration must consequently have adapted itself to the hourly consumptions4 ,the data which formed the basis of ,kirkwood's conclusions are not given in detail1 but it is quite safe to assume that they were obtained from filters regulated as those at ,altona and ,stralau are regulated1 and what is said in regard to the latter will apply equally to his results4 ,piefke#ah shows that among the separate filters at ,stralau1 all connected with the same pure-water reservoir1 those connected through the shorter pipes gave poorer effluents than the more remote filters1 and he attributes the difference to the frictional resistance of the connecting pipes1 which helped to prevent excessive rates in the filters farthest away when the water in the reservoir became low1 and thus the fluctuations in the rates in these filters were less than in those close to the reservoir4 ,he does not1 however1 notice1 in speaking of the filters in which the decreased efficiencies with high heads were specially marked1 that they follow in nearly the same order1 and that of the four open filters mentioned three were near the reservoir and only one was separated by a comparatively long pipe1 indicating that the deterioration with high heads was only noticeable1 or at least was much more conspicuous1 in those filters where the rates fluctuated most violently4 ,it requires no elaborate calculation to show that of two filters connected with the same pure-water reservoir1 as shown by ,fig4 #e1 with only simple gates on the connecting pipes1 one of them clean and throttled by a nearly closed gate1 so that the normal pressure behind the gate is above the highest level of water in the reservoir1 and the other clogged so that the normal pressure of the water in the drain is considerably below the highest level of the water in the reservoir1 the latter will suffer much the more severe shocks with fluctuating water-levels2 and the fact being admitted that fluctuating levels are unfavorable1 we must go farther and conclude that the detrimental action will increase with increasing loss of head4 ,i am inclined to think that this theory is adequate to explain the ,stralau and ,altona results without resource to the breaking-through theory4 ,while the above does not at all prove the breaking-through theory to be false1 it explains the results upon which it rests in another way1 and can hardly fail to throw so much doubt upon it as to make us refuse to allow its application to those works where a regular rate of filtration is maintained regardless of variations in the consumption1 until proof is furnished that it is applicable to them4 ,i have been totally unable to find satisfactory ,european results in regard to this point4 ,the ,english works can furnish nothing1 both on account of the lack of regulating appliances and because the monthly bacterial examinations are inadequate for a discussion of hourly or daily changes4 ,the results from the older ,continental works are also excluded for one or the other1 or more often for both1 of the above reasons4 ,the ,hamburg1 ,tegel1 and ,mggel results1 so far as they go1 show no deterioration with increased heads1 but the heads are limited to #bd or #bh inches by the construction of the filters1 and the results thus entirely fail to show what would be obtained with heads more than twice as high4 ,i am thus forced to conclude that there is no adequate evidence of inferior efficiency with high heads in filters where the rates are independent of the water-level in the pure-water reservoir1 the only results directly to the point--the ,lawrence results mentioned above--indicating that the full efficiency is maintained with heads reaching at least #gb inches4 ,the principal reason for desiring to allow a considerable loss of head is an economical one2 the period will then be lengthened1 while the frequency of scraping and the volume of sand to be washed and replaced will be correspondingly reduced4 ,there may be other advantages in long periods1 such as less trouble with scraping and better work in cold winter weather1 but the cost is the most important consideration4 ,it is the prevalent idea among the ,german engineers that the loss of head after reaching #bd to #cj inches would increase very rapidly1 so that the quantity of water filtered1 in case a much higher head was allowed1 would not be materially increased4 ,no careful investigations1 however1 have been made1 and indeed they are hardly possible with existing arrangements1 as in the older filters the loss of head fluctuates with varying rates of filtration in such a way that only results of very doubtful value can be obtained1 and in the newer works the loss of head is too closely limited1 and the curves which can be drawn by extrapolation are evidently no safe indications of what would actually happen if the process was carried farther4 ,on the other hand1 ,i was told by the attendant at ,darlington1 ,england1 that since the building of the weir a few years ago1 which now limits the loss of head to about #ah inches instead of the #e feet or more formerly used1 the quantity of sand to be removed has been three times as great as formerly4 ,no records are kept1 and this can only be given as the general impression of the man who superintends the work4 ,at ,lawrence the average quantities of water filtered between scrapings with sand of an effective size of #j4bj mm4 have been as follows3 ,maximum ,loss of ,million ,gallons per ,acre filtered ,head4 between ,scrapings4 #ahib4 #ahic4 ,average4 #gj inches #eh #hh #gc #cd foot #cb #bb #bg #bb foot #ag #af #af ,with sand of an effective size of #j4bi mm4 the results were3 #ahic4 #gj inches #gj #bb foot #bi ,these results indicate a great increase in the quantity of water filtered between scrapings with increasing heads1 the figures being nearly proportional to the maximum heads used in the respective cases4 ,it is1 of course1 quite possible that the results would differ in different places with the character of the raw water and of the filtering material4 ,the depth of sand to be removed by scraping at one time is1 within limits1 practically independent of the quantity of dirt which it has accumulated1 and any lengthening of the period means a corresponding reduction in the quantity of sand to be removed1 washed and replaced and consequently an important reduction in the operating cost1 as well as a reduction in the area of filters out of use while being cleaned1 and so1 in the capital cost4 ,among the minor objections to an increased loss of head are the greater head against which the water must be pumped1 and the possible increased difficulty of filling filters with filtered water from below after scraping1 but these would hardly have much weight against the economy indicated by the ,lawrence experiments for the higher heads4 ,high heads will also drive an increased quantity of water through any cracks or passages in the filter4 ,such leaks have at last been found to be the cause of the inferior work of the covered filters at ,stralau1 the water going down unfiltered in certain corners1 especially at high heads2 but with careful construction there should be no cracks1 and with the aid of bacteriology to find the possible leaks this ought not to be a valid objection4 ,in conclusion3 the trend of opinion is strongly in favor of limiting the loss of head to about #bd to #cj inches as was suggested by ,kirkwood1 but ,i am forced to conclude that there is reason to believe that equally good results can be obtained with lower operating expenses by allowing higher heads to be used1 at least in the case of filters with modern regulating appliances1 and1 ,i would suggest that filters should be built so as not to exclude the use of moderately high heads1 and that the limit to be permanently used should be determined by actual tests of efficiency and length of period with various losses of head after starting the works4 ,,chapter ,v4 ,,cleaning ,,filters4 ,when a filter has become so far clogged that it will no longer pass a satisfactory quantity of water with the allowable head it must be cleaned by scraping off and removing the upper layer of dirty sand4 ,to do this without unnecessary loss of time the unfiltered water standing upon the filter is removed by a drain above the sand provided for that purpose4 ,the water in the sand must then be lowered below the surface of the sand by drawing water from the underdrains until the sand is firm enough to bear the weight of the workmen4 ,by the time that this is accomplished the last water on the surface should have soaked away1 and the filter is ready to be scraped4 ,this is done by workmen with wide1 sharp shovels1 and the sand removed is taken to the sand-washing apparatus to be washed and used again4 ,special pains are given to securing rapid and cheap transportation of the sand4 ,in some cases it is wheeled out of the filter on an inclined plane to the washer4 ,in other cases a movable crane is provided which lifts the sand in special receptacles and allows it to fall into cars on a tram-line on which the crane also moves4 ,the cars as filled are run to the washer and also serve to bring back the washed sand4 ,when the dirty sand has been removed1 the surface of the sand is carefully smoothed and raked4 ,this is especially necessary to remove the effects of the workmen's boots4 ,it is customary in the most carefully managed works to fill the sand with filtered water from below1 introduced through the underdrains4 ,in case the ordinary level of the water in the pure-water canal is higher than the surface of the sand in the filters1 this is accomplished by simply opening a gate provided for the purpose1 which allows the water to pass around the regulating apparatus4 ,otherwise filters can be filled from a special pipe taking its water from any filter which at that time can deliver its effluent high enough for that purpose4 ,the quantity of water required for filling the sand from below is ordinarily but a fraction of one per cent of the quantity filtered4 ,formerly1 instead of filling from below1 after cleaning1 the raw water was brought directly onto the surface of the filter4 ,this was said to only imperfectly fill the sand-pores1 which still contained much air4 ,if1 however1 the water is not brought on too rapidly it will sink into the sand near the point where it is applied1 pass laterally through the sand or underlying gravel to other parts of the filter1 and then rise1 so that even in this case all but a little of the filter will be really filled from below4 ,this is1 however1 open to the objection that however slowly the water is introduced1 the sand which absorbs it around the inlet filters it at a very high rate and presumably imperfectly1 so that the water in the underdrains at the start will be poor quality and the sand around the inlet will be unduly clogged4 ,the practice of filling from below is therefore well founded4 ,as soon as the surface of the sand is covered with the water from below1 raw water is introduced from above1 filling the filter to the standard height1 care being taken at first that no currents are produced which might wash the surface of the sand4 ,it has been recommended by ,piefke and others that this water should be allowed to stand for a time up to twenty-four hours before starting the filtration1 to allow the formation of a sediment layer1 and in some places1 especially at ,berlin and the works of some of the ,london companies1 this is done2 but varying importance is attached to the procedure1 and it is invariably omitted1 so far as ,i can learn1 when the demand for water is heavy4 ,the depth of sand removed by scraping must at least equal the depth of the discolored layer1 but there is no sharp dividing line1 the impurities gradually decreasing from the surface downward4 ,fig4 #ab shows the relative number of bacteria found in the sand at various depths in one of the ,lawrence experimental filters1 and is a representative result1 although the actual numbers vary at different times4 ,in general it may be said that the bulk of the sediment is retained in the upper quarter inch1 but it is desirable to remove also the less dirty sand below and1 in fact1 it is apparently impossible with the method of scraping in use to remove so thin a layer as one fourth inch4 ,practically the depth to which sand is removed is stated to be from #j4dj to #a4bj inch4 ,exact statistics are not easily obtained1 but ,i think that #b centimeters or #j4gi inch may be safely taken as about the average depth usually removed in ,european filters1 and it is this depth which is indicated on ,fig4 #ab4 ,illustration3 ,,fig4 #ab4--;,,diagram ,,showing ,,accumulation ,,of ,,bacteria ,,near ,,the ,,surface ,,of ,,the ,,sand4 ,at the ,lawrence ,experiment ,station1 the depth removed is often much less than this1 and depends upon the size of grain of the sand employed1 the coarser sands requiring to be more deeply scraped than the finer ones4 ,the method of scraping1 however1 which allows the removal of very thin sand layers1 is only possible because of the small size of the filters1 and as it is incapable of application on a large scale1 the depths thus removed are only interesting as showing the results which might be obtained in practice with a more perfect method of scraping4 ,the replacing of the washed sand is usually delayed until the filter has been scraped quite a number of times--commonly for a year4 ,the last scraping before refilling is much deeper than usual1 because the sand below the depth of the ordinary scraping is somewhat dirty1 and might cause trouble if left below the clean sand4 ,in ,england it is the usual if not the universal practice to replace the washed sand at the bottom between the old sand and the gravel4 ,this is done by digging up the entire filter in sections about six feet wide4 ,the old sand in the first section is removed clear down to the gravel1 and the depth of washed sand which is to be replaced is put in its place4 ,the old sand from the next six-foot section is then shovelled upon the first section of clean sand1 and its place is in turn filled with fresh sand4 ,with this practice the workmen's boots are likely to disturb the gravel each year1 necessitating a thicker layer of the upper and finest grade than would otherwise be required4 ,in ,germany this is also sometimes done1 but more frequently the upper layer of slightly clogged sand below the regular scraping is removed as far as the slightest discoloration can be seen1 perhaps #f inches deep4 ,the sand below is loosened for another #f inches and allowed to stand dry1 if possible1 for some days2 afterwards the washed sand is brought on and placed above4 ,the washed sand is never replaced without some such treatment1 because the slightly clogged sand below the layer removed would act as if finer than the freshly washed sand1#ai and there would be a tendency to sub-surface clogging4 ,,frequency ,,of ,,scraping4 ,the frequency of scraping depends upon the character of the raw water1 the thoroughness of the preliminary sedimentation1 the grain-size of the filter sand1 the rate of filtration1 and the maximum loss of head allowed4 ,with suitable conditions the period between scrapings should never be less than one week1 and will but rarely exceed two months4 ,under exceptional conditions1 however1 periods have been recorded as low as one day and as high as one hundred and ten days4 ,periods of less than a week's duration are almost conclusive evidence that something is radically wrong1 and the periods of one day mentioned were actually accompanied by very inadequate filtration4 ,in #ahib the average periods at the ,german works varied from #i4e days at ,stettin 7with an excessive rate7 to #dj days at ,brunswick1 the average of all being #be days4#bj ,the quantity of water per acre filtered between scrapings forms the most convenient basis for calculation4 ,the effect of rate 7page #di71 loss of head 7page #fe71 and size of sand grain 7page #cb7 have already been discussed1 and it will suffice to say here that the total quantity filtered between scrapings is apparently independent of the rate of filtration1 but varies with the maximum loss of head and with the grain-size of the sand1 and apparently nearly in proportion to them4 ,eleven ,german filter-works in #ahib1 drawing their waters from rivers1 filtered on an average #ea million gallons of water per acre between scrapings1 the single results ranging from #bh at ,bremen to #ga at ,stuttgart1 while ,zrich1 drawing its water from a lake which is but very rarely turbid1 filtered #bfj million gallons per acre between scrapings4 ,unfortunately1 the quantities at ,berlin1 where 7in #ahib two thirds and now all7 the water is drawn from comparatively large ponds on the rivers1 are not available for comparison4 ,at ,london1 in #ahhd1 the average quantities of water filtered between scrapings varied from #dc to #acf million gallons per acre with the different companies1 averaging #he1 and in #ahib the quantities ranged from #gc to #aeg1 averaging #ij million gallons per acre4 ,the greater quantity filtered at ,london may be due to the greater sizes of the sedimentation-basins1 which for all the companies together hold a nine days' supply at ,london against probably less than one day's supply for the ,german works4 ,there is little information available in regard to the frequency of scraping with water drawn from impounding reservoirs4 ,in some experiments made by ,mr4 ,fitz,gerald at the ,chestnut ,hill reservoir1 ,boston1 the results of which are as yet unpublished1 a filter with sand of an effective size of only 4#ji mm4 averaged #eh million gallons per acre between scrapings for nine periods1 the rate of filtration being #a4ej million gallons per acre daily1 while another filter1 with sand of an effective size of 4#ah mm41 passed an average of #ic million gallons per acre for ten periods at the same rate4 ,these experiments extended through all seasons of the year1 and taking into account the comparative fineness of the sands they show rather high quantities of water filtered between scrapings4 ,the quantity of water filtered between scrapings is usually greatest in winter1 owing to the smaller quantity of sediment in the raw water at this season1 and is lowest in times of flood1 regardless of season4 ,in summer the quantity is often reduced to a very low figure in waters supporting alg growths1 especially when the filters are not covered4 ,thus at ,stralau in #ahic during the alg period the quantity was reduced to #ad million gallons per acre for open filters1#ba but this was quite exceptional1 the much-polluted1 though comparatively clear1 ,spree water furnishing unusually favorable conditions for the alg4 ,,quantity ,,of ,,sand ,,to ,,be ,,removed4 ,in regard to the quantity of sand to be removed and washed1 if we take the average result given above for the ,german works filtering river-waters of #ea1jjj1jjj gallons per acre filtered between scrapings1 and the depth of sand removed at two centimeters or #j4gi inch1 we find that one volume of sand is required for every #bcge volumes of water filtered1 or #b4aj cubic yards per million gallons4 ,at ,bremen1 the highest average result1 the quantity would be #c4hj yards1 and at ,stralau during the alg season #g4gj yards4 ,at ,zrich1 on the other hand1 the quantity is only #j4da yard1 and at ,london1 with #hg1jjj1jjj gallons per acre filtered between scrapings1 the quantity of sand washed would be #a4bd yards per million gallons2 assuming always that the layer removed is #j4gi inch thick4 ,these estimates are for the regular scrapings only1 and do not include the annual deeper scraping before replacing the sand1 which would increase them by about one third4 ,,wasting ,,the ,,effluents ,,after ,,scraping4 ,it has already been stated that an important part of the filtration takes place in the sediment layer deposited on top of the sand from the water4 ,when this layer is removed by scraping its influence is temporarily removed1 and reduced efficiency of filtration may result4 ,the significance of this reduced efficiency became apparent when the bacteria in the water were studied in their relations to disease1 and ,piefke suggested#bb that the first effluent after scraping should be rejected for one day after ordinary scrapings and for one week after replacing the sand4 ,in a more recent paper#bc he reduces these estimates to the first million gallons of water per acre filtered after scraping for open and twice as great a quantity for covered filters1 and to six days after replacing the sand1 which last he estimates will occur only once a year4 ,taking the quantity of water filtered between scrapings at #ac4i million gallons per acre1 the quantity observed at ,stralau in the summer of #ahic1 he finds that it is necessary to waste #i per cent of the total quantity of effluent from open and #ac4h per cent of that from covered filters4 ,the eleven ,german water-works#bd filtering river-waters1 however1 filtered on an average #ea4j instead of #ac4i million gallons per acre between scrapings1 and applying ,piefke's figures to them the quantities of water to be wasted would be only about one fourth of his estimates for ,stralau4 ,the rules of the ,imperial ,board of ,health#be require that every ,german filter shall be so constructed 8that when an inferior effluent results it can be disconnected from the pure-water pipes and the filtrate allowed to be wasted40 ,the drain-pipe for removing the rejected water should be connected below the apparatus for regulating the rate and loss of head1 so that the filter can be operated exactly as usual1 and the effluent can be turned back to the pure-water pipes without stopping or changing the rate4 ,the works at ,berlin and at ,hamburg conform to this requirement1 and most of the older ,german works have been or are being built over to make them do so4 ,in regard to the extent of deterioration after scraping1 ,piefke's experiments have always shown much larger numbers of bacteria both of the ordinary forms and of special applied forms on the first day after scraping1 the numbers frequently being many times as high as at other times4 ,at the ,lawrence ,experiment ,station it was found in #ahib that on an average the number of water bacteria was increased by #gj per cent 7continuous filters only7 for the three days following scraping1 while ,b4 prodigiosus when applied was increased #adj per cent1 the increase being most marked where the depth of sand was least1 and with the highest rate of filtration4 ,the same tendency was found in #ahic1 when the increase in the water bacteria on the first day after scraping was only #ai per cent and ,b4 prodigiosus #fd per cent1 but for a portion of the year the difference was greater1 averaging #acb and #bfb per cent1 respectively4 ,these differences are much less than those recorded by ,piefke1 and with the high efficiencies regularly obtained at ,lawrence they would hardly justify the expensive practice of wasting the effluent4 ,the reduction in efficiency following scraping is much less at low rates1 and if a filter is started at much less than its normal rate after scraping1 and then gradually increased to the standard after the sediment layer is formed1 the poor work will be largely avoided4 ,practically this is done at ,berlin and at ,hamburg4 ,the filters are started at a fourth or less of the usual rates and are gradually increased1 as past experience with bacterial results has shown it can be safely done1 and the effluent is then even at first so well purified that it need not be wasted4 ,practically in building new filters the provision of a suitable connection for wasting the effluents into the drain which is necessary for emptying them involves no serious expense and should be provided1 but it may be questioned how often it should be used for wasting the effluents4 ,if the raw water is so bad that a good effluent cannot be obtained by careful manipulation even just after scraping1 the course of the ,berlin authorities in closing the ,stralau works and seeking a less polluted supply would seem to be the only really safe procedure4 ,,sand-,,washing4 ,illustration3 ,,cleaning ,a ,,filter1 ,,east ,,london4 ,illustration3 ,,washing ,,dirty ,,sand ,,with ,,hose1 ,,antwerp4 ,to face page #gf4 ,the sand-washing apparatus is an important part of most ,european filtering plants4 ,it seldom happens that a natural sand can be found clean enough and sufficiently free from fine particles although such a sand was found and used for the ,lawrence filter4 ,most of the sand in use for filtration in ,europe was originally washed4 ,in the operation of the filters also1 sand-washing is used for the dirty sand1 which can then be used over and over at a much lower cost than would be the case if fresh sand was used for refilling4 ,the methods used for washing sand at the different works present a great variety both in their details and in the underlying principles4 ,formerly boxes with double perforated bottoms in which the sand was placed and stirred by a man as water from below rose through them1 and other similar arrangements were commonly used1 but they are at present only retained1 so far as ,i know1 in some of the smaller ,english works4 ,the cleansing obtained is apparently considerably less thorough than with some of the modern devices4 ,illustration3 ,,fig4 #ac4--;,,hose-,,washing ,,for ,,dirty ,,sand4 ,hose-washing is used in ,london by the ,southwark and ,vauxhall1 ,lambeth and ,chelsea companies1 and also at ,antwerp4 ,for this a platform is constructed about #ae feet long by #h feet wide1 with a pitch lengthwise of #f to #h inches 7,fig4 #ac74 ,the platform is surrounded by a wall rising from one foot at the bottom to three feet high at the top1 except the lower end1 which is closed by a removable plank weir #e or #f inches high4 ,from two to four cubic yards of the sand are placed upon this platform and a stream of water from a hose with a #c_/d or #g_/h-;inch nozzle is played upon it1 moving it about from place to place4 ,the sand itself is always kept toward the upper end of the platform1 while the water with the dirt removed flows down into the pond made by the weir1 where the sand settles out and the dirt overflows with the water4 ,when the water comes off clear1 which is usually after an hour or a little less1 the weir is removed1 and1 after draining1 the sand is removed4 ,these arrangements are built in pairs so that the hose can be used in one while the sand is being changed in the other4 ,they are usually built of brick laid in cement1 but plank and iron are also used4 ,the corners are sometimes carried out square as in the figure1 but are more often rounded4 ,the washing is apparently fairly well done4 ,in ,germany the so-called 8drum0 washing-machine1 drawings of which have been several times published1#bf has come to be almost universally used4 ,it consists of a large revolving cylinder1 on the bottom of the inside of which the sand is slowly pushed up toward the higher end by endless screw-blades attached to the cylinder1 while water is freely played upon it all the way4 ,the machine requires a special house for its accommodation and from #b to #d horse-power for its operation4 ,it washes from #b4e to #d yards of sand per hour most thoroughly1 with a consumption of from #aa to #ad times as large a volume of water4 ,the apparatus is not patented or made for sale1 but full plans can be easily secured4 ,a machine made by ,samuel ,pegg ,sons1 ,leicester1 ,eng41 pushes the sand up a slight incline down which water flows4 ,it is very heavy and requires power to operate it4 ,the patent has expired4 ,a machine much like it but lighter and more convenient and moved by water-power derived from the water used for washing instead of steam-power is used at ,zrich with good results4 ,in ,greenway's machine the sand is forced by a screw through a long narrow cylinder in which there is a current of water in the opposite direction4 ,the power required is furnished by a water-motor1 as with the machine at ,zrich4 ,the apparatus is mounted on wheels and is portable2 it has an appliance for piling up the washed sand or loading it onto cars4 ,it is patented and is manufactured by ,james ,gibb ,co41 ,london4 ,several of the ,london water companies are now using ejector washers1 and such an apparatus has been placed by the side of the 8drum0 washers at ,hamburg4 ,this apparatus was made by ,krting ,brothers in ,hannover1 and combines the ejectors long made by that firm with hoppers from designs by ,mr4 ,bryan1 engineer of the ,east ,london ,water ,company4 ,an apparatus differing from this only in the shape of the ejectors and some minor details has been patented in ,england1 and is for sale by ,messrs4 ,hunter1 ,frazer ,goodman1 ,bow1 ,london4 ,both of these forms consist of a series of conical hoppers1 from the bottom of each of which the sand and water are forced into the top of the next by means of ejectors1 the excess of dirty water overflowing from the top of each hopper4 ,the apparatus is compact and not likely to get out of order1 but is not portable4 ,it can be easily arranged to take the sand at the level of the ground1 or even lower if desired1 and deliver it washed at some little elevation1 thus minimizing hand-labor4 ,the washing is regular and thorough4 ,the objection most frequently raised against its use is the quantity of water required1 but at ,hamburg ,i was informed that the volume of water required was only about #ae times that of the sand1 while almost as much 7#ac-ad volumes7 were required for the 8drum0 washers1 and the saving in power much more than offset the extra cost for water4 ,in addition to the above processes of sand-washing1 ,piefke's method of cleaning without scraping#bg might be mentioned1 although as yet it has hardly passed the experimental stage1 and has only been used on extremely small filters4 ,the process consists of stirring the surface sand of the filter with 8waltzers0 while a thin sheet of water rapidly flows over the surface4 ,this arrangement necessitates a special construction of the filters1 providing for rapidly removing the unfiltered water from the surface1 and for producing a regular and rapid movement of a thin sheet of water over the surface4 ,in the little filters now in use1 one of which ,i saw in a brewery in ,berlin1 the cleaning is rapidly1 cheaply1 and apparently well done4 ,in washing dirty sand it is obvious that any small sand-grains will be removed with the dirt1 and in washing new sand the main object is to remove the grains below a certain size4 ,it is also apparent that the sizes of grains which will and those which will not be removed are dependent upon the mechanical arrangements of the washer1 as1 for example1 with the ejectors1 upon the sizes of the hoppers1 and the quantity of water passing through them1 and care should be taken to make them correspond with the size of grain selected for the filter sand4 ,this can only be done by experiment1 as no results are available on this point4 ,in some places filtered water is used for sand-washing1 although this seems quite unnecessary1 as ordinary river-water answers very well4 ,it is1 however1 often cheaper1 especially in small works1 to use the filtered water from the mains rather than provide a separate supply for the washers4 ,the quantity of water required for washing may be estimated at #ae times the volume of the sand and the sand as #j4jd per cent of the volume of the water filtered 7page #gd71 so that #j4f per cent of the total quantity of water filtered will be required for sand-washing4 ,the cost of sand-washing in ,germany with the 8drum0 washers is said to be from #ad to #bj cents per cubic yard1 including labor1 power1 and water4 ,in ,america the water would cost no more1 but the labor would be perhaps twice as dear4 ,with an ejector apparatus ,i should estimate the cost of washing dirty sand as follows3 ,the sand would be brought and dumped near to the washer1 and one man could easily feed it in1 as no lifting is required4 ,two men would probably be required to shovel the washed sand into barrows or carts with the present arrangements1 but ,i think with a little ingenuity this handling could be made easier4 ,,estimated ,,cost ,,of ,,operating ,,ejector ,,washers #i ,,hours4 ,wages of #c men at #b4jj #f4jj #aaj1jjj gals1 water 7#ae times the volume of sand7 at #j4je a thousand gals4 #e4ej ----- ,total cost of washing #cf cubic yards #aa4ej or #cb cents a cubic yard4 ,the cost of washing new sand might be somewhat less4 ,the other costs of cleaning filters1 scraping1 transporting1 and replacing the sand are much greater than the washing itself4 ,lindley states that at ,warsaw #bi days' labor of #aj hours for one man are required to scrape an acre of filter surface1 and four times as much for the annual deep scraping1 digging up1 and replacing the sand4 ,the first expense occurs in general monthly1 and the second only once a year4 ,at other places where ,i have secured corresponding data the figures range from #ai to #dj days' labor to scrape one acre1 and average about the same as ,lindley estimates4 ,under some conditions sand-washing does not pay1 and in still others it is almost impossible4 ,no apparatus has yet been devised which will wash the dirt out of the fine dune-sands used in ,holland without washing a large part of the sand itself away1 and in these works fresh sand1 which is available in unlimited quantities and close to the works1 is always used4 ,at ,breslau the dirty sand is sold for building purposes for one third of the price paid for new sand dredged from the river1 delivered at the works1 and no sand is ever washed4 ,budapest1 ,warsaw1 and ,rotterdam also use fresh river-sand without washing1 except a very crude washing to remove clay at ,budapest4 ,,chapter ,,vi4 ,,theory ,,and ,,efficiency ,,of ,,continuous ,,filtration4 ,the first filters for a public water-supply were built by ,james ,simpson1 engineer of the ,chelsea ,water ,company at ,london in #ahbi4 ,they were apparently intended to remove dirt from the water in imitation of natural processes1 and without any very clear conception of either the exact extent of purification or the way in which it was to be accomplished4 ,the removal of turbidity was the most obvious result1 and a clear effluent was the single test of the efficiency of filtration1 as it remains the legal criterion of the work of the ,london filters even to-day1 notwithstanding the discovery and use of other and more delicate tests4 ,the invention and use of methods for determining the organic matters in water by ,wanklyn and ,frankland1 about #ahgj1 led to the discovery that the proportion of organic matters removed by filtration was disappointingly low1 and as1 at the time1 and for many years afterward1 an exaggerated importance was given to the mere quantities of organic matters in water1 it was concluded that filtration had only a limited influence upon the healthfulness of the filtered water1 and that practically as much care must be given to securing an unpolluted water as would be the case if it were delivered direct without filtration4 ,this theory1 although not confirmed by more recent investigation1 undoubtedly has had a good influence upon the ,english works by causing the selection of raw waters free from excessive pollutions1 and1 in cases like the ,london supplies1 drawn from the ,thames and the ,lea1 in stimulating a most jealous care of the watersheds and the purification of sewage by the towns upon them4 ,it was only after the discovery of the bacteria in water and their relations to health that the hygenic significance of filtration commenced to be really understood4 ,investigations of the bacteria in the waters before and after filtration were carried out at ,berlin by ,plagge and ,proskauer1 at ,london by ,dr4 ,percy ,frankland1 and also at ,zrich1 ,altona1 and on a smaller scale at other places4 ,these investigations showed that the bacteria were mainly removed by filtration1 the numbers in the effluents rarely exceeding two or three per cent of those in the raw water4 ,this gave a new aspect to the problem4 ,it was further observed1 especially at ,berlin and ,zrich1 that the numbers of bacteria in effluents were apparently quite independent of the numbers in the raw water1 and the theory was formed that all of the bacteria were stopped by the filters1 and that those found in the effluents were the result of contamination from the air and of growths in the underdrains4 ,the logical conclusion from this theory was that filtered water was quite suitable for drinking regardless of the pollution of its source4 ,it was1 however1 found that the numbers of bacteria in the effluents were higher immediately after scraping than at other times1 and it was concluded that before the formation of the sediment layer some bacteria were able to pass the sand1 and it was therefore recommended that the first water filtered after scraping should be rejected4 ,piefke at ,berlin gave the subject careful study1 and came to the conclusion that it was almost entirely the sediment layer which stopped the bacteria1 and that the bacteria themselves in the sediment layer formed a slimy mass which completely intercepted those in the passing water4 ,when this layer was removed by scraping1 the action was stopped until a new crop of bacteria had accumulated4 ,in support of this idea he stated that he had taken ordinary good filter-sand and killed the bacteria in it by heating it1 and that on passing water through1 no purification was effected--in fact1 the effluent contained more bacteria than the raw water4 ,after a little1 bacteria established themselves in the sand1 and then the usual purification was obtained4 ,piefke concluded that the action of the filter was a biological one2 that simple straining was quite inadequate to produce the results obtained2 that the action of the filter was mainly confined to the sediment layer1 and that the depth of sand beyond the slight depth necessary for the support of this layer had no appreciable influence upon the results4 ,the effect of this theory is still seen in the shallow sand layers used at ,berlin and some other ,german works1 although at ,london the tendency is rather toward thicker sand layers4 ,piefke's deductions1 however1 are not entirely supported by his data as we understand them in the light of more recent investigation4 ,the experiment with sterilized sand has been repeatedly tried at the ,lawrence ,experiment ,station with results which quite agree with ,piefke's1 but it has also been found that the high numbers1 often many times as high as in the raw water1 do not represent bacteria which pass in the ordinary course of filtration1 but instead enormous growths of bacteria throughout the sand supported by the cooked organic matter in it4 ,it has been repeatedly found that ordinary sand quite incapable of supporting bacterial growths1 after heating to a temperature capable of killing the bacteria will afterwards furnish the food for most extraordinary numbers4 ,a filter of such sand may stop the bacteria of the passing water quite as effectually as any other filter1 but if so1 the fact cannot be determined without recourse to special methods1 on account of the enormous numbers of bacteria in the sand1 a small part of which are carried forward by the passing water1 and completely mask the normal action of the filter4 ,the theory that all or practically all of the bacteria are intercepted by the sediment layer1 and that those in the effluent are the result of growths in the sand or underdrains1 received two hard blows in #ahhi and #ahia1 when mild epidemics of typhoid fever followed unusually high numbers of bacteria in the effluents at ,altona and at ,stralau in ,berlin1 with good evidence in each case that the fever was directly due to the water4 ,both of these cases came during1 and as the result of1 severe winter weather with open filters and under conditions which are now recognized as extremely unfavorable for good filtration4 ,as a result of the first of these epidemics a series of experiments were made at ,stralau by ,frnkel and ,piefke in #ahij4 ,small filters were constructed1 and water passed exactly as in the ordinary filters4 ,bacteria of special kinds not existing in the raw water or effluents were then applied1 and the presence of a very small fraction of them in the effluents demonstrated beyond a doubt that they had passed through the filters under the ordinary conditions of filtration4 ,these experiments were afterwards repeated by ,piefke alone under somewhat different conditions with similar results4 ,the numbers of bacteria passing1 although large enough to establish the point that some do pass1 were nevertheless in general but a small fraction of one per cent of the many thousands applied4 ,this method of testing the efficiency of filters had already been used quite independently by ,prof4 ,sedgwick at the ,lawrence ,experiment ,station in connection with the purification of sewage1 and has since been extensively used there for experiments with water-filtration4 ,kmmel also found at ,altona that while in the regular samples for bacterial examination1 all taken at the same time in the day1 there was no apparent connection between the numbers of bacteria in the raw water and effluents1 by taking samples at frequent intervals throughout the twenty-four hours1 as has been done in a more recent series of experiments1 and allowing for the time required for the water to pass the filters1 a well-marked connection was found to exist between the numbers of bacteria in the raw water and in the effluents4 ,illustration3 ,,fig4 #ad4--,,showing ,,bacteria ,,supposed ,,to ,,come ,,through ,,filters ,,and ,,from ,,the ,,underdrains4 ,the subject has more recently been studied in much detail at the ,lawrence ,experiment ,station1 and it now appears that the bacteria in the effluent from a filter are from two sources3 directly from the filtered water1 and from the lower layers of the filter and underdrains4 ,thus we may say3 ,bacteria in effluent ,bacteria from underdrains a_/#ajj bacteria in raw water1 where a is the per cent of bacteria actually passing the filter4 ,both of these terms depend upon a whole series of complex and but imperfectly understood conditions4 ,in general the bacteria from the underdrains are low in cold winter weather1 often almost nil1 while at ,lawrence with water temperatures of #gj to #ge degrees1 and over1 in ,july and ,august1 the numbers from this source may reach #bjj or #cjj1 but for the other ten months of the year rarely exceed #ej under normal conditions4 ,in summer especially it seems to be greater at low than at high rates of filtration 7although a high rate for a short time only increases it71 and so varies in the opposite way from the numbers actually passing the filters4 ,this subject is by no means clearly understood2 it is difficult1 almost impossible1 to separate the numbers of bacteria into the two parts--those which come directly through and may be dangerous1 and those which have other origins and are harmless4 ,the sketch1 ,fig4 #ad1 is drawn to represent my idea of the way they may be divided4 ,it has no statistical basis whatever4 ,the light unshaded section shows the percentage number of bacteria which ,i conceive to be coming through a filter under given conditions at various rates of filtration1 while the shaded section above represents the bacteria from other sources1 and the upper line represents the sum of the two1 or the total number of bacteria in the effluent4 ,the relative importance of the two parts would probably vary widely with various conditions4 ,with the conditions indicated by the sketch the number of bacteria in the effluent is almost constant3 for a variation of only from #a4d to #b4e per cent of the number applied for the whole range is not a wide fluctuation for bacterial results1 but the number in the lower and dangerous section is always rapidly increasing with increasing rate4 ,this theory of filtration accounts for many otherwise perplexing facts4 ,the conclusion reached at ,zrich and elsewhere that the efficiency of filtration is independent of rate may be explained in this way4 ,this is especially probable at ,zrich1 where the number of bacteria in the raw water was only about #bjj1 and an extremely large proportion relatively would have to pass to make a well-marked impression upon the total number in the effluent4 ,these underdrain bacteria are1 so far as we know1 entirely harmless2 we are only interested in them to determine how far they are capable of decreasing the apparent efficiency of filtration below the actual efficiency1 or the per cent of bacteria really removed by the filter4 ,this efficiency is dependent upon a large number of conditions many of which have already been discussed in connection with grain-size of filter sand1 underdrains1 rate of filtration1 loss of head1 etc41 and a mere reference to them here will suffice4 ,perhaps the most important single condition is the rate1 the numbers of bacteria passing increase rapidly with it4 ,next1 fine sand and in moderately deep layers tends to give high efficiency4 ,the influence of the loss of head1 often mentioned1 is not shown to be important by the ,lawrence results1 nor can ,i find satisfactory ,european results in support of it4 ,uniformity in the rate of filtration on all parts of the filtering area and a constant rate throughout the twenty-four hours are regarded as essential conditions for the best results4 ,severe winter weather has indirectly1 by disturbing the regular action of open filters1 an injurious influence1 and has been the cause of most of the cases where filtered waters have been known to injure the health of those who have drunk them4 ,this action is excluded in filters covered with masonry arches and soil1 and such construction is apparently necessary for the best results in places subject to cold winters4 ,the efficiency of filtration under various conditions has been studied by a most elaborate series of experiments at ,lawrence with small filters to which water has been applied containing a bacterium 7,b4 prodigiosus7 which does not occur naturally in this country and is not capable of growing in the filter1 so that the results should represent only the bacteria coming through the filter and not include any additions from the underdrains4 ,these results1 which have been published in full in the reports of the ,massachusetts ,state ,board of ,health1 especially for the years #ahib and #ahic1 show that the number of bacteria passing increases rapidly with increasing rate1 and slowly with decreasing sand thickness and increased size of sand-grain4 ,assuming that the number of bacteria passing is expressed by the formula #a 7rate7#b effective size of sand ,per cent bacteria passing -- ---------------------------------------- ---------------------------------------- #b 7sqrt7thickness of the sand in inches77 where the rate is expressed in million gallons per acre daily1 and calculating by it the numbers of bacteria for the seventy-three months for which satisfactory data are available from #aa filters in #ahib and #ahic1 we find that ,in #ad cases the numbers observed were #d to #i times as great as the calculated numbers2 ,in #f cases they were #b to #c times as great2 ,in #ce cases they were between #a_/b and #b times the calculated numbers4 ,in #ag cases they were #a_/b to #a_/c of them4 ,in #aa cases they were less than #a_/c the calculated numbers4 ,the agreement is only moderately good1 and in fact no such formula could be expected to give more than very rough approximations1 because it does not take into consideration the numerous other elements1 such as uniformity and regularity of filtration1 the influence of scraping1 the character of the sediment in the raw water1 etc41 which are known to affect the results4 ,perhaps the most marked general difference is the tendency of new or freshly-filled filters to give higher1 and of old and well-compacted filters to give lower1 results than those indicated by the formula4 ,comparing this formula with ,piefke's results given in his 8,neue ,ermittelungen0#bh the formula gives in the first series 7#j4cd mm4 sand1 #j4ej m4 thick1 and rate #ajj mm4 per hour71 #j4be per cent passing1 while the average number of ,b4 violacious reported1 excluding the first day of decreased efficiency after scraping1 was #j4bf per cent4 ,in the second series1 with half as high a rate the numbers checked exactly the calculated #j4jf per cent4 ,in other experiments1#bi however1 in #ahic1 when the calculated per cent was also #j4be1 only #j4jc1 #j4jd1 and #j4jg per cent were observed in the effluents4 ,comparing the results from the actual filters1 7which numbers also include the bacteria from the underdrains and should therefore be somewhat higher7 with the numbers calculated as passing through1 ,i find that for the #df days1 ,aug4 #bj to ,oct4 #d1 #ahic1 for which detailed results of the ,stralau works are given by ,piefke1 the average calculated number passing is #j4bj per cent1 while twice as many were observed in the effluents2 although three of the filters gave better effluents than the other eight1 and the numbers from them approximated closely the calculated numbers4 ,if we calculate the percentages of bacteria passing a number of filters1 using the maximum rate of filtration allowed for the ,german filters where this is accurately determined1 and for the ,english filters taking the maximum rate at one and one-half times the rate obtained by dividing the daily quantity by the area of filters actually in use1 we obtain3 ---------------------------------------- ------------------------ ,average ,effective ,maximum ,per cent ,depth of ,size of ,rate of ,bacteria ,sand1 ,sand- ,filtration4 passing ,inches4 grain4 #a r#b;d - ---------- #b sqrtsand ---------------------------------------- ------------------------ ,hamburg #cb #j4ca #a4fj #j4jg ,altona #bh #j4cd #b4eg #j4ba ,berlin1 ,stralau #bj #j4cd #b4eg #j4be ,berlin1 ,mggel #bj #j4cd #b4eg #j4be ,berlin1 ,tegel #bj #j4cg #b4eg #j4bg ,london1 ,southwark ,vauxhall #cf #j4cd #b4ha #j4bb ,london1 ,west ,middlesex #ci #j4cg #b4ha #j4bc ,london1 ,chelsea #ed #j4cf #c4bg #j4bf ,london1 ,grand ,junction #cj #j4dj #c4bg #j4ci ,london1 ,lambeth #cf #j4cf #c4ge #j4db ,middlesborough #bj #j4db #e4he #a4eh ,zrich #bf #j4ce #g4ej #a4ij ---------------------------------------- ------------------------ ,the numbers actually observed are in every case higher than the calculated per cents passing1 as indeed they should be on account of those coming from the underdrains1 accidental contamination of the samples1 etc4 ,it may be said that filtration now practised in ,european works under ordinary conditions never allows over #a or #b per cent bacteria of the raw water to pass1 and ordinarily not over one fourth to one half of one per cent1 although exact data cannot be obtained owing to masking effect of the bacteria which come from below and which bear no relation to those of the raw water4 ,by increasing the size of the filters1 fineness and depth of sand 7as at ,hamburg71 the efficiency can be materially increased above these figures4 ,at the same time it must be borne in mind that the effectiveness of a filter may be greatly impaired by inadequate underdraining1 by fluctuating rates of filtration where these are allowed1 by freezing in winter in the case of open filters in cold climates1 and by other irregularities1 all of which can be prevented by careful attention to the respective points4 ,the action of a continuous filter throughout is mainly that of an exceedingly fine strainer1 and like a strainer is mainly confined to the suspended or insoluble matters in the raw water4 ,the turbidity1 sediment1 and bacteria of the raw water are largely or entirely removed1 while hardness1 organic matter1 and color1 so far as they are in solution1 are removed to only a slight extent1 if at all4 ,hardness can be removed by the addition of lime in carefully determined quantity before filtration 7,clark's process71 by means of which the excess of carbonic acid in the water is absorbed and the lime added1 together with that previously in the water1 is precipitated4 ,ordinary filtration will remove from one fourth to one third of the yellow-brown color of peaty water4 ,a larger proportion can be removed by the addition of alum1 which by decomposing forms an insoluble compound of alumina with the coloring matter1 while the acid of the alum goes into the effluent either as free acid1 or in combination with the lime or other base in the water1 according to their respective quantities4 ,freshly precipitated alumina can be substituted for the alum at increased expense and trouble1 and tends to remove the color without adding acid to the water4 ,these will be discussed more in detail in connection with mechanical filters4 ,alum is but rarely used in slow sand filtration1 the most important works where it is used being in ,holland with peaty waters4 ,after all1 the most conclusive test of the efficiency of filtration is the healthfulness of the people who drink the filtered water2 and the fact that many ,european cities take water-supplies from sources which would not be considered fit for use in the ,united ,states and1 after filtering them1 deliver them to populations having death-rates from water-carried diseases which are so low as to be the objects of our admiration1 is the best proof of the efficiency of carefully conducted filtration4 ,it is only necessary to refer to ,london1 drawing its water from the two small and polluted rivers1 the ,thames and the ,lea2 to ,altona1 drawing its water from the ,elbe1 polluted by the sewage of #f1jjj1jjj people1 #gjj1jjj of them within ten miles above the intakes2 to ,berlin1 using the waters of the ,havel and the ,spree2 to ,breslau1 taking its water from the ,oder charged with the sewage of mining districts in ,silicia and ,galicia1 where cholera is so common2 to ,lawrence1 with its greatly decreased death-rate since it has had filtered water1 and to the hundred other places which protect themselves from the infectious matters in their raw waters by means of filtration4 ,a few of these cases are described more in detail in ,appendices ,v to ,,ix1 and many others in the literature mentioned in ,appendix ,x4 ,an adequate presentation of even those data which have been already worked up and published would occupy too much space4 ,i think every one who has carefully studied the recent history of water filtration in its relation to disease has been convinced that filtration carefully executed under suitable and normal conditions1 even if not an absolute1 is at least a very substantial protection against water-carried diseases1 and the few apparent failures to remove objectionable qualities have been without exception due to abnormal conditions which are now understood and in future can be prevented4 ,,bacterial ,,examination ,,of ,,waters4 ,every large filter-plant should have arrangements for the systematic bacterial examination of the water before and after filtration1 especially where the raw water is subject to serious pollution4 ,such examinations need not be excessively expensive1 and they will not only show the efficiency of the plant as a whole1 but may be made to show the relative efficiencies of the separate filters1 the relative efficiencies at different parts of the periods of operation1 the effect of cold weather1 etc41 and will then be a substantial aid to the superintendent in always securing good effluents at the minimum cost4 ,in addition a complete record of the bacteria in the water at different times may aid in determining definitely whether the water was connected with outbreaks of disease4 ,thus if an outbreak of disease of any kind were preceded at a certain interval by a great increase in the number of bacteria1--as has been the case1 for example1 with the typhoid epidemics at ,altona and ,berlin 7see ,appendices ,,ii and ,,vii71--a presumption would arise that they might have been connected with each other1 and each time it was repeated the presumption would be strengthened1 while1 on the other hand1 outbreaks occurring while the bacteria remained constantly low would tend to discredit such a theory4 ,bacterial investigations inaugurated after an epidemic is recognized1 as has frequently been done1 seldom lead to results of value1 both because the local normal bacterial conditions are generally unknown at the commencement of the investigation1 and because the most important time1 the time of infection1 is already long past before the first samples are taken4 ,the fact that such sporadic activities have led to few definite results should throw no discredit upon continued observations1 which have repeatedly proved of inestimable value4 ,considerable misconception of the use of bacterial examinations exists4 ,the simple bacterial count ordinarily used1 and of which ,i am now speaking1 does not and cannot show whether a water contains disease-germs or not4 ,i object to the ,chicago water1 not so much because a glass of it contains a hundred thousand bacteria more or less1 as because ,i am convinced1 by a study of its source in connection with the city's death-rate1 that it actually carries disease-germs which prove injurious to thousands of those who drink it4 ,now the fact being admitted that the water is injurious to health1 variations in the numbers of bacteria in the water drawn from different intakes and at different times probably correspond roughly with varying proportions of fresh sewage1 and indicate roughly the relative dangers from the use of the respective waters4 ,if filters should be introduced1 the numbers of bacteria in the effluents under various conditions would be an index of the respective efficiencies of filtration1 and would serve to detect poor work1 and would probably suggest the measures necessary for better results4 ,i would suggest the desirability of such investigations where mechanical filters are used1 quite as much as in connection with slow filtration2 and it would also be most desirable in the case of many water-supplies which are not filtered at all4 ,such continued observations have been made at ,berlin since #ahhd2 at ,london since #ahhf2 at ,boston and ,lawrence since #ahhh2 and recently at a large number of places1 including ,chicago1 where observations by the city were commenced in #ahid4 ,they are now required by the ,german ,government in the case of all filtered public water-supplies in ,germany1 without regard to the source of the raw water4 ,the ,german standard requires that the effluent from each single filter1 as well as the mixed effluent and raw water1 shall be examined daily1 making at some works #aj to #cj samples daily4 ,this amount of work1 however1 can usually be done by a single man2 and when a laboratory is once started1 the cost of examining #bj samples a day will not be much greater than if only #bj a week are taken4 ,in ,england and at some of the ,continental works drawing their waters from but slightly polluted sources1 much smaller numbers of samples are examined4 ,the question whether the examinations should be made under the direction of the water-works company or department1 or by an independent body--as1 for instance1 by the ,board of ,health--will depend upon local conditions4 ,the former arrangement gives the superintendent of the filters the best chance to study their action1 as he can himself control the collection of samples in connection with the operation of the filters1 and arrange them to throw light upon the points he wishes to investigate2 while examination by a separate authority affords perhaps greater protection against the possible carelessness or dishonesty of water-works officials4 ,an arrangement being adopted in many cases in ,germany is to have a bacterial laboratory at the works which is under the control of the superintendent1 and in which the very numerous compulsory observations are made1 while the ,board of ,health causes to be examined from time to time by its own representatives1 who have no connection with the water-works1 samples taken to check the water-works figures1 as well as to show the character of the water delivered4 ,it seems quite desirable to have a man whose principal business is to make these examinations2 as in case he also has numerous other duties1 the examinations may be found to have been neglected at some time when they are most wanted4 ,such a man should have had thorough training in the principles of bacterial manipulation1 but it is quite unnecessary that he should be an expert bacteriologist1 especially if a competent bacteriologist is retained for consultation in cases of doubt or difficulty4 ,,chapter ,,vii4 ,,intermittent ,,filtration4 ,by intermittent nitration is understood that filtration in which the filtering material is systematically and adequately ventilated1 and where the water during the course of filtration is brought in contact with air in the pores of the sand4 ,in continuous filtration1 which alone has been previously considered1 the air is driven out of the sand as completely as possible before the commencement of filtration1 and the sand is kept continuously covered with water until the sand becomes clogged and a draining1 with an incidental aeration1 is necessary to allow the filter to be scraped and again put in service4 ,in intermittent filtration1 on the other hand1 water is taken over the top of the drained sand and settles into it1 coming in contact with the air in the pores of the sand1 and passes freely through to the bottom when the water-level is kept well down4 ,after a limited time the application of water is stopped1 and the filter is allowed to again drain and become thoroughly aerated preparatory to receiving another dose of water4 ,this system of treating water was suggested by the unequalled purification of sewage effected by a similar treatment4 ,it has been investigated at the ,lawrence ,experiment ,station1 and applied to the construction of a filter for the city of ,lawrence1 both of which are due to the indefatigable energy of ,hiram ,f4 ,mills1 ,c4,e4 ,in its operation intermittent differs from continuous filtration in that the straining action is less perfect1 because the filters yield no water while being aerated1 and must therefore filter at a greater velocity when in use to yield the same quantity of water in a given time1 and also on account of the mechanical disturbance which is almost invariably caused by the application of the water2 but1 on the other hand1 the oxidizing powers of the filter1 or the tendency to nitrify and destroy the organic matters1 are stronger1 and in addition1 if the rate is not too high1 the bacteria die more rapidly in the thoroughly aerated sand than is the case with ordinary filters4 ,it was found at ,lawrence in connection with sewage filters that when nitrification was actively taking place the numbers of bacteria were much lower than under opposite conditions1 and it was thought that nitrification in itself might cause the death of the bacteria4 ,later experiments1 however1 with pure cultures of bacteria of various kinds applied to intermittent filters with water to which ammonia and salts suitable for nitrification were added1 showed that bacteria of all the species tried were able to pass the filter in the presence of nitrification1 producing at least one thousand times as much nitrates as could result in any case of water-filtration1 as freely as was the case when the ammonia was not added and there was but little nitrification4 ,these results showed conclusively that nitrification in itself is not an important factor in bacterial removal1 although nitrification and bacterial purification do to some extent go together2 perhaps in part because the nitrification destroys the food of the bacteria and so starves them out1 but probably much more because the conditions of aeration1 temperature1 etc41 which favor nitrification also favor equally1 and even in its absence1 the death of the bacteria4 ,the rate at which water must pass through an intermittent filter is1 on account of the intervals of rest1 considerably greater than that required to give a corresponding total yield from a continuous filter1 and its straining effect is reduced to an extent comparable to this increase in rate2 and if other conditions did not come in1 the bacterial efficiency of an intermittent filter would remain below that of a continuous one4 ,as a matter of fact the bacterial efficiency has usually been found to be less with intermittent filters at the ,lawrence ,experiment ,station1 when they have been run at rates such as are commonly used for continuous filters in ,europe1 say from one and one half to two million gallons and upwards per acre daily4 ,with lower rates1 and especially with rather fine materials1 the bacterial efficiency is much greater2 but it may be doubted whether it would ever be greater than that of a continuous filter with the same filtering material and the same total yield per acre4 ,the number of bacteria coming from the underdrains is apparently generally less1 and with very high summer temperatures much less1 than in continuous filters1 and this often gives an apparent bacterial superiority to the intermittent filters4 ,the effluents from intermittent often contain less slightly organic matter than those from continuous filters2 but1 on the other hand1 hardly any water proposed for a public water-supply has organic matter enough to be of any sanitary significance whatever1 apart from the living bodies which often accompany it2 and if the latter are removed by straining or otherwise1 we can safely disregard the organic matters4 ,in addition1 the water filtered will in a great majority of cases have enough air dissolved in itself to produce whatever oxidation there is time for in the few hours required for it to pass the filter1 and it is only at very low rates of filtration that intermittent filters produce effluents of greater chemical purity than by the ordinary process4 ,the yellow-brown coloring matter present in so many waters appears to be quite incapable of rapid nitrification2 and where it is to some extent removed by filtration1 the action is dependent upon other and but imperfectly understood causes which seem to act equally in continuous and intermittent filters4 ,the peculiarities of construction involved by this method of filtration will be best illustrated by a discussion of the ,lawrence city filter designed by ,hiram ,f4 ,mills1 ,c4,e41 which is the only filter in existence upon this plan4#cj ,,the ,,lawrence ,,filter4 ,the filter consists of a single bed #b-a_/b acres in area1 the bottom of which is #g feet below low water in the river1 and filled with gravel and sand to an average depth of #d-a_/b feet4 ,the filter is all in a single bed instead of being divided into the three or four sections which would probably have been used for a continuous filter of this size4 ,the water-tight bottom also was dispensed with1 and the gravel was prevented from sinking into the silt by thin intermediate layers of graded materials4 ,the saving in cost was considerable2 but1 on the other hand1 a considerable quantity of ground-water comes up through the bottom and increases the hardness of the water from #a4e to #b4f parts of calcium carbonate in #ajj1jjj2 and while the water when compared with many other waters is still extremely soft1 the addition cannot be regarded as desirable4 ,the ground-water also contains iron1 which increases the color of the water above what it would otherwise be4 ,the underdrains have a frictional resistance ten times as great as would be desirable for a continuous filter1 the idea being to check extreme rates of filtration in case of unequal flooding1 and also to limit the quantity of water which could be gotten through the filter to that corresponding to a moderate rate of filtration4 ,the sand1 instead of being all of the same-sized grain1 is of two grades1 with effective sizes respectively #j4be and #j4cj mm41 the coarser sand being placed farthest away from the underdrains1 where its greater distance is intended to balance its reduced frictional resistance and make all parts filter at an equal rate4 ,the surface instead of being level is waved1 that is1 there are ridges thirty feet apart1 sloping evenly to the valleys one foot deep half way between them1 to allow water to be brought on rapidly without disturbing the sand surface4 ,for the same reason1 as well as to secure equality of distribution1 a system of concrete carriers for the raw water goes to all parts of the filter1 reducing the effective filtering area by #d or #e per cent4 ,the filter is scraped as necessary in sections1 the work being performed when the filter is having its daily rest and aeration4 ,owing to the difference in frictional resistance before and after scraping1 and to the fact that it is impossible to scrape the entire area in one day1 considerable variations in the rate of filtration in different parts of the filter must occur4 ,the heavy frictional resistance of the underdrains when more than the proper quantity of water passes them tends to correct this tendency especially for the more remote parts of the filter1 but perhaps at the expense of those near to the main drain4 ,the filter is not covered as the suggestions in ,chapter ,,ii would require1 but this is hardly on account of its being an intermittent filter4 ,the annual report of the ,massachusetts ,state ,board of ,health for #ahic states that during the first half of ,december1 #ahic1 the surface remained covered1 that is1 it was used continuously1 and after ,december #afth it was so used when the temperature was below #bd1 and was drained only when the temperature was #bd or above4 ,the days on which the filter was drained during the remainder of ,december are not given1 but during ,january and ,february1 #ahid1 the filter remained covered #bi days and was drained #cj days4 ,bacterial samples were taken on #dd of these days1 #bb days when it was drained and #bb when it was not4 ,the average number of bacteria on the days when it was not drained was #acg and on those days when it was drained #beb per cubic centimeter4 ,from ,february #bdth to ,march #abth the number of bacteria were unusually high1 averaging #dib per cubic centimeter1 or #e4bh per cent of the #icjh applied4 ,during this period the filter was used intermittently2 there was ice upon it1 and parts of the surface were scraped under the ice1 and high rates of filtration undoubtedly resulted on the scraped areas4 ,after ,march #abth the ice had disappeared and very much better results were obtained4 ,while there may be some question as to the direct cause of this decreased efficiency with continued cold weather and ice1 the results certainly are not such as to show the advisability of building open filters in the ,lawrence climate4 ,the cost of building the filter in comparison with ,european filters was extraordinarily low--only #fg1jjj1 or #bg1jjj per acre of filter surface4 ,to have constructed open continuous filters of the same area with water-tight bottoms1 divided into sections with separate drains and regulating apparatus1 with the necessary piping1 would have cost at least half as much more1 and with the masonry cover which ,i regard as most desirable in the ,lawrence climate the cost would have been two or three times the expenditure actually required4 ,it was no easy matter to secure the consent of the city government to the expenditure of even the sum used2 there was much skepticism as to the process of filtration in general1 and it was said that mechanical filters could be put in for about the same cost4 ,insisting upon the more complete and expensive form might have resulted either in an indefinite postponement of action1 or in the adoption of an inferior and entirely inadequate process4 ,still ,i feel strongly that in the end the greater expense would have proved an excellent investment in securing softer water and in the greater facility and security of operating the filter in winter4 ,in regard to the effect of the ,lawrence filter upon the health of the city1 ,i can best quote from ,mr4 ,mills' paper in the ,report of the ,massachusetts ,state ,board of ,health for #ahic1 and also published in the ,journal of the ,new ,england ,water-works ,association4 ,mr4 ,mills says3 8,in the following diagram ,fig4 #ae the average number of deaths from typhoid fever at ,lawrence for each month from ,october to ,may1 in the preceding five years1 are given by the heavy dotted line2 and the number during the past eight months are given by the heavy full line4 8,the total number for eight months in past years has been forty-three1 and in the present year seventeen1 making a saving of twenty-six4 ,of the seventeen who died nine were operatives in the mills1 each of whom was known to have drunk unfiltered canal water1 which is used in the factories at the sinks for washing4 ,illustration3 ,,fig4 #ae4--,,typhoid ,,fever ,,in ,,lawrence4 8,the finer full line shows the number of those who died month after month who are not known to have used the poisoned canal water4 ,the whole number in the eight months is eight4 8,it is evident from the previous diagram not reproduced that the numbers above the fine full line1 here1 follow after those at ,lowell in the usual time1 and were undoubtedly caused by the sickness at ,lowell2 but we have satisfactory reason to conclude that the disease was not propagated through the filter but that the germs were conveyed directly into the canals and to those who drank of the unfiltered canal water4 ,among the operatives of one of the large corporations not using the canal water there was not a case of typhoid fever during this period4 ,warnings have been placed in the mills where canal water is used to prevent the operatives from drinking it4 8,we find1 then1 that the mortality from typhoid fever has1 during the use of the filter1 been reduced to #dj per cent of the former mortality1 and that the cases forming nearly one half of this #dj per cent were undoubtedly due to the continued use of unfiltered river water drawn from the canals40 ,the records of typhoid fever in ,lawrence before and after the introduction of filters are as follows3 ,,deaths ,,from ,,typhoid ,,fever ,,in ,,lawrence1 #ahhh-ih4 ---------------------------------------- --------------------------- ,persons who are known to have been ,years4 ,total ,deaths exposed to infection4 ,number per ----------------------------------- of #aj1jjj ,while living out ,deaths4 of ,by drinking of town just before ,population4 ,canal ,water4 falling sick in ,lawrence4 ---------------------------------------- -------------------------- #ahhh #dh #aa4cf #ahhi #ee #ab4ff #ahij #fj #ac4dd #ahia #ee #aa4id #ahib #ej #aj4eb #ahic #ci #g4if #ahid #bd #d4ge #ab #ahie #af #c4jg #i #b #ahif #aj #a4hf #b #d #ahig #i #a4fb #ahih #h #a4ci #a ---------------------------------------- -------------------------- ,filter put in operation ,september1 #ahic4 ,average rate before the introduction of filtered water 7#ahhh-ib7 #aa4ca ,average rate afterward 7#ahid-ih7 #b4ed ,these results show a striking reduction in the deaths from typhoid fever with the introduction of filtered water1 which has been most gratifying in every way4 ,the more recent history of the underdrains of the ,lawrence filter is particularly instructive4 ,owing to the absence of a water-tight bottom to the filter1 and its low position1 a certain amount of water constantly entered the filter from the ground below4 ,this water contained iron in solution as ferrous carbonate4 ,when this water came in contact with the filtered water in the gravel and underdrains1 the iron was oxidized by the dissolved oxygen carried in the filtered water and precipitated4 ,this was accompanied by a growth of crenothrix in the gravel and underdrains1 which gradually reduced their carrying capacity4 ,this reduction in carrying capacity first became apparent in cold weather when the yield from the filter was less free than formerly4 ,there was difficulty in maintaining the supply during the winter of #ahif-g and more difficulty in the following winter4 ,illustration3 ,,fig4 #af4--,,typhoid ,,fever ,,in ,,lawrence1 #ahhh ,,to #ahih4 ,the sand of the filter was as capable of filtering the full supply of water as it ever had been1 and the efficiency was as good2 but the underdrains were no longer able to collect the filtered water and deliver it4 ,as the filtering area was ample for the supply1 it was desired to avoid construction of additional filtering area4 ,the underdrains were dug up and cleaned during the periods when the filter was drained4 ,as the filter is all in one bed1 the times when the filter could be allowed to remain drained1 and when the work could proceed1 were limited4 ,great care was taken to leave the work in good condition1 and free from passages1 at the end of each day's work1 but the numbers of bacteria in the effluent nevertheless increased somewhat4 ,some weeks afterward the number of cases of typhoid fever in the city increased4 ,the numbers did not become as high as they had been prior to the introduction of filtered water1 but they were much higher than they had been since that time1 and they pointed strongly to the disturbance of the underdrains as the cause of the increase4 ,the numbers of bacteria in the applied water and in the effluent from the ,lawrence filter by months1 from the time the filter was put in operation1 compiled from the reports of the ,state ,board of ,health1 as far as available1 are as follows3 ,,bacteria ,,in ,,water ,,applied ,,to ,,and ,,effluent ,,from ,,lawrence ,,filter4 ,,raw ,,water4 ---------------------------------------- ------------------------ #ahic4 #ahid4 #ahie4 #ahif4 #ahig4 #ahih4 ---------------------------------------- ------------------------ ,january #g1gjj #ah1gjj #g1ejj #ac1cad #f1eai ,february #g1fjj #ae1jdj #ab1fjj #ac1aac #d1fec ,march #f1ejj #bj1ggj #e1ijj #ab1jee #c1gdh ,april #aa1bjj #h1dbj #c1hjj #f1ijd #b1cbj ,may #f1jjj #g1jjj #i1fjj #d1fbe #b1jej ,june #h1cjj #i1jjj #f1djj #d1fej #f1gge ,july #b1djj #aj1jjj #c1ijj #f1bdj #b1hdj ,august #c1ajj #e1jjj #b1gjj #aj1gjj #h1ege ,september #eg1ejj #f1ejj #e1jjj #ab1cjj #bg1cjj #f1ajj ,october #bb1bjj #be1cjj #ai1jjj #e1cjj #ac1bjj #e1abj ,november #aj1hjj #af1fjj #h1gjj #e1fjj #f1fdd #d1caj ,december #h1ajj #bc1hjj #f1gjj #i1fie #e1eha #e1bjj ---------------------------------------- -------- ,average #bd1fej #aj1dag #aa1aaa #g1ajh #aj1cfj #d1hej ,,effluent4 ,january #abi #bjf #aff #ia #ci ,february #bdd #bhc #cae #gi #de ,march #dee #dje #acc #fg #cd ,april #bha #hd #dj #dg #ba ,may #acd #fh #ef #ce #dh ,june #aaj #fh #bb #ef #ej ,july #be #ej #ci #ajf #bb ,august #cf #ch #adf #gb #bh ,september #f1hej #db #dj #cg #ih #fg ,october #a1baf #aaf #fj #cj #cc #bh ,november #afa #age #fd #cg #bg #abb ,december #aaa #cfd #hd #fg #bd ---------------------------------------- -------- ,average #b1jhd #agf #aba #ia #fa #df ,average efficiency #ia4ee #ih4ca #ih4ia #ih4gb #ii4da #ih4ie ,,chemnitz ,,water-,,works4 ,the only other place which ,i have found where anything approaching intermittent filtration of water is systematically employed is ,chemnitz1 ,germany4 ,the method there used bears the same relation to intermittent filtration as does broad irrigation of sewage to the corresponding method of sewage treatment2 that is1 the principles involved are mainly the same1 but a much larger filtering area is used1 and the processes take place at a lower rate and under less close control4 ,illustration3 ,,fig4 #ag4--,,plan ,,of ,,area ,,used ,,for ,,intermittent ,,filtration ,,at ,,chemnitz4 ,the water-works were built about twenty years ago by placing thirty-nine wells along the ,zwnitz ,river1 connected by siphon pipes1 with a pumping-station which forced the water to an elevated reservoir near the city 7,fig4 #ag74 ,the wells are built of masonry1 #e or #f feet in diameter and #aj or #ab feet deep1 and are on the rather low bank of the river4 ,the material1 with the exception of the surface soil1 and loam about #c feet deep1 is a somewhat mixed gravel with an effective size of probably from #j4be to #j4ej mm41 so that water is able to pass through it freely4 ,the wells are1 on an average1 about #abj feet apart1 and the line is seven eighths of a mile long4 ,it was found that in dry times the ground-water level in the entire neighborhood was lowered some feet below the level of the river without either furnishing water enough or stopping the flow of the river below4 ,the channel of the river was so silted that1 notwithstanding the porous material1 the water could not penetrate it to go toward the wells4 ,a dam was now built across the river near the pumping-station1 and a canal was dug from above the dam1 crossing the line of wells and running parallel to it on the back side for about half a mile4 ,later a similar canal was dug back of the remaining upper wells4 ,owing to the difference in level in the river above and below1 the canals can be emptied and filled at pleasure4 ,they are built with carefully prepared sand bottoms1 and the sand sides are protected by an open paving1 to allow the percolation of as much water as possible1 and the sand is cleaned by scraping1 as is usual with ordinary sand filters1 once a year or oftener4 ,the yield from the wells was much increased by these canals1 but the water of the river is polluted to an extent which would ordinarily quite prevent even the thought of its being used for water-supply1 and it was found that the water going into the ground from the canals1 and passing through the always saturated gravel to the wells1 without coming in contact with air at any point1 after a time contained iron and had an objectionable odor4 ,to avoid this disagreeable result the meadow below the pumping-station was laid out as an irrigation field 7,fig4 #af74 ,the water from above the dam was taken by a canal on the opposite side of the river through a sedimentation pond 7which1 however1 is not now believed to be necessary and is not always used71 and then under the river by a siphon to a slightly elevated point on the meadow1 from which it is distributed by a system of open ditches1 exactly as in sewage irrigation4 ,the area irrigated is not exactly defined and varies somewhat from time to time2 the rate of filtration may be roughly estimated at from #ajj1jjj to #aej1jjj gallons per acre daily1 although limited portions may occasionally get five times these quantities for a single day4 ,the water passes through the three feet of soil and loam1 and afterward through an average of six feet of drained coarse sand or gravel in which it meets air1 and afterward filters laterally through the saturated gravel to the wells4 ,the water so obtained is invariably of good quality in every way1 colorless1 free from odor and from bacteria4 ,the surface of the irrigated land is covered with grass and has fruit-trees 7mostly apple7 at intervals over its entire area4 ,this first system of irrigation is entirely by gravity4 ,on account of natural limits to the land it could not be conveniently extended at this point1 and to secure more area1 the higher land above the pumping-station was being made into an irrigation field in #ahid4 ,this is too high to be flooded by gravity1 and will be used only for short periods in extremely dry weather4 ,the water is elevated the few feet necessary by a gas-engine on the river-bank4 ,in times of wet weather enough water is obtained from the wells without irrigation1 and the land is only irrigated when the ground-water level is too low4 ,during ,december1 ,january1 and ,february irrigation is usually impossible on account of temperature1 and the canals are then used1 keeping them filled with water so that freezing to the bottom is impossible2 but trouble with bad odors in the filtered water drawn from the wells is experienced at these times4 ,the drainage area of the ,zwnitz ,river is only about #dd square miles1 and upon it are a large number of villages and factories1 so that the water is excessively polluted4 ,the water in the wells1 however1 whether coming from natural sources1 or from irrigation1 or from the canals1 has never had as many as #ajj bacteria per cubic centimeter1 and is regarded as entirely wholesome4 ,in extremely dry weather the river1 even when it is all used for irrigation so that hardly any flows away below1 cannot be made to supply the necessary daily quantity of #b1fej1jjj gallons1 and to supply the deficiency at such times1 as well as to avoid the use of the canals in winter1 a storage reservoir holding #ie1jjj1jjj gallons has recently been built on a feeder of the river4 ,this water1 which is from an uninhabited drainage area1 is filtered through ordinary continuous filters and flows to the city by gravity4 ,owing to the small area of the watershed it is incapable of supplying more than a fraction of the water for the city1 and will be used to supplement the older works4 ,this ,chemnitz plant is of especial interest as showing the successful utilization of a river-water so grossly polluted as to be incapable of treatment by the ordinary methods4 ,results obtained at the ,lawrence ,experiment ,station have shown that sewage is incapable of being purified by continuous filtration1 the action of air being essential for a satisfactory result4 ,with ordinary waters only moderately polluted this is not so2 for they carry enough dissolved air to effect their own purification4 ,in ,chemnitz1 however1 as shown by the results with the canals1 the pollution is so great that continuous filtration is inadequate to purify the water1 and the intermittent filtration adopted is the only method likely to yield satisfactory results in such cases4 ,intermittent filtration is now being adopted for purifying brooks draining certain villages and discharging into the ponds or reservoirs from which ,boston draws its water-supply4 ,the water of ,pegan ,brook below ,natick has been so filtered since #ahic with most satisfactory results1 and affords almost absolute protection to ,boston from any infection which might otherwise enter the water from that town4 ,a similar treatment is soon to be given to a brook draining the city of ,marlborough4 ,the sewage from these places is not discharged into the brooks1 but is otherwise provided for1 but nevertheless they receive many polluting matters from the houses and streets upon their banks4 ,the filtration used resembles in a measure that at ,chemnitz1 and ,i am informed by the engineer1 ,mr4 ,desmond ,fitz,gerald1 that it was adopted on account of its convenience for this particular problem1 and not because he attaches any special virtue to the intermittent feature4 ,,application ,,of ,,intermittent ,,filtration4 ,in regard to the use of waters as grossly polluted as the ,zwnitz1 the tendency is strongly to avoid their use1 no matter how complete the process of purification may be2 but in case it should be deemed necessary to use so impure a water for a public supply1 intermittent filtration is the only process known which would adequately purify it4 ,and it should be used at comparatively low rates of filtration4 ,i believe that an attempt to filter the ,zwnitz at the rate used for the ,merrimac water at ,lawrence1 which is by comparison but slightly polluted1 would result disastrously4 ,the operation in winter must also be considered4 ,intermittent filtration of sewage on open fields in ,massachusetts winters is only possible because of the comparatively high temperature of the sewage 7usually #dj to #ej71 and would be a dismal failure with sewage at the freezing-point1 the temperature to be expected in river-waters in winter4 ,it is impossible to draw a sharp line between those waters which are so badly polluted as to require intermittent filtration for their treatment and those which are susceptible to the ordinary continuous filtration4 ,examples of river-waters polluted probably beyond the limits reached in any ,american waters used for drinking purposes and successfully filtered with continuous filters are furnished by ,altona1 ,breslau1 and ,london4 ,intermittent filtration may be considered in those cases where it is proposed to use a water polluted entirely beyond the ordinary limits1 and for waters containing large quantities of decomposable organic matters and microscopical organisms2 but in those cases where a certain and expeditious removal of mud is desired1 and where waters are only moderately polluted by sewage1 but still in their raw state are unhealthy1 it is not apparent that intermittent filtration has any advantages commensurate with the disadvantages of increased rate to produce the same total yield and of the increased difficulty of operation1 particularly in winter2 and in such cases continuous filtration is to be preferred4 ,in the removal of tastes and odors from pond or reservoir waters which are not muddy1 but which are subject to the growths of low forms of plants1 which either by their growth or decomposition impart to the water disagreeable tastes and odors1 intermittent filtration may have a distinct advantage4 ,in such cases there is often an excess of organic matter to be disposed of by oxidation1 and the additional aeration secured by intermittent filtration is of substantial assistance in disposing of these matters4 ,,chapter ,,viii4 ,,turbidity ,,and ,,color1 ,,and ,,the ,,effect ,,of ,,mud ,,upon ,,sand-,,filters4 ,the ideal water in appearance is distilled water1 which is perfectly clear and limpid1 and has a slight blue color4 ,when other waters are compared with it1 the divergences in color from the color of distilled water are measured1 and not the absolute colors of the waters4 ,many spring waters and filtered waters are indistinguishable in appearance from distilled water4 ,public water-supplies from surface sources contain two substances or classes of substances which injure their appearance1 namely1 peaty coloring matters1 and mud4 ,waters discolored by peaty matters are most common in ,new ,england and in certain parts of the ,northwest1 while muddy waters are found almost everywhere1 but of different degrees of muddiness1 according to the physical conditions of the water-sheds from which they are obtained4 ,muddy waters are often spoken of as colored waters1 and in a sense this is correct where the mud consists of clays or other materials having distinct colors2 but it is more convenient to classify impurities of this kind as turbidities only1 and to limit the term colored waters to those waters containing in solution vegetable matters which color them4 ,the removal of either color or turbidity may be called clarification4 ,colored waters are usually drawn from water-sheds where the underlying rock is hard and does not rapidly disintegrate1 and where the soils are firm and sandy1 and especially from swamps4 ,the water here comes in contact with peat or muck1 which colors it1 but is so firm as not to be washed by flood flows1 and so does not cause turbidity4 ,large parts of the ,united ,states have for rock foundations shales or other soft materials which readily disintegrate when exposed1 and which form clayey soils readily washed by hard rains4 ,waters from such watersheds are generally turbid and very rarely colored4 ,in fact a water carrying much clay in suspension is usually found colorless when the clay is removed1 even if it were originally colored4 ,it thus happens that waters which are colored and turbid at the same time hardly exist in nature4 ,color-producing matters and turbidity-producing matters are different in their natures1 and the methods which must be used to remove them are different4 ,,the ,,measurement ,,of ,,color4 ,the colors of waters are measured and recorded by comparing them with colors of solutions or substances which are permanent1 or which can be reproduced at will4 ,one of the earliest methods of measuring colors of waters was to compare them with the colors of the ,nessler standards used for the estimation of ammonia in water analysis4 ,the ,nessler standards were similar in appearance to yellow waters1 and their colors depended upon the amounts of ammonia which had been used in preparing them1 and a record was made of the standard which most closely resembled the water under examination4 ,the method was open to the serious objections that the hues of the standards did not match closely the hues of the waters2 that the colors produced with different lots of ,nessler reagent differed considerably1 and therefore the exact values of results were more or less uncertain2 and further1 that the numbers obtained for color were not even approximately proportional to the amounts of coloring matter present4 ,because of this peculiarity1 in filtration the percentage of color removal1 as determined by the use of these standards1 is not even approximately correct1 but is much above the truth4 ,in the ,lovibond tintometer1 which has been extensively used in ,england1 the standards of color are based upon the colors of certain glass slips1 which are in turn compared with standard originals kept for that purpose4 ,this process answers quite well1 but is open to some objections because of possible uncertainties in the standardization of the units4 ,another method of measuring colors is to compare them with dilute solutions of platinum and cobalt4 ,the ratio of cobalt to platinum can be varied to make the hue correspond very closely with the hues of natural waters1 and the amount of platinum required to match a water affords a measure of its color1 one part of metallic platinum in #aj1jjj parts of water forming the unit of color4 ,this standard has the advantages that it can be readily prepared with absolute accuracy in any laboratory1 and that by varying the ratio of platinum to cobalt the hues of various waters can be most perfectly matched4 ,it is important that the observations should not be made in too great a depth1 as the discrepancy in hues increases much more rapidly than the depth of color4 ,for further information regarding colors the reader is referred to articles in the ,american ,chemical ,journal1 #ahib1 vol4 xiv1 page #cjj2 ,journal of the ,american ,chemical ,society1 vol4 ii1 page #h2 vol4 xviii1 #ahif1 pp4 #fh1 #bfd1 and #dhd2 ,journal of the ,franklin ,institute1 ,dec4 #ahid1 p4 #djb2 ,journal of the ,new ,england ,water ,works ,association1 vol4 xiii1 #ahih1 p4 #id4 ,,amount ,,of ,,color ,,in ,,american ,,waters4 ,new ,england surface-waters have colors ranging from almost nothing up to #b4jj4 ,the colors of the public water-supplies of ,massachusetts cities have been recorded in the reports of the ,state ,board of ,health for some ten years4 ,the figures given were recorded first upon the ,nessler standard1 and afterwards upon a modification of the same1 known as the natural water standard4 ,the figures given are approximately equal to those for the platinum color standard1 the relations between the two having been frequently determined by various observers and published in the above-mentioned papers4 ,the accompanying diagram shows the colors in several ,massachusetts supplies1 as plotted from the figures given in the published reports4 ,illustration3 ,,fig4 #ah4--;,,colors ,,of ,,waters4 7,analyses of the ,mass4 ,state ,board of ,health47 ,in ,connecticut also the colors of many public water-supplies have been recorded in the reports of the ,state ,board of ,health on the platinum color-standard4 ,the waters of the ,middle ,states1 with rare exceptions1 are almost free from color4 ,in the ,northwest waters are obtained often with very high colors1 even considerably higher than the ,new ,england waters1 and some of the ,southern swamps also yield highly colored waters4 ,,removal ,,of ,,color4 ,peaty coloring-matter is almost perfectly in solution1 and only a portion of it is capable of being removed by any form of simple filtration4 ,in order to remove the coloring-matter it is necessary to change it chemically1 or to bring it into contact with some substance capable of absorbing it4 ,for this reason sand filtration with ordinary sands1 having no absorptive power for color1 commonly removes only from one fourth to one third of the color of the raw water4 ,,measurement ,,of ,,turbidity4 ,the amount of mud or turbidity in a water is often expressed as the weight of the suspended matters in a given weight of the water4 ,most of the data relating to turbidities of waters are stated in this way1 because this was the only method recognized by the earlier investigators4 ,this method of statement has some disadvantages3 it fails to take into account the different sizes of particles which are carried in suspension by different waters1 and at different times4 ,thus the ,merrimac ,river in a great flood may carry #ajj parts in #ajj1jjj of fine sand in suspension1 and still it could hardly be called muddy2 while another stream carrying only a fraction of this amount of fine clay would be extremely muddy4 ,further1 an accurate determination of suspended matters is a very troublesome and tedious operation1 and cannot be undertaken as frequently as is necessary for an adequate study of the mud question4 ,turbidity is principally important as it affects the appearance of water1 and it would seem that optical rather than gravimetric methods should be used for its determination4 ,various optical methods of measuring turbidity have been proposed4 ,the general method employed is to measure the thickness of the layer of water through which some object can be seen under definite conditions of lighting4 ,the most accurate results can probably be obtained in closed receptacles and with artificial light4 ,such a method has been used by ,mr4 ,g4 ,w4 ,fuller at ,louisville and ,cincinnati in connection with his experiments1 and is described by ,parmelee and ,ellms in the ,technology ,quarterly for ,june1 #ahii4 ,this apparatus is called by ,mr4 ,fuller a diaphanometer4 ,at the ,lawrence ,experiment ,station of the ,massachusetts ,state ,board of ,health as early as #ahhi it became necessary to express the turbidities of various waters approximately1 and the very simple device of sticking a pin into a stick1 and pushing it down into the water under examination as far as it could be seen1 was adopted4 ,afterwards a platinum wire #j4jd of an inch in diameter was substituted for the pin1 and the stick was graduated so that the turbidities could be read from it directly4 ,the figures on the stick were inversely proportional to their distances from the wire4 ,when the wire could be seen one inch below the surface1 the turbidity was reported as #a4jj2 when the wire could be seen two inches1 the turbidity was #j4ej1 and when it could be seen ten inches the turbidity was #j4aj1 etc4 ,this scale is much more convenient than a scale showing the depth at which the wire can be seen2 and within certain limits the figures obtained with it are directly proportional to the amount of the elements which obstruct light in the water4 ,thus1 if a water having a turbidity of #a4jj is mixed with an equal volume of clear water1 the mixture will have a turbidity of #j4ej4 ,advantage is taken of this fact for the measurement of turbidities so great that they cannot be accurately determined by direct observation4 ,for turbidities much above #a4jj it is very difficult to read the depth of wire with sufficient accuracy1 and such waters are diluted with one1 two1 or more times their volume of clear water in a pail or other receptacle1 the turbidity of the diluted water is taken1 and multiplied by the appropriate factor4 ,for the greatest accuracy it is necessary that the observations should be taken in the open air and not under a roof4 ,they should preferably be made in the middle of the day when the light is strongest1 and in case the sun is shining1 the wire must be kept in shadow and not in direct sunlight4 ,the turbidities of effluents are usually so slight that they cannot be taken in this manner2 in fact1 turbidities of less than #j4jb1 with the wire visible #ej inches below the surface1 cannot be conveniently read in this way4 ,for the estimation of lower turbidities a water is taken having a turbidity of #j4jc or #j4jd and as free as possible from large suspended particles4 ,the turbidity of this water is measured by a platinum wire in the usual way1 and the water is then diluted with clear water to make standards for the lower turbidities4 ,the comparisons between standards and waters are best made in bottles of perfectly clear glass1 holding at least a gallon1 and the comparison is facilitated by surrounding the bottles with black cloth except at the point of observation1 and lighting the water by electric lights so arranged that the light passes through the water but is hidden from the observer4 ,in case the water under examination is colored1 the comparison is rendered difficult1 and it is often advisable to add a small amount of methyl orange to the standards to make the colors equal4 ,instead of diluting a water of known turbidity for the standards1 a standard can be made by precipitating a known amount of silver chloride in the water4 ,for this purpose about one per cent of common salt is dissolved in clear water and small measured amounts of silver nitrate added1 until the turbidity produced is equal to that of the water under examination4 ,the relation of the amount of silver nitrate used to the turbidity is entirely arbitrary1 and is established by comparisons of standards made in this way with waters having turbidities from #j4jb to #j4jd1 the turbidities of which are measured with the platinum wire1 and which afterwards serve to rate the standards4 ,the silver chloride has a slight color1 which is an objection to its use1 and perhaps some other substance could be substituted for it with advantage4 ,the standards have to be made freshly each day4 ,one disadvantage of the platinum-wire method of observing turbidities in the open air1 as compared with the diaphanometric method using artificial light1 is that observations cannot be made in the night4 ,to get the general character of the water in a stream1 daily observations taken about noon will generally be sufficient2 but for some purposes it is important to know the turbidity at different hours of the day1 and in such cases the platinum-wire method is at a distinct disadvantage4 ,variations in the amount of light1 within reasonable limits1 do not affect the results materially1 although extreme variations are to be avoided4 ,the size of the wire also influences the results somewhat4 ,the wire commonly used is #j4jd of an inch or one millimeter in diameter4 ,a wire only four tenths of this size in some experiments at ,pittsburg gave results #be per cent higher2 with a wire twice as large the results were lower1 but the differences were much less4 ,wire #j4jd of an inch in diameter was adopted as being very well adapted to rather turbid river-waters4 ,for very clear lake or reservoir waters1 usually transparent to a great depth1 a much larger object is preferable4 ,within certain limits the results obtained with an object of any size can be converted into corresponding figures for another object1 or another light1 by the use of a constant factor4 ,thus the turbidities obtained with a platinum wire always have approximately the same ratio to the turbidities of the same waters determined by the diaphanometer4 ,the platinum-wire method has been used in many cases with most satisfactory results4 ,if it lacks something in theoretical accuracy as compared with more elaborate methods1 it more than makes up for it by its simplicity2 and reliable observations can be taken with it by people who would be entirely incompetent to operate more elaborate apparatus2 and it can thus be used in many cases where other methods would be impossible4 ,upon this scale the most turbid waters which have come under the observation of the author have turbidities of about #b4ej1 although waters much more turbid than this undoubtedly exist4 ,a water with a turbidity of #a4jj is extremely muddy1 and only one tenth of this turbidity would cause remark and complaint among those who use it for domestic purposes4 ,in an ordinary pressed-glass tumbler a turbidity of #j4jb is just visible to an ordinary observer who looks at the water closely1 but it is not conspicuous1 nor would it be likely to cause general complaint2 and this amount may be taken as approximately the allowable limit of turbidity in a good public water-supply4 ,in a carefully polished1 and perfectly transparent glass a turbidity of #j4ja will be visible1 and in larger receptacles still lower turbidities may be seen if the water is examined carefully4 ,in gallon bottles of very clear glass1 under electric light and surrounded by black cloth1 a turbidity of #j4jja can be distinguished1 but a turbidity even several times as large as this could hardly be detected except by the use of special appliances1 or where water is seen in a depth of several feet4 ,,relation ,,of ,,platinum-,,wire ,,turbidities ,,to ,,suspended ,,matters4 ,the relation of turbidity to the weight of suspended matters is approximately constant for waters from which the coarser matters have been entirely removed by sedimentation4 ,for these waters the suspended matters in parts per #ajj1jjj are about #af times the turbidity4 ,for river-waters the ratios are always larger4 ,with very sluggish rivers the ratio is only a little larger than for settled waters4 ,for average river-waters the ratio is considerably higher1 and increases with the turbidity1 and for very rapid rivers and torrents the ratio is much wider1 as the suspended matters consist largely of particles which are heavy but do not increase very much the turbidity4 ,the following table gives the amounts of suspended matters for various classes of waters corresponding to the turbidities stated1 which have been deduced from the experience of the author4 ,it is very likely that ratios different from the above would be obtained with waters in which the sediment was of different character4 ---------------------------------------- --------------------- ,suspended ,matters3 ,parts in #ajj1jjj4 ,turbidity1 ---------------------------------------- ------- ,platinum-wire ,river ,river ,river ,standard4 ,settled ,waters1 ,waters1 ,waters1 ,waters4 ,finest ,average ,coarsest ,sediment4 ,sediment4 ,sediment4 ---------------------------------------- ------------------ #j4ja #j4af #j4je #j4hj #j4he #a4cj #b4dj #j4aj #a4fj #a4ge #b4fj #d4ij #j4bj #c4bj #c4fj #e4ej #aj4jj #j4cj #d4hj #e4gj #h4ej #ae4jj #j4dj #f4dj #g4hj #aa4fj #ba4jj #j4ej #h4jj #aj4jj #ae4jj #bf4jj #a4jj #af4jj #bc4jj #cf4jj #ei4jj #a4ej #bd4jj #dj4jj #fb4jj #ig4jj #b4jj #cb4jj #fa4jj #id4jj #adj4jj #c4jj #dh4jj #aaj4jj #age4jj #bej4jj ---------------------------------------- ------------------ ,,source ,,of ,,turbidity4 ,much turbidity originates in plowed fields of clayey soil1 or in fields upon which crops are growing4 ,if it has not rained for some days1 and the surface-soil is comparatively dry1 the first rain that falls upon such land is absorbed by the pores of the soil until they are filled4 ,if the rain is not heavy1 but little runs off over the surface4 ,if1 however1 the rain continues rapidly after the surface-soil is saturated1 the excess runs off over the surface to the nearest watercourse4 ,the impact of the rain-drops upon the soil loosens the particles1 and the water flowing off carries some of them in suspension1 and the water is said to be muddy4 ,the particles carried off in this way are extremely small4 ,mr4 ,george ,w4 ,fuller1 in his report upon water purification at ,louisville1 estimates that many of them are not more than a hundred thousandth of an inch in diameter1 and not more than a tenth as large as common water bacteria4 ,the turbidity of the water flowing from a field of loose soil may be #b4jj or more2 that is to say1 the wire is hidden by a depth of half an inch of water or less4 ,when the water reaches the nearest watercourse it meets with water from other kinds of land1 such as woodlands and grassed fields1 and these waters are less turbid4 ,the water in the first little watercourse is thus a mixture and has a turbidity of perhaps #a4jj4 ,the conditions which control the turbidity of any brook are numerous and complicated4 ,the turbidity of a stream receiving various brooks depends upon the turbidities of all the waters coming into it4 ,generally speaking1 the turbidity of a river depends directly upon the turbidities of its feeders1 and is not affected materially by erosion of its bed or by sedimentation in it4 ,there are1 of course1 some streams which in times of great floods cut their banks1 and all streams pick up and move about from place to place more or less of the sand and other coarse materials upon their bottoms4 ,the materials thus moved1 however1 have but little influence upon the turbidity4 ,after the rain is over some of the water held by the soil will find its way to the watercourses by underground channels1 and will prevent the stream from drying up between rains1 but the average volume of the stream-flows between rains will be much less than the volumes during the rains when the water is most turbid4 ,illustration3 ,,fig4 #ai4--;,,fluctuations ,,in ,,turbidity ,,of ,,the ,,water ,,of ,,the ,,allegheny ,,river ,,at ,,pittsburg ,,during #ahih4 ,these conditions are well illustrated by a few data upon the turbidity of three ,pennsylvania streams1 recently collected by the author4 ,one of these streams is a small brook having a drainage area of less than three square miles4 ,the observations extended over a period of #dg days4 ,during this time there were five floods1 or an average of one flood in ten days4 ,the duration of floods was less than twenty-four hours in each case4 ,selecting the days when the turbidity was the highest1 to the number of one tenth of the whole number of days1 the sum of the turbidities for these days was #fg per cent of the aggregate turbidities for the whole period4 ,that is to say1 #fg per cent of the whole amount of mud was in the water of only a tenth of the days2 the water of the other nine tenths of the days contained only #cc per cent of the whole amount of turbidity4 ,the average turbidity of the water for the flood days was eighteen times as great as the average turbidity for the remaining days4 ,the next stream is a considerable creek having a drainage area of #cej square miles4 ,the observations extended over #aag days1 during which time there were seven floods1 or an average of one flood in #ai days4 ,the floods lasted in each case one or two days1 and the sum of the turbidities for the one tenth of the whole number of days when the water was muddiest was #ee per cent of the aggregate of all the turbidities for the period4 ,the last case is that of a large river1 with a drainage area of over #aa1jjj square miles4 ,the observations extended over a full year4 ,in this period there were sixteen floods1 each lasting from one to six days1 and the sum of the turbidities for the one tenth of the whole number of days when the water was muddiest is #de per cent of the aggregate turbidities for the year4 ,the floods occurred on an average of once in #bb days1 and the average duration was two and one half days4 ,the results are very striking as showing that a very large proportion of the mud is carried by the water in flood flows of comparatively short duration4 ,they also show that in small streams the proportion of mud in the flood-flows is greater1 and the average duration of floods is shorter1 than in larger streams4 ,in other words1 the differences between flood- and low-water flows are greatest in small streams1 and gradually become less as the size of the stream increases4 ,when a stream is used for water-works purposes in the usual way1 a certain quantity of water is taken from the stream each day1 which quantity is nearly constant1 and is not dependent upon the condition of the stream1 or the volume of its flow4 ,the proportions of the total flows taken at high- and low-water stages are very different1 and it thus happens that the average quality of the water taken for water-works purposes is different from the average quality of all the water flowing in the stream4 ,let us assume1 for example1 a stream having a watershed of such a size that in times of moderate floods water from the most distant points reaches the water-works intake in twenty-four hours4 ,let us assume further that rainfalls of sufficient intensity to cause floods and muddy water occur1 on an average1 once in ten days1 and that the turbidity of the water at these times reaches #a4jj1 and that for the rest of the time the turbidity averages #j4aj4 ,let us assume further that at times of storms the average flow of the stream is #ajj units of volume1 and for the nine days between storms the average flow is #aj units of volume4 ,we shall then have in a ten days' period1 for one day1 #ajj volumes of water with a turbidity of #a4jj1 and nine days with #aj volumes each1 or a total of #ij volumes of water with a turbidity of #j4aj4 ,the total discharge of the stream will then be #aij volumes1 and the average turbidity #j4eg4 ,the turbidity of #j4eg represents the average turbidity all the water flowing in the stream1 or1 in other words1 the turbidity which would be found in a lake if all the water for ten days should flow into it and become thoroughly mixed without other change4 ,now let us compute the average turbidity of the water taken from the stream for water-works purposes4 ,the water-works require1 let us say1 one volume each day1 and we have for the first day water with a turbidity of #a4jj1 and then for nine days water with a turbidity of #j4aj4 ,the average turbidity of the water taken by the water-works for the period is thus only #j4ai in place of #j4eg1 the average turbidity of the whole run-off4 ,the average turbidity of all the water flowing in the stream is thus three times as great as that of the water taken from the stream for water-works purposes4 ,it is often noted that with long streams the water becomes muddier farther down1 and it may naturally be thought that it is because of the added erosion of the stream upon its bed in its longer course4 ,this1 of course1 may be a cause1 or the lower tributaries may be muddier than the upper ones1 but the fact that the water taken at the lower point is more muddy than farther up is not an indication of this4 ,let us take1 for example1 a watershed of twice the size of that assumed above1 that is1 so long that #dh hours will be required for the water from the most remote feeders to reach the water-works intake4 ,let us divide this shed into two parts1 which we will assume to be equal1 one of which furnishes water reaching the intake within #bd hours1 and the other water reaching the intake between #bd and #dh hours4 ,now suppose a storm upon the watershed producing turbidities equal to those just assumed for the smaller stream4 ,on the first day the water from the lower half of the shed1 namely1 #ajj volumes having a turbidity of #a4jj1 passes the intake1 but this is mixed with #aj volumes of water from the upper half of the watershed1 having a turbidity of #j4aj1 and the total flow is thus #aaj volumes of water having a turbidity of #j4ib4 ,on the second day the water from the lower half of the watershed has returned to its normal condition1 and the flood-flow of the upper half of the watershed1 #ajj volumes with a turbidity of #a4jj1 is passing1 and mingles with the #aj volumes from the lower half with a turbidity of #j4aj1 and the total flow is again #aaj volumes having a turbidity of #j4ib4 ,the following eight days1 until the next rain1 will have flows of #bj volumes each1 with turbidities of #j4aj4 ,the average turbidity of all of the water flowing off is #j4eg as before1 but the water taken for water-works purposes will consist of #b volumes of water with turbidities of #j4ib1 and #h volumes with turbidities of #j4aj making #aj volumes with an average turbidity of #j4bf4 ,by doubling the length of the watershed we have thus doubled the length of time during which the water is turbid1 and have increased the average turbidity of the water taken for water-works purposes from #j4ai to #j4bf1 although the average turbidity of all the water running off remains exactly the same4 ,if now we assume a watershed so long that three days are required for the water from the most remote points to reach the intake1 with computations as above1 water taken for water-works purposes will have an average turbidity of #j4cb2 and with still longer watersheds this amount will increase1 until with a watershed so long that ten days1 or the interval between rains1 are required for the water from the upper portions to reach the intake1 the average turbidity of the water taken for water-works purposes will reach the average turbidity of the run-off1 namely1 #j4eg4 ,in the above computations the numbers taken are round ones1 and of course do not represent closely actual conditions4 ,they do serve1 however1 to illustrate clearly the principle that the larger the watershed1 other things being equal1 the more muddy will be the water obtained from it for water-works purposes1 and the longer will be the periods of muddy water1 and the shorter the periods of clear water between them4 ,it cannot be too strongly emphasized that the period of duration of muddy water is1 in general1 dependent upon the length of time necessary for the muddy water to run out of the stream system after it is once in it1 and be replaced by clear water2 and that the settling out of the mud in the river has very little to do with it4 ,muddy waters result principally from the action of rains upon the surface of ground capable of being washed1 and the turbidities of the stream at any point below will occur at the times when the muddy waters reach it in the natural course of flow1 and will disappear again when the muddy waters present in the stream system at the end of the rain have run out1 and have been replaced with clear water from underground sources1 or from clearer surface sources4 ,,the ,,amounts ,,of ,,suspended ,,matters ,,in ,,water4 ,there is a large class of waters1 including most lake and reservoir waters1 and surface-waters from certain geological formations1 which are almost free from suspended matters and turbidities4 ,that is to say1 the average turbidities are less than #j4aj1 and the average suspended matters are less than #b parts in #ajj1jjj1 and are often only small fractions of these figures4 ,this class includes the raw waters of the supplies of many ,english cities drawn from impounding reservoirs1 and also the waters of the rivers ,thames and ,lea at ,london1 and the raw waters used by both of the ,berlin water-works1 and in the ,united ,states the waters of the great lakes except at special points near the mouths of rivers1 nearly all ,new ,england waters1 and many other waters along the ,atlantic coast and elsewhere where the geological formations are favorable4 ,data regarding the suspended matters in these waters are extremely meagre4 ,the official examinations of the ,london waters contain no records of suspended matters1 although the clearness of filtered waters is daily reported4 ,dibden1 in his analytical investigations of the ,london water-supply1 mentioned in his book upon 8,the ,purification of ,sewage and ,water10 reports the average suspended matters in the water of the ,thames near the water-works intakes as #j4gg part in #ajj1jjj4 ,no figures are available for the raw waters used by the ,berlin water-works1 but both are taken from lakes1 and are generally quite clear4 ,even in times of floods of the rivers feeding the lakes1 the turbidities are not very high1 because the gathering grounds for the waters are almost entirely of a sandy nature1 yielding waters with low turbidities1 and further1 the streams flow through successions of lakes before finally reaching the lakes from which the waters are taken4 ,it is safe to assume that the suspended matters and turbidities do not exceed those of the ,london waters4 ,even at times when somewhat turbid water is obtained1 due to agitation by heavy winds1 the suspended matter is mainly of a sandy nature1 readily removed by settling1 and it does not seriously interfere with filtration4 ,the examinations of the ,massachusetts ,state ,board of ,health1 with a very few exceptions1 contain no statements of suspended matters4 ,this is due to the fact that the suspended matters1 in most of the waters1 are so small in amount as to make them hardly capable of determination by the ordinary gravimetric processes1 and the determinations if made would have but little value4 ,the ,merrimac ,river at ,lawrence1 at the time of the greatest flood in fifty years1 carried silt to the amount of about #aaa parts in #ajj1jjj4 ,this was for a very short time1 and the suspended matter consisted almost entirely of sand1 which deposited in banks1 the deposited sand having an effective size of #j4jd or #j4je millimeter4 ,no clayey matter is ever carried in quantity by the river4 ,the reports of the ,connecticut ,state ,board of ,health also contain no records of suspended matters for the same reason4 ,it may be safely said that the average suspended matters of ,new ,england waters are almost always less than #a part in #ajj1jjj4 ,lake waters are generally almost entirely free from sediment4 ,at ,chicago the city water drawn from ,lake ,michigan has slightly more than #a part in #ajj1jjj of suspended matters1 as determined by ,professor ,long in #ahhh-i1 and by ,professor ,palmer in #ahif4 ,the suspended matter in this case is probably due to the nearness of the intake to the mouth of the ,chicago ,river1 and to mud brought up from the bottom in times of storms4 ,the lake-water further away from the shore would probably give much lower results4 ,turning now to waters having considerable turbidities1 at ,pittsburg the average suspended matters in the ,allegheny ,river water1 as shown by the weekly or semi-weekly analyses of the ,filtration ,commission during #ahig-h1 were #d parts in #ajj1jjj4 ,during a large part of the time the suspended matters were so small that it was not deemed worth while to determine them1 and the results are returned as zero4 ,this is not quite correct1 and a recomputation of the amount of suspended matters1 based on the observed amounts1 and the amounts calculated from the turbidities when they were very low1 leads to an average of a little less than #e parts in #ajj1jjj1 which is probably more accurate than the direct average4 ,the average turbidity on the platinum-wire scale was #j4af4 ,at ,cincinnati the suspended matters are about #bc parts in #ajj1jjj1 and at ,louisville about #ce parts1 both of these figures being from ,mr4 ,fuller's reports4 ,in all these cases the enormous and rapid fluctuations in the turbidity of the water is a most striking feature of the results4 ,observations on the ,mississippi ,river above the ,ohio have been made by ,professor ,long in #ahhh-i1 and by ,professor ,palmer in #ahif4 ,these results are not as full and systematic as could be desired1 but indicate averages of #bj to #cj parts in #ajj1jjj at the different points4 ,professor ,william ,ripley ,nichols1 in his work on water-supply1 states the amount of suspended matter in the water of the ,mississippi1 probably referring to the lower river1 as #ff4ff parts4 ,investigations of ,professor ,long and ,professor ,palmer for numerous interior ,illinois streams extending over considerable periods give average results ranging from #a to #h parts in #ajj1jjj4 ,the very much lower results for the interior streams as compared with the ,mississippi and ,ohio rivers may be due to the relative sizes and lengths of the streams1 or in part to other causes4 ,regarding muddy ,european rivers there are but few data4 ,the ,maas1 used for the water-supply of ,rotterdam1 is reported by ,professor ,nichols as having from #a4dj to #dg4fa and averaging #aj parts of suspended matters in #ajj1jjj4 ,more recent information is to the effect that the raw water has at most #cj parts of suspended matters1 and that that quantity is very seldom reached4 ,at ,bremen the ,weser often becomes quite turbid4 ,the turbidity of the water is noted every day by taking the depth at which a black line on a white surface can be seen4 ,assuming that this procedure is equivalent to the platinum-wire procedure1 the depths at which the wire can be seen1 namely1 from #ae to #fjj millimeters1 correspond to turbidities of from #j4jd to #a4gj1 a result not very different from the conditions at ,pittsburg4 ,at ,hamburg and ,altona the water is generally tolerably clear1 but at times of flood the ,elbe becomes very turbid1 and the amount of mud deposited in the sedimentation-basins is considerable4 ,at ,dresden1 several hundred miles up the river1 ,i have repeatedly seen the river-water extremely turbid with clayey matter1 the color of the clay varying from day to day1 corresponding to the color of the earth from which it had been washed4 ,at ,budapest1 where filters were used temporarily1 the ,danube water was excessively muddy with clayey material4 ,at first very high rates of filtration were employed and the results were not satisfactory4 ,afterward the rate of filtration was limited to #a4jg million gallons per acre daily1 and good results were secured4 ,there was no preliminary sedimentation4 ,professor ,nichols reports the average suspended matters in the ,danube at #cb4fh parts in #ajj1jjj1 but does not state at what place4 ,many of the ,french and ,german rivers drain prairie country not different in its general aspect from the ,mississippi basin1 and the soil is probably in many places similar4 ,there is no reason to suppose that the turbidities of these streams in general are materially different from those of corresponding streams in the ,united ,states1 although it is true that1 other things being equal1 the average turbidity of water taken for water-works purposes will increase with the size of the stream2 and it may be that some ,american streams1 especially the ,ohio1 ,missouri1 and ,mississippi rivers1 are of larger size than ,european streams1 and consequently that the turbidity of the water taken from them for water-works purposes may be greater4 ,the following are the drainage areas of a number of ,european and ,american streams yielding more or less muddy waters at points where they are used for public water-supplies after filtration1 with a few other ,american points for comparison4 ,the results are obtained in most cases from measurements of the best available maps4 ---------------------------------------- --------------------- ,drainage ,area1 ,place4 ,river4 ,square ,miles4 ---------------------------------------- --------------------- ,new ,orleans1 ,la4 ,mississippi #a1bfa1jjj ,st4 ,louis1 ,mo4 ,mississippi #gjj1jjj ,st4 ,petersburg ,neva #ajh1jjj ,louisville1 ,ky4 ,ohio #ij1jjj ,rock ,island1 ,ill4 ,mississippi #hh1jjj ,budapest ,danube #gi1jjj ,cincinnati1 ,o4 ,ohio #ge1gjj ,dordrecht ,maas #fh1jjj ,rotterdam ,maas #fh1jjj ,schiedam ,maas #fh1jjj ,altona ,elbe #eb1jjj ,hamburg ,elbe #eb1jjj ,stettin ,oder #dj1jjj ,magdeburg ,elbe #cf1jjj ,warsaw ,weichsel #cd1jjj ,odessa ,dneister #bf1jjj ,worms ,rhine #be1jjj ,grand ,forks1 ,n4 ,dak4 ,red ,river of the ,north #bb1jjj ,frankfort on ,oder ,oder #ba1jjj ,bremen ,weser #ae1jjj ,suburbs of ,paris ,seine #ab1jjj ,poughkeepsie1 ,n4 ,y4 ,hudson #aa1fjj ,pittsburg1 ,penn4 ,allegheny #aa1djj ,posen ,wartha #i1djj ,hudson1 ,n4 ,y4 ,hudson #i1bjj ,albany1 ,n4 ,y4 ,hudson #h1bjj ,breslau ,oder #h1bjj ,brieg ,oder #g1ejj ,lawrence1 ,mass4 ,merrimac #d1fcd ,stuttgart ,neckar #a1ffj ,brunswick ,ocker #fej ,somersworth1 ,n4 ,h4 ,salmon #aga ---------------------------------------- --------------------- ,,preliminary ,,processes ,,to ,,remove ,,mud4 ,with both sand and mechanical filtration the difficulty and expense of treatment of a water increase nearly in direct proportion to the turbidity of the water as applied to the filter2 and it is thus highly important to secure a water for filtration with as little turbidity as possible1 and thus to develop to their economical limits the preliminary processes for the removal of mud4 ,one of the most important of these processes is the use of reservoirs4 ,reservoirs serve two purposes in connection with waters drawn from streams3 they allow sedimentation1 and they afford storage4 ,if a water having a turbidity of #a4jj is allowed to remain in a sedimentation-basin for #bd hours1 its turbidity may be reduced by as much as #dj per cent1 or to #j4fj4 ,if it is held a second day the additional reduction is much less4 ,if samples are taken of the water in the reservoir before and after settling and sent to the chemist for analysis1 he will probably report that from #gj to #hj per cent of the suspended matters have been removed by the process4 ,the suspended matters are removed in much larger ratio than the turbidity4 ,this arises from the fact that there is a certain proportion of comparatively coarse material in the water as it is taken from the river4 ,this coarse material increases the weight of the suspended matters without increasing the turbidity in a corresponding degree4 ,in #bd hours the coarser materials are removed completely1 and at the end of that time only the clayey or finer particles remain in suspension4 ,it is these clayey particles1 however1 that constitute the turbidity1 which are most objectionable in appearance1 and which are most difficult of removal by filtration or otherwise4 ,sedimentation thus removes the heavier matters from the water1 but it does not remove the finer matters which principally affect the appearance of the water and are otherwise most troublesome4 ,a sedimentation of #bd hours removes practically all of the coarser matters1 and the clayey material remaining at the end of that time can hardly be removed by further sedimentation4 ,the economic limit of sedimentation is about #bd hours4 ,sedimentation has practically no effect upon the clearer waters between flood periods4 ,let us consider the effect of a sedimentation-basin1 or reservoir holding a #bd-;hours' supply of water1 into which water is constantly pumped at one end1 and from which an equal quantity is constantly withdrawn from the other1 upon the water of a stream of such size that the time of passage of water from the feeders to the intake is less than #bd hours4 ,during the period between storms the water is comparatively clear and passes through the sedimentation basin without change4 ,when a storm comes the water in the stream promptly becomes muddy1 and muddy water is supplied to the reservoir2 but owing to the time required for water to pass through it1 the outflowing water remains clear for some hours4 ,there is a gradual mixing1 however1 and long before the expiration of #bd hours somewhat muddy water appears at the outlet4 ,the turbid-water period rarely lasts in streams of this size more than #bd hours1 and at the expiration of that time the water in the sedimentation-basin is as muddy or muddier than the water flowing in the stream4 ,after the height of the flood the stream clears itself by the flowing away of the turbid water much more rapidly than the water clears itself by sedimentation in the reservoir4 ,that is to say1 if at the time of maximum turbidity we take a certain quantity of water from the stream and put it aside to settle1 at no time will the improvement by settling equal the improvement which has taken place in the stream from natural causes4 ,generally the improvement in the stream is several times as rapid as in the sedimentation-basin1 and the water from it will at times have only a fraction of the turbidity of the water in the basin4 ,let us now consider what the sedimentation has done to improve the water4 ,during the period of clear water1 that is for most of the time1 it has done nothing4 ,for the first day of each flood period very much clearer water has been obtained from it than was flowing in the stream4 ,for the first days following floods the water in the sedimentation-basin has been more muddy than the water in the stream4 ,the only time when the sedimentation-basin has been of use is during the first part of floods1 that is1 when the turbidity of the water in the stream is increasing4 ,during this period it has been of service principally because of its storage capacity1 yielding up water received from the stream previously1 when it was less muddy4 ,such sedimentation as has been secured is merely incidental and generally not important in amount4 ,it will be obvious from the above that for these conditions storage is much more important than sedimentation4 ,this brings us back to the old ,english idea of having storage-reservoirs large enough to carry water-works over flood periods without the use of flood-waters4 ,reservoirs of this kind were1 and still are1 considered necessary for the successful utilization of waters of many ,english rivers1 although these waters do not approach in turbidity the waters of some ,american streams4 ,this idea of storage has been but little used in the ,united ,states4 ,in the above case1 if we use our reservoir for storage instead of as a sedimentation-basin1 the average quality of the water can be greatly improved4 ,the reservoir should ordinarily be kept full1 and pumping to it should be stopped whenever the turbidity exceeds a certain limit1 to be determined by experience2 and the reservoir is then to be drawn upon for the supply until the turbidity again falls to the normal4 ,in the case assumed above1 with a stream in which all of the water reaches the intake in #bd hours1 a reservoir holding a #bd-;hours' supply1 or in practice1 to be safe1 a somewhat larger one1 would yield a water having a very much lower average turbidity than would be obtained with water pumped constantly from the stream without a reservoir4 ,with a river having a watershed so long that #dh hours are required to bring the water down from the most remote feeders1 a reservoir twice as large would be required1 and would result in a still greater reduction in the average turbidity4 ,as the stream becomes larger1 and the turbid periods longer1 the size of a reservoir necessary to utilize this action rapidly becomes larger1 and the times during which it can be filled are shortened1 and thus the engineering difficulties of the problem are increased4 ,for moderately short streams1 cost for cost1 storage is far more effective than sedimentation1 and we must come back to the old ,english practice of stopping our pumps during periods of maximum turbidity4 ,,effect ,,of ,,mud ,,upon ,,sand ,,filters4 ,there are two aspects of the effect of mud upon the operation of sand filters which require particular consideration4 ,the first relates to the rapidity of clogging1 and consequently the frequency of scraping and the cost of operation2 while the second relates to the ability of the filters to yield well-clarified effluents4 ,,effect ,,of ,,turbidity ,,upon ,,the ,,length ,,of ,,period4 ,the amount of water which can be filtered between scrapings is directly dependent upon the turbidity of the raw water4 ,the greater the turbidity1 the more frequently will filters require to be scraped4 ,in the experiments of the ,pittsburg ,filtration ,commission1 with #d feet of sand of an effective size of about #j4cj millimeter1 and with rates of filtration of about three million gallons per acre daily1 and with the loss of head limited to #d feet1 sand filters were operated as follows3 ,for five periods the turbidities of the raw water ranged from #j4jce to #j4jfb1 and averaged #j4jea1 and the corresponding periods ranged from #ajb to #acf1 and averaged #aac million gallons per acre filtered between scrapings4 ,for ten periods the turbidities of the raw water ranged from #j4jgi to #j4abh1 and averaged #j4ajb1 and the periods averaged #gh million gallons per acre between scrapings4 ,for fifteen other periods the turbidities of the raw water ranged from #j4acd to #j4bfi1 and averaged #j4aie1 and the periods averaged #eb million gallons per acre between scrapings4 ,in two other periods the turbidities of the raw water averaged #j4fg1 and the periods between scrapings averaged #af million gallons4 ,in all cases the turbidity is taken as that of the water applied to the filter4 ,usually this was the turbidity of the settled water1 but in some cases raw water was applied1 and in these case the turbidity of the raw water is taken4 ,these results are approximately represented by the formula ,period between scrapings1 #ab_/7turbidity #j4je74 million gallons per acre ,except for very clear waters the amount of water passed between scrapings is nearly inversely proportional to the turbidity4 ,with twice as great an amount of turbidity1 filters will have to be cleaned twice as often1 the reserve area for cleaning will require to be twice as great1 and the cost of scraping filters and of washing and replacing sand1 which is the most important element in the cost of operation1 will be doubled4 ,with waters having turbidities of #j4bj upon this basis1 the average period will be about #ea million gallons per acre between scrapings4 ,this is about the average result obtained at the ,german works filtering river waters1 and there is no serious difficulty in operating filters which require to be scraped with this frequency4 ,with more turbid waters the period is decreased4 ,with an average turbidity of #j4ej the average period is only #bd million gallons per acre between scrapings1 a condition which means very difficult operation and a very high cost of cleaning4 ,with much more turbid waters the difficulties are increased1 and if the duration of turbid water should be long-continued1 the operation of sand filters would clearly be impracticable1 and the expense1 also1 would be prohibitive4 ,in applying these figures to actual cases it must be borne in mind that the turbidity is only one of the several factors which control the length of period2 and that the turbidity of a water of a given stream is never constant1 but fluctuates within wide limits2 and that raw water can be applied to filters for a short time without injurious results1 even though it is so turbid that its continued application would be fatal4 ,it is very likely also that the suspended matters in different streams differ in their natures to such an extent that equal turbidities would give quite different periods1 although the ,pittsburg results were so regular as to give confidence in their application to other conditions within reasonable limits1 and when so applied they afford a most convenient method of computing the approximate cost of operation of filters for waters of known or estimated turbidities4 ,,power ,,of ,,sand ,,filters ,,to ,,produce ,,clear ,,effluents ,,from ,,muddy ,,water4 ,when the turbidity of the applied water is not too great it is entirely removed in the course of filtration4 ,with extremely muddy raw waters1 however1 turbid effluents are often produced with sand filters4 ,the conditions which control the passage of the finest suspended matters through filters have been studied by ,mr4 ,fuller at ,cincinnati at considerable length4 ,they are similar in a general way to the conditions which control the removal of bacteria4 ,that is to say1 the removal is more complete with fine filter sand than with coarse sand2 with a deep sand layer than with a shallow sand layer2 and with low rates of filtration than with high rates4 ,the practicable limits to the size of sand grain1 depth of sand layer1 and rate of filtration are established by other conditions1 and the question remains whether within these limits a clear effluent can be produced4 ,at ,pittsburg the turbidity of the effluent from a sand filter operated as mentioned above1 which received water which had passed through a sedimentation-basin holding about a #bd-;hours' supply1 but without taking any advantage of storage to avoid the use of muddy water1 was nearly always less than #j4jb1 which may be taken as the admissible limit of turbidity in a public water-supply4 ,this limit was exceeded on less than #bj days out of #cfe1 these days being during the winter and spring freshets1 and on these days the excess was not such as would be likely to be particularly objectionable4 ,for the water of the ,allegheny ,river1 then1 sand filtration with one day's sedimentation is capable of yielding a water not absolutely clear1 but sufficiently clear to be quite satisfactory for the purpose of municipal water-supply4 ,at ,cincinnati1 on the other hand1 where the amount of suspended matters was five times as great as at ,pittsburg1 the effluents which could be obtained by sand filtration without recourse to the use of alum1 even under most favorable conditions1 were very much more turbid than those obtained at ,pittsburg1 and were1 in fact1 so turbid as to be seriously objectionable for the purpose of public water-supply4 ,with rivers no more turbid than the ,allegheny ,river at ,pittsburg1 and rivers having floods of such short duration that the use of flood-flows can be avoided by the use of reservoirs1 sand filters are adequate for clarification4 ,for waters which are much muddier than the ,allegheny1 as1 for instance1 the ,ohio at ,cincinnati and at ,louisville1 sand filtration alone is inadequate4 ,mr4 ,fuller1#ca as a result of his ,cincinnati experiments1 has stated the case as follows3 8,for the sake of explicitness it is desired to show1 with the data of the fairly normal year of #ahih1 the proportion of the time when ,english filters 7that is1 sand filters7 would be inapplicable in the purification of the unsubsided ,ohio ,river water at ,cincinnati4 ,this necessitates fixing an average limit of permissible suspended matter in this river water1 and is a difficult matter from present evidence4 8,in part this is due to variations in the character and in the relative amounts of the suspended silt1 clay1 and organic matter2 and in part it is due to different amounts of clay stored in the sand layer1 which affects materially the capacity of the filter to retain the clay of the applied water4 ,during these investigations the unsubsided river-water was not regularly applied to filters2 and1 with the exception of the results of tests for a few days only1 it is necessary to depend upon general information obtained with reference to this point4 ,so far as the information goes1 it appears that an average of #abe parts per million is a conservative estimate of the amount of suspended matters in the unsubsided river-water1 which could be regularly and satisfactorily handled by ,english filters4 ,but at times this estimated average would be too low1 and at other times too high4444 8,while ,english filters are able to remove satisfactorily on an average about #abe parts of silt and clay of the unsubsided water1 actual experience shows that they can regularly handle suspended clay in subsided water in amounts ranging only as high as from #cj to #gj parts 7depending upon the amount of the clay stored in the sand layer71 and averaging about #ej parts per million4 ,but it is true that for two or three days on short rises in the river1 or at the beginning of long freshets1 the retentive capacity of the sand layer allows of satisfactory results with the clay in the applied water considerably in excess of #gj parts4 ,if this capacity is greatly overtaxed1 however1 the advantage is merely temporary1 as the stored clay is washed out later1 producing markedly turbid effluents40 ,translating ,mr4 ,fuller's results into terms of turbidity1 the #abe parts per million of suspended matters in the raw water represent a turbidity of about #j4dj1 and the #cj to #gj parts of suspended matters in the settled water represent turbidities from #j4bj to #j4dj1 the average of #ej parts of suspended matters corresponding to a turbidity of about #j4cj4 ,upon this basis1 then1 sand filters are capable of treating raw waters with average turbidities up to #j4dj1 or settled waters with average turbidities up to #j4cj1 but waters more turbid than this are incapable of being successfully treated without the use of coagulants or other aids to the process4 ,these results are in general accordance with the results of the experiments at ,pittsburg1 and demonstrate that while sand filters as generally used in ,europe are adequate for the clarification of many1 if not most1 river waters in the ,united ,states1 there are other waters carrying mud in such quantities as to make the process inapplicable to them4 ,,effect ,,of ,,mud ,,upon ,,bacterial ,,efficiency ,,of ,,filters4 ,the question is naturally raised as to whether or not the presence of large quantities of mud in the raw water will not seriously interfere with the bacterial efficiency of filters4 ,experiments at ,cincinnati and ,pittsburg have given most conclusive and satisfactory information upon this point4 ,up to the point where the effluents become quite turbid1 the mud in the raw water has no influence upon the bacterial efficiency2 and even somewhat beyond this point1 with effluents so turbid that they would hardly be suitable for the purpose of a public water-supply1 the bacterial efficiency remains substantially equal to that obtained with the clearest waters4 ,only in the case of excessive quantities of mud1 where1 for other reasons1 sand filters can hardly be considered applicable1 is there a moderate reduction in bacterial efficiency4 ,as mentioned above1 particles constituting turbidity are often much smaller than the bacteria1 and in addition1 the bacteria probably have an adhesive power far in excess of that of the clay particles4 ,for these reasons clay particles are able to pass filters under conditions which almost entirely prevent the passage of bacteria4 ,on the other hand1 it does not necessarily follow that the removal of turbidity is accompanied by high bacterial efficiency4 ,although this is often the case1 there are marked exceptions1 particularly in connection with the use of coagulants1 where very good clarification is obtained1 and notwithstanding this1 effluents are produced containing comparatively large numbers of bacteria4 ,,limits ,,to ,,the ,,use ,,of ,,subsidence ,,for ,,the ,,preliminary ,,treatment ,,of ,,muddy ,,waters4 ,when water is too muddy to be applied directly to filters1 the most obvious treatment is to remove as much of the sediment as possible by sedimentation4 ,sedimentation-basins are considered as essential parts of filtration plants for the treatment of muddy waters4 ,the effect of sedimentation1 as noted above1 is to remove principally the larger particles in the raw water4 ,by doing this the deposit upon the surface of the filters and the cost of operation are greatly reduced4 ,these larger particles are mainly removed by a comparatively short period of sedimentation1 and the improvement effected after the first #bd hours is comparatively slight4 ,the particles remaining in suspension at the end of this time consist almost entirely of very fine clay1 and the rate of their settlement through the water is extremely slow2 and currents in the basin1 due to temperature changes1 winds1 etc41 almost entirely offset the natural tendency of the sediment to fall to the bottom4 ,there is thus a practical limit to the effect of sedimentation which is soon reached1 and it has not been found feasible to extend the process so as to allow much more turbid waters to be brought within the range which can be economically treated by sand filtration4 ,,chapter ,,ix4 ,,the ,,coagulation ,,of ,,waters4 ,the coagulation of water consists in the addition to it of some substance which forms an inorganic precipitate in the water1 the presence of which has a physical action upon the suspended matters1 and allows them to be more readily removed by subsidence or filtration4 ,the most common coagulant is sulphate of alumina4 ,when this substance is added to water it is decomposed into its component parts1 sulphuric acid and alumina1 the former of which combines with the lime or other base present in the water1 or in case enough of this is lacking1 it remains partly as free acid and partly undecomposed in its original condition2 while the alumina forms a gelatinous precipitate which draws together and surrounds the suspended matters present in the water1 including the bacteria1 and allows them to be much more easily removed by filtration than would otherwise be the case4 ,in addition1 the alumina has a chemical attraction for dissolved organic matters1 and the chemical purification may be more complete at very high rates than would be possible with sand filtration without coagulant at any rate1 however low4 ,coagulants have been employed in connection with filtration from very early times4 ,as early as #ahca ,d',arcet published in the 8,annales d'hygine publique10#cb an account of the purification of ,nile water in ,egypt by adding alum to the water1 and afterwards filtering it through small household filters4 ,more recently alum has been repeatedly used in connection with sand filters1 particularly at ,leeuwarden1 ,groningen1 and ,schiedam in ,holland1 where the river waters used for public supplies are colored by peaty matter which cannot be removed by simple filtration4 ,,substances ,,used ,,for ,,coagulation4 ,mr4 ,fuller#cc has given a very full account of the substances which can be used for the clarification of waters4 ,without taking up all of the unusual substances which have been suggested1 the most important of the coagulants will be briefly described below4 ,lime4--,lime has been extensively used in connection with the purification of sewage1 and also for softening water4 ,lime is first slaked and converted into calcium hydrate1 which is afterwards dissolved in water1 and applied to the water under treatment4 ,the amount of lime to be used is fixed by the amount of carbonic acid in the water4 ,so much lime is always used as will exactly convert the whole of the carbonic acid of the water into normal carbonate of lime4 ,this substance is but slightly soluble in water and it precipitates4 ,the precipitate is crystalline rather than flocculent1 and is not as well adapted to aid in the removal of clayey matters as some other substances1 although its action in this respect is considerable4 ,the precipitate is quite heavy1 and is largely removed by sedimentation1 although filtration must be used to complete the process4 ,water which has been treated with lime is slightly caustic2 that is to say1 there is a deficiency of carbonic acid in it1 and it deposits lime in the pipes1 in pumps1 etc42 and although the precipitated calcium carbonate is much softer than steel1 it rapidly destroys pumps used for lifting it4 ,principally for these reasons it is necessary to supply carbonic acid to water which has been treated in this way1 and this is done by bringing it in contact with flue-gases1 or by the direct addition of carbonic acid4 ,the use of lime for softening waters is known as ,clark's process4 ,it was patented in ,england many years ago1 and the patent has now expired4 ,various ingenious devices have been constructed for facilitating various parts of the operation4 ,the process has hardly been used in the ,united ,states1 but there is a large field for it in connection with the softening of very hard waters1 and where such waters also contain iron or clay1 these substances will be incidentally removed by the process4 ,larger quantities of lime have an action upon the suspended matters which is entirely different from that secured in ,clark's process1 and the action upon bacteria is particularly noteworthy4 ,this action was noted in experiments at ,lawrence1#cd where it was found that sewage was almost completely sterilized by the application of considerable quantities of lime4 ,an extremely interesting series of experiments upon the application of large quantities of lime to water was made by ,mr4 ,fuller in #ahii4ce ,the bacterial results were extremely favorable1 although the necessity for removing the excess of lime afterward is a somewhat serious matter1 and in these experiments it was not entirely accomplished4 ,aluminum ,compounds4--,sulphate of alumina is most commonly employed4 ,it can be obtained in a state of considerable purity at a very moderate price1 and important improvements in the methods used for its manufacture have been recently introduced4 ,potash and soda alums have no advantage over sulphate of alumina1 and1 in fact1 are less efficient per pound1 while their costs are greater4 ,chloride of alumina is practically equivalent to the sulphate in purifying power1 but is more expensive4 ,sodium ,aluminate has been examined by ,mr4 ,fuller1 who states that experience has shown that its use is impracticable in the case of the ,ohio ,river water4 ,compounds of ,iron4--,iron forms two classes of compounds1 namely1 ferrous and ferric salts4 ,when the ferrous salts are applied to water1 under certain conditions1 ferrous hydrate is precipitated1 but this substance is not entirely insoluble in water containing carbonic acid4 ,under some conditions the precipitated ferrous hydrate is oxidized by oxygen present in the water to ferric hydrate1 and so far as this is the case1 good results can be obtained4 ,ferrous sulphate is not as readily oxidized when applied to water as is the ferric carbonate present in many natural waters1 and for this reason ferrous sulphate has not been successfully used in water purification4 ,in the treatment of sewage1 where the requirements are somewhat different1 it has been one of the most satisfactory coagulants4 ,ferric sulphate acts in much the same way as sulphate of alumina1 and is entirely suitable for use where sulphate of alumina could be employed1 but it has not been used in practice1 due probably to its increased cost as compared with its effect1 and to the practical difficulties of applying it in the desired quantities due to its physical condition4 ,metallic ,iron3 ,the ,anderson ,process4--,the use of metallic iron for water purification in connection with a moderately slow filtration through filters of the usual form is known as ,anderson's process 7patented71 and has been used at ,antwerp and elsewhere on a large scale1 and has been experimentally examined at a number of other places4 ,the process consists in agitating the water in contact with metallic iron1 a portion of which is taken into solution as ferrous carbonate4 ,upon subsequent aeration this is supposed to become oxidized and precipitate out as ferric hydrate1 with all the good and none of the bad effects which follow the use of alum4 ,the precipitate is partially removed by sedimentation1 while filtration completes the process4 ,the process is admirable theoretically1 and in an experimental way upon a very small scale often gives most satisfactory results1 muddy waters very difficult of filtration1 and colored peaty waters yielding promptly clear and colorless effluents4 ,in applying the process on a larger scale1 however1 with peaty waters at least1 it seems impossible to get enough iron to go into solution in the time which can be allowed1 and the small quantity which is taken up either remains in solution or else slowly and incompletely precipitates out1 without the good effects which follow the sudden and complete precipitation of a larger quantity1 and in this case the color is seldom reduced1 and may even be increased above the color of the raw water by the iron remaining in solution4 ,the ingenuity of those who have studied the process has not yet found any adequate means of avoiding these important practical objections2 and even at ,antwerp a great extension of the filtering area1 as well as the use of alum at times of unusual pollution1 is good evidence that simple filtration1 in distinction from the effect of the iron1 is relied upon much more than formerly4 ,at ,dordrecht also1 where the process has been long in use1 the rate of filtration does not exceed the ordinary limits2 nor is the result1 so far as ,i could ascertain1 in any way superior to that obtained a few miles away at ,rotterdam1 by ordinary filtration1 with substantially the same raw water4 ,the results obtained at ,boulogne-sur-,seine1 near ,paris1 have been closely watched by the public chemist and bacteriologist of ,paris1 and have been very favorable1 and a number of new plants of very considerable capacity have been built1 to supply some of the suburbs of ,paris1 but even in these cases only moderate rates of filtration are employed which would yield excellent effluents without the iron4 ,compounds of ,manganese4--,manganese forms compounds similar to those of iron1 that is to say manganous and manganic salts1 but their use in connection with water filtration has not been found possible4 ,in addition1 manganese forms a series of compounds1 known as manganates and permanganates1 quite different in their structure and action from the others4 ,these compounds contain an excess of oxygen which they give up very readily to organic matters capable of absorbing oxygen1 and because of this power1 they have been extensively used in the treatment of sewage4 ,applied to the treatment of waters their action is very slight1 and the compounds are so expensive that they have not been employed for this purpose4 ,theoretically the action is very attractive1 as the oxygen liberated by their decomposition oxidizes some of the organic matter of the water1 thereby purifying it in part1 while the manganese is precipitated as a flocculent precipitate having all of the advantages pertaining to a precipitate of hydrate of alumina1 and without the disadvantage of adding acid to the water1 as is the case with the compounds of alumina and iron4 ,these chemicals1 when used in comparatively concentrated condition1 have powerful germicidal actions1 but in water purification the amounts which can be used are so small that no action of this kind results4 ,the amount which can be applied to a water is limited to the amount which can be decomposed by the organic matters present in the water1 and is not large4 ,the ,use of ,metallic ,iron and ,aluminum1 with the ,aid of ,electricity4--,elaborate experiments were made at ,louisville with metallic iron and aluminum oxidized and made available by the aid of electric currents4 ,the use of iron with electric currents was tried in sewage purification some years ago1 under the name of the ,webster process1 but was never put to practical use4 ,the theory is to oxidize the iron or aluminum in contact with the water1 with the formation of flocculent hydrates1 by the aid of an electric current1 thereby securing the advantages of the application of salts of these metals to the water without the disadvantage of the addition of acid4 ,other ,chemicals ,employed4--,a solution containing chlorine produced by electrical action has been suggested4 ,chlorine is a powerful disinfectant1 and when used in large quantities kills bacteria4 ,it is not possible to use enough chlorine to kill the bacteria in the water without rendering it unfit for human use4 ,the nature of this treatment has been concisely described by ,dr4 ,drown1#cf who shows that the electrically prepared fluids do not differ in their action in any way from well-known chemicals1 the use of which would be hardly considered4 ,the use of ozone and peroxide of hydrogen have also been suggested1 but ,i do not know that they have been successfully used on a large scale4 ,the same is true of many other chemicals1 the consideration of which is hardly necessary in this connection4 ,,coagulants ,,which ,,have ,,been ,,used4 ,in actual work sulphate of alumina is practically the only coagulant which has been employed1 excepting the alums1 which are practically its equivalent in action1 differing only in strength4 ,nearly all important experiments upon the coagulation of water have been made with sulphate of alumina1 and in the further discussion of this subject only this coagulant will be considered4 ,,amount ,,of ,,coagulant ,,required ,,to ,,remove ,,turbidity4 ,in the coagulation of turbid waters a certain definite amount of coagulant must be employed4 ,if less than this amount is used either no precipitate will be formed1 or it will not be formed in sufficient bulk to effect the desired results4 ,it is necessary that the precipitate should be sufficient1 and that it should be formed practically all at one time4 ,the amount of coagulant necessary to accomplish this purpose is dependent upon the turbidity of the raw water4 ,with practically clear waters sulphate of alumina of the ordinary commercial strength1 that is to say1 with about #ag per cent soluble oxide of aluminum1 used in quantities as small as #j4c or #j4d of a grain per gallon1 will produce coagulation4 ,as the turbidity increases larger amounts must be employed4 ,a special study was made of this point in connection with the ,pittsburg experiments4#cg ,as an average of these results it was found that two grains per gallon of sulphate of alumina were required to properly coagulate waters having turbidities of #a4jj1 so that they could be filtered by the ,jewell filter1 and #b4ge grains were required for the ,warren filter4 ,illustration3 ,,fig4 #bj4--;,,amount ,,of ,,coagulant ,,required ,,to ,,remove ,,turbidity4 ,aside from the amount required to produce a precipitate in the clearest waters1 the amount of coagulant required was proportional to the turbidity4 ,as an average for the two filters the required quantity was approximately #j4cj of a grain1 and in addition #j4jb of a grain for each #j4ja of turbidity4 ,thus a water having a turbidity of #j4bj requires #j4gj of a grain per gallon2 a water having a turbidity of #j4ej requires #a4cj grains2 of #a4jj1 #b4cj grains2 of #b4jj1 #d4cj grains1 etc4 ,these are average minimum results4 ,occasionally clear effluents were produced with smaller quantities of coagulant1 while at other times larger quantities were necessary for satisfactory results4 ,the amount of coagulant required for clarification at ,cincinnati has been stated by ,mr4 ,fuller in his report4 ,a number of his results are brought together in the following table1 to which has also been added a column showing approximately the corresponding results at ,pittsburg4 ,,estimated ,,average ,,amounts ,,of ,,required ,,chemical ,,for ,,different ,,grades ,,of ,,water4 ---------------------------------------- --------------- ,chemical ,required1 ,grains per ,gallon4 ---------------------------------------- -- ,suspended ,raw ,subsided ,subsided ,minimum for ,matter1 ,water for ,water for ,water for ,raw ,water ,parts in ,sand ,sand ,mechanical for #ajj1jjj4 ,filters4 ,filters4 ,filters4 ,mechanical ,cincinnati,cincinnati,cincinnati ,filters4 ,report1 ,report1 ,report1 ,page #bij4 ,page #bij4 ,page #cda4 ,pittsburg4 ---------------------------------------- ------------ #a4j #j #j #j4ge #j4dj #b4e #j #j #a4be #j4ej #e4j #j #j #a4ej #j4gj #g4e #j #a4cj #a4ie #j4ij #aj4j #a4ej #a4fj #b4bj #a4jj #ab4e #a4fj #a4hj #b4de #a4ae #ae4j #a4gj #b4jj #b4fe #a4cj #ag4e #a4hj #b4aj #b4he #a4dj #bj4j #a4ie #b4bj #c4jj #a4fj #cj4j #b4be #b4de #c4hj #b4jj #dj4j #b4ej #b4ge #d4dj #b4ej #ej4j #b4hj #fj4j #c4je #ge4j #c4dj #ajj4j #d4jj #abj4j #d4ge ---------------------------------------- ------------ ,mr4 ,fuller's results seem to show that a greater amount of coagulant is required for the preparation of water for mechanical filters than is necessary in connection with sand filters4 ,the results with sand filters indicate that settled waters and raw waters containing equal amounts of suspended matters are about equally difficult to treat4 ,the results at ,pittsburg indicate that the raw waters required much smaller quantities of coagulant for given amounts of suspended matters than was the case with subsided waters at ,cincinnati1 the results agreeing more closely with the amounts required to prepare raw water for sand filters at ,cincinnati4 ,,amount ,,of ,,coagulant ,,required ,,to ,,remove ,,color4 ,the information upon this point is1 unfortunately1 very inadequate4 ,in some experiments made by ,mr4 ,e4 ,b4 ,weston at ,providence in #ahic with a mechanical filter1#ch with quantities of sulphate of alumina averaging #j4f or #j4g of a grain per gallon1 the removal of color was usually from #gj to #ij per cent4 ,the standard used for the measurement of color is not stated1 and there is no statement of the basis of the scale1 consequently no means of determining the absolute color of the raw water upon standards commonly used4 ,at ,westerly1 ,r4 ,i41 with a ,new ,york filter1 the actual quantity of potash alum employed from ,oct4 #aj1 #ahif1 to ,march #a1 #ahig1 was #a4id grains per gallon1 the amount being regulated to as low a figure as it was possible to use to secure satisfactory decolorization4 ,there is no record of the color of the raw water4 ,a very rough estimate would place it at #j4ej upon the platinum scale4 ,the chemical employed in this case was alum1 and two thirds as large a quantity of sulphate of alumina would probably have done corresponding work1 had suitable apparatus for applying it been at hand4 ,at ,superior1 ,wisconsin1 the water in the bay coming from the ,st4 ,louis ,river1 having a color of #b4dj platinum scale1 was treated experimentally with quantities of sulphate of alumina up to #d grains per gallon1 by ,mr4 ,r4 ,s4 ,weston in ,january1 #ahii1 but even this quantity of coagulant utterly failed to coagulate and decolorize it4 ,at ,greenwich1 ,conn41 during #ahih the average amount of sulphate of alumina employed1 as computed from quantities stated in the annual report of the ,connecticut ,state ,board of ,health for #ahih1 was about #j4dd of a grain per gallon1 and this quantity sufficed to reduce the color of the raw water from #j4dj to #j4cj1 platinum standard4 ,this reduction is very slight1 and it is obvious that this quantity of coagulant was not enough for decolorization4 ,some experiments bearing on color removal were made at ,east ,providence1 ,r4 ,i41 by ,mr4 ,e4 ,b4 ,weston1 and are described in the ,proceedings of the ,american ,society of ,civil ,engineers for ,september1 #ahii4 ,in this case the color is reported to have been reduced from #j4eh to #j4aj platinum standard by the use of one grain of sulphate of alumina1 containing #bb per cent of effective alumina1 equivalent to about #a4cj grains of the ordinary article per gallon4 ,the various experiments seem to indicate that a removal from #hj to #ij per cent of the color can be effected by the use of a quantity of sulphate of alumina equal to rather more than two grains per gallon for waters having colors of #a4jj1 platinum standard1 and proportionate quantities for more and less deeply colored waters4 ,with much less sulphate of alumina decolorization is not effected1 and even larger quantities do not remove all of the color4 ,the data are much less complete than could be desired1 and it is to be hoped that experiments will be undertaken to throw more light upon this important subject4 ,,successive ,,application ,,of ,,coagulant4 ,mr4 ,fuller1 in his experiments at ,louisville1 has ascertained that when sulphate of alumina is added to extremely muddy water the sediment absorbs some of the chemical before it has time to decompose1 and carries it to the bottom1 and so far as this is the case1 no benefit is derived from that part of the coagulant which is absorbed4 ,in other words1 it is necessary to add more coagulant than would otherwise be necessary because of this action4 ,the data showed that different kinds of suspended matters took up very different amounts of coagulant in this way4 ,with only moderately turbid waters the loss of chemical from this source is unimportant4 ,hardly any trace of it was found at ,pittsburg with the ,allegheny ,river water4 ,at ,louisville1 however1 it was an important factor1 as shown by ,mr4 ,fuller's results4 ,to avoid this loss of chemical ,mr4 ,fuller has suggested the removal of the greater part of the suspended matters by sedimentation1 without chemicals1 or with the aid of a small quantity of chemical1 followed by the application of the final coagulant prior to filtration4 ,with the worst waters encountered at ,louisville the saving in coagulant to be effected in this way is very great4 ,mr4 ,fuller states in 8,water ,purification at ,louisville10 p4 #dag3 8,the practical conclusions to be drawn from this experience are that with preliminary coagulation1 followed by subsidence for a period of about three hours1 the application of coagulants may be divided to advantage1 and a considerable portion of the suspended matter kept off the filter1 when the total amount of required coagulant ranges from #b to #b4e grains or more of ordinary sulphate of alumina per gallon4 ,in the case of a water requiring more than this amount of coagulating treatment1 a proper division of the application would increase the saving of coagulants and would diminish the frequency of washing the filter40 ,in his final summary and conclusions1 page #dda1 ,mr4 ,fuller estimates the amount of sulphate of alumina required for the clarification of the ,ohio ,river at ,louisville at #c4jj grains per gallon of water filtered if all applied at one point1 or at #a4ge grains by taking advantage of subsidence to its economical limit prior to the final coagulation4 ,the saving to be effected in this way is sufficient to justify the works necessary to allow it to be carried out4 ,with less turbid waters1 or waters highly turbid for only short intervals1 the advantages of double coagulation would be less apparent4 ,,the ,,amount ,,of ,,coagulant ,,which ,,various ,,waters ,,will ,,receive4 ,the amount of coagulant which can be safely used is dependent upon the alkalinity of the raw water4 ,when sulphate of alumina is added to water it is decomposed1 as explained above1 with the formation of alumina1 which is alone useful in the work of purification1 and sulphuric acid1 which combines with the calcium carbonate or lime present in the water4 ,there should always be an excess of alkalinity or lime in the raw water4 ,if for any reason there is not1 there is nothing to combine with the liberated sulphuric acid1 and the decomposition of the coagulant is not complete1 and a portion of it goes undecomposed into the effluent4 ,the effluent then has an acid reaction1 and is unfit for domestic supply4 ,when distributed through iron pipes1 it attacks the iron1 rusting the pipes1 and giving rise to all the disagreeable consequences of an iron containing water4 ,the amount of lime in a water available to combine with the sulphuric acid can be determined by a very simple chemical operation1 namely1 by titration with standard acid with a suitable indicator4 ,the amount of coagulant corresponding to a given quantity of lime can be readily and accurately calculated1 but it is not regarded safe to use as much sulphate of alumina as corresponds to the lime4 ,the quantity of coagulant used is not susceptible to exact control1 but fluctuates somewhat1 and if the exact theoretical quantity should be employed during #bd hours1 there would surely be an excess during some portion of that time from which bad results would be experienced4 ,it is therefore considered only prudent to use three quarters as much sulphate of alumina as corresponds to the lime in the water4 ,with sulphate of alumina containing #ag per cent of soluble aluminum oxide and the corresponding amount of sulphuric acid1 the amount which can be applied to a water in grains per gallon is slightly less than the alkalinity expressed in terms of parts in #ajj1jjj of calcium carbonate4 ,many waters contain sufficient lime to combine with the acid of all the coagulant which is necessary for their coagulation4 ,others will not1 and it thus becomes an important matter to determine whether a given water is capable of decomposing sufficient coagulant for its treatment4 ,it is usually the flood-flows of rivers which control in this respect4 ,the water at such times requires much larger quantities of coagulant for its clarification1 and it also usually contains much less lime than the low-water flows4 ,the reason for this is obviously that the water of the flood-flows is largely rain-water which has come over the surface without coming into very intimate contact with the soil1 and consequently without having taken from it much lime1 while the low-water flows contain a considerable proportion of water which has percolated through the soil and has thus become charged with lime4 ,in some parts of the country1 as1 for instance1 in ,new ,england1 the soil and underlying rock are almost entirely free from lime1 and rivers from such watersheds are capable of receiving only very small quantities of coagulant without injurious results4 ,the deficiency of alkalinity in raw water can be corrected by the addition to it of lime or of soda-ash4 ,lime has been used for this purpose in many cases4 ,when used only in moderate amounts it hardens the water1 and is thus seriously objectionable4 ,the use of so large a quantity as would precipitate out1 as in ,clark's process1 has not been employed in practice4 ,if it should be attempted1 the amount of lime would require to be very accurately controlled1 and the effluent would have to be treated with carbonic acid to make it suitable for supply4 ,waters so hard as to require the use of the ,clark process almost always have sufficient alkalinity1 and do not require to be treated with lime in connection with the use of sulphate of alumina4 ,the use of soda-ash is free from the objections to the use of lime1 but is more expensive1 and would require to be used with caution4 ,its use has often been suggested1 but ,i do not know that it has ever been employed in practice4 ,in small works the use of a filtering material containing marble-dust1 or other calcareous matter1 would seem to have some advantages in case of deficiency of alkalinity1 although it would harden the water so treated4 ,the alkalinities of a number of waters computed as parts in #ajj1jjj of calcium carbonate 7approximately equal to the safe doses of sulphate to alumina in grains per gallon7 are as follows3 ---------------------------------------- --------------------- ,maximum4,minimum4,average4 ---------------------------------------- --------------------- ,boston water1 #ahih #b4hg #j4cc #a4jh ,conestoga ,creek1 ,lancaster1 ,penn4 #ab4bj #c4gj #f4hj ,allegheny ,river1 ,pittsburg #h4jj #a4jb #b4ij ,mahoning ,river and tributaries1 #ahig #bj4jj #b4bj #aj4jj ,scioto ,river and tributaries1 #ahig #ce4jj #aj4jj #bj4jj ,ohio ,river1 ,cincinnati1 #ahih #g4jj #b4jj #d4ej ,ohio ,river1 ,louisville #aj4hg #b4ab #f4gj ,lake ,erie1 ,lorain1 ,ohio #i4ej ,lake ,michigan1 ,chicago #aa4ej ---------------------------------------- --------------------- ,,chapter ,x4 ,,mechanical ,,filters4 ,the term mechanical filters is used to designate a general class of filters differing in many respects quite radically from the sand filters previously described4 ,they had their origin in the ,united ,states1 and consisted originally of iron or wooden cylinders filled with sand through which the water was forced at rates of one to two hundred million gallons per acre daily1 or from fifty to one hundred times the rates usually employed with sand filters4 ,these filters were first used in paper-mills to remove from the large volumes of water required the comparatively large particles1 which would otherwise affect the appearance and texture of the paper2 and in their earlier forms they were entirely inadequate to remove the finer particles1 such as the bacteria1 and the clay particles which constitute the turbidity of river waters4 ,various improvements in construction have since been made1 and1 in connection with the use of coagulants1 much more satisfactory results can now be obtained with filters of this class2 and their use has been extended from manufacturing operations to municipal supplies1 in many cases with most satisfactory results4 ,the information gathered in regard to the conditions essential to the successful design and operation of these filters in the last few years is very great1 and may be briefly reviewed4 ,,providence ,,experiments4#ci ,the first data of importance were secured from a series of experiments conducted by ,mr4 ,edmund ,b4 ,weston of ,providence1 ,r4 ,i41 in #ahic and #ahid1 upon the ,pawtuxet river water used by that city4 ,the experimental filter was #cj inches in diameter1 and had a layer of sand #b feet #aj inches deep4 ,the sand was washed by the use of a reverse current1 the sand being stirred by a revolving rake at the same time4 ,the amount of coagulant employed was about #j4g of a grain per gallon4 ,the raw water was practically free from turbidity1 and the filter was operated to remove color and bacteria4 ,the removal of color1 as stated in ,mr4 ,weston's report1 amounted to from #gj to #ij per cent4 ,the experiments extended over a period of ten months4 ,the rate of filtration employed was about #abh million gallons per acre daily4 ,the bacterial results of the first six months' operations were rejected by ,mr4 ,weston on account of defective methods of manipulation4 ,during the period from ,november #ag1 #ahic1 to ,january #cj1 #ahid1 the average bacterial efficiency of filtration was about #ie per cent1 and the manipulation was considered to be in every respect satisfactory4 ,the efficiency was occasionally below #ij per cent1 but for four selected weeks was as high as #ih4f per cent4 ,the average amount of sulphate of alumina used1 as calculated from ,mr4 ,weston's tables1 was two thirds of a grain per gallon4 ,the highest efficiency followed the application of a solution of caustic soda to the filtering material4 ,the first day following this treatment the bacterial efficiency was above #ii per cent4 ,afterwards it decreased until ,january #cj1 when the experiments were stopped4 ,the high bacterial efficiency following the use of caustic soda was of such short duration as to suggest very grave doubts as to its practical value4 ,it is extremely unfortunate that the experiments stopped only a week after this experiment1 and the results were never repeated4 ,i consider that the average bacterial efficiency of about #ie per cent obtained for the period of ,october #ag to ,january #cj1 when the manipulation was considered to be in every way satisfactory1 more nearly represents what can be obtained under these conditions than the results for certain periods1 particularly after the use of the caustic soda4 ,,louisville ,,experiments4#dj ,these experiments were inaugurated by the ,louisville ,water ,company in connection with the manufacturers of certain patented filters4 ,mr4 ,charles ,hermany1 ,chief ,engineer of the ,company1 had general charge of the experiments4 ,mr4 ,george ,w4 ,fuller was ,chief ,chemist and ,bacteriologist and had direct charge of the work and has made a most elaborate report upon the same4 ,in these examinations many devices were investigated2 but the two which particularly deserve our attention are the filters known as the ,warren ,filter and the ,jewell ,filter4 ,these filters were operated for two periods1 namely1 from ,october #ah1 #ahie1 to ,july #cj1 #ahif1 and from ,april #e to ,july #bd1 #ahig4 ,the investigations were directed toward the clarification of the river water from the mud1 and to the removal of bacteria4 ,the water was substantially free from color4 ,the character of the water at this point was such that in its best condition at least three fourths of a grain of sulphate of alumina were necessary for its coagulation1 and with this and with larger quantities of coagulant fair bacterial purification was nearly always obtained4 ,the problem studied therefore was principally that of clarification from mud4 ,the average efficiencies1 as shown by the total averages1 7page #bdh17 were as follows3 ,warren filter1 bacterial efficiency1 #if4g per cent2 ,jewell filter1 #if4j per cent4 ,,lorain ,,tests4#da ,these tests were made by the author of a set of ,jewell filters at ,lorain1 ,ohio4 ,the filters were six in number1 each #ag feet in diameter1 having an effective filtering area of #bbf square feet each1 or #acef square feet in all4 ,the construction of the filters was in all respects similar to the ,jewell filter used at ,louisville4 ,the raw water was from ,lake ,erie1 and during the examination was always comparatively clear1 but contained considerable numbers of bacteria4 ,the problem was thus entirely one of bacterial efficiency4 ,the question of clarification hardly presented itself4 ,although the water became turbid at times it did not approach in muddiness the condition of the ,ohio ,river water1 and an amount of coagulant sufficient for a tolerable bacterial efficiency in all cases was more than sufficient for clarification4 ,a summary of the results obtained is as follows3 ---------------------------------------- ----------------------- ,average ,rate ,sulphate of ,bacterial ,week ,endingof ,filtration1 ,alumina1 ,bacteria,bacteria ,efficiency #f3jj ,p4,m4 ,gallons per ,grains per in ,lake in per cent4 ,sq4 ,ft4 ,min4 ,gallon4 ,water4 ,effluent4 ---------------------------------------- ----------------------- ,june #ai #a4jf #b4eh #adda #af #ih4i #bf #a4aj #b4ej #che #f #ih4d ,july #c #a4aa #b4bg #cfg #i #ig4e #aj #a4bh #a4jg #aed #ad #ij4i #ag #a4ad #j4id #ahi #bf #hf4c ---------------------------------------- ------------ ,average #a4ad #a4hc #ejg #ad #if4d ---------------------------------------- ----------------------- ,the average bacterial efficiency was #if4d per cent with #a4hc grains of sulphate of alumina per gallon4 ,,pittsburg ,,experiments4#db ,the ,pittsburg experiments were inaugurated by the ,pittsburg ,filtration ,commission4 ,the operation of the filters extended from ,january to ,august1 #ahih4 ,a ,jewell and a ,warren filter were used similar in design to those used at ,louisville4 ,the raw water contained large numbers of bacteria1 and was also often very turbid1 although less turbid than at ,louisville4 ,at times more coagulant was necessary for clarification than was required for bacterial efficiency2 while as a rule more was required for satisfactory bacterial purification than was necessary for clarification4 ,the opportunities were therefore favorable for the study of both of these conditions4 ,the amount of coagulant necessary for clarification has been mentioned in connection with coagulation4 ,the results secured upon the relation of the quantity of coagulant to the number of bacteria in the effluent were more complete than any other experiments available1 and are therefore here reproduced from the ,pittsburg report nearly in full4 ,it was found that the amount of sulphate of alumina employed was more important than any other factor in determining the bacterial efficiency1 and special experiments were made to establish the effect of more and of less coagulant than used in the ordinary work4 ,these experiments were made upon the ,warren filter during ,may1 and with the ,jewell filter during ,june4 ,the monthly averages for these months are thus abnormal and are not to be considered4 ,the remaining six months for each filter may be taken as normal and as representing approximately the work of these filters under ordinary careful working conditions4 ,during the six months when the ,warren filter was in normal order the raw water contained #aa1eca bacteria and the effluent #bja1 the average bacterial efficiency being #ih4bf per cent4 ,the bacterial efficiency was very constant1 ranging only1 by months1 from #ig4dh to #ih4if per cent4 ,during the same period a sand filter receiving the same water yielded an effluent having an average of #aje bacteria per cubic centimeter4 ,the ,jewell filter1 for the six months in which it was in normal order1 received raw water containing an average of #aa1dha bacteria and yielded an effluent containing an average of #bic1 the bacterial efficiency being #ig4de per cent1 and ranging1 in different months1 from #ic4bc to #ih4fa per cent4 ,,wasting ,,effluent ,,after ,,washing ,,filters4 ,after washing a mechanical filter the effluent for the first few minutes is often inferior in quality to that obtained at other times1 and if samples are taken at these times and averaged with other samples taken during the run1 an apparent efficiency may be obtained inferior to the true efficiency4 ,to guard against this source of error1 whenever samples have been taken at such times1 the average work for the day has been taken1 not as the numerical average of the results1 but each sample has been given weight in proportion to the amount of time which it could be taken as representing2 so that the results represent as nearly as possible the average number of bacteria in the effluent for the whole run4 ,as a matter of fact1 however1 comparatively few samples were taken during these periods of reduced efficiency1 and thus most of the results represent the normal efficiency exclusive of this period4 ,a study has been made1 however1 of the results of examinations of samples taken directly after washing1 somewhat in detail4 ,the following is a tabular statement of the average results obtained from each filter by months1 including only the results obtained on those days when samples were taken within twenty minutes after washing1 the results of other days being excluded4 ,,average ,,number ,,of ,,bacteria ,,in ,,effluent4 ---------------------------------------- ------------------------- ,shown by ,within ,ten #aa to #bj ,more than ,record ,minutes after,minutes after ,twenty ,sheets4 ,washing4 ,washing4 ,minutes after ,washing4 ---------------------------------------- ------------------------- ,,warren ,,filter4 ,february #aae #aah #aad ,march #caf #ej #eae #cja ,april #gi #dag #bjg #ge ,may 7,special experiments1 omitted47 ,june #aig #dic #bgb #agj ,july #cjj #edf #bjg ,august #agd #cef #fja #bbc ,,jewell ,,filter4 ,february #bdec #bdbe #bjii ,march #dee #feg #ieh #ced ,april #ii #ffe #dfb #afe ,may #add #iih #cdf #abg ,june 7,special experiments1 omitted47 ,july #bgi #accj #bgb #bgd ,august #cdd #fab #cbc #cgf ---------------------------------------- ------------------------- ,the time of inferior work very rarely exceeded twenty minutes4 ,it will be seen from the tables that the results as shown by the record sheets are never very much higher1 and are occasionally lower than the results of samples taken on corresponding days more than twenty minutes after washing2 and thus while a decrease in bacterial efficiency was noted after washing1 no material increase in the average bacterial efficiency of the mechanical filters would have been obtained if these results had been excluded4 ,the results for the whole time would be affected much less than is indicated by the table1 because the table includes only results of those days when samples were taken just after washing1 while the much larger number of days when no such samples were taken would show no change whatever4 ,it has been suggested that these inferior effluents after washing should be wasted4 ,such a procedure would mean wasting probably on an average two per cent of the water filtered1 and a corresponding increase in the cost of filtering4 ,mr4 ,fuller#dc in his ,louisville report comes to the conclusion that with adequate washing and coagulation it is unnecessary to waste any effluent1 and that inferior results after washing usually indicate incomplete washing4 ,while our experiments certainly indicate a reduction in efficiency after washing so regular and persistent as to make it doubtful whether incomplete washing can be the cause of it1 it may be questioned whether or not wasting the effluent would be necessary or desirable in actual operation4 ,at any rate the results as given in this report are not materially influenced by this factor4 ,,influence ,,of ,,amount ,,of ,,sulphate ,,of ,,alumina ,,on ,,bacterial ,,efficiency ,,of ,,mechanical ,,filters4 ,the number of bacteria passing a mechanical filter is dependent principally upon the amount of sulphate of alumina used2 and by using a larger quantity of sulphate of alumina than was actually used in the experiments the bacterial efficiency could be considerably increased4 ,to investigate this point1 the results obtained each day with each of the mechanical filters were arranged in the order of the sulphate of alumina quantities used1 and averaged by classes4 ,in this and the following tables a few abnormal results were omitted4#dd ,a summary of the results is as follows3 ,,summary ,,of ,,results ,,with ,,warren ,,mechanical ,,filter1 ,,arranged ,,according ,,to ,,sulphate ,,of ,,alumina ,,quantities4 ---------------------------------------- ------------------------------- ,number ,bacteria4 ,sulphate of of ,days ,turbidity4------------------- ,per cent ,per cent ,alumina ,represented4 ,raw ,water4,effluent4remaining4removed4used ,grains per ,gallon4 ---------------------------------------- ------------------------------ #g #j4je #d1ggc #agac #ce4hi #fd4aa #j4jj #b #j4jh #b1ghe #hej #cj4eb #fi4dh #j4ab #d #j4aj #e1aji #gbf #ad4ba #he4gi #j4bf #b #j4bj #h1gac #bad #b4de #ig4ee #j4cf #h #j4jf #c1bbd #aab #c4dg #if4ec #j4dd #ai #j4jf #c1dhh #abc #c4ec #if4dg #j4ee #aa #j4jf #e1fgc #aed #b4ga #ig4bi #j4fd #aj #j4aj #f1ajj #aab #a4hd #ih4af #j4gd #h #j4ji #h1fdg #adh #a4ga #ih4bi #j4he #e #j4af #e1fde #adb #b4eb #ig4dh #j4ic #ac #j4ab #aj1cig #bjj #a4ib #ih4jh #a4jg #aj #j4jh #ab1ggh #aba #j4ie #ii4je #a4ac #ac #j4ad #ac1cig #afd #a4bb #ih4gh #a4be #ai #j4ac #aj1dfb #afj #a4ec #ih4dg #a4cd #aj #j4ab #ab1hea #ajg #j4hc #ii4ag #a4df #d #j4bg #af1jae #gg #j4dh #ii4eb #a4eg #g #j4ec #ab1bfb #aia #a4ah #ih4hb #a4fd #d #j4eh #bf1iej #cdg #a4bi #ih4ga #a4gd #e #j4bi #ad1egj #hf #j4ei #ii4da #a4hd #c #j4bc #ac1hcc #aec #a4aa #ih4hi #a4ib #ai #j4dj #ah1bbb #ib #j4ej #ii4ej #b4dh #e #j4de #bi1cjj #aaai #c4hb #if4ah #c4cg #e #a4jf #cc1jcj #ece #a4fb #ih4ch #h4jf ---------------------------------------- ------------------------------ ,,summary ,,of ,,results ,,with ,,jewell ,,mechanical ,,filter1 ,,arranged ,,according ,,to ,,sulphate ,,of ,,alumina ,,quantities4 ---------------------------------------- ------------------------------ ,number ,bacteria4 ,sulphate of of ,days ,turbidity4------------------- ,per cent ,per cent ,alumina ,represented4 ,raw ,water4,effluent4remaining4removed4used ,grains per ,gallon4 ---------------------------------------- ------------------------------ #f #j4jc #ad1jcg #fbag #dd4bi #ee4ga #j4jj #e #j4jg #d1bfg #fhj #ae4ic #hd4jg #j4bd #ad #j4jf #b1fac #agj #f4ej #ic4ej #j4ce #aj #j4jf #b1ddf #aac #d4fb #ie4ch #j4dd #i #j4aa #g1cjc #bcd #c4bj #if4hj #j4ee #bj #j4ji #f1igi #bbj #c4ae #if4he #j4fe #i #j4jh #e1aia #acj #b4ej #ig4ej #j4ge #af #j4ab #h1ejd #bdb #b4hd #ig4af #j4hc #bb #j4af #h1ejf #ii #a4af #ih4hd #j4if #ab #j4aa #aa1iih #bdf #b4je #ig4ie #a4je #ad #j4ah #ah1ihb #dbc #b4bc #ig4gg #a4af #e #j4ad #ac1iha #bbd #a4fj #ih4dj #a4bc #i #j4bg #ai1hjf #cbe #a4fd #ih4cf #a4cd #ad #j4bg #af1edi #cbd #a4if #ih4jd #a4de #i #j4bi #ab1aid #if #j4gi #ii4ba #a4ed #f #j4be #ac1dhc #ea #j4ch #ii4fb #a4fe #g #j4ec #bd1bdc #bbj #j4ia #ii4ji #a4gb #c #j4ij #bj1iec #fjb #b4hh #ig4ab #a4ij #e #j4dc #be1ieh #cjg #a4ai #ih4ha #b4ai #d #j4hd #ba1jag #bbh #a4ji #ih4ia #c4ga ---------------------------------------- ------------------------------ ,these results are shown graphically by ,fig4 #ba4 ,illustration3 ,,fig4 #ba4--;,,bacterial ,,efficiencies ,,of ,,mechanical ,,filters4 ,,influence ,,of ,,degree ,,of ,,turbidity ,,upon ,,bacterial ,,efficiency ,,of ,,mechanical ,,filters4 ,it will be noticed by referring to the tables that as the sulphate of alumina quantities increased the turbidities increased and the numbers of bacteria increased1 as well as the bacterial efficiencies4 ,that is to say1 with the less turbid waters1 small sulphate of alumina quantities have been used1 the numbers of bacteria in the raw water have been low1 and the bacterial efficiencies have also been low4 ,with turbid waters much larger quantities of sulphate of alumina have been used1 the raw water has contained more bacteria1 and the bacterial efficiencies have been higher4 ,it may be then that the increased efficiencies with increased quantities of sulphate of alumina are not due alone to the increased sulphate of alumina1 but in part also to other conditions4 ,thus it may be easier to remove a large percentage of bacteria from a water containing many than from a water containing only a few4 ,to investigate this matter and eliminate the influence of turbidity and numbers of bacteria in the raw water1 the results were first classified with reference to turbidity4 ,the results with waters having turbidities of #j4aj or less1 and called for convenience turbid waters1 are arranged by alum quantities as before4 ,afterwards the results obtained with turbidities from #j4aa to #j4ej1 and called for convenience muddy waters1 are grouped2 and finally the results with turbid water having turbidities of #j4ea and over1 and called for convenience thick waters4 ,the results thus arranged are as follows3 ,,summary ,,of ,,results ,,with ,,warren ,,mechanical ,,filter1 ,,arranged ,,according ,,to ,,turbidities ,,and ,,sulphate ,,of ,,alumina ,,quantities4 ---------------------------------------- ------------------------------- ,sulphate of ,number ,bacteria4 ,per cent ,per cent ,alumina of ,days ,turbidity4-------------------remaining4 removed4used ,grains ,represented4 ,raw ,water4,effluent4 per ,gallon4 ---------------------------------------- ------------------------------ #g #j4je #d1ggc #agac #ce4hi #fd4aa #j4jj #b #j4jg #b1ghe #hej #cj4eb #fi4dh #j4ab #ab #j4jf #c1bji #bbd #g4jj #ic4jj #j4db #ca #j4jf #d1bch #aai #b4ha #ig4ai #j4fj #i #j4jf #g1iec #acj #a4fd #ih4cf #j4hd #af #j4jd #aa1bfe #acg #a4bb #ih4gh #a4aa #bi #j4jf #aa1ejj #aeh #a4cg #ih4fc #a4eh #e #j4ag #h1ghc #daf #d4gc #ie4bg #j4cf #aj #j4af #f1ece #afe #b4ed #ig4df #j4he #ac #j4ai #ac1bec #ahf #a4dj #ih4fj #a4ac #ae #j4bb #aj1idd #ic #j4he #ii4ae #a4cf #ac #j4bi #ad1jhi #aab #j4hj #ii4bj #a4gc #aj #j4ce #ah1jhh #ajb #j4eg #ii4dc #b4ch #e #j4bi #be1ehj #edj #b4aa #ig4hi #d4cj #f #j4hg #be1dcc #cfi #a4de #ih4ee #a4gd #f #j4gc #bf1eff #gi #j4cj #ii4gj #b4fd #d #a4ce #db1jcg #achh #c4cj #if4gj #h4af ---------------------------------------- ------------------------------ ,,summary ,,of ,,results ,,with ,,jewell ,,mechanical ,,filter1 ,,arranged ,,according ,,to ,,turbidities ,,and ,,sulphate ,,of ,,alumina ,,quantities4 ---------------------------------------- ------------------------------- ,sulphate of ,number ,bacteria4 ,alumina of ,days ,turbidity4------------------- ,per cent ,per centused ,grains ,represented4 ,raw ,water4,effluent4remaining4removed4per ,gallon4 ---------------------------------------- ------------------------------ #f #j4jc #ad1jcg #fbag #dd4bi #ee4ga #j4jj #c #j4jg #e1agj #iia #ai4ae #hj4he #j4ba #be #j4je #b1djc #adc #e4ie #id4je #j4ch #bj #j4jf #f1eca #ahe #b4hd #ig4af #j4fd #bg #j4jf #e1haa #abb #b4aj #ig4ij #j4hh #ad #j4jf #ad1igh #dab #b4ge #ig4be #a4aa #aj #j4jf #ae1ghg #cij #b4dg #ig4ec #a4cg #aj #j4je #aj1hdg #dg #j4dc #ii4eg #b4ag #ad #j4af #g1ebe #bef #c4dj #if4fj #j4fj #ag #j4bd #aa1caj #bjh #a4hd #ih4af #j4ia #ae #j4bd #ae1dda #bfb #a4gj #ih4cj #a4ac #aj #j4bh #ag1hdb #bcb #a4cj #ih4gj #a4dc #h #j4bi #i1eef #ei #j4fb #ii4ch #a4ei #d #j4bi #bj1bab #ace #j4fg #ii4cc #b4jj #e #j4ff #bc1fhj #ccf #a4db #ih4eh #a4db #g #j4if #cj1bjj #dge #a4eg #ih4dc #a4gd #d #a4be #cg1ehg #dif #a4cb #ih4fh #b4ha ---------------------------------------- ------------------------------ ,the following table shows the bacterial efficiencies with turbid1 muddy1 and thick waters1 with substantially equal quantities of sulphate of alumina3 ---------------------------------------- ---------------------------- ,grains of ,sulphate of ,alumina4,corresponding ,bacterial ,efficiencies4 ---------------------------------------- ------------------------ ,turbid4 ,muddy4 ,thick4 ,turbid4 ,muddy4 ,thick4 ---------------------------------------- ------------------------ ,,warren ,,filter4 #j4db #j4cf #ic4jj #ie4bg #j4hd #j4he #ih4cf #ig4df #a4aa #a4ac #ih4gh #ih4fj #a4eh #a4gc #a4gd #ih4fc #ii4bj #ih4ee #b4ch #b4fd #ii4dc #ii4gj #d4cj #h4af #ig4hi #if4gj ,,jewell ,,filter4 #j4fd #j4fj #ig4af #if4fj #j4hh #j4ia #ig4ij #ih4af #a4aa #a4ac #ig4be #ih4cj #a4cg #a4dc #a4db #ig4ec #ih4gj #ih4eh #b4ag #a4ei #a4gd #ii4eg #ii4ch #ih4dc #b4jj #b4ha #ii4cc #ih4fh ---------------------------------------- ------------------------- ,it appears from this table that waters of various degrees of turbidity give substantially equal bacterial efficiencies with equal quantities of sulphate of alumina1 the results varying as often in one direction as the other4 ,within certain limits it may thus be said that turbidity is without influence upon the bacterial efficiency obtained in mechanical filtration4 ,it must be borne in mind1 however1 that the quantities of sulphate of alumina1 with very few exceptions1 were sufficient to produce full coagulation4 ,mr4 ,fuller has shown in his ,louisville report that considerable quantities of sulphate of alumina may be added to turbid waters without producing appreciable coagulation2 and therefore if a quantity of sulphate of alumina sufficient to produce a certain bacterial efficiency in a clear water should be added to a water so turbid that it was unable to coagulate it1 scarcely any effect would be produced4 ,the above statement therefore only applies in those cases where sufficient sulphate of alumina is used to adequately coagulate the water4 ,as the numbers of bacteria often vary with the turbidity1 the variation in the numbers of bacteria in the different classes is much less than in the first tables2 but to further investigate the question of whether the numbers of bacteria in the raw water have an important influence upon the bacterial efficiencies1 each of the two largest classes in the foregoing tables was divided into two parts1 according to the bacterial numbers in the raw water1 namely1 the results from the ,jewell filter with turbid waters and with sulphate of alumina quantities ranging from #j4ge to #a4jj grain per gallon1 and the results from the ,warren filter with turbid waters and with sulphate of alumina quantities of #a4be grains per gallon and upward4 ,the results are as follows3 ---------------------------------------- ------------------------------- ,sulphate ,number ,bacteria4 of ,alumina of ,days ,turbidity4------------------- ,per cent ,per centused ,grains ,represented4 ,raw ,water4,effluent4remaining4removed4per ,gallon4 ---------------------------------------- ------------------------------ ,,jewell ,,filter4 #ad #j4je #c1ich #ha #b4jf #ig4id #j4hh #ac #j4jg #g1hbg #afg #b4ac #ig4hg #j4hg ,,warren ,,filter4 #ae #j4jf #c1ede #ei #a4ff #ih4cd #a4fg #ad #j4jf #bj1jbb #bfe #a4cb #ih4fh #a4dh ---------------------------------------- ------------------------------ ,it will be observed that the bacterial efficiencies are substantially the same1 with the lower and with the higher numbers of bacteria in the raw water4 ,that is to say1 other things being equal1 as the number of bacteria increase in the raw water the number of bacteria in the effluent increase in the same ratio4 ,a further analysis of other groups of results would perhaps show variations in one direction or the other1 but on the whole it is believed that the comparison is a fair one1 and that there is no well-marked tendency for bacterial efficiencies of mechanical filters to increase or decrease with increasing numbers of bacteria4 ,,average ,,results ,,obtained ,,with ,,various ,,quantities ,,of ,,sulphate ,,of ,,alumina4 ,as it appears that neither the turbidity nor the number of bacteria in the raw water has a material influence upon the percentage bacterial efficiency obtained1 we can take the results given above1 which include all the results obtained 7except a very few abnormal ones7 for computing the various efficiencies obtained with various quantities of sulphate of alumina4 ,these results are graphically shown by ,fig4 #ba1 p4 #afg1 on which lines have been drawn indicating the normal efficiencies from various quantities of sulphate of alumina as deduced from our experiments4 ,in computing the amount of sulphate of alumina which it would be necessary to use in operating a plant at a given place to give these efficiencies1 the quantities of sulphate of alumina shown by the diagram can be taken as those which it would be necessary to use during those days in the year when the raw water was clear1 or sufficiently clear1 so that the amounts of sulphate of alumina mentioned would suffice to properly coagulate it4 ,,types ,,of ,,mechanical ,,filters4 ,sections of the ,warren and ,jewell filters used at ,pittsburg are presented herewith4 ,the filters here shown are practically identical with those used at ,lorain and ,louisville1 and nearly all the exact information regarding mechanical filters relates to filters of these types4 ,these sections show clearly the constructions used at ,pittsburg and ,louisville1 but there are some points in connection with the designs of these filters which require to be considered more in detail4 ,the simplest idea of a mechanical filter is a tub1 with sand in the bottom and some form of drainage system4 ,water is run over the sand1 passes through it1 and is collected by the drainage system4 ,when the sand becomes clogged it is washed by the use of a reverse current of water4 ,this reverse current of water is so rapid as to preclude the use of a drainage system consisting of gravel1 tile-drains1 etc41 such as are used in sand filters operated at lower rates1 and instead metallic strainers in some form are used4 ,the sand comes directly against these strainers1 which are made as coarse as it is possible to have them1 without allowing the sand to pass4 ,the rate of washing is usually from five to seven gallons per square foot per minute4 ,in the ,warren filter the openings in the strainers at the bottom are #f to #h per cent of the total area1 and during washing the water has an average velocity of #j4bj foot per second upward through them4 ,this velocity is so slow that the friction of the water in passing through the openings in the screen is practically nothing4 ,a result of this is that if there is any unequal resistance of the sand to the water1 the bulk of the water goes up at the points of least resistance in the sand4 ,illustration3 ,,fig4 #bb4--,,section ,,of ,,jewell ,,mechanical ,,filter ,,used ,,in ,,pittsburg ,,experiments4 ,this tendency would be fatal were it not for the revolving rake which loosens and mixes the sand and largely corrects it4 ,the correction1 however1 is imperfect1 and some parts of the filter are washed more than others4 ,the rake is also necessary to prevent the separation of sand into coarser and finer particles4 ,it is practically impossible to get filter sand the grains of which are all of the same size4 ,when a filter is washed the tendency is for the wash water to go up in limited areas4 ,the larger sand grains tend to collect at these points while the finer grains collect in places where there is no upward current1 or where it is less rapid4 ,in many filters this tendency is very strong4 ,the revolving rake is necessary to correct it1 and to keep the sand thoroughly mixed1 otherwise when a filter is put in operation after washing1 the frictional resistance through the coarse sand being less1 the bulk of the water goes through it1 with the result that a part of the area1 and the part which is least efficient as a filter1 passes nearly all of the water1 and with inferior results4 ,in the ,jewell filter provision is made for the distribution of the wash water over the whole area in another way4 ,the strainers have areas at the surface amounting to #a4b to #a4d per cent of the whole area1 but the water before reaching them passes through throats much smaller in size than the strainer outlets1 and amounting in the aggregate to only about #j4jg per cent of the filter area4 ,when washing at a rate of seven gallons per square foot per minute1 water passes through these necks at a velocity of #bb feet per second4 ,the friction and velocity head in passing these necks is estimated to be about #cj vertical feet1 and is so much greater than the friction of the outlets proper1 and of the sand1 that the water passes through each strainer with approximately the same velocity1 and the wash water is equally distributed over the whole area of the bottom of the filter4 ,this result is accomplished1 however1 at a great loss of head in the wash water4 ,when a filter is washed from the pressure-mains without separate pumping1 the pressure is usually sufficient and there is no disadvantage in the arrangement4 ,when1 however1 the water is specially pumped for washing1 the required head is much greater than would otherwise be necessary4 ,illustration3 ,,mechanical ,,filters ,,at ,,elmira1 ,n4 ,y4 ,,outlet ,,to ,,filters ,,with ,,controller ,,and ,,pure-,,water ,,flume4 ,to face page #agd4 ,it would not be possible to increase the size of the necks1 thereby decreasing the friction1 without increasing very largely the size of the pipes in the underdrainage system into which the strainers are fastened4 ,these pipes are so small that during washing the velocity in them is about #ac feet per second1 and if the throats of the necks were increased without also enlarging these pipes1 the friction would be so reduced that most of the water would go through the necks nearest the supply1 thus failing to reach the object to be attained4 ,a more rational system would be to increase the sizes of all the waterways in the outlet and wash-water system4 ,the ,jewell filter is also provided with a rake to keep the sand mixed during washing1 as this is necessary even with the complete distribution of wash-water over the area of the filter4 ,both the ,warren and the ,jewell filters are provided with receptacles through which the water passes after receiving the coagulant1 and before entering the filter4 ,in the ,jewell filter the receptacle1 called a sedimentation-basin1 is of such size as to hold as much water as is filtered in #ae minutes4 ,in the ,warren filter the receptacle is entirely independent and larger1 holding about an hour's supply4 ,the rates of filtration used in the experiments have ranged from less than #ajj to about #acj million gallons per acre daily4 ,to employ a rate much higher than this involves the use of a much coarser sand1 or an increase in the height of water upon the filter to an impracticable extent4 ,there would seem to be no material advantage in the use of lower rates within certain limits1 while the cost of filters would be greatly increased4 ,the sand used in the ,warren filters has been crushed quartz4 ,in the ,jewell filters a silicious sand from ,red ,wing1 ,minn41 with rounded grains has been used4 ,these sands are somewhat coarser than are commonly used in sand filters1 and the uniformity coefficients are very low4 ,it is necessary to use sand with the very lowest uniformity coefficients to avoid the separation of sand particles according to sizes as mentioned above1 and for this reason the sand must be selected with much greater care than is required for sand filters4 ,illustration3 ,,plan ,,just ,,above ,,copper4 ,,section ,,showing ,,filter ,,during ,,ordinary ,,operation4 ,,fig4 #bc4--,,warren ,,filter3 ,,pittsburg ,,experiments4 ,,section ,,no4 #a4 ,illustration3 ,,plan ,,of ,,agitator1 ,,gutter ,,castings1 ,,etc4 ,,section ,,showing ,,filter ,,during ,,operation ,,of ,,washing4 ,,fig4 #bd4--,,warren ,,filter3 ,,pittsburg ,,experiments4 ,,section ,,no4 #b4 ,the round-grained sand is more readily and completely washed than the angular crushed quartz4 ,it has been claimed that the crushed quartz is more efficient as a filtering material1 but the evidence of this is not very clear4 ,the amount of water filtered by a filter between washings is1 in a general way1 about the same as that filtered by a sand filter between scrapings1 in relation to its area4 ,the amount of water required for washing is1 on an average1 about equal to a vertical column #e or #f feet high equal in area to the area of the filter1 exclusive of water on the top of the filter wasted before the current is reversed4 ,with clear waters1 as for instance1 the ,allegheny at low water1 the amount of washing is almost directly proportional to the amount of sulphate of alumina used4 ,with muddy waters the sulphate of alumina required is proportional to the mud1 and the frequency of washing and the amount of wash-water are proportional to both4 ,the amount of wash-water required averages about five per cent2 with very muddy waters more is required4 ,at ,louisville1 with the worst waters1 the per cents of wash-water rose at times to #cj per cent of the total quantity of water filtered4 ,the rate of filtration with mechanical filters should be kept as constant as possible1 and can be regulated by devices similar to those described in connection with sand filters4 ,owing to the smaller areas and capacities1 the amounts of water to be handled in the units are smaller1 and the regulating devices are thus smaller1 and have always been made of metal1 either cast iron or copper4 ,none of the devices employed in the above-mentioned experiments has been entirely satisfactory in this respect4 ,the devices employed have been too small1 and the water has gone through at too high velocities to allow close adjustment4 ,illustration3 ,,mechanical ,,filters ,,at ,,elmira1 ,n4 ,y4 ,,upper ,,platform ,,and ,,general ,,arrangement ,,of ,,filters4 ,to face page #agh4 ,as between the two types of filters1 the ,jewell filter requires a large loss of head4 ,the water has to be pumped at a sufficient elevation to reach the top of a tank about #ah feet high1 while the effluent must be drawn off at the extreme bottom4 ,the ,warren filter is much more economical in head1 the plants at ,pittsburg and ,louisville only requiring about #i feet from the inlet to the outlet4 ,the earlier mechanical filters were usually constructed of wrought iron or steel plates4 ,more recently wooden tanks have been commonly employed1 although steel is regarded as preferable4 ,concrete or masonry tanks have been suggested1 but they have not as yet been employed4 ,,efficiency ,,of ,,mechanical ,,filters4 ,the efficiency of mechanical filters depends entirely upon the use of coagulants4 ,without coagulants they can only be used to remove very large particles4 ,the efficiency of the filtration depends much more upon the kind1 and amount1 and method of application of coagulant than upon the arrangement of the filter4 ,in fact1 the arrangements of the filter are more directed to the convenience and economy of operation and washing than towards the efficiency of the results4 ,the conditions which control the efficiency of mechanical filters have been discussed in connection with coagulation4 ,with sufficient coagulant the removal of turbidity or mud is complete4 ,color also can be removed with these filters4 ,the bacterial efficiencies secured with them have been discussed at length in connection with the ,pittsburg experiments4 ,with careful coagulation and manipulation it is possible to get #ih per cent bacterial efficiency without difficulty4 ,the results are somewhat irregular1 for reasons not as yet fully understood4 ,on some occasions higher bacterial efficiencies are secured with smaller quantities of coagulant1 while at other times the efficiencies are less without apparent reason4 ,there seems to be a limit to the bacterial efficiency which can be secured with any amount of sulphate of alumina and rapid filtration1 and it is doubtful if a plant could be operated to regularly secure as high a bacterial efficiency as #ii per cent with any amount of sulphate of alumina4 ,,pressure ,,filters4 ,pressure mechanical filters are constructed in entirely closed receptacles1 through which the water is forced under pressure and not by gravity4 ,many of the earlier mechanical filters were of this type4 ,in small plants this system has the distinct advantage that the water can be pumped from a river or other source of supply through a filter direct to the reservoir or into the mains1 while any other system would involve a second pumping4 ,pressure filters are extensively used for hotel supplies1 etc41 where1 from the conditions1 gravity filters are impossible4 ,the practical objections to this system have been found to be so great that it is rarely used under other conditions4 ,some experiments were made at ,louisville with a filter of this type1 but they were not long continued1 and aside from them there is no precise information as to what can be accomplished with filters of this type4 ,,chapter ,,xi4 ,,other ,,methods ,,of ,,filtration4 ,,worms ,,tile ,,system4 ,this system1 invented and patented by ,director ,fischer of the ,worms water-works1 consists of the filtration of water through artificial hollow sandstone tiles1 made by heating a mixture of broken glass and sand1 sifted to determined sizes1 to a point just below the melting-point of the glass1 in suitable moulds or forms4 ,the glass softens and adheres to the sand1 forming a strong porous substance through which water can be passed4 ,these tiles are made hollow and are immersed in the water to be treated1 the effluent being removed from the centre of each tile4 ,they are connected together in groups corresponding in size to the units of a sand-filtration plant4 ,they are washed by a reverse current of filtered water4 ,these tiles have been used for some years at ,worms1 ,germany1 and at a number of smaller places1 and were investigated experimentally at ,pittsburg4 ,some difficulty has been experienced in getting tiles with pores small enough to yield an effluent of the desired purity1 and at the same time large enough to allow a reasonable quantity of water to pass4 ,in fact1 with other than quite clear waters1 it has not been found feasible to accomplish both objects at the same time1 and it has been necessary to treat the water with coagulants and preliminary sedimentation or filtration before applying it to the tiles4 ,the problem of making the joints between the tiles and the collection-pipes water-tight when surrounded by the raw water also is a matter of some difficulty4 ,,the ,,use ,,of ,,asbestos4 ,it has been suggested by ,mr4 ,p4 ,a4 ,maignen that the surface of sand filters should be covered with a thin layer of asbestos1 applied in the form of a pulp1 with the first water put onto the filter after scraping4 ,the asbestos forms a sort of a paper on the sand which intercepts the sediment of the passing water4 ,the advantage of the process is in the cleaning4 ,when dried to the right consistency this asbestos can be rolled up like a carpet1 and taken from the filter without removing any of the sand4 ,this procedure is almost identical with that which has occurred naturally in iron-removal plants1 where alg grow in the water upon the filters1 and form a fibrous substance with the ferric oxide removed from the water1 which can be rolled up and removed in the same way as the asbestos4 ,the advantages of the process1 from an economical standpoint1 are less clear4 ,,filters ,,using ,,high ,,rates ,,of ,,filtration ,,without ,,coagulants4 ,numerous filters have been suggested1 and a few have been constructed for the use of much higher rates of filtration than are usually employed with sand filters1 but without the use of coagulants4 ,the results obtained depend upon the requirements and upon the character of the raw water4 ,if a reservoir water contains an alg growth1 it can often be removed by a coarse and rapid filter4 ,the organisms in this case are many times larger than the bacteria1 and many times larger than the clay particles which constitute turbidity4 ,the requirements in this case are rather in the nature of straining than of filtration4 ,the conditions necessary for the removal of bacteria and turbidity are very well understood1 and it can be stated with the utmost confidence that no system of filtration through sand at rates many times as high as are used in ordinary sand filtration1 and without the use of coagulants1 will be satisfactory where either bacterial efficiency or clarification is required4 ,the application of such systems of filtration would therefore seem to be somewhat limited4 ,illustration3 ,,removing ,,dirty ,,asbestos ,,covering ,,from ,,an ,,experimental ,,filter4 ,,maignen ,,system4 ,to face page #ahb4 ,,household ,,filters4 ,the subject of household filters is a somewhat broad one1 as the variety in these filters is even greater than in the larger filters1 and the range in the results to be expected from them is at least as great4 ,i shall only attempt to indicate here some of the leading points in regard to them4 ,household filters may be used to remove mud or iron rust from the tap water1 or to remove the bacteria in case the latter is sewage-polluted1 or to do both at once4 ,perhaps oftener they are used simply because it is believed to be the proper thing1 and without any clear conception either of the desired result or the way in which it can be accomplished4 ,i shall consider them only in their relations to the removal of bacteria1 as ,i credit the people who employ them with being sufficiently good judges of their efficiency in removing visible sediment4 ,in the first place1 as a general rule1 which has very few if any exceptions1 we may say that all small filters which allow a good stream of water to pass do not remove the bacteria4 ,the reason for this is simply that a material open enough to allow water to pass through it rapidly is not fine enough to stop such small bodies as the bacteria4 ,the filters which are so often sold as 8germ-proof10 consisting of sand1 animal charcoal1 wire-cloth1 filter-paper1 etc41 do not afford protection against any unhealthy qualities which there may be in the raw water4 ,animal charcoal removes color without retaining the far more objectionable bacteria4 ,the other household filters have filtering materials of much finer grain1 unglazed porcelain and natural sandstone being the most prominent materials1 while infusorial earth is also used4 ,the smaller sizes of these filters allow water to pass only drop by drop1 and when a fair stream passes them the filters have considerable filtering area 7as a series of filter-tubes connected together74 ,on account of their slow action1 filters of this class are1 as a rule1 provided with storage reservoirs so that filtered water to the capacity of the reservoir can be drawn rapidly 7provided the calls do not come too often74 ,some of these filters are nearly germ-proof1 and are comparable in their efficiency to large sand-filters4 ,there is no sharp line between the filters which stop and which do not stop the bacteria2 but in general the rule that a filter which works rapidly in proportion to its size does not do so1 and vice versa1 will be found correct4 ,in thinking of the efficiency of household filters we must distinguish between the filter carefully prepared for an award at an exhibition and the filter of the same kind doing its average daily work in the kitchen4 ,if we could be sure in the latter case that an unbroken layer of fine sandstone or porcelain was always between ourselves and the raw tap-water we could feel comparatively safe4 ,the manufacturers of the filters claim that leaky joints1 cracked tubes1 etc41 are impossible2 but ,i would urge upon the people using water filtered in this way that they personally assure themselves that this is actually the case with their own filters1 for in case any such accident should happen the consequences might be most unpleasant4 ,the increased yield of a filter due to a leaky joint is sure not to decrease it in favor with the cook1 who is probably quite out of patience with it because it works so slowly1 that is1 in case it is good for anything4 ,the operation of household filters is necessarily1 with rare exceptions1 left to the kitchen-girl and luck4 ,scientific supervision is practically impossible4 ,with a large filter1 on the other hand1 concentrating all the filters for the city at a single point1 a competent man can be employed to run them in the best-known way2 and if desired1 and as is actually done in very many places1 an entirely independent bacteriologist can be employed to determine the efficiency of filtration4 ,with the methods of examination now available1 and a little care in selecting the times and places of collecting the samples1 it is quite impossible for a filter-superintendent to deliver a poor effluent very often or for any considerable length of time without being caught4 ,the safety of properly-conducted central filtration is thus infinitely greater than that from even the best household filters4 ,further1 it may be doubted whether an infected water can be sent into every house in the city to be used for washing and all the purposes to which water is put except drinking1 without causing disease1 although less than it would if it were also used for drinking4 ,the use of household filters must be regarded as a somewhat desperate method of avoiding some of the bad consequences of a polluted water-supply1 and they are adopted for the most part by citizens who in some measure realize the dangers from bad water1 but who cannot persuade their fellow-citizens to a more thorough and adequate solution of the problem4 ,such citizens1 by the use of the best filters1 and by carefully watching their action1 or by having their drinking-water boiled1 can avoid the principal dangers from bad water1 but their vigilance does not protect their more careless neighbors4 ,,chapter ,,xii4 ,,removal ,,of ,,iron ,,from ,,ground-,,waters4 ,the filtration of ground-waters is a comparatively recent development4 ,ground-waters are filtered by their passage through soil generally much more perfectly than it is possible to filter other waters1 and any further filtration of them is useless4 ,such waters1 however1 occasionally contain iron in solution as ferrous carbonate4 ,waters containing iron have been used as mineral waters for a very long time4 ,such waters have an astringent taste1 and have been esteemed for some purposes4 ,as ordinary water-supplies1 however1 they are objectionable4 ,the iron deposits in the pipes when the current is slow1 and is flushed out when it is rapid1 and makes the water turbid and disagreeable2 and still worse1 the iron often gets through the pipe-system in solution1 and deposits in the wash-tub1 coloring the linen a rusty brown and quite spoiling it4 ,an organism called crenothrix grows in pipes carrying waters containing iron1 and after a while this organism dies1 and decomposes1 and gives rise to very disagreeable tastes and odors4 ,it thus happens that ground-waters containing iron are unsatisfactory as public water-supplies1 and are sources of serious complaint4 ,,amount ,,of ,,iron ,,required ,,to ,,render ,,water ,,objectionable4 ,three hundredths of a part in #ajj1jjj of metallic iron very rarely precipitate or cause any trouble4 ,five hundredths occasionally precipitate1 and this amount may be taken as about the allowable limit of iron in a satisfactory water4 ,one tenth of a part is quite sure to precipitate and give rise to serious complaint4 ,two or three tenths make the water entirely unsuitable for laundry purposes1 and are otherwise seriously objectionable1 and will hardly be tolerated by a community4 ,under some conditions ground-waters carry as much as #a part in #ajj1jjj of iron1 and such waters are hardly usable4 ,in iron-removal plants an effluent containing less than #j4je is regarded as satisfactory4 ,one containing less than #j4jb1 as is the case with many plants1 is all that can be desired4 ,the percentage of removal is of no significance1 but only the amount left in the effluent4 ,,cause ,,of ,,iron ,,in ,,ground-,,waters4 ,natural sands1 gravels1 and rocks almost always contain iron1 often in considerable amount4 ,the iron is usually combined with oxygen as ferric oxide1 and in this condition it is insoluble in water4 ,water passing through iron containing materials will not ordinarily take up iron4 ,when1 however1 the water contains a large amount of organic matter in solution1 this organic matter takes part of the oxygen away from the iron1 and reduces the ferric oxide to ferrous oxide4 ,the ferrous oxide combines with carbonic acid1 always present under these conditions1 forming ferrous carbonate1 which is soluble and which goes into solution4 ,surface-waters nearly always carry free oxygen1 and when such waters enter the ground they carry oxygen with them1 and the organic matters in the water use up the free oxygen before they commence to take oxygen away from the iron of the ground4 ,it is thus only in the presence of organic matters1 and in the absence of free oxygen1 that the solution of iron is possible4 ,it sometimes happens that the organic matters which reduce the iron are contained in the soil itself1 in which case iron may be taken up even by water originally very pure1 as for instance1 by rain-water4 ,generally speaking1 iron is everywhere present in sufficient quantity in the strata from which ground-waters are obtained1 and wherever the conditions of the organic matters and oxygen necessary for solution occur1 iron-containing waters are secured1 and the iron is usually present in the earth in such quantity that the water can dissolve as much as it will take up for a long series of years1 or for centuries1 without exhausting the supply4 ,there is thus little prospect of improvement of such waters from exhaustion of the supply of iron4 ,the circumstances which control the solution of iron are very complicated and difficult to determine4 ,wells near a river1 and drawing their water largely from it by seepage1 are apt to yield a water containing iron sooner or later1 especially where the river-water carries a large amount of organic matter in solution4 ,waters drawn from extensive gravel deposits1 in which the water is renewed principally by the rainfall upon the surface of the deposits themselves1 often remain entirely free from iron indefinitely4 ,the rain-water is almost free from organic matter1 and the air is able to take care of decomposing organic matters in the surface soil1 and below this there are no accumulations of organic matter sufficient to cause the solution of iron4 ,under other conditions there are subterranean sources of organic matter which result in the solution of iron under conditions which1 on the surface1 appear most favorable for securing good water4 ,wells are often used for many years without developing iron1 when suddenly iron will appear4 ,this appearance of iron is often connected with increasing consumption of water4 ,in some cases it may result from drawing water from areas not previously drawn upon4 ,when iron once makes its appearance in a water1 it seldom disappears completely afterward1 although it often fluctuates widely at different seasons of the year and under different conditions of pumping4 ,in some cases a decrease in the quantity of iron is noted after a number of years1 but in other cases this does not happen4 ,in a few cases manganese has been found in ground-waters4 ,manganese in water behaves much like iron1 but there are some points of difference1 so that the possibility of the presence of this substance should be borne in mind4 ,iron-containing waters are generally entirely free from oxygen1 and when first drawn from the ground they are bright and clear and do not differ in appearance from other ground-waters4 ,on exposure to the air they quickly become turbid from the oxidation of the iron1 and its precipitation as ferric hydrate4 ,at ,west ,superior1 ,wisconsin1 a water was found containing both iron and dissolved oxygen4 ,it was turbid as pumped from the well4 ,this condition of affairs seemed abnormal1 but was repeatedly checked1 and the theory was advanced by ,mr4 ,r4 ,s4 ,weston1 who made the observations1 that it resulted from a mixture in the wells of two entirely different waters1 namely1 a water resulting from the rainfall on sand deposits back of the wells1 containing dissolved oxygen and no iron1 and water from the lake which had seeped through the sand1 and which contained a considerable amount of iron in solution but no dissolved oxygen4 ,the wells thus drew water from opposite directions1 and the two waters were entirely different in character1 and the mixture thus had a composition which would not have been possible in a water all of which came from a single source4 ,,treatment ,,of ,,iron-,,containing ,,waters4 ,the removal of iron from ground-water is ordinarily a very simple procedure4 ,it is simply necessary to aerate the water1 by which process the ferrous carbonate is decomposed1 and oxidized with the formation of ferric hydrate1 which forms a flocculent precipitate and is readily removed by filtration4 ,the aeration required varies in different cases4 ,the quantity of oxygen required to oxidize the iron is only a small fraction of the amount which water will dissolve1 and allowing water to simply fall through the air for a few feet in fine streams will usually supply several times as much oxygen as is necessary for this purpose4 ,aerating devices of this kind have proved sufficient in a number of cases1 as at ,far ,rockaway1 ,l4 ,i41 and at ,red ,bank1 ,n4 ,j4 ,in some cases1 however1 a further aeration is necessary1 not for the purpose of getting more oxygen into the water1 but to get the excess of carbonic acid out of it4 ,carbonic acid seems to retard in some way the oxidation of the iron1 and it is occasionally present in ground-waters in considerable quantity1 and quite seriously interferes with the process4 ,it can be removed sufficiently by aeration1 but the necessary amount of exposure to air is much greater than that required to simply introduce oxygen4 ,coke-towers have sometimes been used for this purpose4 ,the towers are filled with coarse coke and have open sides1 and water is sprinkled over the tops of them and allowed to drip through to the bottoms4 ,in general the simple exposure of water to the air for a sufficient length of time1 in any form of apparatus or simply in open channels1 will accomplish the desired results4 ,mr4 ,h4 ,w4 ,clark#de has called attention to the fact that in some cases coke seems to have a direct chemical action upon the water which is entirely independent of its aerating effect4 ,in his experiments there seemed to be some property in the coke which caused the iron to oxidize and flocculate in many cases when it refused to do so with simple aeration and filtration4 ,when the right conditions are reached the oxidation of the iron is very rapid1 and it separates out in flakes of such size that they can be removed by filtration at almost any practicable rate4 ,mechanical filters have been used for this purpose1 with rates of filtration of #ajj million gallons per acre daily4 ,in ,germany1 where plants for the removal of iron are quite common1 modified forms of sand filters have usually been employed which have been operated at rates up to #be million gallons per acre daily4 ,in experiments made by the ,massachusetts ,state ,board of ,health rates from #aj to #be million gallons per acre daily have been employed4 ,the sand used for filtration may appropriately be somewhat coarser than would be used for treating surface-waters1 and the thickness of the sand layer may be reduced4 ,owing to the higher rates the underdrainage system must be more ample than is otherwise necessary4 ,the rate of filtration employed is usually not a matter of vital importance1 but by selecting a rate that is not too high it is possible to use a moderate loss of head4 ,it is thus not necessary to clean the filters too often1 and the expenses of operation are not as high as with an extreme rate4 ,in some cases it is desired to accomplish other results than the removal of iron by filtration1 and this may lead to the selection of a rate lower than would otherwise be used4 ,under normal conditions of operation all of the iron separates on the top of the sand4 ,no appreciable amount of it penetrates the sand at all4 ,with open filters at ,far ,rockaway and at ,red ,bank there is an alg growth in the water upon the filters which1 with the iron1 forms a mat upon the surface of the filter2 and when the filter is put out of service and allowed to partially dry1 this mat can be rolled up like a carpet and thrown off without removing any sand1 and the filters have been in use for several years without renewing any sand and without any important decrease in the thickness of the sand layer4 ,some waters contain iron in such a form that it cannot be successfully removed in this manner4 ,thus at ,reading1 ,mass41 it was reported by ,dr4 ,thomas ,m4 ,drown that the iron was present in the form of ferrous sulphate instead of ferrous carbonate1 and that it was not capable of being separated by simple aeration and filtration4 ,a ,warren mechanical filter was installed1 and the water is treated by aeration and with the addition of lime and alum4 ,the cost of the process is thereby much increased1 and the hardness of the water is increased threefold4 ,several other cases have been reported where it was believed that simple aeration and filtration were inadequate2 but the advantages of the simple procedure are so great as to make it worth a very careful study to determine if more complete aeration1 or the use of coke-towers and perhaps slower filtration1 would not serve in these cases without resorting to the use of chemicals and their attendant disadvantages4 ,,iron-,,removal ,,plants ,,in ,,operation4 ,iron-removal plants are now in use at ,amsterdam and ,the ,hague in ,holland1 at ,copenhagen in ,denmark1 at ,kiel1 ,charlottenburg1 ,leipzig1 ,halle1 and many other places in ,germany2 at ,reading1 ,mass42 ,far ,rockaway1 ,l4 ,i42 ,red ,bank1 ,asbury ,park1 ,atlantic ,highlands1 and ,keyport1 ,n4 ,j4 ,among the earliest plants for the removal of iron were the filters constructed at ,amsterdam and ,the ,hague in ,holland4 ,at ,amsterdam the water is derived from open canals in the dunes draining a large area4 ,the water has its origin in the rain-water falling upon the sand4 ,the sand is very fine and contains organic matter in sufficient amount so that the ground-water is impregnated with iron4 ,in flowing to a central point in the open canals the water becomes aerated and the iron oxidized4 ,there are also alg growths in the water which perhaps aid the process4 ,sand filters of ordinary construction are used1 and remove both the iron and the alg1 and the rate of filtration is not higher than is usually used in the treatment of river-waters1 although it could probably be largely increased without detriment to the supply4 ,the works at ,the ,hague are very similar to those at ,amsterdam1 but covered collectors are used to supplement the open canals4 ,both of these plants were built before much was known about iron in ground-waters and the means for its removal1 but they have performed their work with uniformly satisfactory results4 ,in the more recent ,german works various aerating devices are employed1 and filters similar in general construction to ordinary sand filters1 but with larger connections suited to very high rates of filtration1 are employed4 ,the plant at ,asbury ,park was the first of importance constructed in ,america4 ,the water is raised from wells from #djj to #aajj feet deep by compressed air by a ,pohle lift4 ,it is delivered into a square masonry receiving-basin holding some hours' supply4 ,the aeration of the water by this means is very complete4 ,it is afterwards pumped through ,continental pressure filters direct into the service-pipes4 ,the reservoir for the aerated water was not a part of the original plant1 but was added afterwards to facilitate operation1 and to give more complete aeration before filtration4 ,at ,far ,rockaway1 ,l4 ,i41 the water is lifted from wells by a ,worthington ,pump1 and is discharged over the bell of a vertical #af-;inch pipe1 from which it falls through the air to the water in a receiving chamber around it4 ,the simple fall through the air aerates the water sufficiently4 ,from the receiving-chamber the water is taken to either or both of two filters1 each with an area of #bj1jjj square feet4 ,these filters are open1 with brick walls and concrete bottoms1 three feet of sand and one foot of gravel1 and the underdrains are of the usual type4 ,the water flows through regulator-chambers to a well #be feet in diameter and #ab feet deep1 from which it is pumped to a stand-pipe in the town4 ,the plant was built to treat easily three million gallons per day1 and has occasionally treated a larger quantity4 ,either filter yields the whole supply while the other is being cleaned4 ,the rate of filtration in this case was made lower than would have otherwise been necessary1 as there was an alternate supply1 namely1 the water from two brooks1 which could be used on occasions1 and to purify which a lower rate of filtration was regarded necessary1 than would have been required for the well-water4 ,the removal of iron is complete4 ,illustration3 ,,fig4 #be4 ,the plant of the ,rumson ,improvement ,company at ,red ,bank1 ,n4 ,j41 is quite similar to that at ,far ,rockaway1 but is much smaller4 ,the outlet is a #f-;inch pipe perforated with #a_/d-;inch holes which throws the water out in a pine-tree shape to the receiving-tank1 thoroughly aerating it4 ,each of the two filters has #ggj square feet of area4 ,the filtering material is three feet of beach sand4 ,from the regulator-chamber the water flows to a circular well #ah feet in diameter1 covered by a brick dome and holding #ag1jjj gallons1 from which it is pumped to the stand-pipe4 ,either of the filters will treat ten thousand gallons of water per hour1 which is equal to the capacity of the pumps2 and as the consumption is considerably less than this figure1 they are only in use for a part of each day1 the number of hours depending upon the consumption4 ,these filters are shown by the accompanying plan4 ,the cost of the work was as follows3 ,filters and pure-water reservoir1 with piping and drains complete #c1gii4dg ,new pump and connections #dib4fh ,engineering and superintendence #iib4ia --------- ,total cost of plant #e1bhe4jf ,the engineer who operates the pumps takes care of the filters1 and no additional labor has been required4 ,the entire cost of operation is thus represented by the additional coal required for the preliminary lift from the wells to the filters4 ,the effluent is always free from iron4 ,the plant at ,reading1#df ,mass41 was installed by the ,cumberland ,manufacturing ,company1 and combines aeration1 treatment with lime and sulphate of alumina and rapid filtration4 ,the aeration is effected by pumping air through the water1 after the water has received the lime4 ,it afterwards receives sulphate of alumina and passes to a settling-tank holding #dj1jjj gallons1 in which the water remains for about an hour4 ,there are six filters of the ,warren type1 each with an effective filtering area of #ed square feet4 ,the cost of coagulant is considerable4 ,the chief disadvantage of the process is that it hardens the water1 which is naturally soft4 ,from the completion of the plant in ,july1 #ahif1 to the end of the year the hardness of the water was increased1 according to analyses of the ,state ,board of ,health1 from #d4a to #aa4c parts in #ajj1jjj1 and for the year #ahig the increase was from #d4j to #ab4g4 ,the iron1 which is present in the raw water to the extent of about #j4bf part in #ajj1jjj1 is removed sufficiently at all times4 ,prior to the erection of this plant ,mr4 ,desmond ,fitz,gerald advised aeration followed by sedimentation in two reservoirs holding half a million gallons each1 and by rapid filtration4 ,mr4 ,bancroft states that in his opinion1 if the reservoir recommended by ,mr4 ,fitz,gerald had been built1 the filters could be run with very little or no coagulation1 and consequently without increase in hardness1 which is the most obvious disadvantage to the procedure4 ,the nominal capacity of the plant is one million gallons1 and the average consumption about #bjj1jjj gallons daily4 ,the plant at ,keyport1 ,n4 ,j41 is similar1 but smaller4 ,,chapter ,,xiii4 ,,treatment ,,of ,,waters4 ,having now reviewed the most important methods in use for the treatment of waters1 we may take a general view of their application to various classes of waters4 ,different raw waters vary so much1 and the requirements of filtration are so different1 that it is not possible to outline any general procedure or combination of procedures1 but each problem must be taken up by itself4 ,nevertheless1 some general suggestions may be of service4 ,in the first place1 we may consider the case of waters containing very large quantities of oxidizable organic matter4 ,such waters are obtained from some reservoirs containing very active vegetable and animal growths1 or from rivers receiving large amounts of sewage4 ,waters of both of these classes are1 if possible1 to be avoided for public water-supplies4 ,when circumstances require their use1 they can best be treated by intermittent filtration1 this process being best adapted to the destruction by oxygen of excessive quantities of organic matter4 ,where the pollution is less1 so that the dissolved oxygen contained in the raw water is sufficient for the oxidation of the organic matters1 continuous filtration will give substantially as good results as intermittent filtration1 and in other respects it has important advantages4 ,the application of intermittent filtration for the treatment of public water-supplies is thus somewhat limited1 and1 as a matter of fact1 it has been used in only a few cases4 ,for the treatment of very highly polluted waters double filtration has been used in a number of cases1 notably by the ,grand ,junction ,company at ,london1 at ,schiedam in ,holland1 and at ,bremen and ,altona in ,germany4 ,at the two first-mentioned places two separate systems of filters are provided differing somewhat in construction1 the first filters being at a higher level than the after filters4 ,the first filters supply water of comparative purity1 and very constant composition1 to the after filters1 which are able to treat it with great efficiency and at very low operating cost4 ,this procedure is probably the most perfect which has been used for the removal of disease-producing qualities from highly polluted waters2 and the cost of the process may not be as much greater than that of simple filtration as would at first appear1 because the cost of cleaning the after filters is merely nominal1 and the attendance1 pumping1 etc41 are practically common to both sets of filters1 and are not materially greater than they would be for a single set4 ,for very bad waters the first filters might appropriately be intermittent1 while the after filters should be continuous4 ,this was the procedure originally intended for ,lawrence1 but the intermittent filter first constructed yielded such very good results that it has not been considered necessary to complete the plant as originally projected4 ,at ,bremen and at ,altona a different procedure has been adopted4 ,the filters are all upon the same level1 and of the same construction4 ,when a filter is put in service the effluent from it1 instead of being taken to the pure-water reservoir1 is taken to another filter which has already been some time in service4 ,after the first filter has been in operation for some time its effluent is taken to the pure-water reservoir1 and in turn it is supplied with the effluent from a filter more recently cleaned4 ,the loss of head of water passing a freshly cleaned filter is comparatively slight1 and the water of the second filter is allowed to fall a few inches below the high-water mark1 at which level it will take the effluent from the other filter4 ,the connections between the filters are made by siphons of large pipe1 the summits of which are considerably above the high-water line4 ,these siphons are filled by exhausting the air1 and when opened to the air there is no possibility of a flow of water through them4 ,the process has given extremely good results in practice1 yielding effluents of the very greatest purity and at a quite moderate cost of operation4 ,an objection to the method is the possible filling of a siphon some time when the water standing upon the after-filter is higher than that in the pure-water well of the fore-filter1 and while the fore-filter is connected with the pure-water reservoir4 ,such a connection would send unfiltered water into the pure-water reservoir direct4 ,i do not know that any trouble of this kind has ever been experienced at ,bremen or at ,altona2 and the objection to this system is perhaps not well founded where the management is careful and conscientious4 ,the fact that an unscrupulous attendant can make the connection at any time to help out a deficiency of supply1 or simply through carelessness1 is certainly objectionable4 ,for the treatment of river-waters and lake-waters containing only a small quantity of sediment1 and where the removal of bacteria or disease-producing qualities is the most important object of filtration1 sand filters can be used4 ,where the rivers are subject to floods and moderate amounts of muddy water1 sedimentation-basins or storage reservoirs for raw water will often be found advantageous4 ,for the treatment of extremely muddy waters1 and waters which are continuously muddy for long periods of time1 and for the removal of color from very highly colored waters1 resource must be had to coagulants4 ,the coagulants which are necessary in each special case and which can be used without injury to the water must be determined by most careful investigation of the raw water4 ,for the filtration of these waters after coagulation either sand or mechanical filters can be employed4 ,as the principal work in this case is done by the coagulant1 the kind of filtration employed is of less consequence than where filtration alone is relied upon1 and the cheapest form of filter will naturally be employed4 ,under present conditions mechanical filters will usually be cheaper than sand filters for use in this way2 but where waters1 in addition to the mud1 carry bacteria in such large numbers as to make high bacterial efficiency a matter of importance1 sand filters may be selected1 as the bacterial efficiency obtained with them is not dependent upon the use of coagulant2 and is therefore less subject to interruptions from the failure to apply coagulant in the right proportion4 ,mechanical filters have also been used for the treatment of comparatively clear waters where bacterial efficiency was the principal object of filtration4 ,for this purpose the efficiencies obtained with them are usually inferior to those obtained with sand filters1 while the cost of coagulants is so great as to make their use often more expensive than that of sand filters4 ,in the case of many streams which are comparatively clear for a part of the year1 but occasionally are quite turbid1 the use of sand filters has this advantage1 that the use of coagulants can be stopped and the cost of operation reduced whenever the water is clear enough to allow of satisfactory treatment by them2 and that coagulant can be employed on those days when otherwise insufficient clarification would be obtained4 ,in this case the high bacterial efficiency is secured at all times1 while the cost of coagulant is saved during the greater part of the time4 ,in such cases1 also1 the preliminary process of sedimentation and storage should be developed as far as possible4 ,the application of other processes of filtration to special problems are not sufficiently well understood to allow general discussion1 and must be taken up separately with reference to the requirements of each special situation4 ,,cost ,,of ,,filtration4 ,the cost of filtration of water depends upon the character of the raw water1 upon the nature of the plant employed1 upon its size1 and upon the skill and economy of manipulation4 ,these conditions affect the cost to such an extent as to make any accurate general estimate quite impossible4 ,nevertheless a little consideration of the subject1 although not leading to exact results1 may be helpful as furnishing a rough idea of the probable cost before estimates for local conditions are made4 ,open sand filters1 with masonry walls1 with reasonably favorable conditions of construction1 and not too small in area1 have averaged to cost in the ,united ,states within the last few years perhaps about thirty thousand dollars per acre4 ,the relative cost of small plants is somewhat greater1 and with embankments instead of masonry walls1 the cost is somewhat reduced4 ,the cost is less where natural deposits of sand can be made use of practically in their original condition1 and is increased where the filtering materials have to be transported by rail for long distances1 or where the sites are difficult to build upon4 ,covered filters cost about a half more than open filters4 ,mechanical filters at current prices cost about #bj per square foot of filtering area1 to which must be added the cost of foundations and buildings1 which perhaps average to cost half as much more1 but are dependent upon local conditions and the character of the buildings4 ,to these figures must be added the costs of pumps1 reservoirs1 sedimentation-basins1 and pipe-connections1 which are often greater than the costs of the filters1 but which differ so widely in different cases as to make any general estimate impossible4 ,filters must be provided sufficient to meet the maximum and not the average consumption4 ,the excess of maximum over average requirements varies greatly in different cities1 and depends largely upon reservoir capacities and arrangements4 ,as a result of a considerable number of estimates made by the author for average ,american conditions1 the cost of installing filters may be taken very roughly as five dollars per inhabitant1 but the amounts differ widely in various cases4 ,the cost of operation of sand filters in ,england probably averages about one dollar per million gallons of water filtered4 ,the following table shows the costs of operation of the filters of the seven ,london companies for fifteen years1 compiled in the office of ,mr4 ,w4 ,b4 ,bryan1 ,chief ,engineer of the ,east ,london ,water ,company4 ,the results have been computed to dollars per million ,u4 ,s4 gallons1 and include the cost of all labor1 sand1 and supplies for the filters1 but do not include any pumping or interest costs4 ,,cost ,,of ,,filtration1 ,,london ,,water ,,companies4 7,computed from data furnished ,wm4 ,b4 ,bryan1 ,c4,e41 ,east ,london ,water ,works47 ,dollars per ,million ,u4 ,s4 ,gallons4 ---------------------------------------- --------------------------- ,east ,grand ,new ,southwark ,west ,chelsea,london,junction,lambeth,river ,middlesex,average4 ,co4 ,co4 ,co4 ,co4 ,co4 ,vauxhall ,co4 ,co4 ---------------------------------------- --------------------------- #ahhj-a #a4af #a4af #a4jj #j4hc #a4cd #a4af #a4fg #a4ai #ahha-b #a4ai #a4ci #j4ie #j4hb #a4ae #a4cg #a4ed #a4bj #ahhb-c #a4aj #a4bc #a4ci #j4if #a4dj #a4dg #a4gd #a4cc #ahhc-d #a4jj #a4jf #a4gc #j4ib #a4aa #a4fb #a4fg #a4cj #ahhd-e #a4jf #a4jf #a4hb #j4ij #a4jb #a4dj #a4cj #a4bb #ahhe-f #a4ae #a4af #a4ce #j4ij #a4jj #a4ae #a4jg #a4aa #ahhf-g #j4hj #j4if #a4ci #j4hg #j4ih #a4dc #a4gj #a4af #ahhg-h #a4jg #a4bb #a4gd #j4ij #j4ib #a4bh #a4jj #a4af #ahhh-i #j4hc #a4bh #a4ee #j4ie #j4ih #a4eb #j4hc #a4ac #ahhi-ij #j4ff #a4ej #a4bb #j4hh #j4ij #a4gj #c4ef #a4di #ahij-a #j4gb #a4db #a4cb #j4he #a4jb #a4af #a4jj #a4jg #ahia-b #j4ge #a4ed #a4bc #a4jj #j4ib #a4ae #j4if #a4jh #ahib-c #j4fg #a4db #a4cj #a4ai #a4af #a4bf #a4db #a4bj #ahic-d #a4ae #b4fc #b4jj #a4df #a4dc #a4eb #j4ie #a4ei #ahid-e #j4fj #a4fh #a4fg #b4ec #a4jc #a4cd #j4if #a4dj ---------------------------------------- --------------------------- ,average #j4ic #a4ch #a4dd #a4jf #a4ji #a4cg #a4dc #a4bd ---------------------------------------- --------------------------- ,average of seven companies for #ae years1 #a4bd per million gallons4 ,variations from year to year are caused by differences in the amounts of ice1 and in the quantities of new sand purchased4 ,wages average about #a4jj per day4 ,at ,liverpool for #ahif the cost was #a4jh per million ,u4 ,s4 gallons4 ,in ,germany1 with more turbid river-waters1 the costs of operation are somewhat higher than the ,london figures1 while at ,zrich1 where the water is very clear1 they are lower4 ,in the ,united ,states the data regarding the cost of operation of sand filters are less complete4 ,at ,mt4 ,vernon1 ,n4 ,y41 with reservoir-water1 the cost has averaged about two dollars per million gallons4 ,at ,poughkeepsie1 ,n4 ,y41 with the ,hudson ,river water1 which is occasionally moderately turbid1 the cost for twenty years has averaged three dollars per million gallons4 ,this cost includes the cost of handling ice1 and as the average winter temperature is considerably below that suggested for open filters1 the expense of this work has been considerable1 and has increased considerably the total cost of operation4 ,at ,far ,rockaway1 ,l4 ,i41 and ,red ,bank ,n4 ,j41 for iron-removal plants1 the cost of operation has hardly been appreciable4 ,the plants are both close to the pumping-stations1 and it has been possible to operate them with the labor necessarily engaged at the pumping-station without additional cost1 except a very small amount of labor on the sand at ,far ,rockaway4 ,no computation has been made in these cases of the additional coal required for pumping4 ,at ,lawrence1 ,mass41 the cost of operation for #ahie was as follows3 ,cost of scraping and replacing sand #c1dfg ,cost of care of ice #b1ijc ------ ,total cost of operation #f1cgj ,water filtered1 millions of gallons #a1jig ,cost per million gallons #e4hj ,the cost of care of ice has been excessive at ,lawrence1 and it has been repeatedly recommended to cover the filter to avoid this expense4 ,the cost of handling sand has been very greatly increased1 because the filter is built in one bed1 and all work upon it has to be done during the comparatively short intervals when the filter is not in use1 an arrangement which is not at all economical in the use of labor4 ,the cost of operation is thus much higher than it would be had the plant been constructed in several units1 each of which could be disconnected for the purpose of being cleaned in the ordinary manner4 ,as against this the first cost of construction was extremely low1 and the saving in interest charges should be credited against the increased cost of labor in cleaning4 ,the cost of operating filters at ,ashland1 ,wis41 has been estimated by ,mr4 ,william ,wheeler at #b4bf per million gallons4 ,this estimate is based upon the performance for the first year that they were in service4 ,in the operation of mechanical filters one of the largest items of expense is for the coagulant1 and the amount of this depends entirely upon the character of the raw water and the thoroughness of the treatment required4 ,the data regarding the other or general costs of operation of mechanical filters are few and unsatisfactory4 ,i recently made some estimates of cost of clarifying waters of various degrees of turbidity by sand and mechanical filters4 ,these estimates were made for a special set of conditions1 and ,i do not know that they will fit others1 but they have at least a suggestive value4 ,the results shown by ,fig4 #bf include only the cost of operation1 and not interest and depreciation charges4 ,these figures1 when used for plants in connection with which preliminary treatments are used1 should be applied to the turbidity of the water as applied to the filters1 and not to the raw water1 and the costs of the preliminary processes should be added4 ,with sand filters the frequency of scraping is nearly proportional to the turbidity2 and as scraping represents most of the expenses1 the costs of operation are proportional to the turbidity1 except the general costs1 and the cost of the amount of scraping1 which is necessary with even the clearest waters4 ,with mechanical filters the amount of sulphate of alumina required for clarification increases with the turbidity1 and most of the costs of operation increase in the same ratio4 ,the diagram shows the amount of sulphate of alumina in grains per gallon necessary for clarification with different degrees of turbidity4 ,with the clearest waters the costs of operation on the two systems are substantially equal4 ,with muddy waters1 the expense of operating sand filters increases more rapidly than the expense of operating mechanical filters4 ,illustration3 ,,turbidity ,,fig4 #bf4--;,,cost ,,of ,,operation ,,of ,,filters4 ,there is another element which often comes into the comparison1 namely1 the question of purification from the effects of sewage-pollution4 ,nearly all rivers used for public water-supplies receive more or less sewage1 and in filtering such waters it is regarded as necessary to remove as completely as possible the bacteria4 ,the quantities of sulphate of alumina required for the clarification of the least turbid waters are not sufficient to give even tolerably good bacterial efficiencies4 ,to secure a reasonably complete removal of bacteria with mechanical filters1 the use of a considerable quantity of sulphate of alumina is required4 ,let us assume that #ih per cent bacterial efficiency is required1 and that to produce this efficiency it is necessary to use one grain of coagulant to the gallon4 ,with water requiring less than this quantity of coagulant for clarification this quantity must nevertheless be used1 and the costs will be controlled by it1 and not by the lower quantities which would suffice for clarification1 but would not give the required bacterial efficiency4 ,i have added this line to the diagram1 and this1 combined with the upper portion of the line showing cost of clarification1 represents the cost of treating waters with mechanical filters1 where both bacterial efficiency and clarification are required4 ,this line1 considered as a whole1 increases much less rapidly with increasing turbidity than does the corresponding line for sand filters1 and the two lines cross each other4 ,with the clearest waters sand filters are cheaper than mechanical filters1 and for the muddiest waters they are more expensive4 ,it does not appear from the diagram1 but it is also true in each case1 that the cheaper system is also the more efficient4 ,sand filters are more efficient in removing bacteria from clear waters than are mechanical filters1 and mechanical filters are more efficient in clarifying very muddy waters than are sand filters4 ,,what ,,waters ,,require ,,filtration8 ,from the nature of the case a satisfactory general answer to this question cannot be given1 but a few suggestions may be useful4 ,in the first place1 ground-waters obviously do not require filtration3 they have already in most cases been thoroughly filtered in the ground through which they have passed1 and in the exceptional cases1 as1 for instance1 an artesian well drawing water through fissures in a ledge from a polluted origin1 a new supply will generally be chosen rather than to attempt to improve so doubtful a raw material4 ,river-waters should be filtered4 ,it cannot be asserted that there are no rivers in mountainous districts in which the water is at once clear and free from pollution1 and suitable in its natural state for water-supply2 but if so1 they are not common1 least of all in the regions where water-supplies are usually required4 ,the use of river-waters in their natural state or after sedimentation only1 drawn from such rivers as the ,merrimac1 ,hudson1 ,potomac1 ,delaware1 ,schuylkill1 ,ohio1 and ,mississippi1 is a filthy as well as an unhealthy practice1 which ought to be abandoned4 ,the question is more difficult in the case of supplies drawn from lakes or storage reservoirs4 ,many such supplies are grossly polluted and should be either abandoned or filtered4 ,others are subject to alg growths1 or are muddy1 and would be much improved by filtration4 ,still others are drawn either from unpolluted water-sheds1 or the pollution is so greatly diluted and reduced by storage that no known disadvantage results from their use4 ,in measuring the effects of the pollution of water-supplies1 the typhoid-fever death-rate is a most important aid4 ,not that typhoid fever is the sole evil resulting from polluted water1 but because it is also a very useful index of other evils for which corresponding statistics cannot be obtained1 as1 for instance1 the causation of diarrhal diseases or the danger from invasion by cholera4 ,i think we shall not go far wrong at the start to confine our attention to those cities where there are over #be deaths from typhoid fever per #ajj1jjj of population4 ,this will at once throw out of consideration a large number of relatively good supplies1 including those of ,new ,york and ,brooklyn4 ,it is not my idea that none of these supplies cause disease4 ,many of them1 as for instance that of ,new ,york1 are known to receive sewage1 and it is an interesting question worthy of most careful study whether there are cases of sickness resulting from this pollution4 ,the point that ,i wish to make now is simply that in those cases the death-rate itself is evidence that1 with existing conditions of dilution and storage1 the resulting damage of which we have knowledge is not great enough to justify the expense involved by filtration4 ,in this connection it should not be forgotten that1 especially with very small watersheds1 there may be a danger as distinct from present damage which requires consideration4 ,thus a single house or groups of houses draining into a supply may not appreciably affect it for years1 until an outbreak of fever on the water-shed results in infecting the water with the germs of disease and in an epidemic in the city below4 ,this danger decreases with increasing size of the water-shed and volume of the water with which any such pollution would be mixed1 and also with the population draining into the water1 as there is a probability that the amount of infection continually added from a considerable town will not be subject to as violent fluctuation as that from only a few houses4 ,thus in ,plymouth1 ,pa41 in #ahhe1 there were #aajd cases of typhoid fever and #aad deaths among a population of #hjjj1 as the result of the discharge of the dejecta from a single typhoid patient into the water of a relatively small impounding reservoir4 ,the cost of this epidemic was calculated with unusual care4 ,the care of the sick cost in cash #fg1ajj4ag1 and the loss of wages for those who recovered amounted to #cj1jbj4jh4 ,the #aad persons who died were earning before their sickness at the rate of #ah1dai4eb annually4 ,such an outbreak would hardly be possible with the ,croton water-shed of the ,new ,york water-supply1 on account of the great dilution and delay in the reservoirs1 but it must be guarded against in small supplies4 ,of the cities having more than #be deaths per #ajj1jjj from typhoid fever1 some will no doubt be found where milk epidemics or other special circumstances were the cause2 but ,i believe in a majority of them1 and in nearly all cases where the rate is year after year considerably above that figure1 the cause will be found in the water-supply4 ,investigation should be made of this point2 and if the water is not at fault1 the responsibility should be located4 ,if the water is guilty1 it should be either purified or a new supply obtained4 ,,chapter ,,xiv4 ,,water-,,supply ,,and ,,disease--,,conclusions4 ,one of the most characteristic and uniform results of the direct pollution of public water-supplies is the typhoid fever which results among the users of the water4 ,in the ,english and ,german cities with almost uniformly good drinking-water1 typhoid fever is already nearly exterminated1 and is decreasing from year to year4 ,american cities having unpolluted water-supplies have comparatively few deaths from this cause1 although the figures never go so low as in ,europe1 perhaps on account of the fresh cases which are always coming in from less healthy neighborhoods in ever-moving ,american communities4 ,in other ,american cities the death-rates from typhoid fever are many times what they ought to be and what they actually are in other cities1 and the rates in various places1 and in the same place at different times1 bear in general a close relation to the extent of the pollution of the drinking-water4 ,the power of suitable filtration to protect a city from typhoid fever is amply shown by the very low death-rates from this cause in ,london1 ,berlin1 ,breslau1 and large numbers of other cities drawing their raw water from sources more contaminated than those of any but the very worst ,american supplies1 and by the marked and great reductions in the typhoid-fever death rates which have followed at once the installation of filters at ,zrich1 ,switzerland2 ,hamburg1 ,germany2 ,lawrence1 ,mass41 and other places4 ,the following is a list of the cities of #ej1jjj inhabitants and upward in the ,united ,states1 with deaths from typhoid fever and the sources of their water-supplies4 ,the deaths and populations are from the ,u4 ,s4 ,census for #ahij2 the sources of the water-supplies1 from the ,american ,water-,works ,manual for the same year4 ,four cities of this size--,grand ,rapids1 ,lincoln1 ,st4 ,joseph1 and ,des ,moines--are not included in the census returns of mortality4 ,two cities with less than #ej1jjj inhabitants with exceptionally high death-rates have been included1 and at the foot of the list are given corresponding data for some large ,european cities for #ahic4 ,,typhoid ,,fever ,,death-,,rates ,,and ,,water-,,supplies ,,of ,,cities4 ---------------------------------------- --------------------------- ,deaths from ,typhoid ,fever4 ,city4 ,population4------------- ,water-supply4 ,per ,total4#ajj1jjj living4 ---------------------------------------- -------------------------- ,birmingham #bf1agh #fi #bfd ,five ,mile ,creek #a4 ,denver #ajf1gac #bcb #bag ,north ,platte ,river and wells #b4 ,allegheny #aje1bhg #aib #ahb ,allegheny ,river #c4 ,camden #eh1cac #gg #acb ,delaware ,river #d4 ,pittsburg #bch1fag #cjd #abg ,allegheny and ,monongahela rivers ,lawrence #dd1fed #ed #aba ,merrimac ,river #e4 ,newark #aha1hcj #aha #ajj ,passaic ,river #f4 ,charleston #ed1iee #ed #ih ,artesian wells yielding #a1fjj1jjj gallons daily #g4 ,washington #bcj1cib #bjj #hg ,potomac ,river #h4 ,lowell #gg1fif #fd #hb ,merrimac ,river #i4 ,jersey ,city #afc1jjc #acd #hb ,passaic ,river #aj4 ,louisville #afa1abi #abb #gf ,ohio ,river #aa4 ,philadelphia #a1jdf1ifd #ggj #gd ,delaware and ,schuylkill rivers #ab4 ,chicago #a1jii1hej #gid #gb ,lake ,michigan #ac4 ,atlanta #fe1ecc #dg #gb ,south ,river #ad4 ,albany #id1ibc #fg #ga ,hudson ,river #ae4 ,wilmington #fa1dca #dc #gj ,brandywine ,creek #af4 ,st4 ,paul #acc1aef #ib #fi ,lakes #ag4 ,troy #fj1ief #db #fi ,hudson ,river and impounding reservoirs #ah4 ,los ,angeles #ej1cie #cd #fg ,los ,angeles ,river and springs #ai4 ,nashville #gf1afh #di #fd ,cumberland ,river #bj4 ,cleveland #bfa1cec #afd #fc ,lake ,erie #ba4 ,richmond #ha1chh #ej #fa ,james ,river #bb4 ,hartford #ec1bcj #cb #fj ,connecticut ,river and impounding reservoir #bc4 ,fall ,river #gd1cih #dd #ei ,watupa ,lake #bd4 ,minneapolis #afd1gch #id #eg ,mississippi ,river #be4 ,san ,francisco #bih1iig #aff #ef ,lobus ,creek1 ,lake ,merced1 and mountain streams #bf4 ,indianapolis #aje1dcf #eg #ed ,white ,river #bg4 ,cincinnati #bif1ijh #aea #ea ,ohio ,river #bh4 ,memphis #fd1die #cc #ea ,artesian ,wells #bi4 ,reading #eh1ffa #bi #di ,maiden ,creek and ,springs #cj4 ,baltimore #dcd1dci #bjb #dg ,impounding reservoir #ca4 ,omaha #adj1deb #fc #de ,missouri ,river #cb4 ,columbus #hh1aej #ch #dc ,surface-water and wells #cc4 ,providence #acb1adf #ec #dj ,pawtuxet ,river #cd4 ,kansas ,city #acb1gaf #ec #dj ,missouri ,river #ce4 ,rochester #acc1hif #ec #ci ,hemlock and ,candice lakes #cf4 ,evansville #ej1gef #bj #ci ,ohio ,river #cg4 ,boston #ddh1dgg #agd #ci ,impounding reservoirs #ch4 ,toledo #ha1dcd #bi #cf ,maumee ,river #ci4 ,cambridge #gj1jbh #bd #cd ,impounding reservoir #dj4 ,st4 ,louis #dea1ggj #ade #cb ,mississippi ,river #da4 ,scranton #ge1bae #bd #cb ,impounding reservoir #db4 ,buffalo #bee1ffd #hj #ca ,niagara ,river #dc4 ,milwaukee #bjd1dfh #fa #cj ,lake ,michigan #dd4 ,new ,haven #ha1bih #bb #bg ,impounding reservoir #de4 ,worcester #hd1fee #bb #bf ,impounding reservoir #df4 ,paterson #gh1cdg #bj #bf ,passaic ,river 7higher up7 #dg4 ,dayton #fa1bbj #ae #be ,wells #dh4 ,brooklyn #hjf1cdc #aid #bd ,wells1 ponds1 and impounding reservoirs #di4 ,new ,york #a1eae1cja #cdh #bc ,impounding reservoir #ej4 ,syracuse #hh1adc #ah #bj ,impounding reservoir and springs #ea4 ,new ,orleans #bdb1jci #de #ai ,mississippi ,river #eb4 ,detroit #bje1hgf #dj #ai ,detroit ,river #ec4 ,lynn #ee1gbg #i #af ,impounding reservoir #ed4 ,trenton #eg1deh #i #af ,delaware ,river ,london #d1cjf1daa #gai #ag ,filtered ,thames and ,lea rivers and #a_/d from wells ,glasgow #ffg1hhc #ach #bj ,loch ,katrine ,paris #b1dbd1gje #fji #be ,spring water ,amsterdam #dcg1hib #fi #af ,filtered dune-water ,rotterdam #bbb1bcc #ab #e ,filtered ,maas ,river ,hague #afi1hbh #c #b ,filtered dune-water ,berlin #a1gad1ich #afa #i ,filtered ,havel and ,spree rivers ,hamburg #fcd1hgh #aae #ah ,filtered ,elbe ,river ,breslau #cec1eea #cg #aa ,filtered ,oder ,river ,dresden #cjh1icj #ad #e ,ground-water ,vienna #a1dce1ica #ajd #g ,spring-water ---------------------------------------- -------------------------- ,any full discussion of these data would require intimate acquaintances with the various local conditions which it is impossible to take up in detail here1 but some of the leading facts cannot fail to be instructive4 ,each of the places having over #ajj deaths per #ajj1jjj from typhoid fever used unfiltered river-water4 ,lower in the list1 but still very high1 ,charleston1 said to have been supplied only from artesian wells1 had an excessive rate2 but the reported water-consumption is so low as to suggest that private wells or other means of supply were in common use4 ,chicago and ,cleveland both drew their water from lakes where they were contaminated by their own sewage4 ,st4 ,paul's supply came from ponds1 of which ,i do not know the character4 ,with these exceptions all of the #bb cities with over #ej1jjj inhabitants1 at the head of the list1 had unfiltered river-water4 ,the cities supplied from impounding reservoirs as a rule had lower death rates and are at the lower end of the list1 together with some cities taking their water supplies from rivers or lakes at points where they were subject to only smaller or more remote infection4 ,only three of the ,american cities in the list were reported as being supplied entirely with ground-water4 ,it is not my purpose to make too close comparisons between the various cities on the list2 some of them may have been influenced by unusual local conditions in #ahij4 ,others have in one way or another improved their water-supplies since that date1 and there are several cities in which ,i know the present typhoid-fever death-rates to be materially lower than those of #ahij given in the table4 ,on the other hand1 it is equally true that a number of cities1 including some of the larger ones1 have since had severe epidemics of typhoid fever which have given very much higher rates than those for #ahij4 ,these fluctuations would change the order of cities in the list from year to year2 they would not change the general facts1 which are as true to-day as they were in #ahij4 ,nearly all of the great cities of the ,united ,states are supplied with unfiltered surface-waters1 and a great majority of the waters are taken from rivers and lakes at points where they are polluted by sewage4 ,the death-rates from typhoid fever in those cities1 whether they are compared with better supplied cities of this country1 or with ,european cities1 are enormously high4 ,such rates were formerly common in ,european cities1 but they have disappeared with better sanitary conditions4 ,the introduction of filters has often worked marvellous changes in ,europe1 and in ,lawrence the improvement in the city's health with filtered water was prompt and unquestionable4 ,there is every reason to believe that the general introduction of better water in ,american cities will work corresponding revolutions2 and looking at it from a merely money standpoint1 the value of the lives and the saving of the expenses of sickness will pay handsomely when compared with the cost of good water4 ,the reasons for believing that cholera is caused by polluted water are entirely similar to those in the case of typhoid fever4 ,it was no accident that the epidemic of cholera which caused the death of #cdjj persons followed the temporary supply of unfiltered water by the ,east ,london ,water ,company in #ahff1 while the rest of ,london remained nearly free1 or that the only serious outbreak of cholera in ,western ,europe in #ahib was at ,hamburg1 which was also the only city in ,germany which used raw river-water4 ,this latter caused the sickness of #bj1jjj and the death of over #hjjj people within a month1 and an amount of suffering and financial loss1 with the panics which resulted1 that cannot be estimated1 but that exceeded many times the cost of the filters which have since been put in operation4 ,hamburg had several times before suffered severely from cholera1 and the removal of this danger was a leading1 although not the sole1 motive for the construction of filters4 ,how little cities supplied with pure water have to dread from cholera is shown by the experience of ,altona and other suburbs of ,hamburg with good water-supplies1 which had but few cases of cholera not directly brought from the latter place1 and by the experience of ,england1 which maintained uninterrupted commercial intercourse with the plague-stricken city1 absolutely without quarantine1 and1 notwithstanding a few cases which were directly imported1 the disease gained no foothold in ,england4 ,i do not know of a single modern ,european instance where a city with a good water-supply not directly infected by sewage has suffered severely from cholera4 ,i shall leave to others more familiar with the facts the discussion of what happened before the introduction of modern sanitary methods1 as well as of the present conditions in ,asia2 although ,i believe that in these cases also there is plenty of evidence as to the part water plays in the spread of the disease4 ,a considerable proportion of the water-supplies of the cities of the ,united ,states are so polluted that in case cholera should gain a foothold upon our shores we have no ground for hoping for the favorable experience of the ,english cities rather than the plague of ,hamburg in #ahib4 ,the fces from a man contain on an average perhaps #a1jjj1jjj1jjj bacteria per gram1#dg most of them being the normal bacilli of the intestines1 ,bacillus coli communis4 ,assuming that a man discharges #bjj grams or about #g ounces of fces daily1 this would give #bjj1jjj1jjj1jjj bacteria discharged daily per person4 ,the number of bacteria actually found in ,american sewage is usually higher1 often double this number per person2 but there are other sources of bacteria in sewage1 and in addition growths or the reverse may take place in the sewers1 according to circumstances4 ,this number of bacteria in sewage is so enormously large that the addition of the sewage from a village or city to even a large river is capable of affecting its entire bacterial composition4 ,thus taking the population of ,lowell in #ahib at #he1jjj1 and the average daily flow of the ,merrimac at #fjjj cubic feet per second1 and assuming that #bjj1jjj1jjj1jjj bacteria are discharged daily in the sewage from each person1 they would increase the number in the river by #aafj per cubic centimeter1 or about #cjj1jjj in an ordinary glass of water4 ,the average number found in the water eight miles below1 at the intake of the ,lawrence water-works1 was more than six times as great as this1 due in part to the sewage of other cities higher up4 ,there is every reason to believe that the bulk of these bacteria were harmless to the people of ,lawrence1 who drank them2 but some of them were not4 ,fces of people suffering from typhoid fever contain the germs of that disease4 ,what proportion of the total number of bacteria in such fces are injurious is not known2 but assuming that one fourth only of the total number are typhoid germs1 and supposing the fces of one man to be evenly mixed with the whole daily average flow of the river1 it would put one typhoid germ into every glass of water at the ,lawrence intake1 and at low water several times as many proportionately would be added4 ,this gives some conception of the dilution required to make a polluted water safe4 ,one often hears of the growth of disease-germs in water1 but as far as the northern ,united ,states and ,europe are concerned there is no evidence whatever that this ever takes place4 ,there are harmless forms of bacteria which are capable of growing upon less food than the disease-germs require and they often multiply in badly-polluted waters4 ,typhoid-fever germs live for a longer or shorter period1 and finally die without growth4 ,the few laboratory experiments which have seemed to show an increase of typhoid germs in water have been made under conditions so widely different from those of natural watercourses that they have no value4#dh ,the proportionate number of cases of typhoid fever among the users of a polluted water varies with the number of typhoid germs in the water4 ,excessive pollution causes severe epidemics or continued high death-rates according as the infection is continued or intermittent4 ,slight infection causes relatively few cases of fever4 ,pittsburg and ,allegheny1 taking their water-supplies from below the outlets of some of their own sewers1 have suffered severely 7#ajc4b and #abg4d deaths from typhoid fever annually per #ajj1jjj1 respectively1 from #ahhh to #ahib74 ,wheeling1 ,w4 ,va41 with similar conditions in #ahij1 was even worse1 a death rate of #cde per #ajj1jjj from this cause being reported1 while ,albany had only comparatively mild epidemics from the less directly and grossly polluted ,hudson4 ,lawrence and ,lowell1 taking their water from the ,merrimac1 both had for many years continued excessive rates1 increasing gradually with increasing pollution2 and the city having the most polluted source had the higher rate4 ,in ,berlin and ,altona1 in winter1 with open filters1 epidemics of typhoid fever followed decreased efficiency of filtration1 but the epidemics were often so mild that they would have entirely escaped observation under present ,american conditions4 ,chicago has for years suffered from typhoid fever1 and the rate has fluctuated1 as far as reliable information can be obtained1 with the fluctuations in the pollution of the lake water4 ,an unusual discharge of the ,chicago ,river results in a higher death-rate4 ,abandoning the shore inlet near the mouth of the ,chicago ,river in #ahib1 resulted in the following year in a reduction of #fj per cent in the typhoid fever death-rate4#di ,this reduction shows1 not that the present intakes are safe1 but simply that they are less polluted than the old ones to an extent measured by the reduction in the death-rate4 ,it is not supposed that in an epidemic of typhoid fever caused by polluted water every single person contracts the disease directly by drinking the water4 ,on the contrary1 typhoid fever is often communicated in other ways4 ,if we have in the first place a thousand cases in a city caused directly by the water1 they will be followed by a large number of other cases resulting directly from the presence in the city of the first thousand cases4 ,the conditions favoring this spread may vary in different wards1 resulting in considerable local variations in the death-rates4 ,some persons also will suffer who did not drink any tap-water4 ,these facts1 always noted in epidemics1 afford no ground for refusing to believe1 in the presence of direct evidence1 that the water was the cause of the fever4 ,these additional cases are the indirect if not the direct result of the water4 ,the broad fact that cities with polluted water-supplies as a rule have high typhoid-fever death-rates1 and cities with good water-supplies do not 7except in the occasional cases of milk epidemics1 or where they are overrun by cases contracted in neighboring cities with bad water1 as is the case with some of ,chicago's suburbs71 is at once the best evidence of the damage from bad water and measure of its extent4 ,the conditions which remove or destroy the sewage bacteria in a water tend to make it safe4 ,the most important of them are3 7#a7 dilution2 7#b7 time1 allowing the bacteria to die 7sunlight may aid in this process1 although effective sunshine cannot reach the lower layer of turbid waters or through ice72 7#c7 sedimentation1 allowing them to go to the bottom1 where they eventually die2 and 7#d7 natural or artificial filtration4 ,in rivers1 distance is mainly useful in affording time1 and also1 under some conditions1 in allowing opportunities for sedimentation4 ,thus a distance of #ejj miles requires a week for water travelling three miles an hour to pass1 and will allow very important changes to take place4 ,the old theory that water purifies itself in running a certain distance has no adequate foundation as far as bacteria are concerned4 ,some purification takes place with the time involved in the passage1 but its extent has been greatly overestimated4 ,the time required for the bacteria to die simply from natural causes is considerable2 certainly not less than three or four weeks can be depended upon with any confidence4 ,in storage reservoirs this action is often considerable1 and it is for this reason that ,american water-supplies from large storage reservoirs are1 as a rule1 much more healthy than those drawn from rivers or polluted lakes1 even when the sources of the former are somewhat polluted4 ,the water-supplies of ,new ,york and ,boston may be cited as examples4 ,in many other water-works operations the entire time from the pollution to the consumption of the water is but a few days or even less1 and time does not materially improve water in this period4 ,sedimentation removes bacteria only slowly1 as might be expected from their exceedingly small size2 and in addition their specific gravity probably is but slightly greater than that of water4 ,the ,lawrence reservoir1 holding from #aj to #ad days' supply1 effected1 by the combined effect of time and sedimentation1 a reduction of #ij per cent of the bacteria in the raw water4 ,in spite of this the city suffered severely and continuously from fever4 ,it would probably have suffered even more1 however1 had it not been for this reduction4 ,nothing is known of the removal of bacteria by sedimentation from flowing rivers1 but1 considering the slowness with which the process takes place in standing water1 it is evident that we cannot hope for very much in streams1 and especially rapid streams1 where the opportunities for sedimentation are still less favorable4 ,filtration as practiced in ,europe removes promptly and certainly a very large proportion of the bacteria--probably1 under all proper conditions1 over #ii per cent1 and is thus much more effective in purification than even weeks of storage or long flows in rivers4 ,the places using filtered water have1 in general1 extremely low death-rates from typhoid fever4 ,the fever which has occurred at a few places drawing their raw water from greatly polluted sources has resulted from improper conditions which can be avoided1 and affords no ground for doubt of the efficiency of properly conducted filtration4 ,corresponding evidence has not yet been produced in connection with the mechanical filters which have been largely used in the ,united ,states2 but the bacterial efficiencies secured with them1 under proper conditions1 and with enough coagulant1 have been such as to warrant the belief that they also will serve to greatly diminish the danger from such infection1 although they have not shown themselves equal in this respect to sand filters4 ,the main point is that disease-germs shall not be present in our drinking-water4 ,if they can be kept out in the first place at reasonable expense1 that is the thing to do4 ,innocence is better than repentance4 ,if they cannot be kept out1 we must take them out afterwards2 it does not matter much how this is done1 so long as the work is thorough4 ,sedimentation and storage may accomplish much1 but their action is too slow and often uncertain4 ,filtration properly carried out removes bacteria promptly and thoroughly and at a reasonable expense4 ,,appendices4 ,appendix ,i4 ,,rules ,,of ,,the ,,german ,,government ,,in ,,regard ,,to ,,the ,,filtration ,,of ,,surface-,,waters ,,used ,,for ,,public ,,water-,,supplies4 ,rules somewhat similar to those of which a translation is given below were first issued by the ,imperial ,board of ,health in #ahib4 ,these rules were regarded as unnecessarily rigid1 and a petition was presented to the government signed by #cg water-works engineers and directors requesting a revision4#ej ,as a result a conference was organized consisting of #ad members4#ea ,khler presided1 and ,koch1 ,gaffsky1 ,werner1 ,gnther1 and ,reincke represented the ,imperial ,board of ,health4 ,the bacteriologists were represented by ,flgge1 ,wolffhgel1 and ,frnkel1 while ,beer1 ,fischer1 ,lindley1 ,meyer1 and ,piefke were the engineer members4 ,this conference prepared the #ag articles given below in the first days of ,january1 #ahid4 ,a little later the first #af articles were issued to all ,german local authorities1 signed by ,bosse1 minister of the 8,geistlichen10 and ,haase1 minister of the interior1 and they are considered as binding upon all water-works using surface-water4 ,the bacterial examinations were commenced ,april #a1 #ahid1 by most of the cities which had not previously had them4 ,although the articles do not deal with rate of filtration1 or the precautions against snow and ice1 they have a very great interest both because they are an official expression1 and on account of the personal standing of the men who prepared them4 99 99 99 99 99 #a4 ,in judging of the quality of a filtered surface-water the following points should be especially observed3 a4 ,the operation of a filter is to be regarded as satisfactory when the filtrate contains the smallest possible number of bacteria1 not exceeding the number which practical experience has shown to be attainable with good filtration at the works in question4 ,in those cases where there are no previous records showing the possibilities of the works and the influence of the local conditions1 especially the character of the raw water1 and until such information is obtained1 it is to be taken as the rule that a satisfactory filtration will never yield an effluent with more than about #ajj bacteria per cubic centimeter4 b4 ,the filtrate must be as clear as possible1 and1 in regard to color1 taste1 temperature1 and chemical composition1 must be no worse than the raw water4 #b4 ,to allow a complete and constant control of the bacterial efficiency of filtration1 the filtrate from each single filter must be examined daily4 ,any sudden increase in the number of bacteria should cause a suspicion of some unusual disturbance in the filter1 and should make the superintendent more attentive to the possible causes of it4 #c4 ,filters must be so constructed that samples of the effluent from any one of them can be taken at any desired time for the bacteriological examination mentioned in #a4 #d4 ,in order to secure uniformity of method1 the following is recommended as the standard method for bacterial examination3 ,the nutrient medium consists of #aj per cent meat extract gelatine with peptone1 #aj cc4 of which is used for each experiment4 ,two samples of the water under examination are to be taken1 one of #a cc4 and one of #a_/b cc4 ,the gelatine is melted at a temperature of #cj to #ce ,c41 and mixed with the water as thoroughly as possible in the test-tube by tipping back and forth1 and is then poured upon a sterile glass plate4 ,the plates are put under a bell-jar which stands upon a piece of blotting-paper saturated with water1 and in a room in which the temperature is about #bj ,c4 ,the resulting colonies are counted after #dh hours1 and with the aid of a lens4 ,if the temperature of the room in which the plates are kept is lower than the above1 the development of the colonies is slower1 and the counting must be correspondingly postponed4 ,if the number of colonies in #a cc4 of the water is greater than about #ajj1 the counting must be done with the help of the ,wolffhgel's apparatus4 #e4 ,the person entrusted with the carrying-out of the bacterial examinations must present a certificate that he possesses the necessary qualifications1 and wherever possible he shall be a regular employ of the water-works4 #f4 ,when the effluent from a filter does not correspond to the hygienic requirements it must not be used1 unless the cause of the unsatisfactory work has already been removed during the period covered by the bacterial examinations4 ,in case a filter for more than a very short time yields a poor effluent1 it is to be put out of service until the cause of the trouble is found and corrected4 ,it is1 however1 recognized from past experience that sometimes unavoidable conditions 7high water1 etc47 make it impossible1 from an engineering standpoint1 to secure an effluent of the quality stated in #a4 ,in such cases it will be necessary to get along with a poorer quality of water2 but at the same time1 if the conditions demand it 7outbreak of an epidemic1 etc471 a suitable notice should be issued4 #g4 ,every single filter must be so built that1 when an inferior effluent results1 which does not conform to the requirements1 it can be disconnected from the pure-water pipes and the filtrate allowed to be wasted1 as mentioned in #f4 ,this wasting should in general take place1 so far as the arrangement of the works will permit it3 7#a7 ,immediately after scraping a filter2 and 7#b7 ,after replacing the sand to the original depth4 ,the superintendent must himself judge1 from previous experience with the continual bacterial examinations1 whether it is necessary to waste the water after these operations1 and1 if so1 how long a time will probably elapse before the water reaches the standard purity4 #h4 ,the best sand-filtration requires a liberal area of filter-surface1 allowing plenty of reserve1 to secure1 under all local conditions1 a moderate rate of filtration adapted to the character of the raw water4 #i4 ,every single filter shall be independently regulated1 and the rate of filtration1 loss of head1 and character of the effluent shall be known4 ,also each filter shall1 by itself1 be capable of being completely emptied1 and1 after scraping1 of having filtered water introduced from below until the sand is filled to the surface4 #aj4 ,the velocity of filtration in each single filter shall be capable of being arranged to give the most favorable results1 and shall be as regular as possible1 quite free from sudden changes or interruptions4 ,on this account reservoirs must be provided large enough to balance the hourly fluctuation in the consumption of water4 #aa4 ,the filters shall be so arranged that their working shall not be influenced by the fluctuating level of the water in the filtered-water reservoir or pump-well4 #ab4 ,the loss of head shall not be allowed to become so great as to cause a breaking through of the upper layer on the surface of the filter4 ,the limit to which the loss of head can be allowed to go without damage is to be determined for each works by bacterial examinations4 #ac4 ,filters shall be constructed throughout in such a way as to insure the equal action of every part of their area4 #ad4 ,the sides and bottoms of filters must be made water-tight1 and special pains must be taken to avoid the danger of passages or loose places through which the unfiltered water on the filter might find its way to the filtered-water channels4 ,to this end special pains should be taken to make and keep the ventilators for the filtered-water channels absolutely tight4 #ae4 ,the thickness of the sand-layer shall be so great that under no circumstances shall it be reduced by scraping to less than #cj cm4 7 #ab inches71 and it is desirable1 so far as local conditions allow1 to increase this minimum limit4 ,special attention must be given to the upper layer of sand1 which must be arranged and continually kept in the condition most favorable for filtration4 ,for this reason it is desirable that1 after a filter has been reduced in thickness by scraping and is about to be refilled1 the sand below the surface1 as far as it is discolored1 should be removed before bringing on the new sand4 #af4 ,every city in the ,german empire using sand-filtered water is requested to make a quarterly report of its working results1 especially of the bacterial character of the water before and after filtration1 to the ,imperial ,board of ,health 7,kaiserlichen ,gesundheitsamt71 which will keep itself in communication with the commission chosen by the water-works engineers in regard to these questions2 and it is believed that after such statistical information is obtained for a period of about two years some farther judgments can be reached4 #ag4 ,the question as to the establishment of a permanent inspection of public water-works1 and1 if so1 under what conditions1 can be best answered after the receipt of the information indicated in #af4 ,,appendix ,,ii4 ,,extracts ,,from 8,,bericht ,,des ,,medicinal-,,inspectorats ,,des ,,hamburgischen ,,staates ,f,r ,,das ,,jahr #ahib40 ,the following are translations from ,dr4 ,reincke's most valuable report upon the vital statistics of ,hamburg for #ahib4 ,i much regret that ,i am unable to reproduce in full the very complete and instructive tables and diagrams which accompany the report4 ,diarrha and ,cholera ,infantum 7page #aj74 8,it is usually assumed that the increase of diarrhal diseases in summer is to be explained by the high temperature1 especially by the action of the heat upon the principal food of infants--milk4 ,our observations1 however1 indicate that a deeper cause must be sought40 7,tables and diagrams of deaths from cholera infantum by months for ,hamburg and for ,altona with the mean temperatures1 #ahga-ahib47 8,from these it appears that the highest monthly mortality of each year in ,hamburg occurred #g times in ,july1 #ac times in ,august1 and #c times in ,september1 and substantially the same in ,altona4 ,if one compares the corresponding temperatures1 it is found that in the three years #ahhf1 #ahia1 and #ahib1 with high ,september mortalities1 especially the first two of them1 had their maximum temperature much earlier1 in fact earlier than usual4 ,throughout1 the correspondence between deaths and temperatures is not well marked4 ,repeated high temperatures in ,may and ,june have never been followed by a notable amount of cholera infantum1 although such periods have lasted for a considerable time4 ,for example1 toward the end of ,may1 #ahib1 for a long time the temperature was higher than in the following ,august1 when the cholera infantum appeared4 8,the following observations are still more interesting4 ,as is seen from the diagram1 in addition to the annual rise in summer there is also a smaller increase in the winter1 which is especially marked in ,altona4 ,in #ahib this winter outbreak was greater than the summer one1 and nearly as great in #ahhj and in #ahhh4 ,the few years when this winter increase was not marked1 #ahgf-g1 #ahgg-h1 #ahha-b1 #ahhc-d1 were warm winters in which the mean temperature did not go below the freezing-point4 ,it is also to be noted that the time of this winter outbreak is much more variable than that of the summer one4 ,in #ahhg the greatest mortality was in ,november2 in #ahhi in ,february2 in other years in ,december or ,january1 and in ,altona1 in #ahhf and #ahhh1 in ,march1 which is sufficient evidence that it was not the result of ,christmas festivities4 8,farther1 the winter diarrha of ,hamburg and of ,altona are not parallel as is the case in summer4 ,in ,hamburg the greatest mortality generally comes before ,new ,year's2 in ,altona one to two months later4 8,in ,bockendahl's ,generalbericht ber das ffentliche ,gesundheitswesen der ,provinz ,schleswig-,holstein fr das ,jahr #ahgj1 page #aj1 we read3 #8,yet more remarkable was an epidemic of cholera infantum in ,altona in ,february which proved fatal to #dc children4 ,these cases were distributed in every part of the city1 and could not be explained by the health officer until he ascertained that the water company had supplied unfiltered water to the city4 ,this occurred for a few days only in ,january1 and was the only time in the whole year that unfiltered ,elbe water was delivered4 ,however little reason there may be to believe that there was a connection between these circumstances1 future interruptions of the service of filtered water should be most critically watched1 as only in this way can reliable conclusions be reached4 ,without attempting to draw any scientific conclusions from the fact1 ,i cannot do less than record that1 prior to the outbreak of cholera on ,august #bj1 #ahga1 unfiltered together with filtered water had been supplied to the city ,august #aa to #ah4 ,the action of the authorities was then justified when they forbade in future the supply of unfiltered water except in cases of most urgent necessity1 as in case of general conflagration2 and in such a case1 or in case of interruption due to broken pipes1 that the public should be suitably warned4' 8,the author of this paragraph1 ,dr4 ,kraus1 became later the health officer of ,hamburg1 and in an opinion written by him in #ahgd1 and now before me1 he most earnestly urged the adoption of sand-filtration in ,hamburg1 and cites the above observations in support of his position4 ,in the annual report of vital statistics of ,hamburg for #ahge he says that it is quite possible that the addition of unfiltered ,elbe water to milk is the cause of the high mortality from cholera infantum1 as compared with ,london1 and this idea was often afterward expressed by him4 ,since then so much evidence has accumulated that his view may fairly be considered proved4 8,for the information of readers not familiar with local conditions1 a mention of the sources of the water-supplies up to the present time used by ,hamburg and ,altona will be useful4 ,both cities take their entire water-supplies from the ,elbe--,altona from a point about #g miles below the discharge of the sewage of both cities1 ,hamburg from about #g miles above4 ,the raw water at ,altona is thus polluted by the sewage from the population of both cities1 having now together over #gjj1jjj inhabitants1 and contains in general #bj1jjj to #dj1jjj or more bacteria per cubic centimeter4 ,the raw water of ,hamburg has1 however1 according to the time of year and tide1 from #bjj to #ejjj1 but here also occasionally much higher numbers are obtained when the ebb tide carries sewage up to the intake4 ,how often this takes place is not accurately known1 but most frequently in summer when the river is low1 more rarely in winter and in times of flood4 ,recent bacterial examinations show that it occurs much more frequently than was formerly assumed from float experiments4 ,this water is pumped directly to the city raw1 while that for ,altona is carefully filtered4 8,years ago ,i expressed the opinion that the repeated typhoid epidemics in ,altona stood in direct connection with disturbances of the action of the filters by frost1 which result in the supply of insufficiently purified water4 ,wallichs in ,altona has also come to this conclusion as a result of extended observation1 and recently ,robert ,koch has explained the little winter epidemic of cholera in ,altona in the same way1 thus supporting our theory4 ,when open filters are cleaned in cold1 frosty weather the bacteria in the water are not sufficiently held back by the filters4 ,such disturbances of filtration not only preceded the explosive epidemics of typhoid fever of #ahhf1 #ahhg1 #ahhh1 #ahia1 and #ahib1 and the cholera outbreaks of #ahga and #ahic1 but also the winter outbreaks of cholera infantum which have been so often repeated4 ,it cannot be doubted that these phenomena bear the relation to each other of cause and effect4 ,it is thus explained why in the warm winters no such outbreaks have taken place1 and also why the cholera infantum in winter is not parallel in ,hamburg and ,altona4 99 99 99 99 99 8,a farther support of this idea is furnished by ,berlin1 where in the same way frost has repeatedly interfered with filtration4 ,in the following table are shown the deaths from diarrha and cholera infantum for a few winter periods having unusual increases in mortality in comparison with the bacteria in the water-supply40 7,these tables show that in ,march1 #ahhf1 ,march1 #ahhh1 ,february-,march1 #ahhi1 and ,february1 #ahia1 high numbers of bacteria resulted from frost disturbance at the ,stralau works1 and in every case they were followed by greatly increased death-rates from diarrhal diseases4--,a4 ,h47 8,no one who sees this exhibition can doubt that here also the supply of inadequately purified water has every time cost the lives of many children40 7#ajj to #djj or more each time4--,a4 ,h47 8,even more conclusive is the evidence1 published by the ,berlin ,health ,office1 that this increase was confined to those parts of the city supplied from ,stralau0 7with open filters4--,a4 ,h471 8and that the parts supplied from the better ,tegel works took no part in the outbreaks1 which was exactly the case with the well-known typhoid epidemic of ,february and ,march1 #ahhi4444 ,it was also found that those children nursed by their mothers or by wet-nurses did not suffer1 but only those fed on the milk of animals or other substitutes1 and which in any case were mixed with more or less water40 ,under ,cholera1 page #bh1 he says3 8,the revised statistics here given differ slightly from preliminary figures previously issued and widely published40 7,the full tables1 which cannot be here reproduced1 show #af1ief cases and #hfje deaths4 #hadf of the deaths occurred in the month ending ,september #ba4 ,of these1 #agii were under #e years old2 #ggf were #e to #ae2 #gdd1 #ae to #be2 #cebj1 #be to #ej2 #acfi1 #ej to #gj2 and #cig over #gj or of unknown age4 ,the bulk of the cases were thus among mature people1 children1 except very young children1 suffering the least severely of any age class47 8,the epidemic began on ,august #af1 in the port where earlier outbreaks have also had their origin4 ,the original source of the infection has not been ascertained with certainty1 but was probably from one of two sources4 ,either it came from certain ,jews1 just arrived from cholera-stricken ,russia1 who were encamped in large numbers near the ,american pier1 or the infection came from ,havre1 where cholera had been present from the middle of ,july4 ,perhaps the germs came in ships in water-ballast which was discharged at ,hamburg1 which is so much more probable1 as the sewage of ,havre is discharged directly into the docks4 8,it is remarkable that in ,altona1 compared to the total number of cases1 very few children had cholera1 while in the epidemic of #ahga the children suffered severely4 ,this may be explained by supposing that the cholera of #ahib in ,altona was not introduced by water1 but by other means of infection4444 8,it is well known that the drinking-water 7of ,hamburg7 is supposed to have been from the first the carrier of the cholera-germs4 ,in support of this view the following points are especially to be noted3 8#a4 ,the explosive rapidity of attack4 ,the often-compared epidemic in ,munich in #ahed1 which could not have come from the water is characteristically different in that its rise was much slower and was followed by a gradual decline4 ,in ,hamburg1 with six times as large a population1 the height of the epidemic was reached ,august #bg1 only #ab days after the first cases of sickness1 while in ,munich #be days were required4 ,in ,hamburg also the bulk of the cases were confined to #ab days1 from ,august #be to ,september #e1 while in ,munich the time was twice as long4 8#b4 ,the exact limit of the epidemic to the political boundary between ,hamburg and ,altona and ,wandsbeck1 which also agrees with the boundary between the respective water-supplies1 while other differences were entirely absent4 ,hamburg had for #ajjj inhabitants #bf4ca cases and #ac4ci deaths1 but ,altona only #c4ha cases and #b4ac deaths1 and ,wandsbeck #c4jf cases and #b4ji deaths4 8#c4 ,the old experience of cholera in fresh-water ports1 and the analogy of many earlier epidemics4 ,in this connection the above-mentioned epidemic of #ahga in ,altona has a special interest1 even though some of the conclusions of ,bockendahl's in his report of #ahga are open to objection4 ,first there were #c deaths ,august #c1 which were not at once followed by others4 ,then unfiltered ,elbe water was supplied ,august #aa to #ah4 ,on the #aith an outbreak of cholera extended to all parts of the city1 which reached its height ,august #be and #bf1 and afterwards gradually decreased4 ,in all #aje persons died of cholera and #ahf 7#agi of them children7 of diarrha4 ,in ,hamburg1 four times as large1 only #ada persons died of cholera at this time1 thus proportionately a smaller number4 ,the conditions were then the reverse of those of #ahib1 an infection of the ,altona water and a comparative immunity in ,hamburg4 8,it is objected that the cholera-germs were not found in the water in #ahib4 ,to my knowledge they were first looked for1 and then with imperfect methods1 in the second half of ,september4 ,in the after-epidemics at ,altona1 they were found in the river-water by ,r4 ,koch by the use of better methods4 8,it is quite evident that the germs were also distributed by other methods than by the city water1 especially by dock-laborers who became infected while at their work and thus set up little secondary epidemics where they went or lived4444 ,these laborers and sailors1 especially on the smaller river-boats1 had an enormously greater proportionate amount of cholera than others4444 ,these laborers do not live exclusively near the water1 but to a measure in all parts of the city40 7,and in ,altona and ,wandsbeck4--,a4 ,h47 8,altona had #e deaths from cholera ,december #be to ,january #d1 and #ai ,january #bc to ,february #aa1 and no more4 ,as noted above1 this is attributed to the water-supply1 and to defective filtration in presence of frost4444 8,the cholera could never have reached the proportion which it did1 had the improvements in the drinking-water been earlier completed40 ,further accounts of the water-supplies of ,altona and of ,hamburg and of the new filtration works at the latter city are given in ,appendices ,,vii and ,,viii4 ,,appendix ,,iii4 ,,methods ,,of ,,sand-,,analysis4 7,from the ,annual ,report of the ,massachusetts ,state ,board of ,health for #ahib47 ,a knowledge of the sizes of the sand-grains forms the basis of many of the computations4 ,this information is obtained by means of mechanical analyses4 ,the sand sample is separated into portions having grains of definite sizes1 and from the weight of the several portions the relative quantities of grains of any size can be computed4 ,collection of ,samples4--,in shipping and handling1 samples of sand are best kept in their natural moist condition1 as there is then no tendency to separation into portions of unequal-sized grains4 ,under no circumstances should different materials be mixed in the same sample4 ,if the material under examination is not homogeneous1 samples of each grade should be taken in separate bottles1 with proper notes in regard to location1 quantity1 etc4 ,eight-ounce wide-necked bottles are most convenient for sand samples1 but with gravels a larger quantity is often required4 ,duplicate samples for comparison after obtaining the results of analyses are often useful4 ,separation into ,portions having ,grains of ,definite ,sizes4--,three methods are employed for particles of different sizes--hand-picking for the stones1 sieves for the sands1 and water elutriation for the extremely fine particles4 ,ignition1 or determination of albuminoid ammonia1 might be added for determining the quantity of organic matter1 which1 as a matter of convenience1 is assumed to consist of particles less than #j4ja millimeter in diameter4 ,the method of hand-picking is ordinarily applied only to particles which remain on a sieve two meshes to an inch4 ,the stones of this size are spread out so that all are in sight1 and a definite number of the largest are selected and weighed4 ,the diameter is calculated from the average weight by the method to be described1 while the percentage is reckoned from the total weight4 ,another set of the largest remaining stones is then picked out and weighed as before1 and so on until the sample is exhausted4 ,with a little practice the eye enables one to pick out the largest stones quite accurately4 ,with smaller particles this process becomes too laborious1 on account of the large number of particles1 and sieves are therefore used instead4 ,the sand for sifting must be entirely free from moisture1 and is ordinarily dried in an oven at a temperature somewhat above the boiling-point4 ,the quantity taken for analysis should rarely exceed #ajj-bjj grams4 ,the sieves are made from carefully-selected brass-wire gauze1 having1 as nearly as possible1 square and even-sized meshes4 ,the frames are of metal1 fitting into each other so that several sieves can be used at once without loss of material4 ,it is a great convenience to have a mechanical shaker1 which will take a series of sieves and give them a uniform and sufficient shaking in a short time2 but without this good results can be obtained by hand-shaking4 ,a series which has proved very satisfactory has sieves with approximately #b1 #d1 #f1 #aj1 #bj1 #dj1 #gj1 #ajj1 #adj1 and #bjj meshes to an inch2 but the exact numbers are of no consequence1 as the actual sizes of the particles are relied upon1 and not the number of meshes to an inch4 ,it can be easily shown by experiment that when a mixed sand is shaken upon a sieve the smaller particles pass first1 and as the shaking is continued larger and larger particles pass1 until the limit is reached when almost nothing will pass4 ,the last and largest particles passing are collected and measured1 and they represent the separation of that sieve4 ,the size of separation of a sieve bears a tolerably definite relation to the size of the mesh1 but the relation is not to be depended upon1 owing to the irregularities in the meshes and also to the fact that the finer sieves are woven on a different pattern from the coarser ones1 and the particles passing the finer sieves are somewhat larger in proportion to the mesh than is the case with the coarser sieves4 ,for these reasons the sizes of the sand-grains are determined by actual measurements1 regardless of the size of the mesh of the sieve4 ,it has not been found practicable to extend the sieve-separations to particles below #j4aj millimeter in diameter 7corresponding to a sieve with about #bjj meshes to an inch71 and for such particles elutriation is used4 ,the portion passing the finest sieve contains the greater part of the organic matter of the sample1 with the exception of roots and other large undecomposed matters1 and it is usually best to remove this organic matter by ignition at the lowest possible heat before proceeding to the water-separations4 ,the loss in weight is regarded as organic matter1 and calculated as below #j4ja millimeter in diameter4 ,in case the mineral matter is decomposed by the necessary heat1 the ignition must be omitted1 and an approximate equivalent can be obtained by multiplying the albuminoid ammonia of the sample by #ej4eb ,in this case it is necessary to deduct an equivalent amount from the other fine portions1 as otherwise the analyses when expressed in percentages would add up to more than one hundred4 ,five grams of the ignited fine particles are put in a beaker #ij millimeters high and holding about #bcj cubic centimeters4 ,the beaker is then nearly filled with distilled water at a temperature of #bj ,c41 and thoroughly mixed by blowing into it air through a glass tube4 ,a larger quantity of sand than #e grams will not settle uniformly in the quantity of water given1 but less can be used if desired4 ,the rapidity of settlement depends upon the temperature of the water1 so that it is quite important that no material variation in temperature should occur4 ,the mixed sand and water is allowed to stand for fifteen seconds1 when most of the supernatant liquid1 carrying with it the greater part of the particles less than #j4jh millimeter1 is rapidly decanted into a suitable vessel1 and the remaining sand is again mixed with an equal amount of fresh water1 which is again poured off after fifteen seconds1 carrying with it most of the remaining fine particles4 ,this process is once more repeated1 after which the remaining sand is allowed to drain1 and is then dried and weighed1 and calculated as above #j4jh millimeter in diameter4 ,the finer decanted sand will have sufficiently settled in a few minutes1 and the coarser parts at the bottom are washed back into the beaker and treated with water exactly as before1 except that one minute interval is now allowed for settling4 ,the sand remaining is calculated as above #j4jd millimeter1 and the portion below #j4jd is estimated by difference1 as its direct determination is very tedious1 and no more accurate than the estimation by difference when sufficient care is used4 ,determination of the ,sizes of the ,sand-grains4--,the sizes of the sand-grains can be determined in either of two ways--from the weight of the particles or from micrometer measurements4 ,for convenience the size of each particle is considered to be the diameter of a sphere of equal volume4 ,when the weight and specific gravity of a particle are known1 the diameter can be readily calculated4 ,the volume of a sphere is #a_/f;d1 and is also equal to the weight divided by the specific gravity4 ,with the ,lawrence materials the specific gravity is uniformly #b4fe within very narrow limits1 and we have w_/#b4fe #a_/f;d4 ,solving for d we obtain the formula d 4#iw1 where d is the diameter of a particle in millimeters and w its weight in milligrams4 ,as the average weight of particles1 when not too small1 can be determined with precision1 this method is very accurate1 and altogether the most satisfactory for particles above #j4aj millimeter2 that is1 for all sieve separations4 ,for the finer particles the method is inapplicable1 on account of the vast number of particles to be counted in the smallest portion which can be accurately weighed1 and in these cases the sizes are determined by micrometer measurements4 ,as the sand-grains are not spherical or even regular in shape1 considerable care is required to ascertain the true mean diameter4 ,the most accurate method is to measure the long diameter and the middle diameter at right angles to it1 as seen by a microscope4 ,the short diameter is obtained by a micrometer screw1 focussing first upon the glass upon which the particle rests and then upon the highest point to be found4 ,the mean diameter is then the cube root of the product of the three observed diameters4 ,the middle diameter is usually about equal to the mean diameter1 and can generally be used for it1 avoiding the troublesome measurement of the short diameters4 ,the sizes of the separations of the sieves are always determined from the very last sand which passes through in the course of an analysis1 and the results so obtained are quite accurate4 ,with the elutriations average samples are inspected1 and estimates made of the range in size of particles in each portion4 ,some stray particles both above and below the normal sizes are usually present1 and even with the greatest care the result is only an approximation to the truth2 still1 a series of results made in strictly the same way should be thoroughly satisfactory1 notwithstanding possible moderate errors in the absolute sizes4 ,calculation of ,results4--,when a material has been separated into portions1 each of which is accurately weighed1 and the range in the sizes of grains in each portion determined1 the weight of the particles finer than each size of separation can be calculated1 and with enough properly selected separations the results can be plotted in the form of a diagram1 and measurements of the curve taken for intermediate points with a fair degree of accuracy4 ,this curve of results may be drawn upon a uniform scale1 using the actual figures of sizes and of per cents by weight1 or the logarithms of the figures may be used in one or both directions4 ,the method of plotting is not of vital importance1 and the method for any set of materials which gives the most easily and accurately drawn curves is to be preferred4 ,in the diagram published in the ,report of the ,mass4 ,state ,board of ,health for #ahia1 page #dcj1 the logarithmic scale was used in one direction1 but in many instances the logarithmic scale can be used to advantage in both directions4 ,with this method it has been found that the curve is often almost a straight line through the lower and most important section1 and very accurate results are obtained even with a smaller number of separations4 ,examples of ,calculation of ,results4--,following are examples of representative analyses1 showing the method of calculation used with the different methods of separation employed with various materials4 ,i4 ,,analysis ,,of ,a ,,gravel ,,by ,,hand-,,picking1 #aa1hgj ,,grams ,,taken ,,for ,,analysis4 ---------------------------------------- --------------------------- ,number ,total ,average ,estimated ,corresponding ,total ,per ,cent of ,weight of ,weight of ,weight of ,size4 ,weight of ,stones ,portion4 ,stones4 ,smallest ,millimeters4 of ,total in ,grams4 ,milligrams4 ,stones4 ,stones ,weight ,portion4 ,milligrams4 ,smaller,smaller 7,largest than than ,selected this this ,stones47 ,size4 ,size4 ---------------------------------------- --------------------------- 4444 4444 4444 4444 #aa1hgj #ajj #aj #c1cbj #ccb1jjj #bej1jjj #ef #h1eej #gb #aj #a1icj #aic1jjj #afe1jjj #di #f1fbj #ef #aj #a1chj #ach1jjj #abd1jjj #de #e1bdj #dd #bj #b1bjj #aaj1jjj #ic1jjj #da #c1jdj #bf #bj #a1ebj #gf1jjj #fd1jjj #cf #a1ebj #ac #bj #a1jjj #ej1jjj #cf1jjj #cj #ebj #d4d #bj #dfj #bc1jjj #aj1jjj #bj #fj 4#e #aj #dj #d1jjj #b1jjj #aa #bj 4#b ,dust #bj 4444 4444 4444 4444 4444 ---------------------------------------- --------------------------- ,the weight of the smallest stones in a portion given in the fourth column is estimated in general as about half-way between the average weight of all the stones in that portion and the average weight of the stones in the next finer portion4 ,the final results are shown by the figures in full-faced type in the last and third from the last columns4 ,by plotting these figures we find that #aj per cent of the stones are less than #ce millimeters in diameter1 and #fj per cent are less than #ea millimeters4 ,the 8uniformity coefficient10 as described below1 is the ratios of these numbers1 or #a4df1 while the 8effective size0 is #ce millimeters4 ,,ii4 ,,analysis ,,of ,a ,,sand ,,by ,,means ,,of ,,sieves4 ,a portion of the sample was dried in a porcelain dish in an air-bath4 ,weight dry1 #aaj4i grams4 ,it was put into a series of sieves in a mechanical shaker1 and given one hundred turns 7equal to about seven hundred single shakes74 ,the sieves were then taken apart1 and the portion passing the finest sieve weighed4 ,after noting the weight1 the sand remaining on the finest sieve1 but passing all the coarser sieves1 was added to the first and again weighed1 this process being repeated until all the sample was upon the scale1 weighing #aaj4g grams1 showing a loss by handling of only #j4b gram4 ,the figures were as follows3 ------------------------------------ ,size of ,separation ,quantity,per ,cent ,sieve of this of ,sand of ,marked4 ,sieve4 ,passing4 ,total ,millimeters4,grams4 ,weight4 ------------------------------------ #aij 4#aje 4#e 4#e #adj 4#ace #a4c #a4b #ajj 4#ahb #d4a #c4g #fj 4#cbj #bc4b #ba4j #dj 4#df #ef4g #ea4b #bj 4#ic #hi4a #hj4e #aj #b4jd #ajd4f #id4c #f #c4ij #aaj4g #ajj4j ----------------------------------- ,plotting the figures in heavy-faced type1 we find from the curve that #aj and #fj per cent respectively are finer than 4#be and 4#fb millimeter1 and we have for effective size1 as described above1 4#be1 and for uniformity coefficient #b4e4 ,,iii4 ,,analysis ,,of ,a ,,fine ,,material ,,with ,,elutriation4 ,the entire sample1 #gd grams1 was taken for analysis4 ,the sieves used were not the same as those in the previous analysis1 and instead of mixing the various portions on the scale they were separately weighed4 ,the siftings were as follows3 ,remaining on sieve marked #aj1 above #b4b millimeters #a4e grams ,remaining on sieve marked #bj1 above 4#ih millimeters #g4j grams ,remaining on sieve marked #dj1 above 4#df millimeters #bb4j grams ,remaining on sieve marked #gj1 above 4#bd millimeters #bj4b grams ,remaining on sieve marked #adj1 above 4#ac millimeters #i4b grams ,passing sieve #adj1 below 4#ac millimeters #ad4a grams ,the #ad4a grams passing the #adj sieve were thoroughly mixed1 and one third1 #d4g grams1 taken for analysis4 ,after ignition just below a red heat in a radiator1 the weight was diminished by #j4dg gram4 ,the portion above 4#jh millimeter and between 4#jd and 4#jh millimeter1 separated as described above1 weighed respectively #a4bg and #a4ga grams1 and the portion below 4#jd millimeter was estimated by difference #d4g - 7#j4dg #a4bg #a4ga7 to be #a4be grams4 ,multiplying these quantities by #c1 we obtain the corresponding quantities for the entire sample1 and the calculation of quantities finer than the various sizes can be made as follows3 ---------------------------------------- -------------------------- ,size of ,weight of all,per ,cent by ,weight4 ,largest the ,finer ,weight of ,size of ,grain4 ,grams4 ,particles4 ,particles4 all ,finer ,millimeters4 ,grams4 ,particles4 ---------------------------------------- -------------------------- ,above #b4bj millimeters #a4ej 4444 #gd4jj #ajj 4#ih-b4bj millimeters #g4jj #b4bj #gb4ej #ih 4#df- 4#ih millimeters #bb4jj 4#ih #fe4ej #hi 4#bd- 4#df millimeters #bj4bj 4#df #dc4ej #fj 4#ac- 4#bd millimeters #i4bj 4#bd #bc4cj #cb 4#jh- 4#ac millimeters #c4ha 4#ac #ad4aj #ai 4#jd- 4#jh millimeters #e4ac 4#jh #aj4bi #ad 4#ja- 4#jd millimeters #c4ge 4#jd #e4af #g ,loss on ignition 7assumed to be less than 4#ja millimeter7 #a4da 4#ja #a4da #a4i ---------------------------------------- -------------------------- ,by plotting the heavy-faced figures we find that #aj and #fj per cent are respectively finer than 4#jee and 4#df millimeter1 and we have effective size 4#jee millimeter and uniformity coefficient #h4 99 99 99 99 99 ,the effective size and uniformity coefficient calculated in this way have proved to be most useful in various calculations1 particularly in estimating the friction between the sands and gravels and water4 ,the remainder of the article in the ,report of the ,mass4 ,state ,board of ,health is devoted to a discussion of these relations which were mentioned in ,chapter ,,iii of this volume4 ,,appendix ,,iv4 ,,filter ,,statistics4 ,,statistics ,,of ,,operation ,,of ,,sand ,,filters4 ---------------------------------------- ------------------------------- ,total ,area ,average ,area of,period1 ,quantity of ,daily ,filter of ,water ,filters ,yield1 ,surface,million filtered ,millionin use1 cleaned,gallons ,place4 ,year for ,gallons ,million in ,one per ,acre ,ending4 ,one ,year4 ,daily4 ,acres4 ,gallons ,year1 filtered ,million per ,acre4 between ,gallons4 ,acres4 ,scrapings4 ---------------------------------------- ------------------------------- ,altona ,mar41 #ahie #a1fbj #d4dd #c4jh #a4de #ca4j #eb ,mar41 #ahif #a1gcj #d4ge #c4jh #a4ee #dh4e #cf ,mar41 #ahig #a1ifj #e4dj #c4jh #a4ge #dd4j #de ,mar41 #ahih #a1idj #e4cj #c4jh #a4gb #cf4e #ec ,amsterdam1 ,dec41 #ahid #a1cij #c4hj #e4dc #j4ga #bc #fb ,river ,dec41 #ahif #a1dij #d4jh #e4dc #j4ge #dh #ca ,dec41 #ahig #a1fjj #d4dj #e4dc #j4ha #cj #ec ,amsterdam1 ,dec41 #ahid #b1ccj #f4dj #d4id #a4bi #aaf #bj ,dunes ,dec41 #ahif #b1cfj #f4ej #d4ge #a4cg #ij #bf ,dec41 #ahig #b1bij #f4be #d4ge #a4ca #aji #ba ,ashland1 ,feb41 #ahig #cih #a4ji #j4ej #b4ah #d4hc #hc ,wis4 ,berlin1 ,mar41 #ahif #ac1jjj #ce4fj #be4aj #a4db total ,mar41 #ahig #ab1ijj #ce4dj #be4aj #a4dj ,mar41 #ahih #ac1bjj #cf4bj #bg4jj #a4cd ,bremen ,mar41 #ahie #a1aij #c4bg #b4ea #a4ca #ej #bd ,mar41 #ahif #a1bbj #c4cd #c4ba #a4jd #cb4e #ch ,mar41 #ahig #a1bhj #c4ej #c4ba #a4ji #be4b #ej ,mar41 #ahih #a1djj #d4aj #c4ba #a4bh #cd4j #da ,breslau ,mar41 #ahie #b1hdj #g4hj #e4ab #a4eb #de #fd ,mar41 #ahif #b1ifj #h4aj #e4ab #a4eh #dj4j #gd ,mar41 #ahig #b1iij #h4bj #e4ab #a4fj #cg #ha ,mar41 #ahih #c1jfj #h4dj #e4ab #a4fd #dc #ga ,brunn ,dec41 #ahif #a1aaj #c4jd #a4fb #a4hg #h4f #abh ,dec41 #ahig #a1aij #c4be #a4fb #b4jj #i4a #aca ,brunswick ,mar41 #ahie #hae #b4bc #a4dh #a4ea #ad4h #ee ,mar41 #ahif #hdj #b4cj #a4dh #a4ef #ac4c #fc ,mar41 #ahig #hbj #b4be #a4dh #a4eb #ac4g #fj ,mar41 #ahih #hgj #b4ch #a4dh #a4fa #aa4i #gc ,budapest ,dec41 #ahib #g1cfj #bj4bj #c4jj #f4gj #bed #bi ,copenhagen ,dec41 #ahie #b1ccj #f4dj #b4hh #b4bb #de #eb ,dec41 #ahif #b1dij #f4hj #b4hh #b4ce #eb #dh ,dec41 #ahig #b1ehj #g4aj #b4hh #b4dg #ed #dh ,dordrecht ,dec41 #ahid #cfe #a4jj #j4ef #a4gi ,frankfort ,dec41 #ahie #caj #j4he #j4cg #b4bh #b4i #ajg on ,oder ,dec41 #ahif #cbe #j4hi #j4cg #b4dj #g4d #dd ,dec41 #ahig #cef #j4ih #j4cg #b4fe #h4h #da ,hamburg ,dec41 #ahid #aa1dej #ca4dj #cd4j #j4ib #cej #cc ,dec41 #ahie #aa1gjj #cb4aj #cd4j #j4id #bge #dc ,dec41 #ahif #aa1ejj #ca4gj #cd4j #j4ic #bff #dc ,dec41 #ahig #ab1jjj #cb4gj #cd4j #j4if #bhe #db ,dec41 #ahih #aa1ijj #cb4fj #dc4j #j4gf #bdf #dh ,hudson1 ,dec41 #ahib #fig #a4ia #j4gd #b4eh ,n4 ,y4 ,dec41 #ahic #edc #a4di #j4gd #b4ja ,dec41 #ahie #ece #a4df #j4gd #a4ih ,ilion1 ,n4 ,y4,feb41 #ahii #ahb #j4ej #j4ad #c4eg #a4dj #acj ,knigsberg ,mar41 #ahie #a1jfj #b4ij #b4gj #a4jg #ch4e #bg ,mar41 #ahif #a1jhe #b4ig #b4gj #a4aj #ce4j #ca ,mar41 #ahig #a1jhe #b4ig #b4gj #a4aj #da4j #bg ,mar41 #ahih #a1adj #c4ab #b4gj #a4af #dd4j #bf ,lawrence ,dec41 #ahid #a1jej #b4hh #b4ej #a4ae #aj #aje ,dec41 #ahie #a1jig #c4jj #b4ej #a4bj #bg #da ,dec41 #ahif #a1aja #c4jb #b4ej #a4bj #cj #cg ,dec41 #ahig #a1aad #c4jf #b4ej #a4bb #da #bg ,liverpool ,dec41 #ahif #h1ebj #bc4dj #aj4ib #b4ad #aeh #edec ,london1 all ,dec41 #ahib #fe1ghc #ahj #aji4ge #a4fd #ij filters ,dec41 #ahic #aie #aaf4jj #a4fh but not ,dec41 #ahid #fh1gjj #ahh #aag4jj #a4fj including ,dec41 #ahie #gf1ijj #baj #abc4ge #a4gj ground ,dec41 #ahif #gb1dhb #aih #abc4ge #a4fj water ,dec41 #ahig #gc1cdj #bja #abe4jj #a4fa ,london1 ,dec41 #ahig #e1cgj #ad4gj #h4jj #a4he ,chelsea ,e4 ,london ,dec41 #ahig #ah1jjj #di4jj #ca4jj #a4eh ,grand ,dec41 #ahig #h1efj #bc4dj #ba4ge #a4jg ,junction ,lambeth ,dec41 #ahig #aj1cgj #bh4dj #ab4be #b4cj ,new ,river ,dec41 #ahig #ae1gej #dc4jj #af4ej #b4fj ,southwark ,dec41 #ahig #ad1hjj #dj4ej #bj4ej #a4ih ,vauxhall ,west ,dec41 #ahig #h1iaj #bd4cj #ae4jj #a4fa ,middlesex ,lbeck ,mar41 #ahie #a1ebj #d4ae #a4dj #b4ie #af4b #id ,mar41 #ahif #a1fjj #d4ch #a4dj #c4ac #bd4d #ff ,mar41 #ahig #a1fej #d4ej #a4dj #c4bb #bg4j #fa ,mar41 #ahih #a1gej #d4hj #a4dj #c4db #ch4e #de ,magdeburg ,mar41 #ahie #ahhj #e4ae #c4gf #a4cg #dg4e #dj ,mar41 #ahif #aiej #e4ce #c4gf #a4db #fe4j #cj ,mar41 #ahig #ahhj #e4ae #c4gf #a4cg #ei4j #cb ,mar41 #ahih #bjgj #e4ff #c4gf #a4ej #fc4j #cc ,mt4 ,vernon1 ,dec41 #ahie #dic #a4ce #a4aj #a4bb #g4c #fh ,n4 ,y ,dec41 #ahif #fjh #a4ff #a4aj #a4ea #i4b #ff ,dec41 #ahig #hjh #b4ba #a4aj #b4jj #af4f #di ,dec41 #ahih #icc #b4ef #a4aj #b4cd #ah4d #ea ,posen ,mar41 #ahie #cje #j4hd #j4gj #a4bj #aj4c #cj ,mar41 #ahif #cdf #j4id #j4gj #a4ce #aj4d #cc ,mar41 #ahig #cbe #j4hi #j4gj #a4bg #aj4a #cb ,mar41 #ahih #cfj #j4ii #j4gj #a4db #i4f #ch ,poughkeepsie,dec41 #ahib #fif #a4ia #j4fh #b4ha #ad4j #ej ,dec41 #ahic #ffg #a4hc #j4fh #b4gj #ab4j #ef ,dec41 #ahid #fcc #a4gc #j4fh #b4ee #ad #de ,dec41 #ahie #fhf #a4hh #j4fh #b4gg #ad #di ,dec41 #ahif #ffd #a4hb #j4fh #b4fh #i #gc ,dec41 #ahig #fae #a4fi #a4cf #a4bd ,dec41 #ahih #faa #a4fg #a4cf #a4bc #aj4hh #eg ,rostock ,june1 #ahig #efj #a4ed #a4aa #a4ch #i4c #fj ,june1 #ahih #fbe #a4ga #a4aa #a4ee #i4j #gj ,rotterdam ,dec41 #ahic #dhej #ac4cj #f4cj #b4aa ,stettin ,mar41 #ahie #aacj #c4aj #b4bf #a4cg #bf4e #dc ,mar41 #ahif #ajcj #b4hc #b4bf #a4be #ae4e #ff ,mar41 #ahig #ihj #b4gj #b4bf #a4ai #af4a #fa ,mar41 #ahih #ajbj #b4hj #b4bf #a4bd #bj4c #ej ,stockholm ,dec41 #ahie #bcge #f4ej #b4gh #b4cc #gj4j #cd ,dec41 #ahif #bejj #f4he #b4gh #b4de #fh4j #cg ,dec41 #ahig #bgej #g4ej #c4fj #b4jh #gf4j #cf ,stralsund ,mar41 #ahig #bae #j4ei #a4aa #j4ec #af4j #ac ,mar41 #ahih #baj #j4eh #a4aa #j4ea #ag4c #ab ,stuttgart ,mar41 #ahie #ajdj #b4he #a4df #a4if #ac4g #gf ,mar41 #ahif #abbj #c4cd #a4ff #b4jd #ag4g #fi ,mar41 #ahig #abgj #c4dh #b4cb #a4ej #ah4g #fh ,mar41 #ahih #acbj #c4fj #b4cb #a4ed #bj4b #fe ,utrecht ,dec41 #ahif #eaj #a4dj #j4fj #b4cc #ca #af ,zrich ,dec41 #ahia #bjaj #e4ej #j4hd #f4ej #h #bej ,dec41 #ahib #baej #e4ij #j4hd #g4jj #aj #bae ,dec41 #ahic #bcaj #f4ch #a4ai #e4ce #ac #agg ,dec41 #ahid #bbej #f4ae #a4ai #e4ah #ag #acc ,dec41 #ahie #bdfj #f4gj #a4ai #e4fb #bg #ia ,dec41 #ahif #bcfj #f4de #a4ff #c4hh #cj #gi ,dec41 #ahig #bejj #f4hd #a4ff #d4ac #ce #ga ,dec41 #ahih #bgcj #g4ej #a4ff #d4ej #dg #eh ---------------------------------------- --------------------------------- ,,partial ,,list ,,of ,,cities ,,using ,,sand ,,filters4 ---------------------------------------- ------------------------- ,when ,population4 ,area ,number ,average ,place4 ,built4 #ahij4 of of ,daily ,filters4,filters4,consumption4 ---------------------------------------- ------------------------ ,,united ,,states4 ,poughkeepsie4 ,n4 ,y4 #ahgb #bd1jjj #a4cf #c #a4fg ,hudson1 ,n4 ,y4 #ahgd #i1igj #j4gd #b #a4ej ,st4 ,johnsbury1 ,vt4 #ahg787 #c1heg #j4ad #c #j4gj ,nantucket1 ,mass4 #ahic #c1bfh #j4aa #a #j4ji ,lawrence1 ,mass4 #ahic #dd1fed #b4ej #a #c4jj ,ilion1 ,n4 ,y4 #ahic #d1jeg #j4ad #b #j4ej ,mount ,vernon1 ,n4 ,y4 #ahid #aj1hcj #a4aj #c #a4ff ,grand ,forks1 ,n4 ,d4 #ahid #d1igi #j4db #a 4444 ,milford1 ,mass4 #ahie #i1ief #j4be #a #j4gj ,ashland1 ,wis4 #ahie #i1ief #j4ej #c #a4ji ,hamilton1 ,n4 ,y4 #ahie #a1gdd #j4ab #a #j4jc ,lambertville1 ,n4 ,j4 #ahif #d1adb #j4bh #b #j4be ,far ,rockaway1 ,n4 ,y4 #ahif #b1bhh #j4ib #b #j4ic ,red ,bank1 ,n4 ,j4 #ahig #ejj #j4jc #b #j4aj ,somersworth1 ,n4 ,h4 #ahig #f1bjg #j4ej #a 4444 ,little ,falls1 ,n4 ,y4 #ahih #h1ghc #j4gf #a 4444 ,berwyn1 ,penna4 #ahih #hbf #j4eb #c 4444 ,harrisburg1 ,penna4 #ahii #a1bjj #j4ab #b #j4ae ,albany1 ,n4 ,y4 #ahii #id1ibc #e4fj #h #aa4jjed ,rock ,island1 #ahii #ac1fcd #a4bj #c #c4ej ,illinois ---------------------------------------- ----- ,total #bei1ggd #ag4ca #de #bf4hg ,,british ,,columbia4 ,victoria #af1hda #j4hb #c #a4hj ,,south ,,america4 ,buenos ,ayres #ejj1jjj #d4ae #c 4444 ,montevidio ,filters reported 4444 ,,holland4 ,amsterdam #eee1hba #aj4ah #ab #aa4bj ,rotterdam #bij1jjj #f4cj #ah #ac4jj ,the ,hague #aia1jjj #b4hh #f #d4bj ,schiedam #be1cjj #a4cc #e #j4fh ,utrecht #adj1jjj #j4fj 4444 #a4dj ,groningen #eg1ijj #j4ei #b 4444 ,dordrecht #cd1ajj #j4ef #b #a4jj ,leeuwarden #cj1gjj #j4ca #b 4444 ,vlaardingen 4444 4444 4444 4444 ,sliedrecht 4444 4444 4444 4444 ,gorinchem #aj1jjj 4444 4444 4444 ,zutphen #ah1jjj 4444 4444 4444 ,leyden #dd1bjj 4444 4444 4444 ,enschede 4444 4444 4444 4444 ,middelburg #ag1jjj 4444 4444 4444 ---------------------------------------- ----- ,total #a1dad1jba #bb4ge #dg #ca4dh ---------------------------------------- ------------------------ ,,great ,,britain4 ,london #e1jcj1bfg #abe4jj #abj #bjj4jj ,liverpool #gij1jjj #aj4ib 4444 #bf4fg ,dublin #cdi1jjj #e4jj #aj #ah4jj ,leeds #dbj1jjj #f4jj #h #ag4ii ,bradford #dcf1bfj #d4fb #f #ac4ca ,leicester #bbj1jje #b4ej 4444 #d4ge ,york #gb1jhc #b4jd #f #c4jj ,edinburgh #bib1cfd #b4jj #d #ah4jj ,darlington #dc1jjj #a4cb #g 4444 ,wakefield #cf1hae #a4be 4444 4444 ,carlisle #dj1jjj #j4ij 4444 4444 ,dumfries #ag1hba #j4be 4444 4444 ,accrington #db1jjj 4444 4444 4444 ,birmingham #fhj1adj 4444 4444 #ai4je ,blackburn #acj1jjj 4444 4444 #d4aj ,bolton #bej1jjj 4444 4444 #f4fj ,chester #dj1jjj 4444 4444 4444 ,halifax #bag1jjj 4444 4444 #e4ah ,hereford #bj1jjj 4444 4444 4444 ,middlesborough #ahg1cca 4444 4444 #aa4ci ,newcastle #cbj1jjj 4444 4444 #ad4jj ,oldham #ade1hjj 4444 4444 #e4cj ,oxford #ec1jjj 4444 4444 #a4ei ,preston #aac1hfd 4444 4444 #d4bj ,reading #ga1eeh 4444 4444 #c4jj ,southampton #gf1dcj 4444 4444 #c4de ,wigan #fj1jjj 4444 4444 #a4bb ,worcester #de1jjj 4444 4444 #a4ic --------------------------------------- ,total #aj1aii1gch #afa4hj #afa #chb4gc ,,germany4 ,hamburg #ffa1bjj #db4jj #bb #cc4jj ,berlin #a1gdf1dbd #ca4de #ee #cf4jj ,breslau #chj1jjj #e4ab #e #h4bj ,magdeburg #bag1jfg #c4gf #aa #e4ff ,bremen #aeg1ejj #c4ba #ab #c4ej ,altona #afb1dbg #c4jh #ac #e4dj ,knigsberg #agf1jjj #b4gj #g #c4jj ,stuttgart #afb1eaf #b4cb 4444 #d4jj ,stettin #ade1jjj #b4bf #i #c4jj ,lbeck #gj1jjj #a4dj #f #d4ej ,brunswick #ajj1hhc #a4dh #d #b4cj ,stralsund #cj1aje #a4aa #f #j4fj ,rostock #di1hia #a4aa #c #a4ed ,lignitz #df1heb #j4if #f #a4dj ,posen #ge1jjj #j4gj #d #j4ij ,schwerin #cf1jjj #j4fe #d #j4ej ,chemnitz #afd1gdc #j4ei #c 4444 ,worms #cj1jjj #j4ej #c #j4fd ,ratibor #bj1gbi #j4db #c ,frankfort on ,oder #ei1afa #j4cg #e #j4hi ,kiel #fi1bad #j4ca #a4ej ,tilsit #cj1jjj #j4be #j4bj ,brieg #bj1aed #j4bj #d ,gluckstadt #f1bad #j4ad #j4aj ,wandsbeck #bb1jjj #j4ac #j4cj --------------------------------------- ,total #d1fci1jhj #ajf4bb #ahe #aag4ac ,,other ,,european ,,filters4 ,warsaw #ejj1jjj #f4bj #ab #f4jj ,st4 ,petersburg #ied1jjj #e4he #aa #ci4jj ,odessa #chj1jjj #d4ge #e #h4jj ,choisy le ,roi and #bjj1jjj #c4he #be #aj4jj ,neuilly sur ,marne #b4ca #ae ,copenhagen #cdj1jjj #b4hh #i #f4hj ,stockholm #bgd1jjj #b4gh #g4jj ,antwerp #bdj1jjj #b4aj #h #b4jj ,zrich #if1hci #a4ff #g4jj ,brunn #a4fb #c4jd ,constantinople1 #j4gd #c ,south side --------------------------------------- ,total #b1ihd1hci #cd4gd #hh #hh4hd ,,asia4 ,blandarwada1 ,india #a4ig #f ,agra1 ,india #a4cg ,bombay1 ,india #hba1jjj #a4bb #d ,shanghai1 ,china #j4hh #d ,hong ,kong #j4fg #f ,yokohama1 ,japan #aaj1jjj #j4eh #c ,calcutta1 ,india #dff1jjj ,tokyo1 ,japan ,baroda1 ,india ,allahabad1 ,india --------------------------------------- ,total #a1cig1jjj #f4fi #bc ,,summary4 ,united ,states #bei1ggd #ag4ca #de #bf4hg ,british ,columbia #af1hda #j4hb #c #a4hj ,south ,america #ejj1jjj #d4ae #c ,holland #a1dad1jba #bb4ge #dg #ca4dh ,great ,britain #aj1aii1gch #afa4hj #afa #chb4gc ,germany #d1fci1jhj #ajf4bb #ahe #aag4ac ,other ,european #b1ihd1hci #cd4gd #hh #hh4hd countries ,asia #a1cig1jjj #f4fi #bc --------------------------------------- ,total #ba1daa1bic #ced4dh #eee #fdh4he ---------------------------------------- ------------------------ ,,list ,,of ,,cities ,,and ,,towns ,,using ,,mechanical ,,filters4 ,,arranged ,,by ,,populations4 ,abbreviations4--,p41 ,pressure filters2 ,g41 ,gravity filters2 ,j41 ,jewell system2 ,n4 ,y41 ,new ,york system2 ,w41 ,warren system2 ,c41 ,continental system2 ,am41 ,american system4 ---------------------------------------- ------------------ ,nominal ,capacity ,place4 ,population1 ,filters of ,filters1 #ahij4 ,first #ahii4 ,installed4 ,million ,gallons4 ---------------------------------------- ------------------ ,denver1 ,col4 #ajh1bjd ,atlanta1 ,ga4 #fe1ecc #ahhg #h ,st4 ,joseph1 ,mo4 #eb1cbd #ahih #aj4b ,oakland1 ,cal4 #dh1fhb #ahia #e ,kansas ,city1 ,kan4 #ch1caf #ahih #f ,wilkesbarre1 ,pa4#ee #cg1gah #aj ,norfolk1 ,va4 #cd1hga #ahii #f ,augusta1 ,ga4 #cc1cjj #ahii #f ,quincy4 ,ill4 #cj1did #ahib #d ,dubuque1 ,iowa#ef #cj1caa #ahii #b ,terre ,haute1 ,ind4 #cj1bag #ahij #d ,elmira1 ,n4 ,y4 #bi1gjh #ahig #f ,chattanooga1 ,tenn4 #bi1ajj #ahhg #i ,davenport1 ,iowa #bf1hgb #ahia #g4e ,little ,rock1 ,ark4 #be1hgd #ahia #e4e ,winnipeg1 ,mann4 #be1fdb #ahhg #a4e ,oshkosh1 ,wis4 #bb1hcf #ahia #b4d ,macon1 ,ga4 #bb1gdf #ahic #d ,burlington1 ,ia4 #bb1efe #ahid #c4e ,knoxville1 ,tenn4 #bb1ece #ahid #e ,lexington1 ,ky4 #ba1efg #ahie #b ,kingston1 ,n4 ,y4 #ba1bfa #ahig #d ,york1 ,penna4 #bj1gic #ahii #d ,biddeford1 ,maine #bj1ejj #ahif #c ,newport1 ,r4 ,i4 #ai1dfg #d ,bangor1 ,maine #ai1ajc #ahig #e ,cedar ,rapids1 ,ia4 #ah1jbj #ahif #b4e ,elgin1 ,ill4 #ag1hbc #ahhh #d4c ,decatur1 ,ill4 #af1hda #ahic #c ,belleville1 ,ill4 #ae1cfa #a ,columbia1 ,s4 ,c4 #ae1cec #ahib #c ,keokuk1 ,ia4 #ad1aja #ahic #c ,ottumwa1 ,ia4 #ad1jja #ahie #b ,rock ,island1 ,ill4#ee #ac1fcd #b ,raleigh1 ,n4 ,c4 #ab1fgh #ahhg #a ,shreveport1 ,la4 #aa1igi #ahhi #a ,new ,castle1 ,penna #aa1fjj #ahih #d ,charlotte1 ,n4 ,c4 #aa1eeg #ahif #a ,nebraska ,city1 ,neb4 #aa1did #ahia #j4d ,streator1 ,ill4 #aa1dad #b ,hornelsville1 ,n4 ,y4#eh #aj1iff #ahii #c ,augusta1 ,maine #aj1ebg #ahhg #j4f ,st4 ,thomas1 ,ont4 #aj1cgj #ahia #b4e ,cairo1 ,ill4 #aj1cbd #ahhi #j4h ,alton1 ,ill4 #aj1bid #ahih #c ,asheville1 ,n4 ,c4 #aj1bce #ahhi #a ,greenwich1 ,conn4 #aj1aca #ahhg #b ,huntington1 ,w4 ,va4 #aj1ajh #ahii #b ,beaver ,falls1 ,pa4 #i1gce #b ,champaign1 ,ill4#eg #i1gai ,chatham1 ,ont4 #i1jeb #ahie #a ,adrian1 ,mich4 #h1gef #ahii #a4ge ,athens1 ,ga4 #h1fci #ahic #a ,east ,providence1 ,r4 ,i4 #h1dbb #ahii #j4e ,winston1 ,n4 ,c4 #h1jah #ahie #j4e ,danville1 ,penna4 #g1iih #ahif #a ,clarksville1 ,tenn4#eh #g1ibd #ahii #a4e ,stevens ,point1 ,wis4 #g1hif #ahhi #j4e ,carlisle1 ,pa4 #g1fbj #ahif #a4e ,calais1 ,me4 #g1bij #ahic #a4e ,long ,branch1 ,n4 ,j4 #g1bca #ahhh #c ,creston1 ,ia4 #g1bjj #ahia #j4e ,st4 ,hyacinthe1 ,que4 #g1jaf #ahih #a ,rome1 ,ga4#eh #f1ieg #ahii #a4e ,westerly1 ,r4 ,i4 #f1hac #ahif #a4e ,merrill1 ,wis4 #f1hji #ahig #a ,dennison1 ,ohio#eh #f1gfg #ahii #a4be ,parsons1 ,kan4 #f1gcf #ahid #b ,waterloo1 ,iowa #f1fgd #ahia #a4e ,somerville1 ,n4 ,j4 #f1dag #ahhe #a4i ,athol1 ,mass4 #f1cai #ahhh #a4e ,owego1 ,n4 ,y4 #f1bjj #ahhg #a ,brunswick1 ,maine #f1jab #ahhg #j4f ,bucyrus1 ,ohio #e1igd #ahhg #j4e ,warren1 ,ohio #e1igc #ahif #a4e ,hopkinsville1 ,ky4 #e1hcc #ahie #j4e ,brainerd1 ,minn4 #e1gjc #ahig #j4e ,new ,brighton1 ,pa4 #e1faf #ahhi #j4e ,niagara ,falls1 ,n4 ,y4 #e1ejb #ahif #d4e ,durham1 ,n4 ,c4 #edhe #ahic #j4i ,winfield1 ,kan4 #eahd #ahid #a ,louisiana1 ,mo4 #ejij #ahhh #j4h ,trenton1 ,mo4 #ejci #ahhi #j4d ,lorain1 ,ohio #dhfc #ahif #c ,sidney1 ,ohio#ei #dhej ,mexico1 ,mo4 #dghi #ahhi #j4c ,mt4 ,clemens1 ,mich4 #dgdh #ahhh #a ,riverside1 ,cal4 #dfhc #ahib #j4ji ,columbus1 ,miss4#fj #deei #ahii #j4e ,winchester1 ,ky4 #deai #ahid #j4ge ,salisbury1 ,n4 ,c4 #ddah #ahhi #j4e ,eufaula1 ,ala4 #dcid #ahig #j4e ,greenville1 ,tex4 #dccj #ahhh #j4h ,exeter1 ,n4 ,h4 #dbhd #ahhg #j4aad ,bordentown1 ,n4 ,j4 #dbcb #ahij #j4e ,lake ,forest1 ,ill4 #dbjc #ahib #a ,henderson1 ,n4 ,c4 #daia #ahii #j4be ,reading1 ,mass4 #djhh #ahif #a ,goldsboro1 ,n4 ,c4 #djag #ahif #j4e ,rich ,hill1 ,mo4 #djjh #ahic #j4e ,mt4 ,pleasant1 ,ia4 #ciig #ahhh #j4e ,murphysboro1 ,ill4 #chhj #ahij #j4b ,brandon1 ,manitoba #cggh #ahic #a ,danville1 ,ky4 #cgff #ahid #j4e ,royersford1 ,pa4 #cfab #ahic #a ,warsaw1 ,ind4 #cead #ahif #j4e ,asbury ,park1 ,n4 ,j4 #cejj #b ,keyport1 ,n4 ,j4 #cdaa #ahie #j4e ,deseronto1 ,ont4 #ccch #ahif #j4e ,milledgeville1 ,ga4 #ccbb #ahic #j4e ,carlinville1 ,ill4 #cbic #j4a ,gettysburg1 ,pa4 #cbba #ahid #j4c ,independence1 ,kan4 #cabg #ahia #j4ge ,la,grange1 ,ga4 #cjij #ahic #j4be ,paola1 ,kan4 #bidc #ahhg #j4be ,benwood1 ,w4 ,va4#fj #bicd #ahii #a ,gadsden1 ,ala4 #bija #ahhg #a4cbe ,lamar1 ,mo4 #bhfj #ahia #j4be ,longueuil1 ,que4 #bgeg #ahie #j4d ,washington1 ,mo4 #bgbe #ahhh #j4b ,renfrew1 ,ont4 #bfaa #ahig #j4dcb ,oswego1 ,kan4 #begd #ahic #j4e ,holden1 ,mo4 #bebj #ahic #j4b ,burlington1 ,kan4 #bbci #j4e ,council ,grove1 ,kan4 #bbaa #ahih #j4e ,wakefield1 ,r4 ,i4#fa #bagj #j4ae ,catonsville1 ,md4 #baae #ahij #j4be ,attica1 ,n4 ,y4 #aiid #ahif #j4d ,hightstown1 ,n4 ,j4 #ahge #ahii #j4be ,no4 ,berwick1 ,me4 #ahjc #ahif #j4c ,dunnville1 ,ont4 #aggf #ahii #j4e ,rogers ,park1 ,ill4 #agjh #ahhi #j4d ,eatonton1 ,ga4 #afhb #ahig #j4e ,caldwell1 ,kan4 #afdb #ahij #j4e ,la,grange1 ,tex4 #afbf #ahia #j4be ,richfield ,springs1 ,n4 ,y4 #afbc #ahhi #j4ce ,valatie1 ,n4 ,y4 #adcg #ahid #j4ae ,tunkhannock1 ,pa4 #abec #j4a ,mechanics ,falls1 ,me4 #ajcj #ahih #j4gb ,new ,bethlehem1 ,pa4 #ajbf #ahii #j4a ,fairmount1 ,w4 ,va4 #ajbc #ahih #a ,atlantic ,highlands1 ,n4 ,j4 #ide #j4c ,rumford ,falls1 ,me4 #hih #ahig #j4e ,lakewood1 ,n4 ,j4 #gcj #ahhi #j4e ,veazie1 ,me4 #fej #ahhi #a ,portersville1 ,cal4 #fjf #ahij #j4aea ,holmesburg1 ,pa4 #ahif #a ,pickering ,creek1 ,pa4 #ahif #j4ge ,overbrook1 ,penna4 #ahie #j4be ,vandergrift1 ,pa4 #ahig #j4e ,frazerville1 ,p4 ,q4#fb #ahii #j4b ,arnate1 ,pa4 #ahii #j4ab ,chihuahua1 ,mex4#fb #ahii #a ,west ,reading1 ,pa4 ----------- ----------- ,totals #a1efe1hha #beb ---------------------------------------- ------------------ ---------------------------------------- --------------------------- ,average ,consumption1,area of ,place4 ,million ,filters1 ,filter ,gallons3 ,sq4 ,ft4 ,system4 ,water ,works #ahii4 ,manual4 ---------------------------------------- --------------------------- ,denver1 ,col4 #bbfj ,special4 ,atlanta1 ,ga4 #d4ed #bjef ,n4 ,y4 ,p4 ,st4 ,joseph1 ,mo4 #chdb ,j4 ,g4 ,oakland1 ,cal4 #aj #aifj ,n4 ,y4 ,p4 ,kansas ,city1 ,kan4 #b #bbfj ,j4 ,g4 ,wilkesbarre1 ,pa4#ee #caff ,j4 ,g4 ,norfolk1 ,va4 #c4e #baab ,j4 ,g4 ,augusta1 ,ga4 #c4h #baab ,n4 ,y4 ,g4 ,quincy4 ,ill4 #a4b #aehb ,j4 ,g4 ,dubuque1 ,iowa#ef #hhj ,j4 ,g4 ,terre ,haute1 ,ind4 #c #ajgf ,n4 ,y4 ,p4 #bbf ,j4 ,g4 ,elmira1 ,n4 ,y4 #c #bjcd ,j4 ,g4 ,chattanooga1 ,tenn4 #bjhj ,j4 ,n4 ,y4 ,p4 ,davenport1 ,iowa #c #bchj ,am4 ,p4 ,little ,rock1 ,ark4 #aedd ,am41 ,j41 ,n4 ,y4 ,p4 ,winnipeg1 ,mann4 #cij ,n4 ,y4 ,p4 ,oshkosh1 ,wis4 #b4a #eej ,w4 ,g4 ,macon1 ,ga4 #a4fe #adcg ,j41 ,w41 ,n4 ,y4 ,burlington1 ,ia4 #abdc ,j4 ,g4 ,knoxville1 ,tenn4 #a4ic #adjd ,w4 ,g4 ,lexington1 ,ky4 #a4b #fgh ,j4 ,g4 ,kingston1 ,n4 ,y4 #a4e #aabj ,n4 ,y4 ,p4 ,york1 ,penna4 #b4cg #adjh ,j4 ,g4 ,biddeford1 ,maine #b #ghj ,w4 ,g4 ,newport1 ,r4 ,i4 #b4a ,special4 ,bangor1 ,maine #c #adjd ,w4 ,g4 ,cedar ,rapids1 ,ia4 #b #ije ,j4 ,g4 ,elgin1 ,ill4 #a #ghj ,am4 ,p4 ,decatur1 ,ill4 #b #ajjh ,w4 ,g4 ,belleville1 ,ill4 #j4f #cci ,j4 ,g4 ,columbia1 ,s4 ,c4 #fgh ,j4 ,g4 ,keokuk1 ,ia4 #ihj ,n4 ,y4 ,p4 ,ottumwa1 ,ia4 #a4b #fgh ,j4 ,g4 ,rock ,island1 ,ill4#ee #c4e #deb ,j4 ,g4 ,raleigh1 ,n4 ,c4 #a #bif ,n4 ,y4 ,p4 ,shreveport1 ,la4 #cab ,n4 ,y4 ,p4 ,new ,castle1 ,penna #b #adjh ,n4 ,y4 ,g4 ,charlotte1 ,n4 ,c4 #j4e #ecj ,n4 ,y4 ,g4 ,nebraska ,city1 ,neb4 #j4g #aaf ,n4 ,y4 ,p4 ,streator1 ,ill4 #a4c #ajj ,western ,am4 ,p4 ,hornelsville1 ,n4 ,y4#eh #gjj ,n4 ,y4 ,p4 ,augusta1 ,maine #a4f #ajj ,w4 ,st4 ,thomas1 ,ont4 #j4f #gjj ,n4 ,y4 ,p4 ,cairo1 ,ill4 #b4e #aig ,n4 ,y4 ,p4 ,alton1 ,ill4 #a #ajef ,n4 ,y4 ,g4 ,asheville1 ,n4 ,c4 #j4ce #cab ,n4 ,y4 ,p4 ,greenwich1 ,conn4 #j4d #eib ,n4 ,y4 ,p4 ,huntington1 ,w4 ,va4 #gjd ,n4 ,y4 ,g4 ,beaver ,falls1 ,pa4 #d4e ,n4 ,y4 ,champaign1 ,ill4#eg #j4ge ,n4 ,y4 ,chatham1 ,ont4 #j4d #bhj ,n4 ,y4 ,p4 ,adrian1 ,mich4 #j4de #efe ,j4 ,g4 ,athens1 ,ga4 #j4de #dbj ,w4 ,g4 ,east ,providence1 ,r4 ,i4 #agf ,j4 ,g4 ,winston1 ,n4 ,c4 #j4c #aef ,w4 ,g4 ,danville1 ,penna4 #a #bbf ,j4 ,g4 ,clarksville1 ,tenn4#eh #j4e #gjd ,j4 ,g4 ,stevens ,point1 ,wis4 #j4be #aef ,n4 ,y4 ,p4 ,carlisle1 ,pa4 #cci ,j4 ,g4 ,calais1 ,me4 #j4he #bge ,w4 ,g4 ,long ,branch1 ,n4 ,j4 #a4c #ijd ,n4 ,y4 ,p4 ,creston1 ,ia4 #j4c #aej ,j4 ,st4 ,hyacinthe1 ,que4 #j4hd #bid ,j4 ,p4 ,rome1 ,ga4#eh #a4c #ebh ,j4 ,g4 ,westerly1 ,r4 ,i4 #j4cge #cif ,n4 ,y4 ,g4 ,merrill1 ,wis4 #cci ,j4 ,g4 ,dennison1 ,ohio#eh #a #ebh ,j4 ,g4 ,parsons1 ,kan4 #j4f #deb ,j4 ,g4 ,waterloo1 ,iowa #j4g #efe ,j4 ,g4 ,somerville1 ,n4 ,j4 #j4ge #eeb ,n4 ,y4 ,p4 ,athol1 ,mass4 #j4e #cej ,n4 ,y4 ,p4 ,owego1 ,n4 ,y4 #j4ge #bcd ,n4 ,y4 ,p4 ,brunswick1 ,maine #j4cc #ajj ,w4 ,bucyrus1 ,ohio #j4ee #aef ,n4 ,y4 ,p4 ,warren1 ,ohio #a4e #dfb ,w4 ,g4 ,hopkinsville1 ,ky4 #j4ae #adj ,n4 ,y4 ,p4 ,brainerd1 ,minn4 #aef ,n4 ,y4 ,p4 ,new ,brighton1 ,pa4 #aef ,n4 ,y4 ,p4 ,niagara ,falls1 ,n4 ,y4 #b4fb #ajai ,j4 ,g4 ,durham1 ,n4 ,c4 #j4g #beb ,w4 ,g4 ,winfield1 ,kan4 #ccf ,w4 ,g4 ,louisiana1 ,mo4 #bdb ,n4 ,y4 ,p4 ,g4 ,trenton1 ,mo4 #abh ,n4 ,y4 ,p4 ,lorain1 ,ohio #a4e #acef ,j4 ,g4 ,sidney1 ,ohio#ei #j4e ,n4 ,y4 ,mexico1 ,mo4 #j4d #ff ,n4 ,y4 ,p4 ,mt4 ,clemens1 ,mich4 #j4f #bea ,n4 ,y4 ,p4 ,riverside1 ,cal4 #bj ,n4 ,y4 ,p4 ,columbus1 ,miss4#fj #j4age #agf ,j4 ,g4 ,winchester1 ,ky4 #j4ajg #aeb ,j4 ,p4 ,salisbury1 ,n4 ,c4 #j4ce #aef ,n4 ,y4 ,p4 ,eufaula1 ,ala4 #adj ,n4 ,y4 ,p4 ,greenville1 ,tex4 #j4age #aef ,n4 ,y4 ,p4 ,exeter1 ,n4 ,h4 #j4agi #cd ,n4 ,y4 ,p4 ,bordentown1 ,n4 ,j4 #j4e #aef ,n4 ,y4 ,p4 ,lake ,forest1 ,ill4 #afh ,j4 ,p4 ,henderson1 ,n4 ,c4 #aah ,w4 ,g4 ,reading1 ,mass4 #j4aih #ccf ,w4 ,g4 ,goldsboro1 ,n4 ,c4 #j4a #aef ,w4 ,g4 ,rich ,hill1 ,mo4 #j4bd #adj ,n4 ,y4 ,p4 ,mt4 ,pleasant1 ,ia4 #aef ,n4 ,y4 ,p4 ,murphysboro1 ,ill4 #fj ,n4 ,y4 ,p4 ,brandon1 ,manitoba #j4cf #bdj ,n4 ,y4 ,p4 ,danville1 ,ky4 #j4a #adj ,n4 ,y4 ,p4 ,royersford1 ,pa4 #j4jh #bbf ,j4 ,g4 ,warsaw1 ,ind4 #j4e #aef ,n4 ,y4 ,p4 ,asbury ,park1 ,n4 ,j4 #j4e #fgj ,c4 ,keyport1 ,n4 ,j4 #j4jf #aef ,w4 ,g4 ,deseronto1 ,ont4 #j4hd #adg ,j4 ,p4 ,milledgeville1 ,ga4 #aef ,n4 ,y4 ,p4 ,carlinville1 ,ill4 #ch ,am4 or ,jackson4 ,gettysburg1 ,pa4 #j4jge #gh ,w4 ,g4 ,independence1 ,kan4 #j4be #abi ,am4 ,p4 ,la,grange1 ,ga4 #cd ,n4 ,y4 ,p4 ,paola1 ,kan4 #j4de #ff ,n4 ,y4 ,p4 ,benwood1 ,w4 ,va4#fj #cjf ,j4 ,g4 ,gadsden1 ,ala4 #dcj ,n4 ,y4 ,p4 ,g4 ,lamar1 ,mo4 #gh ,n4 ,y4 ,p4 ,longueuil1 ,que4 #j4c #ajj ,n4 ,y4 ,p4 ,washington1 ,mo4 #j4jge #ej ,n4 ,y4 ,p4 ,renfrew1 ,ont4 #ajj ,n4 ,y4 ,p4 ,oswego1 ,kan4 #j4c #adj ,n4 ,y4 ,p4 ,holden1 ,mo4 #j4je #ajj ,n4 ,y4 ,p4 ,burlington1 ,kan4 #gi ,j4 ,council ,grove1 ,kan4 #j4jh #gh ,n4 ,y4 ,wakefield1 ,r4 ,i4#fa #j4be ,n4 ,y4 ,catonsville1 ,md4 #gh ,n4 ,y4 ,p4 ,attica1 ,n4 ,y4 #ajj ,n4 ,y4 ,p4 ,hightstown1 ,n4 ,j4 #j4jbe #gh ,n4 ,y4 ,g4 ,no4 ,berwick1 ,me4 #gh ,w4 ,g4 ,dunnville1 ,ont4 #adj ,n4 ,y4 ,p4 ,rogers ,park1 ,ill4 #j4ce #ajj ,n4 ,y4 ,p4 ,eatonton1 ,ga4 #acb ,n4 ,y4 ,g4 ,caldwell1 ,kan4 #aef ,n4 ,y4 ,p4 ,la,grange1 ,tex4 #cd ,n4 ,y4 ,p4 ,richfield ,springs1 ,n4 ,y4 #ajj ,n4 ,y4 ,p4 ,valatie1 ,n4 ,y4 #ej ,n4 ,y4 ,tunkhannock1 ,pa4 ,n4 ,y4 ,mechanics ,falls1 ,me4 #agf ,w4 ,g4 ,new ,bethlehem1 ,pa4 #ej ,j4 ,g4 ,fairmount1 ,w4 ,va4 #bhj ,n4 ,y4 ,p4 ,atlantic ,highlands1 ,n4 ,j4 #j4aji #acj ,c4 ,rumford ,falls1 ,me4 #aac ,w4 ,g4 ,lakewood1 ,n4 ,j4 #aef ,n4 ,y4 ,p4 ,veazie1 ,me4 #j4a #agf ,w4 ,g4 ,portersville1 ,cal4 #j4jfj #cd ,n4 ,y4 ,p4 ,holmesburg1 ,pa4 #j4jdf #bhj ,n4 ,y4 ,p4 ,pickering ,creek1 ,pa4 #bcd ,w4 ,g4 ,overbrook1 ,penna4 #gh ,w4 ,g4 ,vandergrift1 ,pa4 #aef ,w4 ,g4 ,frazerville1 ,p4 ,q4#fb #gh ,n4 ,y4 ,g4 ,arnate1 ,pa4 #ej ,n4 ,y4 ,g4 ,chihuahua1 ,mex4#fb #fab ,j4 ,g4 ,west ,reading1 ,pa4 #j4jg ,w4 ,g4 -------------------- ,totals #ajh #gg1hjf ---------------------------------------- --------------------------- ,special filters1 neither sand nor mechanical3 ,wilmington1 ,del42 ,pop41 #fa1dca2 area1 #aj1jjj sq4 ft42 nominal capacity1 #aj million gallons4 ,see ,eng4 ,news1 ,vol4 #dj1 p4 #adf4 ,,notes ,,regarding ,,sand ,,filters ,,in ,,the ,,united ,,states4 ,,poughkeepsie1 ,n4 ,y4 ,designed by ,james ,p4 ,kirkwood1 built in #ahgb1 was the earliest of its kind in the ,united ,states4 ,it was enlarged by the ,superintendent1 ,charles ,e4 ,fowler1 in #ahif4 ,the walls of the original filters were of rubble1 and in course of time developed cracks and leaked badly4 ,the walls of the new filter are of rubble1 faced with vitrified brick4 ,the filters treat the water of the ,hudson ,river1 which is sewage-polluted and more or less muddy4 ,description3 ,jour4 ,n4 ,e4 ,water ,works ,assoc41 ,vol4 #ab1 p4 #bji4 ,,hudson1 ,n4 ,y4 ,designed by ,james ,p4 ,kirkwood1 built in #ahgd4 enlarged in #ahhh4 ,the filters are open and are used for treating the ,hudson ,river water1 which is sewage-polluted and more or less muddy4 ,description3 ,eng4 ,news1 ,vol4 #ca1 p4 #dhg4 ,,st4 ,,johnsbury1 ,,vt4 7,e4 ,t4 ,fairbanks ,co47 ,these filters were built about #cj years ago1 and have been recently enlarged4 ,the filters were originally open1 but were afterwards covered with a roof4 ,the single roof proved inadequate to keep them from freezing1 and a second roof was added inside and under the main roof4 ,they are used for filtering pond water1 which is quite clear and not subject to much pollution4 ,the water supply is one of two1 the other is the town supply and is taken from the ,passumpsic ,river4 ,no published description4 ,,nantucket1 ,,mass4 ,designed by ,j4 ,b4 ,rider1 built in #ahib4 ,this filter is used to remove organisms from the reservoir water supply4 ,it is only used when the organisms are troublesome1 and is satisfactory in preventing the tastes and odors which formerly resulted from their presence4 ,description3 ,jour4 ,n4 ,e4 ,water ,works ,assoc41 ,vol4 #h1 p4 #aga2 ,eng4 ,news1 ,vol4 #ca1 p4 #ccf4 ,,lawrence1 ,,mass4 ,designed by ,hiram ,f4 ,mills1 built in #ahib-c1 and put in operation ,september1 #ahic4 ,it is used for treating the water of the ,merrimac ,river1 which contains a large amount of sewage4 ,description3 ,report of the ,mass4 ,state ,board of ,health1 #ahic1 p4 #edc2 ,jour4 ,n4 ,e4 ,water ,works ,assoc41 ,vol4 #i1 p4 #dd2 ,eng4 ,news1 ,vol4 #cj1 p4 #ig4 ,,ilion1 ,n4 ,y4 ,designed by the ,stanwix ,engineering ,company and are used for treating reservoir water1 which is generally clear and not subject to pollution4 ,description3 ,eng4 ,news1 ,vol4 #ca1 p4 #dff4 ,,mount ,,vernon1 ,n4 ,y4 7,new ,york ,suburban ,water ,company47 ,designed by ,j4 ,n4 ,chester1 built in #ahid4 ,these filters are similar in general construction to the ,lawrence filter1 although the dimensions both vertical and horizontal are reduced1 and the area is divided into three parts4 ,the filters are used for treating reservoir water1 which is generally quite clear1 but which is polluted by a considerable amount of sewage4 ,since the use of filters the reduction in the typhoid fever death-rate has been very great4 ,description3 ,eng4 ,news1 ,vol4 #cb1 p4 #aee4 ,,milford1 ,,mass4 ,designed by ,f4 ,l4 ,northrop4 ,this filter is very simple in construction1 and is used for filtering ,charles ,river water as an auxiliary supply4 ,description3 ,jour4 ,n4 ,e4 ,water ,works ,assoc41 ,vol4 #aj1 p4 #bfb4 ,,grand ,,forks1 ,n4 ,d4 ,designed by ,w4 ,s4 ,russell4 ,these filters are covered with roofs4 ,they treat the water from the ,red ,river1 which is very muddy1 and also sewage-polluted1 and which formerly caused typhoid fever4 ,description3 ,eng4 ,news1 ,vol4 #cc1 p4 #cda4 ,,ashland1 ,,wis4 ,designed by ,william ,wheeler1 built in #ahie4 ,the ,ashland filters were the first vaulted masonry filters to be constructed in the ,united ,states1 and are used for treating the bay water1 which is polluted with sewage1 and is at times muddy from the river water discharging into the bay near the intake4 ,the filters are below the bay level1 and receive water from it by gravity4 ,description3 ,jour4 ,n4 ,e4 ,water ,works ,assoc41 ,vol4 #aa1 p4 #cja2 ,eng4 ,news1 ,vol4 #ch1 p4 #cch4 ,,lambertville1 ,n4 ,j4 ,designed by ,churchill ,hungerford1 and built in #ahif4 ,these are open filters with earth embankments1 for filtration of reservoir water4 ,description3 ,eng4 ,news1 ,vol4 #cf1 p4 #d4 ,,far ,,rockaway1 ,l4 ,i4 7,queens ,county ,water ,company47 ,designed by ,charles ,r4 ,bettes1 ,engineer in ,charge2 ,charles ,b4 ,brush ,co41 ,chief ,engineers2 and ,allen ,hazen1 ,consulting ,engineer4 ,constructed in #ahif4 ,these masonry filters were used for the removal of iron from well waters4 ,they are also designed to be suitable for the filtration of certain brook waters which are available as auxiliary supplies1 but the brook water has been but rarely used4 ,description3 ,eng4 ,record1 ,vol4 #dj1 p4 #dab4 ,,red ,,bank1 ,n4 ,j4 7,rumson ,improvement ,company47 ,designed by ,allen ,hazen1 built in #ahig4 ,they are similar in construction to the ,far ,rockaway filters1 and are used for iron removal only4 ,description3 ,eng4 ,record1 ,vol4 #dj1 p4 #dab4 ,,hamilton1 ,n4 ,y4 ,designed by the ,stanwix ,engineering ,company1 and were built in #ahie to filter lake water4 ,description3 ,eng4 ,news1 ,vol4 #ci1 p4 #bed4 ,,little ,,falls1 ,n4 ,y4 ,designed by ,stephen ,e4 ,babcock4 ,these filters are open1 and were built in #ahih1 and are used for filtering river water4 ,description3 ,eng4 ,record1 ,vol4 #ch1 p4 #g4 ,,somersworth1 ,n4 ,h4 ,designed by ,william ,wheeler4 ,these were the second vaulted filters to be built in the ,united ,states4 ,the supply is from the ,salmon ,falls ,river and flows to the filters by gravity1 the filters being below the river level4 ,description3 ,eng4 ,news1 ,vol #dj1 p4 #ceh2 ,eng4 ,record1 ,vol4 #ch1 p4 #bgj4 ,,berwyn1 ,,penna4 ,designed by ,j4 ,w4 ,ledoux4 ,these open filters are used for filtering creek water4 ,description3 ,eng4 ,news1 ,vol4 #da1 p4 #aej4 ,,harrisburg1 ,,penna4 7,state ,lunatic ,hospital47 ,designed by ,allen ,hazen2 open masonry filters1 used for treating the water from a small creek which is often muddy and is subject to pollution4 ,no published description4 ,,albany1 ,n4 ,y4 ,designed by ,allen ,hazen4 ,constructed #ahih-ii4 ,this was the third and is the largest vaulted masonry filter plant yet constructed in the ,united ,states4 ,it is used for filtering the ,hudson ,river water1 which is slightly muddy and much polluted by sewage4 ,description3 ,eng4 ,news1 ,vol4 #ci1 p4 #ia2 ,vol4 #dj1 p4 #bed4 ,,rock ,,island1 ,,ill4 ,designed by ,jacob ,a4 ,harman4 ,open filters with embankments1 used for filtering the ,mississippi ,river water1 which is very muddy and also polluted by sewage4 ,no published description4 99 99 99 99 99 ,,capacity ,,of ,,filters4 ,estimating the total additional area of sand filters for which figures are not available at #ajj acres1 and the maximum capacity of sand filters at three million gallons per acre daily1 and of mechanical filters at three million gallons per thousand square feet of filtering area1 the total filtering capacity of all the filters in the world used for public water supplies in #ahii is nearly #afjj million gallons daily1 of which #ae per cent is represented by mechanical filters and #he per cent by sand filters4 ,in the ,united ,states1 including ,wilmington1 the total filtering capacity is nearly #cjj million gallons daily1 of which #ah per cent is represented by sand filters1 #gi per cent by mechanical filters1 and #c per cent by a special type of filters4 ,,appendix ,v4 ,,london',s ,,water-,,supply4 ,london alone among great capitals is supplied with water by private companies4 ,they are1 however1 under government supervision1 and the rates charged for water are regulated by law4 ,there are eight companies1 each of which supplies its own separate district1 so that there is no competition whatever4 ,one of the companies supplying #dfj1jjj people uses only ground-water drawn from deep wells in the chalk1 but the other seven companies depend mainly upon the rivers ,thames and ,lea for their water4 ,all water so drawn is filtered1 and must be satisfactory to the water examiner1 who is required to inspect the water supplied by each company at frequent intervals1 and the results of the examinations are published each month4 ,in #ahic the average daily supply was #bce1jjj1jjj gallons1 of which about #dj1jjj1jjj were drawn from the chalk1 #abe1jjj1jjj from the ,thames1 and #gj1jjj1jjj from the ,lea4 ,formerly some of the water companies drew water from the ,thames within the city where it was grossly polluted1 and the plagues and cholera which formerly ravaged ,london were in part due to this fact4 ,these intakes were abandoned many years ago1 and all the companies now draw their water from points outside of the city and its immediate suburbs4 ,the area of the watershed of the ,thames above the intakes of the water companies is #cedh square miles1 and the population living upon it in #ahia was #a1jef1dae4 ,the ,thames ,conservancy ,board has control of the main river for its whole length1 and of all tributaries within ten miles in a straight line of the main river1 but has no jurisdiction over the more remote feeders4 ,the area drained is essentially agricultural1 with but little manufacturing1 and there are but few large towns4 ,in the area coming under the conservators there are but six towns with populations above #aj1jjj and an aggregate population of #agj1jjj1 and there are but two or three other large towns on the remaining area more than ten miles from the river4 ,these principal towns are as follows3 ,town4 ,population #ahia4 ,distance above ,water ,intakes4 ,reading #fj1jed #di miles ,oxford #de1gia #hg miles ,new ,swindon #bg1bie #aaf miles ,high ,wycomb #ac1dce #cc miles ,windsor #ab1cbg #ah miles ,maidenhead #aj1fjg #be miles ,guildford #ad1cai #bj miles ,guildford is outside of the conservators' area4 ,all of the above towns treat their sewage by irrigation4 ,among the places that are regarded as the most dangerous are ,chertsey and ,staines1 with populations of #ibae and #ejfj1 only #h and #aa miles above the intakes respectively4 ,these towns are only partially sewered and still depend mainly on cesspools4 ,an attempt is made to treat the little sewage which they produce upon land1 but the work has not as yet been systematically carried out4 ,there are also several small towns of #cjjj inhabitants or less upon the upper river which do not treat their sewage so far as they have any1 but1 owing to their great distance1 the danger from them is much less than from ,chertsey and ,staines4 ,twenty-one of the principal towns upon the watershed have sewage farms1 and there are no chemical precipitation plants now in use4 ,boats upon the river are not allowed to drain into it1 but are compelled to provide receptacles for their sewage1 and facilities are provided for removing and disposing of it2 and as an additional precaution no boat is allowed to anchor within five miles of the intakes4 ,the conservators of the river ,lea have control of its entire drainage area1 which is about #dfj square miles1 measured from the ,east ,london water intakes1 and has a population of #ahi1bhg4 ,on this watershed there is but a single town with more than #aj1jjj inhabitants1 this being ,lutton near the headwaters of the river1 with a population of #cj1jje4 ,the sewage from ,lutton and from seventeen smaller places is treated upon land4 ,no crude sewage is known to be ordinarily discharged into the river4 ,at ,hereford1 eleven miles above the ,east ,london intakes1 there is a chemical precipitation plant4 ,the conservators do not regard this treatment as satisfactory1 and have recently conducted an expensive lawsuit against the local authorities to compel them to further treat their effluent4 ,the suit was lost1 the court holding that no actual injury to health had been shown4 ,it is especially interesting to note that of the thirty-nine places on the ,thames and the ,lea giving their sewage systematic treatment there is but a single place using chemical precipitation1 and there it is not considered satisfactory4 ,formerly quite a number of these towns used other processes than land treatment1 but in every case but ,hereford land treatment has been substituted4 ,in regard to the efficiency of the sewage farms1 it is believed that in ordinary weather the whole of the sewage percolates through the land1 and the inspectors of the ,conservancy ,boards strongly object to its being allowed to pass over the surface into the streams4 ,the land1 however1 is for the most part impervious1 as compared to ,massachusetts and ,german sewage farms1 and in times of heavy storms the land often has all the water it can take without receiving even the ordinary flow of sewage1 and much less the increased storm-flow4 ,at such times the sewage either does go over the surface1 or perhaps more frequently is discharged directly into the rivers without even a pretence of treatment4 ,the conservators apparently regard this as an unavoidable evil and do not vigorously oppose it4 ,it is the theory that1 owing to the increased dilution with the storm-flows1 the matter is comparatively harmless1 although it would seem that the reduced time required for it to reach the water-works intakes might largely offset the effect of increased dilution4 ,the water companies have large storage and sedimentation basins with an aggregate capacity equal to nine days' supply1 but the proportion varies widely with the different companies4 ,it is desired that the water held in reserve shall be alone used while the river is in flood1 as1 owing to its increased pollution1 it is regarded as far more dangerous than the water at other times2 but as no record is kept of the times when raw sewage is discharged1 and no exact information is available in regard to the times when the companies do not take in raw water1 it can safely be assumed that a considerable amount of raw sewage does become mixed with the water which is drawn by the companies4 ,the water drawn from the river is filtered through #aac filters having an area of #aaf acres4 ,none of the filters are covered1 and with an average ,january temperature of #ci but little trouble with ice is experienced4 ,a few new filters are provided with appliances for regulating the rate on each filter separately and securing regular and determined rates of filtration1 but nearly all of the filters are of the simple type described on page #dh1 and the rates of filtration are subject to more or less violent fluctuation1 the extent of which cannot be determined4 ,the area of filters is being continually increased to meet increasing consumption2 the approximate areas of filters in use having been as follows3 #ahci ,first filters built #ahee #cg acres #ahff #dg acres #ahgf #gg acres #ahhf #ajd acres #ahid #aaf acres ,there has been a tendency to reduce somewhat the rate of filtration4 ,in #ahfh1 with #ea acres of filters1 the average daily quantity of water filtered was #aaa1jjj1jjj gallons1 or #b1ahj1jjj gallons per acre4 ,in #ahhd1 with #ig acres of filter surface1 the daily quantity filtered was #aeg1jjj1jjj gallons1 or #a1fbj1jjj gallons per acre2 and in #ahic1 with #aaf acres of filter surface and #aie1jjj1jjj gallons daily1 the yield per acre was #a1fhj1jjj gallons4 ,owing to the area of filter surface out of use while being cleaned1 the variations in consumption of water1 and the imperfections of the regulating apparatus1 the actual rates of filtration are often very much higher and at times may easily be double the figures given4 ,evidence regarding the healthfulness of the filtered river-water was collected and examined in a most exhaustive manner in #ahic by a ,royal ,commission appointed to consider the water-supply of the metropolis in all its aspects with reference to future needs4 ,this commission was unable to obtain any evidence whatever that the water as then supplied was unhealthy or likely to become so1 and they report that the rivers can safely be depended upon for many years to come4 ,the numbers of deaths from all causes and from typhoid fever annually per million of inhabitants for the years #ahhe-ahia in the populations receiving their waters from different sources in ,london were as follows3 ,water used4 ,deaths from ,deaths from ,all ,causes4 ,typhoid ,fever4 ,filtered ,thames water only #ai1eja #abe ,filtered ,lea water only #ba1ccd #afg ,kent wells only #ah1jja #abc ,thames and ,lea jointly #ah1ide #ach ,thames and ,kent jointly #ah1egg #acc ,the population supplied exclusively from the ,lea by the ,east ,london ,company is of a poorer class than that of the rest of ,london1 and this may account for the slightly higher death-rate in this section4 ,aside from this the rate is remarkably uniform and shows no great difference between the section drinking ground-water only and those drinking filtered river-waters4 ,the death-rate from typhoid fever is also very uniform and1 although higher than that of some ,continental cities with excellent water-supplies 7,berlin1 ,vienna1 ,munich1 ,dresden71 is very low--lower than in any ,american city of which ,i have records4 ,in this connection1 it was shown by the ,registrar-,general that there is only a very small amount of typhoid fever on the watersheds of the ,thames and ,lea1 so that the danger of infection of the water as distinct from pollution is less than would otherwise be the case4 ,thus for the seven years above mentioned the numbers of deaths from typhoid fever per million of population were only #aje and #abj on the watersheds of the ,thames and the ,lea respectively1 as against #agf for the whole of ,england and ,wales4 ,,london ,,filters1 #ahif4 ,twenty-sixth ,annual ,report of the ,local ,government ,board1 pages #bjf-bac4 ---------------------------------------- --------------------------------- ,amount ,average ,average ,rate ,bacterial ,efficiency4 of ,thickness of ,filtration4 ,storage of ---------------------------------------- ,raw ,sand1 ,imperial,millions,maximum4,minimum4,ave rage4 ,company4 ,water1 ,feet4 ,gallons ,u4 ,s4 ,days4 per ,gallons ,square per ,acre ,foot per ,daily4 ,hour4 ---------------------------------------- ------------------------------ ,chelsea #ab4j #d4j #a4ge #b4ai #ii4ib #ii4fb #ii4hf ,west ,middlesex #e4f #b4ge #a4be #a4ef #ii4id #ia4dh #ii4gi ,southwark ,vauxhall #d4a #b4e #a4e #a4hh #ajj4jj #hd4cc #ig4gg ,grand ,junction #c4c #b4be #a4fc #b4je #ii4ih #hd4jc #ii4ca ,lambeth #f4j #b4h #b4jh #b4fj #ii4ig #if4de #ii4ha ,new ,river #b4b #d4d #a4hi #b4cg #ajj4jj #gg4ad #ii4jg ,east ,london #ae4j #b4j #a4cc #a4fg #ii4ic #ig4jc #ii4ef ---------------------------------------- ------------------------------ ,,appendix ,,vi4 ,,the ,,berlin ,,water-,,works4 ,the original works were built by an ,english company in #ahef1 and were sold to the city in #ahgc for #g1bjj1jjj4 ,the water was taken from the river ,spree at the ,stralau ,gate1 which was then above1 but is now surrounded by1 the growing city4 ,the water was always filtered1 and the original filters remained in use until #ahic1 when they were supplanted by the new works at ,lake ,mggel4 ,soon after acquiring the works the city introduced water from wells by ,lake ,tegel as a supplementary supply1 but much trouble was experienced from crenothrix1 an organism growing in ground-waters containing iron1 and in #ahhc this supply was replaced by filtered water from ,lake ,tegel4 ,with rapidly-increasing pollution of the ,spree at ,stralau the purity of this source was questioned1 and in #ahic it was abandoned 7although still held as a reserve in case of urgent necessity71 the supply now being taken from the river ten miles higher up1 at ,mggel4 ,the watershed of the ,spree above ,stralau1 as ,i found by map measurement1 is about #chjj square miles2 the average rainfall is about #be inches yearly4 ,at extreme low water the river discharges #deg cubic feet per second1 or #bie million gallons daily1 and when in flood #egjj cubic feet per second may be discharged4 ,the city is allowed by law to take #df million gallons daily for water-supply1 and this quantity can be drawn either at ,stralau or at ,mggel4 ,above ,stralau the river is polluted by numerous manufactories and washing establishments1 and by the effluent from a considerable part of the city's extensive sewage farms4 ,the shipping on this part of the river also is heavy1 and sewage from the boats is discharged directly into the river4 ,the average number of bacteria in the ,spree at this point is something over ten thousand per cubic centimeter1 and #ii4f per cent of them were removed by the filters in #ahic4 ,the watershed of the ,spree above the new water-works at ,mggel ,i found by map measurement to be #bhjj square miles1 and the low water-discharge is said to be #bfi million gallons daily4 ,the river at this point flows through ,lake ,mggel1 which forms a natural sedimentation-basin1 and the raw water is quite clear except in windy weather4 ,there were #af towns on the watershed with populations above #bjjj each in #ahij1 and an aggregate population of #acb1jjj1 which does not include the population of the smaller places or country districts4 ,none of these places purify their sewage so far as they have any4 ,frstenwalde with a population of #ab1ice1 and #bb miles above ,mggel1 has surface sewers discharging directly into the river4 ,above ,frstenwalde the river runs through numerous lakes which probably remove the effect of the pollution from the more distant cities4 ,there is considerable shipping on the river for some miles above ,frstenwalde 7which forms a section of the ,friedrich ,wilhelm ,canal71 but hardly any between ,mggel and ,frstenwalde4 ,the raw water at ,mggel contains two or three hundred bacteria per cubic centimeter1 and is thus a comparatively pure water before filtration4 ,it is slightly peaty and the filtered water has a light straw color4 ,lake ,tegel1 which supplies the other part of the city's supply1 is an enlargement of the river ,havel4 ,the watershed above ,tegel ,i find to be about #acej square miles1 and the annual rainfall is about #bb inches4 ,the low water-discharge is said to be #ahb million gallons daily1 and the city is allowed by law to take #bc million gallons for water-supply4 ,there were ten towns upon the watershed with populations above #bjjj each in #ahij1 and with an aggregate population of #dd1jjj4 ,of these ,tegel is directly upon the lake with a population of #cjjj1 and ,oranienburg1 #ad miles above1 has a population of #fjjj and is rapidly increasing4 ,the shipping on the lake and river is heavy4 ,the lake water ordinarily contains two or three hundred bacteria per cubic centimeter4 ,the lake is shallow and becomes turbid in windy weather4 ,there are #ba filter-beds at ,tegel with a combined area of #ab4dj acres to furnish a maximum of #bc million gallons of water daily1 and #bb filters at ,mggel with a combined area of #ab4g acres to deliver the same quantity4 ,twenty-two more filters will be built at ,mggel within a few years to purify the full quantity which can be taken from the river4 ,all of these filters are covered with brick arches supported by pillars about #af feet apart from centre to centre in each direction1 and the whole is covered by nearly #c feet of earth1 making them quite frost-proof4 ,the original filters at ,stralau were open1 but much difficulty was experienced with them in winter4 ,the bottom of the filters at ,tegel consists of #h inches of concrete above #bj inches of packed clay and with #b inches of cement above1 and slopes slightly from each side to the centre4 ,the central drain goes the whole length of the filters and has a uniform cross-section of about #a_/gcjj of the area of the whole bed4 ,there are no lateral drains1 but the water is brought to the central drain by a twelve-inch layer of stones as large as a man's fist2 above this there is another foot of gravel of graded sizes supporting two feet of fine sand1 which is reduced by scraping to half its thickness before the sand is replaced4 ,the average depth of water above the sand is nearly #e feet4 ,the filters are not allowed to filter at a rate above #b4eg million gallons per acre daily1 and at this rate with #gj per cent of the area in service the whole legal quantity of water can be filtered4 ,the filters work at precisely the same rate day and night1 and the filtered water is continuously pumped as filtered to ample storage reservoirs at ,charlottenburg4 ,the pumps which lift the water from the lake to the filters work against a head of #ad feet4 ,the apparatus for regulating the rate of filtration was described on page #ea4 ,as yet no full description of the ,mggel works has been published1 but they resemble closely the ,tegel works4 ,both were designed by or under the direction of the late director of the water-works1 ,mr4 ,henry ,gill4 ,the average daily quantity of water supplied for the fiscal year ending ,march #ca1 #ahic1 was #bi1jjj1jjj gallons daily1 which estimate allows #aj percent for the slip of the pumps4 ,of this quantity #i1fej1jjj was furnished by ,stralau and #ai1cej1jjj by ,tegel4 ,the greatest consumption in a single day was #dc1cjj1jjj gallons1 or #bf4f gallons per head1 while the average quantity for the year was #ah4d gallons per head4 ,all water without exception is sold by meter1 the prices ranging from #bg4b cents a thousand gallons for small consumers to #ac4f cents for large consumers and manufacturers4 ,the average receipts for all water pumped1 including that used for public purposes and not paid for1 were #ae4d cents a thousand gallons1 against the cost of production1 #i4h cents1 which covers operating expenses1 interest on capital1 and provision for sinking fund4 ,this leaves a handsome net profit to the city4 ,on account of the comparatively high price of the city water and the ease with which well-water is obtained1 the latter is almost exclusively used for running engines1 manufacturing purposes1 etc41 and this in part explains the very low per-capita consumption4 ,the volume of sewage1 however1 for the same year1 including rain-water1 except during heavy showers1 was only #bi gallons per head1 showing even with the private water-supplies an extraordinarily low consumption4 ,the friction of the water in the #d4ge miles of #c-;foot pipe between ,tegel and the reservoir at ,charlottenburg presents an interesting point4 ,when well-water with crenothrix was pumped1 the friction rose to #cd4e feet1 when the velocity was #b4df feet per second4 ,according to ,herr ,anklamm1 who had charge of the works at the time1 the friction was reduced to #ai4g feet when filtered water was used and after the pipe had been flushed1 and this has not increased with continued use4 ,he calculated the friction for the velocity according to ,darcy #ae4j feet1 ,lampe #ag4h feet1 ,weisbach #ah4g feet1 and ,prony #ba4e feet4 ,,appendix ,,vii4 ,,altona ,,water-,,works4 ,the ,altona water-works are specially interesting as an example of a water drawn from a source polluted to a most unusual extent3 the sewage from cities with a population of #ggj1jjj1 including its own1 is discharged into the river ,elbe within ten miles above the intake and upon the same side4 ,the area of the watershed of the ,elbe above ,altona is about #eb1jjj square miles1 and the average rainfall is estimated to be about #bh inches1 varying from #bd or less near its mouth to much higher quantities in the mountains far to the south4 ,on this watershed there are #df cities1 which in #ahij had populations of over #bj1jjj each1 and in addition there is a permanent population upon the river-boats estimated at #bj1jjj1 making in all #e1hid1jjj inhabitants1 without including either country districts or the numberless cities with less than #bj1jjj inhabitants each4 ,the sewage from about #a1gjj1jjj of these people is purified before being discharged2 and assuming that as many people living in cities smaller than #bj1jjj are connected with sewers as live in larger places without being so connected1 the sewage of over four million people is discharged untreated into the ,elbe and its tributaries4 ,the more important of these sources of pollution are the following3 ,city ,population ,on what ,approximate in #ahij4 ,river4 ,distance1 ,miles4 ,shipping #bj1jjj ,altona #adc1cec ,elbe #f ,hamburg #egj1ecd ,elbe #g ,wandsbeck #bj1ehf ,elbe #h ,harburg #ce1aja ,elbe #aa ,magdeburg #bjb1cbe ,elbe #ahe ,dresden #bgf1jhe ,elbe #ced ,berlin and suburbs #a1ghg1hei ,havel #bdc ,halle #aja1dja ,saale #bgb ,leipzig #cee1dhe ,elster #cje ,chemnitz #ach1iee ,mulde #cdj ,prague #caj1dhc ,moldau #ejj ,the sewage of ,berlin and of most of its suburbs is treated before being discharged1 and in addition the ,havel flows through a series of lakes below the city1 allowing better opportunities for natural purification than in the case of any of the other cities4 ,halle treats less than a tenth of its sewage4 ,magdeburg will treat its sewage in the course of a few years4 ,leipzig1 ,chemnitz1 and other places are thinking more or less seriously of purification4 ,the number of bacteria in the raw water at ,altona fluctuates with the tide and is extremely variable2 numbers of #ej1jjj and #ajj1jjj are not infrequent1 but #aj1jjj to #dj1jjj is perhaps about the usual range4 ,the works were originally built by an ,english company in #ahfj1 and have since been greatly extended4 ,they were bought by the city some years ago4 ,the water is pumped directly from the river to a settling-basin upon a hill #bhj feet above the river4 ,from this it flows by gravity through the filters to the slightly lower pure-water reservoir and to the city without further pumping4 ,the filters are open1 with nearly vertical masonry walls1 as described in ,kirkwood's report4 ,the cross-section of the main underdrain is #a_/bhjj of the area of the beds4 ,considerable trouble has been experienced from frost4 ,with continued cold weather it is extremely difficult to satisfactorily scrape the filters1 and very irregular rates of filtration may result at such times4 ,in the last few years1 with systematic bacterial investigation1 it has been found that greatly decreased efficiency frequently follows continued cold weather1 and the mild epidemics of typhoid fever from which the city has long suffered have generally occurred after these times4 ,thus a light epidemic of typhoid in #ahhf came in ,march1 following a light epidemic in ,hamburg4 ,in #ahhg a severe epidemic in ,february followed a severe epidemic in ,hamburg in ,december and ,january4 ,in #ahhh a severe epidemic in ,march followed an epidemic in ,hamburg lasting from ,november to ,january4 ,hamburg's epidemic of #ahhi1 coming in warm weather1 ,september and ,october1 was followed by only a very slight increase in ,altona4 ,in #ahia ,altona suffered again in ,february from a severe epidemic1 although very little typhoid had been in ,hamburg4 ,a less severe outbreak also came in ,february1 #ahib1 and a still slighter one in ,february1 #ahic4 ,in the ten years #ahhb-ahib1 of five well-marked epidemics1 three broke out in ,february and two in ,march1 while two smaller outbreaks came in ,december and ,january4 ,no important outbreak has ever occurred in summer or in the fall months1 when typhoid is usually most prevalent1 thus showing clearly the bad effect of frost upon open filters 7see ,appendix ,,ii74 ,with steadily increasing consumption the sedimentation-basin capacity of late years has become insufficient as well as the filtering area1 and it is not unlikely that with better conditions a much better result could be obtained in winter even with open filters4#fc ,the brilliant achievement of the ,altona filters was in the summer of #ahib1 when they protected the city from the cholera which so ravaged ,hamburg1 although the raw water at ,altona must have contained a vastly greater quantity of infectious matter than that which worked such havoc in ,hamburg4 ,from these records it appears that for about nine months of the year the ,altona filters protect the city from the impurities of the ,elbe water1 but that during cold weather1 with continued mean temperatures below the freezing-point1 such protection is not completely afforded1 and bad effects have occasionally resulted4 ,notwithstanding the recent construction of open filters in ,hamburg it appears to me that there must always be more or less danger from open filters in such a climate4 ,hamburg's danger1 however1 will be much less than ,altona's on account of its better intake above the outlets of the sewers of ,hamburg and ,altona1 which are the most important points of pollution at ,altona4 ,,appendix ,,viii4 ,,hamburg ,,water-,,works4 ,the source and quality of the water previously supplied has been sufficiently indicated in ,appendix ,,ii4 ,it was originally intended to filter the water1 but the construction of filters was postponed from time to time until the fall of #ahij1 when the project was seriously taken up1 and work was commenced in the spring of #ahia4 ,three years were allowed for construction4 ,in #ahib1 however1 the epidemic of cholera came1 killing #hfje residents and doing incalculable damage to the business interests of the city4 ,the health authorities found that the principal cause of this epidemic was the polluted water-supply4 ,to prevent a possible recurrence of cholera in #ahic1 the work of construction of the filters was pressed forward much more rapidly than had been intended4 ,electric lights were provided to allow the work to proceed nights as well as days1 and as a result the plant was put in operation ,may #bg1 #ahic1 a full year before the intended time4 ,owing to the forced construction the cost was materially increased4 ,the new works take the raw water from a point one and a half miles farther up-stream1 where it is believed the tide can never carry the city's own sewage1 as it did frequently to the old intake4 ,the water is pumped from the river to settling-basins against heads varying with tide and the water-level in the basins from #h to #bb feet4 ,each of the four settling-basins has an area of about #aj acres1 and1 with the water #f4ef feet deep1 holds #bj1ejj1jjj gallons1 or #hb1jjj1jjj gallons in all4 ,the works are intended to supply a maximum of #dh1jjj1jjj gallons daily1 but the present average consumption is only about #ce1jjj1jjj gallons 7#ahib71 or #ei gallons per head for #fjj1jjj population4 ,this consumption is regarded as excessive1 and it is hoped that it will be reduced materially by the more general use of meters4 ,the sedimentation-basins are surrounded by earthen embankments with slopes of #a3c1 the inner sides being paved with brick above a clay layer4 ,the water flows by gravity from these basins to the filters1 a distance of #a-a_/b miles1 through a conduit #h-a_/b feet in diameter4 ,the flow of the water out of the basins and from the lower end of the conduit is regulated by automatic gates connected with floats1 shown by ,fig4 #aa1 page #fj4 ,the filters are #ah in number1 and each has an effective area of #a4hi1 or #cd acres in all4 ,they are planned to filter at a rate of #a4fj million gallons per acre daily1 which with #af filters in use gives a daily quantity of #dh1jjj1jjj gallons as the present limit of the works4 ,the sides of the filters are embankments with #a3b slopes4 ,both sides and bottoms have #bj inches of packed clay1 above which are #d inches of puddle1 supporting a brick pavement laid in cement4 ,the bricks are laid flat on the bottom1 but edge-wise on the sides where they will come in contact with ice4 ,the main effluent-drain has a cross-section for the whole length of the filter of #d4gc square feet1 or #a_/agjjj of the area of the filter2 and even at the low rate of filtration proposed1 the velocity in the drain will reach #j4ig foot4 ,the drain has brick sides1 #a4hj feet high1 covered with granite slabs4 ,the lateral drains are all of brick with numerous large openings for admission of water4 ,they are not ventilated1 and ,i am unable to learn that any bad results follow this omission4 ,the filling of the filters consists of #b feet of gravel1 the top being of course finer than the bottom layers1 above which are #dj inches of sand1 which are to be reduced to #bd inches by scraping before being refilled4 ,the water over the sand1 when the latter is of full depth1 is #dc inches deep1 and will be increased to #ei inches with the minimum sand-thickness4 ,the apparatus for regulating the rate of filtration was described page #eb4 ,the cost of the entire plant1 including #cd acres effective filter-surface1 #dj acres of sedimentation-basins1 over #b miles of #h-a_/b-;foot conduit1 pumping-machinery1 sand-washing apparatus1 laboratory1 etc41 was about #i1ejj1jjj marks1 or #b1bhj1jjj4 ,this all reckoned on the effective filter area is #fg1jjj per acre1 or #c4hj per head for a population of #fjj1jjj4 ,the death-rate since the introduction of filtered water has been lower than ever before in the history of the city1 but as it is thought that other conditions may help to this result1 no conclusions are as yet drawn4 ,,deaths ,,in ,,hamburg ,,from ,,all ,,causes1 ,,and ,,from ,,typhoid ,,fever1 ,,before ,,and ,,after ,,the ,,introduction ,,of ,,filters4 ---------------------------------------- ---------------- ,deaths from,deaths from all ,causes ,typhoid ,year4 per #ajjj ,fever per ,living4 #ajj1jjj ,living4 ---------------------------------------- ---------------- #ahhj #bd4i #bf #ahha #bd4a #cj #ahhb #bc4g #bg #ahhc #be4b #be #ahhd #be4a #bf #ahhe #be4c #db #ahhf #bi4j #ga #ahhg #bf4f #hh #ahhh #bd4e #ed #ahhi #bc4e #dc #ahij #bb4j #bg #ahia #bc4d #bd #ahib #da4a #cd ,cholera year4 #ahic #bj4b #ah ,filtered water from ,may #bh4 #ahid #ag4i #g #ahie #ai4j #aa #ahif #ag4c #f #ahig #ag4j #g #ahih #ag4e #e ,average for #e years1 excluding cholera year1 before filtration1 #ahhg to #ahia #bd4j #dg4b ,average for #e years with filtration1 #ahid to #ahih #ag4g #g4b ---------------------------------------- ---------------- ,,appendix ,,ix4 ,,notes ,,on ,,some ,,other ,,european ,,water-,,supplies4 ,amsterdam4--,the water is derived from open canals in the dunes4 ,these canals have an aggregate length of about #ae miles1 and drain about #fbjj acres4 ,the water1 as it enters the canals from the fine dune-sand1 contains iron1 but this is oxidized and deposited in the canals4 ,the water after collection is filtered4 ,it has been suggested that by using covered drains instead of open canals for collecting the water1 the filtration would be unnecessary2 but1 on the other hand1 the cost of building and maintaining covered drains in the very fine sand would be much greater than that of the canals1 and it is believed1 also1 that the water so collected would contain iron1 the removal of which might prove as expensive as the present filtration4 ,in #ahhg filters were built to take water from the river ,vecht1 but the city has refused to allow the ,english company which owns the water-works to sell this water for domestic purposes1 and it is only used for public and manufacturing purposes1 only a fraction of the available supply being required4 ,leyden1 the ,hague1 and some other ,dutch cities have supplies like the dune supply of ,amsterdam1 and they are invariably filtered4 ,antwerp is also supplied by an ,english company4 ,the raw water is drawn from a small tidal river1 which at times is polluted by the sewage of ,brussels4 ,it is treated by metallic iron in ,anderson revolver purifiers1 and is afterward filtered at a rather low average rate4 ,the hygienic results are closely watched by the city authorities1 and are said to be satisfactory4 ,rotterdam4--,the raw water is drawn from the ,maas1 as the ,dutch call the main stream of the ,rhine after it crosses their border4 ,the population upon the river and its tributaries in ,switzerland1 ,germany1 ,holland1 ,france1 and ,belgium is very great2 but the flow is also great1 and the low water flow is exceptionally large in proportion to the average flow1 on account of the melting snow in summer in ,switzerland1 where it has its origin4 ,the original filters had wooden under-drains1 and there was constant trouble with crenothrix until the filters were reconstructed without wood1 since which time there has been no farther trouble4 ,the present filters are large and well managed4 ,there is ample preliminary sedimentation4 ,schiedam4--,the filters at ,schiedam are comparatively small1 but are of unusual interest on account of the way in which they are operated4 ,the intake is from the ,maas just below ,rotterdam4 ,the city was unable to raise the money to seek a more distant source of supply1 and the engineer1 ,h4 ,p4 ,n4 ,halbertsma1 was unwilling to recommend a supply from so doubtful a source without more thorough treatment than simple sand-filtration was then thought to be4 ,the plan adopted is to filter the supply after preliminary sedimentation through two filters of #j4bfe acre each1 and the resulting effluent is then passed through three other filters of the same size4 ,river sand is used for the first1 and the very fine dune sand for the second filtration4 ,the cost both of construction and operation was satisfactory to the city1 and much below that of any other available source2 and the hygienic results have been equally satisfactory1 notwithstanding the unfavorable position of the intake4 ,magdeburg4--,the supply is drawn from the ,elbe1 and is filtered through vaulted filters after preliminary sedimentation4 ,the pollution of the river is considerable1 although less than at ,altona or even at ,hamburg4 ,the city has been troubled at times by enormous discharges of salt solution from salt-works farther up1 which at extreme low water have sometimes rendered the whole river brackish and unpleasant to the taste2 but arrangements have now been made which1 it is hoped1 will prevent the recurrence of this trouble4 ,breslau is supplied with filtered water from the river ,oder1 which has a watershed of #hbjj square miles above the intake1 and is polluted by the sewage from cities with an aggregate population of about #bjj1jjj1 some of which are in ,galicia1 where cholera is often prevalent4 ,in recent years the city has been free from cholera1 and from more than a very limited number of typhoid-fever cases2 but the pollution is so great as to cause some anxiety1 notwithstanding the favorable record of the filters1 and there is talk of the desirability of securing another supply4 ,until #ahic there were four filter-beds1 with areas of #a4jc acres each1 and not covered4 ,in #ahic a fifth bed was added4 ,this is covered by vaulting and is divided into four sections1 which are separately operated1 so that it is really four beds of #j4be acre each4 ,the vaulting is concrete arches1 supported by steel ,i beams in one direction4 ,budapest4--,a great variety of temporary water-supplies have at different times been used by this rapidly growing city4 ,the filters which for some years have supplied a portion of the supply have not been altogether satisfactory2 but perhaps this was due to lack of preliminary sedimentation for the extremely turbid ,danube water1 and also to inadequate filter-area4 ,the city is rapidly building and extending works for a supply of ground-water1 and in #ahid the filters were only used as was necessary to supplement this supply1 and it was hoped that enough well-water would be obtained to allow the filters to be abandoned in the near future4 ,the ,danube above the intake receives the sewage of ,vienna and innumerable smaller cities1 but the volume of the river is very great compared to other ,european streams1 so that the relative pollution is not so great as in many other places4 ,zrich4--,the raw water is drawn by the city from the ,lake of ,zrich near its outlet1 and but a few hundred feet from the heart of the city4 ,although no public sewers discharge into the lake1 there is some pollution from boats and bathers and other sources1 and1 judging by the number of bacteria in the raw water1 this pollution is increasing4 ,the raw water is extremely free from sediment1 and the filters only become clogged very slowly4 ,the rate of filtration is high1 habitually reaching #g1jjj1jjj gallons per acre daily2 but1 with the clear lake water and long periods between scrapings1 the results are excellent even at this rate4 ,the filters are all covered with concrete groined arches4 ,filtration was commenced in #ahhf1 and was followed by a sharp decline in the amount of typhoid fever1 which1 up to that time1 had been rather increasing2 for the six years before the change there were sixty-nine deaths from this cause annually per #ajj1jjj living1 and for the six years after only ten1 or one seventh as many2 and this reduction is attributed by the local authorities to the filtration4#fd ,st4 ,petersburg4--,the supply is drawn from the ,neva ,river by an ,english company1 and is filtered through vaulted filters at a very high rate4 ,warsaw4--,the supply is drawn from the ,weichsel ,river by the city1 and is filtered through vaulted filters after preliminary sedimentation at a rate never exceeding #b1egj1jjj gallons per acre daily4 ,,the ,,use ,,of ,,unfiltered ,,surface-,,waters4 ,the use of surface-water without filtration in ,europe is comparatively limited4 ,in ,germany this use is now prohibited by the ,imperial ,board of ,health4 ,in ,great ,britain1 ,glasgow draws its supply unfiltered from ,loch ,katrine2 and ,manchester and some other towns use unfiltered waters from lakes or impounding reservoirs the watersheds of which are entirely free from population4 ,the best ,english practice1 however1 as in ,germany1 requires the filtration of such waters even if they are not known to receive sewage1 and the unpolluted supplies of ,liverpool1 ,bradford1 ,dublin1 and many other cities are filtered before use4 ,,the ,,use ,,of ,,ground-,,water4#fe ,ground-waters are extensively used in ,europe1 and apparently in some localities the geological formations are unusually favorable to this kind of supply4 ,paris derives all the water it now uses for domestic purposes from springs1 but has a supplementary supply from the river for other purposes4 ,vienna and ,munich also obtain their entire supplies from springs1 while ,budapest1 ,cologne1 ,leipzig1 ,dresden1 ,frankfurt1 many of the great ,french cities1 ,brussels1 a part of ,london1 and many other ,english cities derive their supplies from wells or filter-galleries1 and among the smaller cities all over ,europe ground-water supplies are more numerous than other kinds4 ,,appendix ,x4 ,,literature ,,of ,,filtration4 ,the following is a list of a number of articles on filtration4 ,the list is not complete1 but it is believed that it contains the greater part of articles upon slow sand-filtration1 and that it will prove serviceable to those who wish to study the subject more in detail4 ,,anklamm4 ,glasers ,annalen1 #ahhf1 p4 #dh4 ,a description of the ,tegel filters at ,berlin1 with excellent plans4 ,,baker4 ,engineering ,news4 ,water purification in ,america3 a series of descriptions of filters1 as follows3 ,aug4 #c1 #ahic1 ,lawrence filter and description of apparatus of screening sand and gravel2 ,apr4 #bf1 #ahid1 filter at ,nantucket1 ,mass42 ,june #g1 #ahid1 filters at ,ilion1 ,n4 ,y41 plans2 ,june #ad1 #ahid1 filters at ,hudson1 ,n4 ,y42 ,july #ab1 #ahid1 filters at ,zrich1 ,switzerland1 plans2 ,aug4 #bc1 #ahid1 filters at ,mt4 ,vernon1 ,n4 ,y41 plans4 ,,bertschinger4 ,journal fr ,gas- und ,wasserversorgung1 #ahhi1 p4 #aabf4 ,a record of experiments made at ,zrich upon the effect of rate of filtration1 scraping1 and the influence of vaulting4 ,rate and vaulting were found to be without effect1 but poorer results followed scraping4 ,the numbers of bacteria in the lake-water were too low to allow conclusive results4 ---- ,journal fr ,gas- und ,wasserversorgung1 #ahia1 p4 #fhd4 ,a farther account of the ,zrich results1 with full analyses and a criticism of ,frnkel and ,piefke's experiments4 ,,bolton4 ,pamphlet1 #ahhd4 ,descriptions and statistics of ,london filters4 ,b,,ttcher and ,,ohnesorge4 ,zeitschrift fr ,bauwesen1 #ahgf1 p4 #cdc4 ,a description of the ,bremen works1 with full plans4 ,,burton4 ,water-supply of ,towns4 ,london1 #ahid4 ,pages #id-aae are upon filtration and mention a novel method of regulating the rate4 ,,codd4 ,engineering ,news1 ,apr4 #bf1 #ahid4 ,a description of a filter at ,nantucket1 ,mass4 ,,cramer4 ,centralblatt fr ,bauwesen1 #ahhf1 p4 #db4 ,a description of filters built at ,brieg1 ,germany4 ,,crook4 ,london ,water-supply4 ,london1 #ahhc4 ,,delbruck4 ,allgemeine ,bauzeitung1 #ahec1 p4 #ajc4 ,a general article on filtration2 particularly valuable for notices of early attempts at filtration and of the use of alum4 ,deutsche ,verein von ,gas- und ,wasserfachmnner4 ,stenographic reports of the proceedings of this society are printed regularly in the ,journal fr ,gas- und ,wasserversorgung1 and the discussions of papers are often most interesting4 ,,drown4 ,journal ,association ,eng4 ,societies1 #ahij1 p4 #cef4 ,filtration of natural waters4 ,,fischer4 ,vierteljahresschrift fr ,gesundheitspflege1 #ahia1 p4 #hb4 ,discussion of papers on water-filtration4 ,,fr,,nkel4 ,vierteljahresschrift fr ,gesundheitspflege1 #ahia1 p4 #ch4 ,on filters for city water-works4 ,,fr,,nkel and ,,piefke4 ,zeitschrift fr ,hygiene1 #ahia1 p4 #ch1 ,leistungen der ,sandfiltern4 ,e4 ,,frankland4 ,report in regard to the ,london filters for #ahic in the ,annual ,summary of ,births1 ,deaths1 and ,causes of ,death in ,london and ,other ,great ,towns1 #ahic4 ,published by authority of the ,registrar-,general4 ,p4 ,,frankland4 ,proc4 ,royal ,society1 #ahhe1 p4 #cgi4 ,the removal of micro-organisms from water4 ---- ,proceedings ,inst4 ,civil ,engineers1 #ahhf1 lxxxv4 p4 #aig4 ,water-purification2 its biological and chemical basis4 ---- ,trans4 of ,sanitary ,institute of ,great ,britain1 #ahhf4 ,filtration of water for town supply4 ,,fr,,hling4 ,handbuch der ,ingenieurwissenschaften1 vol4 ii4 ,chapter on water-filtration gives general account of filtration1 with details of ,knigsberg filters built by the author and not elsewhere published4 ,,fuller4 ,report ,mass4 ,state ,board of ,health1 #ahib1 p4 #ddi4 ,report ,mass4 ,state ,board of ,health1 #ahic1 p4 #dec4 ,accounts of the ,lawrence experiments upon water-filtration for #ahib and #ahic4 ---- ,american ,public ,health ,association1 #ahic1 p4 #aeb4 ,on the removal of pathogenic bacteria from water by sand filtration4 ---- ,american ,public ,health ,association1 #ahid1 p4 #fd4 ,sand filtration of water with special reference to results obtained at ,lawrence1 ,mass4 ,,gill4 ,deutsche ,bauzeitung1 #ahha1 p4 #efg4 ,on ,american rapid filters4 ,the author shows that they are not to be thought of for ,berlin1 as they would be more expensive as well as probably less efficient than the usual procedure4 ---- ,journal fr ,gas- und ,wasserversorgung1 #ahib1 p4 #eif4 ,a general account of the extension of the ,berlin filters at ,mggel4 ,no drawings4 ,,grahn4 ,journal fr ,gas- und ,wasserversorgung1 #ahgg1 p4 #edc4 ,on the filtration of river-waters4 ---- ,journal fr ,gas- und ,wasserversorgung1 #ahij1 p4 #eaa4 ,filters for city water-works4 ---- ,vierteljahresschrift fr ,gesundsheitpflege1 #ahia1 p4 #gf4 ,discussion of papers presented on filtration4 ---- ,journal fr ,gas- und ,wasserversorgung1 #ahid1 p4 #ahe4 ,a history of the 8,rules for ,water-filtration0 7,appendix ,i71 with some discussion of them4 ,,grahn and ,,meyer4 ,reiseberichte ber knstliche central ,sandfiltration4 ,hamburg1 #ahgf4 ,an account of the observations of the authors in numerous cities1 especially in ,england4 ,,grenzmer4 ,centralblatt der ,bauverwaltung1 #ahhh1 p4 #adh4 ,a description of new filters at ,amsterdam1 with plans4 ,,gruber4 ,centralblatt fr ,bakteriologie1 #ahic1 p4 #dhh4 ,salient points in judging of the work of sand-filters4 ,,halbertsma4 ,journal fr ,gas- und ,wasserversorgung1 #ahib1 p4 #dc4 ,filter-works in ,holland4 ,gives sand1 gravel1 and water thickness1 with diagrams4 ---- ,journal fr ,gas- und ,wasserversorgung1 #ahib1 p4 #fhf4 ,description of filters built by the author at ,leeuwarden1 ,holland1 with plans4 ,,hart4 ,proceedings ,inst4 of ,civil ,engineers1 #ahij1 c4 p4 #bag4 ,description of filters at ,shanghai4 ,,hausen4 ,journal fr ,gas- und ,wasserversorgung1 #ahib1 p4 #ccb4 ,an account of experiments made for one year with three #af-;inch filters at ,helsingfors1 ,finland1 with weekly analyses of effluents4 ,,hazen4 ,report of ,mass4 ,state ,board of ,health1 #ahia1 p4 #fja4 ,experiments upon the filtration of water4 ---- ,report of ,mass4 ,state ,board of ,health1 #ahib1 p4 #eci4 ,physical properties of sands and gravels with reference to their use in filtration4 7,appendix ,,iii47 ,,hunter4 ,engineering1 #ahib1 vol4 #ec1 p4 #fba4 ,description of author's sand-washing apparatus4 ,,kirkwood4 ,filtration of ,river-waters4 ,new ,york1 #ahfi4 ,a report upon ,european filters for the ,st4 ,louis ,water ,board in #ahff4 ,contains a full account of thirteen filtration-works visited by the author1 and of a number of filter-galleries1 with a project for filters for ,st4 ,louis4 ,this project was never executed1 but the report is a wonderful work which appeared a generation before the ,american public was able to appreciate it4 ,it was translated into ,german1 and the ,german edition was widely circulated and known4 ,,koch4 ,zeitschrift fr ,hygiene1 #ahic4 ,water-filtration and ,cholera3 a discussion of the ,hamburg epidemic of #ahib in reference to the effect of filtration4 ,,kr,,hnke4 ,journal fr ,gas- und ,wasserversorgung1 #ahic1 p4 #eac4 ,an account of experiments made at ,hamburg1 as a result of which the author recommends the addition of cuprous chloride to the water before filtration to secure greater bacterial efficiency4 ,k,,mmel4 ,journal fr ,gas- und ,wasserversorgung1 #ahgg1 p4 #deb4 ,operation of the ,altona filters1 with analyses4 ---- ,vierteljahresschrift fr ,gesundheitspflege1 #ahha1 p4 #ib4 ,the water-works of the city of ,altona4 ---- ,journal fr ,gas- und ,wasserversorgung1 #ahhg1 p4 #ebb4 ,an article opposing the use of rapid filters 7,david's process74 ---- ,journal fr ,gas- und ,wasserversorgung1 #ahij1 p4 #eca4 ,a criticism of ,frnkel and ,piefke's results1 with some statistics of ,german and ,english filters4 7,the ,english results are taken without credit from ,kirkwood47 ---- ,vierteljahresschrift fr ,gesundheitspflege1 #ahia1 p4 #hg4 ,discussion of papers on filtration1 with some statistics4 ---- ,vierteljahresschrift fr ,gesundheitspflege1 #ahib1 p4 #che4 ,the epidemic of typhoid-fever in ,altona in #ahia4 ---- ,journal fr ,gas- und ,wasserversorgung1 #ahic1 p4 #afa4 ,results of experiments upon filtration made at ,altona1 and bacterial results of the ,altona filters in connection with typhoid death-rates4 ---- ,trans4 ,am4 ,society of ,civil ,engineers1 #ahic1 xxx4 p4 #ccj4 ,questions of water-filtration4 ,,leslie4 ,trans4 ,inst4 ,civil ,engineers1 #ahhc1 lxxiv4 p4 #aaj4 ,a short description of filters at ,edinburgh4 ,,lindley4 ,a report for the commissioners of the ,paris ,exposition of #ahhi upon the purification of river-waters1 and published in ,french or ,german in a number of journals1 among them ,journal fr ,gas- und ,wasserversorgung1 #ahij1 p4 #eja4 ,this is a most satisfactory discussion of the conditions which modern experience has shown to be essential to successful filtration4 ,,mason4 ,engineering ,news1 ,dec4 #g1 #ahic4 ,filters at ,stuttgart1 ,germany1 with plans4 ,,meyer and ,,samuelson4 ,deutsche ,bauzeitung1 #ahha1 p4 #cdj4 ,project for filters for ,hamburg1 with diagrams4 ,except in detail1 this project is the same as that executed twelve years later4 ,,meyer4 ,deutsche ,bauzeitung1 #ahib1 p4 #eai4 ,description of the proposed ,hamburg filters1 with diagrams4 ---- ,the ,water-works of ,hamburg4 ,a paper presented to the ,international ,health ,congress at ,rome1 ,march #ahid1 and published as a monograph4 ,it contains a full description of the filters as built1 with drawings and views in greater detail than the preceding paper4 ,,mills4 ,special ,report ,mass4 ,state ,board of ,health on the ,purification of ,sewage and ,water1 #ahij1 p4 #fja4 ,an account of the ,lawrence experiments1 #ahhh-ahij4 ---- ,report ,mass4 ,state ,board of ,health1 #ahic1 p4 #edc4 ,the ,filter of the ,water-supply of the ,city of ,lawrence and its ,results4 ---- ,trans4 ,am4 ,society of ,civil ,engineers1 #ahic1 xxx4 p4 #cej4 ,purification of ,sewage and ,water by ,filtration4 ,,neville4 ,engineering1 #ahgh1 xxvi4 p4 #cbd4 ,a description of the ,dublin filters1 with plans4 ,,nichols4 ,report ,mass4 ,state ,board of ,health1 #ahgh1 p4 #acg4 ,the filtration of potable water4 ,,oester4 ,gesundheits-,ingenieur1 #ahic1 p4 #eje4 ,what is the ,rate of ,filtration8 ,a purely theoretical discussion4 ,,orange4 ,trans4 ,inst4 ,civil ,engineers1 #ahij1 c4 p4 #bfh4 ,filters at ,hong ,kong4 ,,pfeffer4 ,deutsche ,bauzeitung1 #ahhj1 p4 #cii4 ,a description of filters at ,liegnitz1 ,germany4 ,,piefke4 ,results of ,natural and ,artificial ,filtration4 ,berlin1 #ahha4 ,pamphlet4 ---- ,journal fr ,gas- und ,wasserversorgung1 #ahhg1 p4 #eie4 ,die ,principien der ,reinwassergewinnung vermittelst ,filtration4 ,a sketch of the theory and practical application of filtration4 ---- ,zeitschrift fr ,hygiene1 #ahhi1 p4 #abh4 ,aphorismen ber ,wasserversorgung4 ,a discussion of the theory of filtration1 with a number of experiments on the thickness of sand-layers1 etc4 ,,piefke4 ,vierteljahresschrift fr ,gesundheitspflege1 #ahia1 p4 #ei4 ,on filters for city water-works4 ,,fr,,nkel and ,,piefke4 ,zeitschrift fr ,hygiene1 #ahia1 p4 #ch4 ,leistungen der ,sandfiltern4 ,an account of the partial obstruction of the ,stralau filters by ice1 and a typhoid epidemic which followed4 ,experiments were then made upon the passage of cholera and typhoid germs through small filters4 ,,piefke4 ,journal fr ,gas- und ,wasserversorgung1 #ahia1 p4 #bjh4 ,neue ,ermittelungen ber ,sandfiltration4 ,the above mentioned experiments being objected to on certain grounds1 they were repeated by ,piefke alone1 confirming the previous observations on the passage of bacteria through filters1 but under other conditions4 ---- ,zeitschrift fr ,hygiene1 #ahid1 p4 #aea1 ber ,betriebsfhrung von ,sandfiltern4 ,a full account of the operation of the ,stralau filters in #ahic1 with discussion of the efficiency of filtration1 etc4 ,,plagge ,,and ,,proskauer4 ,zeitschrift fr ,hygiene1 #aa4 p4 #djc4 ,examination of water before and after filtration at ,berlin1 with theory of filtration4 ,,reincke4 ,bericht ber die ,medicinische ,statistik des ,hamburgischen ,staates fr #ahib4 ,contains a most valuable discussion of the relations of filtration to cholera1 typhoid fever1 and diarrha1 with numerous tables and charts4 7,abstract in ,appendix ,,ii47 ,,reinsch4 ,centralblatt fr ,bakteriologie1 #ahie1 p4 #hha4 ,an account of the operation of the ,altona filters4 ,high numbers of bacteria in the effluents have often resulted from the discharge of sludge from the sedimentation-basins onto the filters1 due to the interference of ice on the action of the floating outlet for the basins1 and this1 rather than the direct effect of cold1 is believed to be the direct cause of the low winter efficiency4 ,the author urges the necessity of a deeper sand-layers in no case less than #ah inches thick4 ,,renk4 ,gesundheits-,ingenieur1 #ahhf1 p4 #ed4 ---- ber die ,ziele der knstliche ,wasserfiltration4 ,,ruhlmann4 ,wochenblatt fr ,baukunde1 #ahhg1 p4 #dji4 ,a description of filters at ,zrich4 ,,salbach4 ,glaser's ,annalen1 #ahhb4 ,filters at ,groningen1 ,holland1 built in #ahhj4 ,alum used4 ,,samuelson4 ,translation of ,kirkwood's 8,filtration of ,river-waters0 into ,german1 with additional notes especially on the theory of filtration and the sand to be employed4 ,hamburg1 #ahgf4 ,,samuelson4 ,filtration and constant water-supply4 ,pamphlet4 ,hamburg1 #ahhb4 ---- ,journal f4 ,gas- und ,wasserversorgung1 #ahib1 p4 #ffj4 ,a discussion of the best materials and arrangement for sand-filters4 ,,schmetzen4 ,deutsche ,bauzeitung1 #ahgh1 p4 #cad4 ,notice and extended criticism of ,samuelson's translation of ,kirkwood4 ,,sedden4 ,jour4 ,asso4 ,eng4 ,soc41 #ahhi1 p4 #dgg4 ,in regard to the sedimentation of river-waters4 ,,sedgwick4 ,new ,england ,water-works ,association1 #ahib1 p4 #ajc4 ,european methods of ,filtration with ,reference to ,american ,needs4 ,,sokal4 ,wochenschrift der streichen ,ingenieur-,verein1 #ahij1 p4 #chf4 ,a short description of the filters at ,st4 ,petersburg1 and a comparison with those at ,warsaw4 ,,sturmh,,fel4 ,zeitschrift f4 ,bauwesen1 #ahhj1 p4 #cd4 ,a description of the ,magdeburg filters1 with plans4 ,,tomlinson4 ,american ,water-works ,association1 #ahhh4 ,a paper on filters at ,bombay and elsewhere4 ,,turner4 ,proc4 ,inst4 ,civil ,engineers1 #ahij1 c4 p4 #bhe4 ,filters at ,yokohama4 ,,van ,,der ,,tak4 ,tijdschrift van de ,maatschapping van ,bouwkunde1 #ahge7874 ,a description 7in ,dutch7 of the ,rotterdam water-works1 including the wooden drains which caused the trouble with crenothrix1 and which have since been removed4 ,diagrams4 ,,van ,,ijsselsteyn4 ,tijdschrift van het ,koninklijk ,instituut van ,ingenieurs1 #ahib-e1 p4 #agc4 ,a description of the new ,rotterdam filters1 with full drawings4 ,,veitmeyer4 ,verhandlungen d4 polyt4 ,gesell4 zu ,berlin1 ,april1 #ahhj4 ,filtration and purification of water4 ,,wolffh,,gel4 ,arbeiten aus dem ,kaiserliche ,gesundheitsamt1 #ahhf1 p4 #a4 ,examinations of ,berlin water for #ahhd-e1 with remarks showing superior bacterial efficiency with open filters4 ---- ,journal fr ,gas- u4 ,wasserversorgung1 #ahij1 p4 #eaf4 ,on the bacterial efficiency of the ,berlin filters1 with diagrams4 ,,zobel4 ,zeitschrift des ,vereins deutsche ,ingenieure1 #ahhd1 p4 #ecg4 ,description of filters at ,stuttgart4 ,,other ,,literature4 ,many scientific and engineering journals publish from time to time short articles or notices on filtration which are not included in the above list4 ,among such journals none gives more attention to filtration than the ,journal fr ,gasbeleuchtung und ,wasserversorgung1 which publishes regularly reports upon the operation of many ,german filters1 and gives short notices of new construction4 ,the first articles upon filtration in this journal were a series of descriptions of ,german water-works in #ahgj-gc1 including descriptions of filters at ,altona1 ,brunswick1 ,lbeck1 etc4 ,stenographic reports of many scientific meetings have been published1 particularly since #ahij1 and since #ahib there has been much discussion in regard to the 8,rules for ,filtration0 given in ,appendix ,i4 ,a ,report of a ,royal ,commission to inquire into the water-supply of the metropolis1 with minutes of evidence1 appendices1 and maps 7,london1 #ahic-d71 contains much valuable material in regard to filtration4 ,the monthly reports of the water examiner1 and other papers published by the ,local ,government ,board1 ,london1 are often of interest4 ,the ,german 8,verein von ,gas- u4 ,wasserfachmnner0 prints without publishing a most useful annual summary of ,german water-works statistics for distribution to members4 ,many of the statistics given in this volume are from this source4 ,description of the filters at ,worms was given in the ,deutsche ,bauzeitung1 #ahib1 p4 #ejh2 of the filters at ,liverpool in ,engineering1 #ahhi1 p4 #aeb1 and #ahib1 p4 #gci4 ,the latter journal also has given a number of descriptions of filters built in various parts of the world by ,english engineers1 but1 excepting the articles mentioned in the above list1 the descriptions are not given in detail4 ,,more ,,recent ,,articles4 ,the following are a few of the more important articles which have appeared since the first edition of this book4 ,in addition many articles of current interest have appeared in the technical journals1 particularly in the journals mentioned above4 ,,clark4 ,reports of ,mass4 ,state ,board of ,health1 #ahid to #ahig1 inclusive4 ,articles on the filtration of water1 giving accounts of experiments at the ,lawrence ,experiment ,station1 and records of the operation of the ,lawrence city filter4 ,these experiments are directed principally to the removal of bacteria from sewage-polluted waters4 ---- ,jour4 ,new ,england ,water ,works ,assoc41 ,,xi41 p4 #bgg4 ,removal of ,iron from ,ground ,waters4 ,a description of certain experiments4 ,,fowler4 ,jour4 ,new ,england ,water ,works ,assoc41 ,,xii41 p4 #bji4 ,the ,operation of a ,slow ,sand ,filter4 ,a most helpful and thorough description of the operation of sand filters at ,poughkeepsie for a long period of years4 ,,fuller4 ,water ,purification at ,louisville4 ,d4 ,van ,nostrand ,co41 #ahih4 ,a report upon a series of most exhaustive experiments carried out at ,louisville1 directed principally to the clarification of excessively muddy waters4 ,contains a full account of methods of coagulation1 and of experiments with the electrical treatment of water4 ---- ,report on ,water ,filtration at ,cincinnati4 ,city document1 #ahii4 ,account of experiments with sand filters1 with and without coagulants1 and with other processes applied to the ,ohio ,river water at ,cincinnati4 ,,gill4 ,filters at ,muggel4 ,proc4 ,institute of ,civil ,engineers1 #ahid-e2 vol4 #aai1 p4 #bcf4 ,a description of the new vaulted filter plant designed by the author for ,berlin1 ,germany4 ,plans and views4 ,,goetze4 ,journal fr ,gasbeleuchtung und ,wasserversorgung1 #ahig1 p4 #afi4 ,selbstthtige ,wasseraustrittsregler besonders fr ,filter4 ,a description of the automatic regulating device for filters used at ,bremen4 ---- ,zeitschrift des ,vereines deutscher ,ingenieure1 ,,xxx4 ,reinigung des ,trinkwassers in ,bremen durch mehrmalige ,sandfiltration4 ,a description of the method of double filtration used at ,bremen1 giving results obtained in full4 ,no drawings4 ,,grahn4 ,journal fr ,gasbeleuchtung und ,wasserversorgung1 #ahie4 ,water purification plant at the city of ,magdeburg4 ,a description of the old plant1 and the changes which have been made in it to increase its capacity1 and make it conform to the requirements of the ,german official instructions regarding filtration4 ,many illustrations and plans4 ,,halbertsma4 ,journal fr ,gasbeleuchtung und ,wasserversorgung1 #ahif4 ,die ,resultate der doppelten ,filtration zu ,schiedam4 ,a description of double filtration at ,schiedam1 with the bacterial results for the two years1 #ahid and #ahie1 showing an average bacterial efficiency of #ii4gf per cent4 ,,hazen4 ,report to ,filtration ,commission1 ,pittsburgh4 ,city document1 #ahii4 ,a description of experiments upon the treatment of the ,allegheny ,river water by sand and mechanical filters4 ---- ,ohio ,state ,board of ,health ,report1 #ahig1 p4 #aed4 ,report on the ,mechanical ,filtration of the ,public ,water ,supply of ,lorain4 ,gives the results of a five-weeks test of the ,jewell mechanical filters at ,lorain1 treating ,lake ,erie water4 ,,kemna4 ,the ,biology of ,sand ,filtration4 ,read before the annual convention of the ,british ,association of ,water ,works ,engineers4 ,abstract in ,engineering ,news1 ,,xli41 p4 #dai4 ,describing organisms which develop in open sand filters1 both animal and vegetable1 and their effects upon the process4 ,a quite full account of the author's extended experience1 and the only paper treating this subject4 ,,magar4 ,journal fr ,gasbeleuchtung und ,wasserversorgung1 #ahig1 p4 #d4 ,reinigungsbetrieb der offener ,sandfilter des ,hamburger ,filterwerkes in ,frostzeiten4 ,a new method of cleaning open filters in winter without the removal of the ice4 ,,panwitz4 ,arbeiten aus dem ,kaiserlichen ,gesundheitsamte1 ,,xiv41 p4 #aec4 ,die ,filtration von ,oberflchenwasser in den deutschen ,wasserwerken whrend der ,jahre #ahid bis #ahif4 ,a description of the filtration works in ,germany1 and the results obtained from them1 particularly from the point of view of bacterial efficiency4 ,results are graphically shown by a series of charts4 ,,reynard4 ,le ,gnie ,civil1 #ahif1 ,,xxviii41 p4 #cba4 ,purification of water with the aid of metallic iron4 ,describing the works of the ,compagnie ,gnral des ,eaux for supplying the suburbs of ,paris with filtered water1 the capacity of the works being over #bc1jjj1jjj gallons daily4 ,,weston4 ,rhode ,island ,state ,board of ,health1 #ahid4 ,report of the ,results ,obtained with ,experimental ,filters at the ,pattaconset ,pumping ,station of the ,providence ,water ,works4 ,relates particularly to the bacterial purification obtained with rapid filtration aided by sulphate of alumina4 ,these were the first systematic experiments made with mechanical filters4 ,,wheeler4 ,journal of the ,new ,england ,water ,works ,assoc41 ,,xi41 p4 #cja4 ,covered ,sand ,filter at ,ashland1 ,wis4 ,a description of the covered filters built by the author at ,ashland ,wis4 for the purification of the bay water4 ,views and drawings4 ,,appendix ,,xi4 ,,the ,,albany ,,water-,,filtration ,,plant4 7,abridged from ,proceedings ,american ,society of ,civil ,engineers1 ,nov4 #ahii47 ,albany1 ,n4 ,y41 was originally supplied with water by gravity from certain reservoirs on small streams west and north of the city4 ,in time1 with increasing consumption1 the supply obtained from these sources became inadequate1 and an additional supply from the ,hudson ,river was introduced4 ,the water was obtained from the river through a tunnel under the ,erie ,basin1 and a pumping-station was erected in ,quackenbush ,street to pump it to reservoirs1 one of which served also as the distributing point for one of the gravity supplies4 ,the intake1 which was used first in #ahgc1 drew water from the river opposite the heart of the city4 ,in recent years1 the amount of water drawn from this source has greatly exceeded that obtained from the gravity sources4 ,the ,hudson ,river1 at the point of intake1 has a drainage area of #hbdj square miles4 ,of this1 #deda square miles are tributary to the ,hudson above ,troy1 #cdic are tributary to the ,mohawk1 and #afh are tributary to the ,hudson below the ,mohawk4 ,the minimum flow may be estimated at #afeg cubic feet per second1 or #a1jfj1jjj1jjj gallons per #bd hours1 or at least fifty times the maximum consumption4 ,the cities and larger towns upon the river above the intake1 with estimated populations and distances1 are as follows3 ,,most ,,important ,,cities1 ,,towns1 ,,and ,,villages ,,on ,,the ,,watershed ,,of ,,the ,,hudson ,,above ,,albany4 ---------------------------------------- ----------------------- ,approximate ,population in ,place4 ,county4 ,distance --------------------------- above #ahhj4 #ahij4 #aijj4 ,intake1 ,miles4 7,estimated47 ---------------------------------------- --------------------- ,troy ,rensselaer #d #ef1gdg #fj1ief #fe1dgj ,watervliet ,albany #d #h1hbj #ab1ifg #ai1jdj ,green ,island,rensselaer #e #d1afj #d1dfc #d1ghh ,cohoes ,albany #h #ai1daf #bb1eji #bf1dej ,lansingburg ,rensselaer #h #g1dcb #aj1eej #ad1ihj ,waterford ,saratoga #i 7#a1hbb7 #a1hbb 7#a1hbb7 ,schenectady ,schenectady #bh #ac1fee #ai1jjb #bf1dej ,hoosic ,falls,rensselaer #dd #d1ecj #g1jad #aj1hfj ,amsterdam ,montgomery #dd #i1dff #ag1ccf #ca1gcj ,glens ,falls ,warren #di #d1ijj #i1eji #ah1dej ,saratoga ,saratoga #ea #h1dba #aa1ige #ag1jaj ,springs ,johnstown ,fulton #ef #e1jac #g1gfh #ab1jdj ,gloversville,fulton #eh #g1acc #ac1hfd #bf1icj ,north ,adams1 ,mass4 ,berkshire #fh #aj1aia #af1jgd #be1cdj ,adams1 ,mass4,berkshire #ge #e1eia #i1bac #ae1aha ,little ,falls,herkimer #hb #f1iaj #h1ghc #aa1afj ,utica ,oneida #ajg #cc1iad #dd1jjg #eg1jij ,rome ,oneida #abg #ab1aid #ad1iia #ah1dcj #cb villages #eb1ebc #fa1hfi #gf1aid ---------------------------------------- --------------------- ,total1 not including rural population #bgb1hch #ced1fgb #dgi1dae ,per square mile #cc #dc #ei ---------------------------------------- ----------------------- ,without entering into a detailed discussion1 it may be said that the amount of sewage1 with reference to the size of the river and the volume of flow1 is a fraction less than that at ,lawrence1 ,mass41 where a filter-plant has also been constructed1 but the pollution is much greater than that of most ,american rivers from which municipal water-supplies are taken4 ,the filtration-plant completed in #ahii takes the water from a point about two miles above the old intake4 ,pumps lift the water to the sedimentation-basin1 from which it flows to the filters and thence through a conduit to the pumping-station previously used4 ,,description ,,of ,,plant4 ,intake4--,the intake consists of a simple concrete structure in the form of a box1 having an open top covered with rails #f inches apart1 and connected below1 through a #cf-;inch pipe1 with a well in the pumping-station4 ,before going to the pumps the water passes through a screen with bars #b inches apart1 so arranged as to be raked readily4 ,the rails over the intake and this screen are intended to stop matters which might obstruct the passageways of the pumps1 but no attempt is made to stop fish1 leaves1 or other floating matters which may be in the water4 ,the arrangement1 in this respect1 is like that of the filter at ,lawrence1 ,mass41 where the raw water is not subjected to close screening4 ,there is room1 however1 to place finer screens in the pump-well1 should they be found desirable4 ,illustration3 ,,hudson ,,river ,,near ,,intake ,,fig4 #a4 ,illustration3 ,,sedimentation-,,basin1 ,,pumping-,,station1 ,,and ,,outlets4 ,illustration3 ,,sedimentation-,,basin1 ,,an ,,outlet1 ,,and ,,laboratory4 ,to face page #bij4 ,pumping-station4--,the centrifugal pumps have a guaranteed capacity of #af1jjj1jjj gallons per #bd hours against a lift of #ah feet1 or #ab1jjj1jjj gallons per #bd hours against a lift of #bd feet4 ,the ordinary pumping at low water is against the higher lift1 and under these conditions either pump can supply the ordinary consumption1 the other pump being held in reserve4 ,the pumping-station building1 to a point above the highest flood-level1 is of massive concrete construction1 without openings4 ,nearly all the machinery is necessarily below this level1 and in high water the sluice-gates are closed1 and the machinery is thus protected from flooding4 ,the superstructure is of pressed brick1 with granite trimmings4 ,meter for ,raw ,water4--,upon leaving the pumping-station the water passes through a #cf-;inch ,venturi meter having a throat diameter of #ag inches1 the throat area being two ninths of the area of the pipe4 ,the meter records the quantity of water pumped1 and is also arranged to show on gauges in the pumping-station the rate of pumping4 ,aeration4--,after leaving the meter1 the water passes to the sedimentation-basin through eleven outlets4 ,these outlets consist of #ab-;inch pipes on end1 the tops of which are #d feet above the nominal flow-line of the sedimentation-basin4 ,each of these outlet-pipes is pierced with #bif #c_/h-;inch holes extending from #j4e to #c4e feet below the top of the pipe4 ,these holes are computed so that when #aa1jjj1jjj gallons of water per day are pumped all the water will pass through the holes1 the water in the pipes standing flush with the tops4 ,the water is thus thrown out in #cbef small streams1 and becomes aerated4 ,when more than the above amount is pumped1 the excess flows over the tops of the outlet-pipes in thin sheets1 which are broken by the jets4 ,illustration3 ,,general ,,plan ,,fig4 #b4 ,regarding the necessity for aeration1 no observations have been taken upon the ,hudson ,river1 but1 judging from experience with the ,merrimac at ,lawrence1 where the conditions are in many respects similar1 the water is at all times more or less aerated1 and1 for the greater part of the year1 it is nearly saturated with oxygen1 and aeration is not necessary4 ,during low water in summer1 however1 there is much less oxygen in the water1 and at these times aeration is a distinct advantage4 ,further1 the river-water will often have a slight odor1 and aeration will tend to remove it4 ,the outlets are arranged so that they can be removed readily in winter if they are not found necessary at that season4 ,sedimentation-basin4--,the sedimentation-basin has an area of #e acres and is #i feet deep4 ,to the overflow it has a capacity of #ad1fjj1jjj gallons1 and to the flow-line of the filters #h1ijj1jjj gallons4 ,there is thus a reserve capacity of #e1gjj1jjj gallons between these limits1 and this amount can be drawn upon1 without inconvenience1 for maintaining the filters in service while the pumps are shut down4 ,this allows a freedom in the operation of the pumps which would not exist with the water supplied direct to the filters4 ,the water enters the sedimentation-basin from eleven inlets along one side1 and is withdrawn from eleven outlets directly opposite4 ,the inlets and aerating devices described previously bring the water into the basin without current and evenly distributed along one side4 ,both inlets and outlets are controlled by gates1 so that any irregularities in distribution can be avoided4 ,the concrete floor of the sedimentation-basin is built with even slopes from the toe of each embankment to a sump1 the heights of these slopes being #a foot1 whatever their lengths4 ,the sump is connected with a #bd-;inch pipe leading to a large manhole in which there is a gate through which water can be drawn to empty the basin4 ,there is an overflow from the basin to this manhole which makes it impossible to fill the basin above the intended level4 ,illustration3 ,,longitudinal ,,section ,,on a-b-c-d-e-f-g-h ,,filter ,,beds ,,plan ,,and ,,section ,,of ,,filter ,,no4 #b ,,fig4 #c4 ,illustration3 ,,outside ,,wall1 ,,ready ,,for ,,concrete ,,backing4 ,illustration3 ,,sedimentation-,,basin3 ,,showing ,,construction ,,of ,,floor4 ,to face page #bid4 ,filters4--,the filters are of masonry1 and are covered to protect them against the winters1 which are quite severe in ,albany4 ,the piers1 cross-walls1 and linings of the outside walls1 entrances1 etc41 are of vitrified brick4 ,all other masonry is concrete4 ,the average depth of excavation for the filters was #d feet1 and the material at the bottom was usually blue or yellow clay4 ,in some places shale was encountered4 ,in one place soft clay was found1 and there the foundations were made deeper4 ,the floors consisted of inverted1 groined1 concrete arches1 arranged to distribute the weight of the walls and vaulting over the whole area of the bottom4 ,the groined arch-vaulting is of concrete with a clear span of #aa feet #aa inches1 a rise of #b-a_/b feet1 and a thickness of #f inches at the crown4 ,it was put in in squares1 the joints being on the crowns of the arches parallel with the lines of the piers1 and each pier being the centre of one square4 ,the manholes are in alternate sections1 and are of concrete1 built in steel forms with castings at the tops1 securely jointed to the concrete4 ,above the vaulting there are #b feet of earth and soil1 grassed on top4 ,the tops of the manholes are #f inches above the soil to prevent rain-water from entering them4 ,the drainage of the soil is effected by a depression of the vaulting over each pier1 partially filled with gravel and sand1 from which water is removed by a #b-;inch tile-drain going down the centre of the pier and discharging through its side just above the top of the sand in the filter4 ,in order to provide ready access to each filter1 a part of the vaulting near one side is elevated and made cylindrical in shape1 making an inclined runway from the sand-level to a door the threshold of which is #f inches above the level of the overflow4 ,illustration3 ,,filter ,,beds ,,section ,,of ,,filters ,,fig4 #d4 ,this sand-run is provided with permanent timber runways and with secure doors4 ,illustration3 ,section4 ,elevation4 ,,fig4 #e4--;,,entrance ,,to ,a ,,filter4 ,the manholes of the filters are provided with double covers of steel plates to exclude the cold4 ,the covers also exclude light4 ,when cleaning the filters1 light can be admitted by removing the covers4 ,supports for electric lights are placed in the vaulting1 so that the filters can be lighted by electricity and the work of cleaning can be done at night1 and in winter under heavy snow1 without removing the covers4 ,the electric lights have not yet been installed4 ,the regulator-houses1 the entrances to the sand-runs1 and all exposed work are of pressed brick with ,milford granite trimmings and slate roofs4 ,the regulator-houses have double walls and double windows and a tight ceiling in the roof1 to make them as warm as possible and to avoid the necessity of artificial heat to prevent freezing4 ,illustration3 ,,computed ,,frictional ,,resistance ,,of ,,drainage ,,system ,,of ,,one ,,filter ,,when ,,operating ,,at ,a ,,rate ,,of #ajj ,m4,m4 ,,per ,,hour1 ,,equal ,,to #b1egj1jjj ,,gals4 ,,per ,,acre ,,daily4 ,,standard ,,gravel ,,sections4 ,,fig4 #f4 ,illustration3 ,,placing ,,the ,,floor ,,of ,a ,,filter4 ,illustration3 ,,building ,,the ,,brick ,,piers4 ,to face page #bih4 ,the main underdrains for removing the filtered water are of vitrified pipe surrounded by concrete and are entirely below the floors of the filters4 ,connections with the main drain are made through thirty-eight #f-;inch outlets in each filter1 passing through the floor and connected with #f-;inch lateral drains running through the whole width of the filter4 ,these drains were made with pipes having one side of the bell cut off so that they would lie flat on the floor and make concentric joints1 without support and without having to be wedged4 ,they were laid with a space of about #a inch between the barrels1 leaving a large opening for the admission of water from the gravel4 ,the underdrainage system is so designed that1 when starting a filter after cleaning1 the friction of the sand is about #ej mm4 at a rate of #c1jjj1jjj gallons per acre daily1 and the friction of the underdrainage system is estimated at #aj mm4 ,this very low friction1 which is necessary1 is obtained by the use of ample sizes for the underdrains and low velocities in them4 ,in the outlet and measuring devices moderate losses of head are not objectionable1 and the sizes of the pipes and connections are1 therefore1 smaller than the main underdrains4 ,the gravel surrounding the underdrains is of three grades4 ,the material was obtained from the river-bed by dredging1 and was of the same stock as that used for preparing ballast for the concrete4 ,it was separated and cleaned by a special1 cylindrical1 revolving screen4 ,the coarsest grade of gravel was that which would not pass round holes #a inch in diameter1 and free from stones more than about #b inches in diameter4 ,at first it was required to pass a screen with holes #b inches in diameter1 but this screen removed many stones which it was desired to retain1 and the screen was afterward changed to have holes #c inches in diameter4 ,the intermediate grades of gravel passed the #a-;inch holes1 and were retained by a screen with round holes #c_/h inch in diameter4 ,the finest gravel passed the above screens and was retained by a screen with round holes #c_/af inch in diameter4 ,the gravel was washed1 until free from sand and dirt1 by water played upon it during the process of screening1 and it was afterward taken over screens in the chutes1 where it was separated from the dirty water1 and1 when necessary1 further quantities of water were played upon it at these points4 ,illustration3 ,,inlet ,,to ,,filter ,,bed4 ,,section ,,on ,m-,n-,o ,,regulator ,,chamber ,,longitudinal ,,section ,,on ,a-,b-,c-,d ,,regulator ,,chamber ,,section ,,on ,k-,l ,,filter ,,beds ,,inlet ,,valves ,,and ,,regulator ,,chamber ,,inlet ,,to ,,filter ,,bed ,,sectional ,,plan ,,on ,p-,q ,,orifice ,,indicator ,,marker ,,details ,,of ,,apparatus ,,in ,,regulator ,,house ,,regulator ,,chamber ,,sectional ,,plan ,,on ,e-,f-,g-,h-,j ,,fig4 #g4 ,the average mechanical analyses of the three grades of gravel are shown by ,fig4 #h4 ,their effective sizes were #bc1 #h1 and #c mm4 respectively1 and for convenience they are designated by these numbers4 ,the average uniformity coefficient for each grade was about #a4h4 ,the #bc-mm4 gravel entirely surrounded the #f-;inch pipe-drains1 and was carried slightly above their tops4 ,in some cases it was used to cover nearly the whole of the floor1 but this was not insisted upon4 ,the #h-mm4 gravel was obtained in larger quantity than the other sizes1 and was used to fill all spaces up to a plane #b-a_/b inches below the finished surface of the gravel1 this layer being about #b inches thick over the tops of the drains1 and somewhat thicker elsewhere4 ,the #c-mm4 gravel was then applied in a layer #b-a_/b inches deep1 and the surface levelled4 ,the preliminary estimates of cost were based upon the use of filter-sand from a bank near the filter-site4 ,further examination showed that this sand contained a considerable quantity of lime1 and it was found by experiment with a small filter constructed for that purpose that the use of this sand would harden the water by about #b parts in #ajj1jjj1 and the amount of lime contained in the sand1 namely1 about #g per cent1 was sufficient to continue this hardening action for a considerable number of years4 ,this was regarded as a serious objection to its use1 and the specifications were drawn limiting the amount of lime in the sand4 ,this excluded all of the local bank sands4 ,the river-sands which were used were nearly free from lime1 and in the end the sand as secured was probably not only free from lime1 but more satisfactory in other ways1 and also cheaper than the bank-sand would have been4 ,illustration3 ,,mechanical ,,composition ,,of ,,filter ,,sand ,,and ,,gravels4 7,,arrows ,,show ,,requirement ,,of ,,specification7 ,diameters in ,millimeters ,,fig4 #h4 ,the specifications of the filter-sand require that 8,the filter-sand shall be clean river-1 beach-1 or bank-sand1 with either sharp or rounded grains4 ,it shall be entirely free from clay1 dust1 or organic impurities1 and shall1 if necessary1 be washed to remove such materials from it4 ,the grains shall1 all of them1 be of hard material which will not disintegrate1 and shall be of the following diameters3 ,not more than #a per cent1 by weight1 less than #j4ac mm41 nor more than #aj per cent less than #j4bg mm42 at least #aj per cent1 by weight1 shall be less than #j4cf mm41 and at least #gj per cent1 by weight1 shall be less than #a mm41 and no particles shall be more than #e mm4 in diameter4 ,the diameters of the sand-grains will be computed as the diameters of spheres of equal volume4 ,the sand shall not contain more than #b per cent1 by weight1 of lime and magnesia taken together and calculated as carbonates40 ,illustration3 ,,placing ,,the ,,concrete ,,vaulting4 ,illustration3 ,,general ,,view ,,of ,,vaulting1 ,,under ,,construction4 ,to face page #cjb4 ,illustration3 ,,fig4 #i4 ,the sand was obtained from the river at various places by dredging4 ,it was first taken up by dipper-dredges1 and brought in scows to a point in the back channel a little north of the filter-plant4 ,it was there dumped in a specially prepared place in the bottom of the river1 from which it was lifted by a hydraulic dredge and pumped through a #ae-;inch pipe an average distance of #ebe feet to points selected1 and varied from time to time1 on the flats north of the filters4 ,the water containing the sand was then put through screens having meshes which excluded all stones #e mm4 in diameter and over1 and was then taken into basins where the sand was deposited and afterward carted to the filters4 ,two ejector sand-washing machines1 shown in ,fig4 #i1 are provided at convenient places between the filters4 ,in them the dirty sand is mixed with water1 and is thrown up by an ejector1 after which it runs through a chute into a receptacle1 from which it is again lifted by another ejector4 ,it passes in all through five ejectors1 part of the dirty water being wasted each time4 ,the sand is finally collected from the last ejector1 where it is allowed to deposit from the water4 ,water is admitted to each filter through a #bj-;inch pipe from a pipe system connecting with the sedimentation-basin4 ,just inside of the filter-wall is placed a standard gate1 and beyond that a balanced valve connected with an adjustable float to shut off the water when it reaches the desired height on the filter4 ,these valves and floats were constructed from special designs1 and are similar in principle to valves used for the same purpose in the ,berlin water-filters4 ,each filter is provided with an overflow1 so arranged that it cannot be closed1 which prevents the water-level from exceeding a fixed limit in case the balanced valve fails to act4 ,an outlet is also provided near the sand-run1 so that unfiltered water can be removed quickly from the surface of the filter1 should it be necessary1 to facilitate cleaning4 ,the outlet of each filter is through a #bj-;inch gate controlled by a standard graduated to show the exact distance the gate is open4 ,the water rises in a chamber and flows through an orifice in a brass plate #d by #bd inches1 the centre of which is #a foot below the level of the sand-line4 ,at the nominal rate of filtration1 #c1jjj1jjj gallons per acre daily1 #a foot of head is required to force the water through the orifice4 ,with other rates the head increases or decreases approximately as the square of the rate and forms a measure of it4 ,with water standing in the lower chamber1 so that the orifice is submerged1 it is assumed that the same rates will be obtained with a given difference in level between the water on the two sides of the orifice as from an equal head above the centre of the orifice when discharging into air4 ,measurement of ,effluent4--,in order to show the rate of filtration two floats are connected with the water on the two sides of the orifice4 ,these floats are counterbalanced2 one carries a graduated scale1 and the other a marker which moves in front of the scale and shows the rate of filtration corresponding to the difference in level of the water on the two sides4 ,when the water in the lower chamber falls below the centre of the orifice1 the water in the float-chamber is nevertheless maintained at this level4 ,this is accomplished by making the lower part of the tube water-tight1 with openings just at the desired level1 so that when the water falls below this point in the outer chamber it does not fall in the float-chamber4 ,to prevent the loss of water in the float-chamber by evaporation or from other causes1 a lead pipe is brought from the other chamber and supplies a driblet of water to it constantly2 this overflows through the openings1 and maintains the water-level at precisely the desired point4 ,the floats thus indicate the difference in water-level on the two sides of the orifice whenever the water in the lower chamber is above the centre of the orifice2 otherwise they indicate the height of water in the upper chamber above the centre of the orifice1 regardless of the water-level in the lower chamber4 ,the scale is graduated to show the rates of filtration in millions of gallons per acre of filtering area4 ,in computing this scale the area of the filters is taken as #j4g acre1 and the coefficient of discharge as #j4fa4 ,at the ordinary rates of filtration the errors introduced by the different conditions under which the orifice operates will rarely amount to as much as #ajj1jjj gallons per acre daily1 or one thirtieth of the ordinary rate of filtration4 ,usually they are much less than this4 ,the apparatus thus shows directly1 and with substantial accuracy1 the rate of filtration under all conditions4 ,measurement of ,loss of ,head4--,two other floats with similar connections show the difference in level between the water standing on the filter and the water in the main drain-pipe back of the gate1 or1 in other words1 the frictional resistance of the filter1 including the drains4 ,this is commonly called the loss of head1 and increases from #j4b foot or less1 with a perfectly clean filter1 to #d feet with the filter ready for cleaning4 ,when the loss of head exceeds #d feet the rate of filtration cannot be maintained at #c1jjj1jjj gallons per acre daily with the outlet devices provided1 and1 in order to maintain the rate1 the filter must be cleaned4 ,adjustment of ,gauges4--,the adjustment of the gauges showing the rate of filtration and loss of head is extremely simple4 ,when a filter is put in service the gates from the lower chamber to the pure-water reservoir and to the drain are closed1 the outlet of the filter opened1 and both chambers allowed to fill to the level of the water on the filter4 ,the length of the wire carrying the gauge is then adjusted so that the gauge will make the desired run without hitting at either end1 and then the marker is adjusted4 ,as both the rate of filtration and loss of head are zero under these conditions1 it is only necessary to set the markers to read zero on the gauges to adjust them4 ,the gates can then be opened for regular operation1 and the readings on the gauges will be correct4 ,illustration3 ,,interior ,,of ,a ,,filter3 ,,drain1 ,,gravel ,,and ,,sand ,,layers4 ,illustration3 ,,interior ,,of ,a ,,filter1 ,,ready ,,for ,,use4 ,to face page #cjf4 ,it is necessary to use wires which are light1 flexible1 and which will not stretch4 ,at first piano-wire1 ,no4 #bg ,b4 ,s4 gauge1 was used1 and was well adapted to the purpose1 except that it rusted rapidly4 ,because of the rusting it was found necessary to substitute another wire1 and cold-drawn copper wire1 ,no4 #bd ,b4 ,s4 gauge1 was used with fair results4 ,stretching is less serious than it would otherwise be1 as the correctness of the adjustment can be observed and corrected readily every time a filter is out of service4 ,from the lower chambers in the regulator-houses the water flows through gates to the pipe system leading to the pure-water reservoir4 ,drain-pipes are also provided which allow the water to be entirely drawn out of each filter1 should that be necessary for any reason1 and without interfering with the other filters or with the pure-water reservoir4 ,the outlets of the filters are connected in pairs1 so that filtered water can be used for filling the underdrains and sand of the filters from below prior to starting1 thus avoiding the disturbance which results from bringing dirty water upon the sand of a filter not filled with water4 ,laboratory ,building4--,the scientific control of filters is regarded as one of the essentials to the best results1 and to provide for this there is a laboratory building at one end of the central court between the filters and close to the sedimentation-basin1 supplied with the necessary equipment for full bacterial examinations1 and also with facilities for observing the colors and turbidities of raw and filtered waters1 and for making such chemical examinations as may be necessary4 ,this building also provides a comfortable office1 dark room1 and storage room for tools1 etc41 used in the work4 ,pure-water ,reservoir4--,a small pure-water reservoir1 #id feet square and holding about #fjj1jjj gallons1 is provided at the filter-plant4 ,the construction is similar to that of the filters1 but the shapes of the piers and vaulting were changed slightly1 as there was no necessity for the ledges about the bottoms of the piers and walls2 while provision is made for taking the rain-water1 falling upon the vaulting above1 to the nearest filters instead of allowing it to enter the reservoir4 ,the floor and roof of the reservoir are at the same levels as those of the filters4 ,,capacity ,,of ,,plant ,,and ,,means ,,of ,,regulation4 ,the various filters have effective filtering areas of from #j4gjb to #j4gjd acre1 depending upon slight differences in the thickness of the walls in different places4 ,for the purpose of computation1 the area of each filter is taken at #j4g acre4 ,the nominal rate of filtration is taken as #c1jjj1jjj gallons per acre daily1 at which rate each filter will yield #b1ajj1jjj gallons daily1 and1 with one filter out of use for the purpose of being cleaned1 seven filters normally in use will yield #ad1gjj1jjj gallons4 ,the entrances and outlets are all made of sufficient size1 so that rates #ej per cent greater than the foregoing are possible4 ,the capacities of the intake1 pumping-station1 and piping are such as to supply any quantity of water which the filters can take1 up to an extreme maximum of #be1jjj1jjj gallons in #bd hours4 ,the pure-water conduit from the filters to ,quackenbush ,street is nominally rated at #be1jjj1jjj gallons per #bd hours1 after it has become old and somewhat tuberculated4 ,in its present excellent condition it will carry a larger quantity1 ,at the pumping-station at ,quackenbush ,street there are three ,allis pumps1 each capable of pumping #e1jjj1jjj gallons per #bd hours4 ,in addition to the above there are the old reserve pumps with a nominal capacity of #aj1jjj1jjj gallons per #bd hours1 which can be used if necessary1 but which require so much coal that they are seldom used4 ,for practical purposes the #ae1jjj1jjj gallons represents the pumping capacity of this station and also the capacity of the filters1 but the arrangements are such that in case of emergency the supply can be increased to #bj1jjj1jjj or even #be1jjj1jjj gallons for a short time4 ,the water is pumped through rising mains to reservoirs holding #cg1jjj1jjj gallons1 not including the ,tivoli low-service reservoir1 which is usually supplied from gravity sources4 ,the reservoir capacity is such that the pumping can be suspended at ,quackenbush ,street for considerable periods if necessary1 and in practice it has been suspended at certain times1 especially on ,sundays4 ,the amount of water required is also somewhat irregular4 ,the drainage areas supplying the gravity reservoirs are much larger1 relatively1 than the reservoirs1 and at flood periods the volume of the gravity supply is much greater than that which can be drawn in dry weather4 ,thus it happens that1 at certain seasons of the year1 the amount of water to be pumped is but a fraction of the nominal capacity of the pumps1 and at these times it is possible to shut the pumps down for greater lengths of time4 ,capacity of ,pure-water ,reservoir4--,the storage capacity provided between the filters and the ,quackenbush ,street pumps is comparatively small1 namely1 #fjj1jjj gallons1 or one hour's supply at the full nominal rate4 ,a larger basin1 holding as much as one third or one half of a day's supply1 would be in many respects desirable in this position1 but the conditions were such as to make it practically impossible4 ,the bottom of the reservoir could not be put lower without deepening and increasing greatly the expense of the conduit-line4 ,on the other hand1 the flow-line of the reservoir could not be raised without raising the level of the filters1 which was hardly possible upon the site selected4 ,the available depth of the reservoir was thus limited between very narrow bounds1 and to secure a large capacity would have necessitated a very large area1 and consequently a great expense4 ,under these circumstances1 and especially in view of the abundant storage capacity for filtered water in the distributing reservoirs1 it was not deemed necessary to provide a large storage1 and only so much was provided as would allow the pumps to be started at the convenience of the engineer1 and give a reasonable length of time for the filters to be brought into operation4 ,for this the pure-water reservoir is ample1 but it is not enough to balance any continued fluctuations in the rate of pumping4 ,method of ,regulating and ,changing the ,rate of ,filtration4--,with all the ,allis pumps running at their nominal capacity1 the quantity of water required will just about equal the nominal capacity of the filters4 ,when only one or two pumps are running1 the rate of filtration can be reduced4 ,with the plant operating up to its full capacity1 the water-level in the pure-water reservoir will be below the level of the standard orifices in the filter outlets4 ,when the rate of pumping is reduced1 if no change is made in the gates controlling the filter outlets1 the water will gradually rise in the pure-water reservoir and in the various regulator chambers1 and will submerge the orifices and gradually reduce the head on the filters1 and consequently the rates of filtration1 until those rates equal the quantity pumped4 ,in case the pumping is stopped altogether1 the filters will keep on delivering at gradually reduced rates until the water-level in the pure-water reservoir reaches that of the water on the filters4 ,when the pumps are started up1 after such stoppage or reduced rate of pumping1 the water-levels in the pure-water reservoir and in the gate-chambers will be lowered gradually1 and the filters will start to operate it first with extremely low rates1 which will increase gradually until the water is depressed below the orifices1 when they will again reach the rates at which they were last set4 ,the regulators during all this time will show the rate of filtration on each filter1 and1 if any inequalities occur which demand correction1 the gates on the various outlets can be adjusted accordingly4 ,illustration3 ,,central ,,court1 ,,showing ,,sand-,,washer1 ,,dirty ,,sand1 ,,etc4 ,illustration3 ,,sedimentation ,,basin1 ,,filters1 ,,etc4 ,to face page #caj4 ,the arrangement1 in this respect1 combines some of the features of the ,english and ,german plants4 ,in the ,english plants the filters are usually connected directly with the clear-water basin1 and that in turn with the pumps1 and the speed of filtration is required to respond to the speed of the pumps1 increasing and decreasing with it1 being regulated at all times by the height of water in the pure-water reservoir4 ,this arrangement has been subject to severe criticism1 because the rate of filtration fluctuates with the consumption1 and especially because the rates of filtration obtained simultaneously in different filters may be different4 ,there was no way to determine at what rate any individual filter was working1 and there was always a tendency for a freshly scraped filter to operate much more rapidly than those which had not been scraped for some time4 ,this led to the procedure1 first formulated by the ,commission of ,german ,water-works ,engineers in #ahid1 and provided for in most of the ,german works built or remodelled since that time1 of providing pure-water storage sufficient in amount to make the rate of filtration entirely independent of the operation of the pumps4 ,each filter was to be controlled by itself1 be independent of the others1 and deliver its water into a pure-water reservoir lower than itself1 so that it could never be affected by back-water1 and so large that there would never be a demand for sudden changes in the rate of filtration4 ,this procedure has given excellent results in the ,german works2 but it leads oftentimes to expensive construction4 ,it involves1 in the first place1 a much greater loss of head in passing through the works1 because the pure-water reservoir must be lower than the filters1 and the cost of the pure-water reservoir is increased greatly because of its large size4 ,the regulation of the filters is put upon the attendants entirely1 or upon automatic devices1 and regulation by what is known as 8responding to the pumps0 is eliminated4 ,more recently1 the ,german authorities have shown less disposition to insist rigidly upon the principles advanced in #ahid4 ,in a compilation of the results of several years' experience with ,german water-filters1 ,dr4 ,pannwiz#ff makes a statement of particular interest1 of which a free translation is as follows3 8,most of the ,german works have sufficient pure-water reservoir capacity to balance the normal fluctuations in consumption1 so that the rate of filtration is at least independent of the hourly fluctuations in consumption4 ,of especial importance is the superficial area of the pure-water reservoir4 ,if it is sufficiently large1 there is no objection to allowing the water-level in it to rise to that of the water upon the filters4 ,with very low rates of consumption during the night the filters may work slowly and even stop1 without damage to the sediment layers when the stopping and starting take place slowly and regularly1 because of the ample reservoir area40 8,the very considerable fluctuations from day to day1 especially those arising from unusual and unforeseen occurrences1 are not provided for entirely by even very large and well-arranged reservoirs4 ,to provide for these without causing shock1 the rate of filtration must be changed carefully and gradually1 and the first essential to success is a good regulation apparatus40 8,responding to the pumps0 has a great deal to recommend it4 ,it allows the pure-water reservoir to be put at the highest possible level1 it reduces to a minimum the loss of head in the plant1 and yet provides automatically1 and without the slightest trouble on the part of the attendants1 for the delivery of the required quantity of water by the filters at all times4 ,if the filters are connected directly to the pumps there is a tendency for the pulsations of the pumps to disturb their operation1 which is highly objectionable1 even if the pumps are far removed2 and this exists where filters are connected directly to the pumps1 and a pure-water reservoir is attached to them indirectly4 ,by taking all the water through the pure-water reservoir and having no connection except through it1 this condition is absolutely avoided1 and the pull on the filters is at all times perfectly steady4 ,much has been said as to the effect of variation in the rate of filtration upon the efficiency of filters4 ,experiments have been made at ,lawrence and elsewhere which have shown that1 as long as the maximum rate does not exceed a proper one1 and under reasonable regulations1 and with the filter in all respects in good order1 no marked decrease in efficiency results from moderate fluctuations in rate4 ,there is probably a greater decrease in efficiency by stopping the filter altogether1 especially if it is done suddenly1 than by simply reducing the rate4 ,the former sometimes results in loosening air-bubbles in the sand1 which rise to the surface and cause disturbances1 but this is not often caused by simple change in rate4 ,on the whole1 there is little evidence to show that1 within reasonable limits1 fluctuations in rate are objectionable1 or should be excluded entirely1 especially in such cases as at ,albany1 where arrangements to prevent them would have resulted in very greatly increased first cost4 ,the inferior results sometimes obtained with the system of 8responding to the pumps0 as it existed in earlier works1 and still exists in many important places1 undoubtedly arises from the fact that there is no means of knowing and controlling the simultaneous rate of filtration in different filters1 and that one filter may be filtering two or three times as fast as another1 with nothing to indicate it4 ,this contingency is fully provided for in the ,albany plant4 ,the orifices are of such size that even with a filter just scraped and put in service1 with the minimum loss of head1 with the outlet-gate wide open1 and with the water-level in the pure-water reservoir clear down--that is1 with the most unfavorable conditions which could possibly exist--the rate of filtration cannot exceed #e1jjj1jjj or #f1jjj1jjj gallons per acre daily1 or double the nominal rate4 ,this rate1 while much too high for a filter which has just been cleaned1 is not nearly as high as was possible1 and in fact actually occurred in the old ,stralau filters at ,berlin1 and in many ,english works2 and1 further1 such a condition could only occur through the gross negligence of the attendants1 because the rate of filtration is indicated clearly at all times by the gauges4 ,these regulating-devices have been specially designed to show the rate with unmistakable clearness1 so that no attendant1 however stupid1 can make an error by an incorrect computation from the gauge heights4 ,it is believed that the advantage of clearness by this procedure is much more important than any increased accuracy which might be secured by refinements in the method of computation1 which should take into account variations in the value of the coefficient of discharge1 but which would render direct readings impossible4 ,in designing the ,albany plant the object has been to combine the best features of ,german regulation with the economical and convenient features of the older ,english system1 and filters are allowed to respond to the pumps within certain limits1 while guarding against the dangers ordinarily incident thereto4 ,,results ,,of ,,operation4 ,the filters were designed to remove from the water the bacteria which cause disease4 ,they have already reached a bacterial efficiency of over #ii per cent1 and it is expected that their use will result in a great reduction in the death-rate from water-borne diseases in the city4 ,they also remove a part of the color and all of the suspended matters and turbidity1 so that the water is satisfactory in its physical properties4 ,the filters have reached with perfect ease their rated capacity1 and on several occasions have been operated to deliver one third more than this amount2 that is to say1 at a rate of #d1jjj1jjj gallons per acre1 daily4 ,,cost ,,of ,,construction4 ,the approximate cost of the filtration-plant complete was as follows3 ,land #h1bij ,pumping-station and intake #di1gde ,filters and sedimentation-basin1 with piping #cbc1ifj ,pure-water conduit and connection with ,quackenbush ,street pumping-station #hf1fch ,engineering and minor expenses #bh1jjj ---------------- ,total #dif1fcc ,the filters1 sedimentation-basin1 and pure-water reservoir are connected in such a way as to make an exact separation of their costs impossible2 but1 approximately1 the sedimentation-basin cost #fj1jjj1 the pure-water reservoir #i1jjj1 and the filters #bee1jjj4 ,the sedimentation-basin thus cost #d1ajj per million gallons capacity2 and the filters complete cost #de1fjj per acre of net filtering area1 including all piping1 office and laboratory building1 but exclusive of land and engineering4 ,,acknowledgment4 ,the general plan and location of the plant were first conceived by the ,superintendent of ,water-works1 ,george ,i4 ,bailey1 ,m4 ,am4 ,soc4 ,c4 ,e41 and the successful execution is largely due to his efforts4 ,the members of the ,water ,board1 and especially the ,construction ,committee1 have followed the work in detail closely and personally1 and their interest and support have been essential factors in the results accomplished4 ,in the designs and specifications for the pure-water conduit the author is greatly indebted to ,emil ,kuichling1 ,m4 ,am4 ,soc4 ,c4 ,e41 and also for most valuable suggestions relative to the performance of this part of the work4 ,to ,william ,wheeler1 ,m4 ,am4 ,soc4 ,c4 ,e41 of ,boston1 the author is indebted for advice upon the vaulting and cross-sections of the walls1 and these matters were submitted to him before the plans were put in final shape4 ,all the architectural designs have been supplied by ,mr4 ,a4 ,w4 ,fuller1 of ,albany4 ,w4 ,b4 ,fuller1 ,m4 ,am4 ,soc4 ,c4 ,e41 as ,resident ,engineer1 has been in direct charge of the work1 and its success is largely due to his interest in it and the close attention which he and the assistant engineers have given it4 ,,footnotes3 #a ,the ,american gallon is #bca cubic inches or #j4hccc of the imperial gallon4 ,in this work ,american gallons are always used1 and ,english quantities are stated in ,american1 not imperial1 gallons4 #b ,filtration of ,river ,waters4 ,van ,nostrand ,co41 #ahfi4 #c ,annual ,report of ,albert ,f4 ,noyes1 ,city ,engineer for #ahia4 #d ,rept4 ,mass4 ,state ,board of ,health1 #ahib1 p4 #eda4 ,see ,appendix ,,iii4 #e ,the method of calculating the size is given in ,appendix ,,iii4 #f ,a full table of frictions with various velocities and gravels was given in the ,rept4 of ,mass4 ,state ,board of ,health1 #ahib1 p4 #eee4 #g ,frhling1 ,handbuch der ,ingenieurwissenschaften1 ,,ii4 ,band1 ,,vi4 ,kapitel4 #h ,the ,american gallon is used throughout this book2 the ,english gallon is one fifth larger4 #i ,piefke1 ,zeitschrift fr ,hygiene1 #ahid1 p4 #agg4 #aj ,zeitschrift fr ,hygiene1 #ahia1 page #ch4 #aa ,journal fr ,gas- u4 ,wasserversorgung1 #ahia1 #bjh and #bbh4 #ab ,journal fr ,gas- u4 ,wasserversorgung1 #ahic1 #afa4 #ac ,samuelson's translation of ,kirkwood's 8,filtration of ,river-waters20 ,lindley1 ,die ,nutzbarmachung des ,flusswassers1 ,journal fr ,gas- u4 ,wasserversorgung1 #ahij1 #eja2 ,kaiserlichen ,gesundheitsamt1 ,grundstze fr die ,reinigung von ,oberflchenwasser durch ,sandfiltration2 ,journal fr ,gas- u4 ,wasserversorgung1 #ahid1 ,appendix ,i4 #ad ,lindley1 ,journal fr ,gas- u4 ,wasserversorgung1 #ahij1 #eja2 ,grahn1 ,journal fr ,gas- u4 ,wasserversorgung1 #ahij1 #eaa2 ,halbertsma1 ,journal fr ,gas- u4 ,wasserversorgung1 #ahib1 #fhf2 ,piefke1 ,zeitschrift fr ,hygiene1 #ahid1 #aea2 and others4 #ae ,appendix ,i4 #af ,the ,water ,supply of ,towns4 ,london1 #ahid4 #ag ,a special species of bacteria artificially added to secure more precise information in regard to the passage of germs through the filter4 #ah ,zeitschrift fr ,hygiene1 #ahid1 p4 #agc4 #ai ,report ,mass4 ,state ,board of ,health for #ahia1 p4 #dch2 #ahib1 page #dji4 #bj ,appendix ,,iv4 #ba ,piefke1 ,zeitschrift fr ,hygiene1 #ahid1 p1 #agg4 #bb ,journal fr ,gas- und ,wasserversorgung1 #ahhg1 p4 #eie4 #bc ,zeitschrift fr ,hygiene1 #ahid1 p4 #agb4 #bd ,appendix ,,iv4 #be ,appendix ,i4 #bf ,glaser's ,annalen1 #ahhf1 p4 #dh2 ,zeit4 f4 ,hygiene1 #ahhi1 p4 #abh4 #bg ,vierteljahresschrift fr ffentliche ,gesundheitspflege1 #ahia1 p4 #ei4 #bh ,journal fr ,gas- und ,wasserversorgung1 #ahia1 #ajh4 #bi ,zeitschrift fr ,hygiene1 #ahid1 #ahb4 #cj ,i am informed that several other filters upon the same principle have been more recently built4 #ca ,report on ,water ,purification at ,cincinnati1 page #cgh4 #cb ,translation in ,german in ,dingler's ,polytechnical ,journal1 #ahcb1 #chf4 #cc ,water ,purification at ,louisville1 page #cgh4 #cd ,special ,report ,mass4 ,state ,board of ,health #ahij1 ,purification of ,sewage and ,water1 page #gdg4 #ce ,water ,purification at ,cincinnati1 p4 #dhe4 #cf ,jour4 of the ,new ,england ,water ,works ,assoc41 ,vol4 ,,viii1 page #ahc4 #cg ,report of the ,pittsburg ,filtration ,commission1 #ahii1 page #ee4 #ch ,rhode ,island ,state ,board of ,health ,report for #ahid4 #ci ,report of the ,rhode ,island ,state ,board of ,health for #ahid4 #dj ,report on the ,investigations into the ,purification of the ,ohio ,river ,water at ,louisville1 ,kentucky4 ,d4 ,van ,nostrand ,co41 #ahih4 #da ,ohio ,state ,board of ,health ,report1 #ahig1 page #aed4 #db ,report of the ,pittsburg ,filtration ,commission1 ,city ,document1 #ahii4 #dc ,fuller1 ,water ,purification at ,louisville1 page #dbe4 #dd ,warren1 ,feb4 #i2 ,june #a2 ,july #f4 ,jewell1 ,july #a2 ,feb4 #i1 #af1 #ag4 #de 8,removal of ,iron from ,ground ,waters10 ,journal of the ,new ,england ,water ,works ,association1 ,vol4 xi1 #ahig1 page #bgg4 #df ,journal of the ,new ,england ,water ,works ,association1 ,vol4 ii1 page #bid4 ,description of plant by ,supt4 ,lewis ,m4 ,bancroft4 #dg ,this number was the result of numerous counts made from fces from persons suffering with typhoid fever in the ,lawrence ,city ,hospital in #ahia and #ahib4 ,mr4 ,g4 ,w4 ,fuller afterward made at the ,lawrence ,experiment ,station some further investigation of fces from healthy people in which the numbers were considerably lower1 usually less than #bjj1jjj1jjj1 per gram and sometimes as low as #aj1jjj1jjj per gram4 #dh ,these experiments1 so far as they have come to the notice of the author1 have been made with water sterilized by heating1 usually in small tubes stoppered with cotton-wool or other organic matter4 ,in this case the water1 no matter how carefully purified in the first place1 becomes an infusion of organic matters capable of supporting bacterial growths1 and not at all to be compared to natural waters4 ,in experiments often repeated under my direction1 carefully distilled water in bottles1 most scrupulously clean1 with glass stoppers1 and protected from dust1 but not sterilized1 has uniformly refused to support bacterial growths even when cautiously seeded at the start1 and the same is usually true of pure natural waters4 ,some further experiments showed hardly any bacterial growth even of the most hardy water bacteria in a solution #a part of peptone in #a1jjj1jjj1jjj parts of distilled water1 and solutions ten times as strong only gave moderate growths4 #di ,the ,water-supply of ,chicago3 ,its ,source and ,sanitary ,aspects4 ,by ,arthur ,r4 ,reynolds1 ,m4,d41 ,commissioner of ,health of ,chicago1 and ,allen ,hazen4 ,american ,public ,health ,association1 #ahic4 ,page #adf4 #ej ,journal fr ,gas- u4 ,wasserversorgung1 #ahic1 #fid4 #ea ,journal fr ,gas- u4 ,wasserversorgung1 #ahid1 #ahe4 #eb ,the method of making this determination was given in the ,american ,chemical ,journal1 vol4 #ab1 p4 #dbg4 #ec ,some of the companies secure some ground water which they mix with the filtered water1 and this is included in the quantities for the separate companies1 but is excluded from the totals for all the companies by years4 #ed ,exclusive of gravity supplies4 #ee ,not in use4 #ef ,under construction4 #eg ,not in use4 #eh ,under construction4 #ei ,not in use4 #fj ,under construction4 #fa ,not in use4 #fb ,under construction4 #fc ,in the ,centralblatt fr ,bakteriologie1 #ahie1 page #hha1 ,reinsch discusses at length the cause of the inferior results at ,altona in winter1 and has apparently discovered a new factor in producing them4 ,owing to defective construction of the outlets for the sedimentation-basins they have failed to act properly in presence of excessive quantities of ice1 and the sediment from the basins has been discharged in large quantity upon the filters1 and a small fraction of the many millions of bacteria in it have passed through the filters4 ,he has experimented with this sediment applied to small filters1 and has become convinced that to secure good work under all conditions a much deeper layer of sand than that generally considered necessary must be used1 and his work emphasizes the importance of the action of the sand in distinction from the action of the sediment layer1 which has often been thought to be the sole1 or at least the principal1 requirement of good filtration4 #fd ,licht- u4 ,wasserwerke1 ,zrich1 #ahib1 page #cb4 #fe ,descriptions of some of the leading ,european ground-water supplies were given by the author in the ,jour4 ,asso4 ,eng4 ,soc41 ,feb4 #ahie1 p4 #aac4 #ff 8,arbeiten aus dem ,kaiserlichen ,gesundheitsamte10 vol4 xiv4 p4 #bfj4 ,,index4 ,albany1 ,n4 ,y41 filters at1 #bed1 #bhh4 ,alkalinity1 #aee4 ,altona1 double filtration at1 #aih4 filters at1 #bfe4 ,alum1 use of1 in filtration1 #ib1 #add4 ,american cities1 water-supplies of1 and typhoid fever in1 #baa4 ,amsterdam1 filters at1 #bgb4 iron removal at1 #aib4 ,anderson process1 #adg4 ,antwerp1 filters at1 #bgb4 ,asbestos as filtering material1 #aha4 ,asbury ,park1 iron removal at1 #aib4 ,ashland1 ,wis41 filters at1 #beb4 ,area of filters to be provided1 #dg4 ,bacteria1 apparent and actual removal of1 by filters1 #hg4 from underdrains1 #hg4 in ,elbe at ,altona1 #bbh4 in fces1 #bae4 in water1 #hd4 number to be allowed in filtered water1 #bbb4 of cholera in river water1 #bca4 of typhoid fever1 life of1 in water1 #baf4 of special kinds to test efficiency of filtration1 #hf4 to be determined daily1 #bbb4 ,bacterial examination of water1 #ic4 ,berlin1 regulation of depth of water1 #ei4 cholera infantum from water1 #bbi4 friction in underdrains1 #dd4 regulation of rate1 #ec1 #ee4 water works1 #bfa4 ,berwyn1 ,penn41 filters at1 #bec4 ,boston1 protection of purity of water-supply1 #aaj4 experimental filters at1 #gc4 ,bremen1 double filtration at1 #aih4 ,breslau1 filters at1 #bgd4 ,brussels1 ground-water1 supply of1 #bgf4 ,budapest1 filters at1 #bgd4 ,burton1 regulation of rate at ,tokyo1 ,japan1 #eh4 ,carpenter1 ,prof4 ,l4 ,g41 #bd4 ,chemnitz1 intermittent filtration at1 #ajg4 ,chicago1 reduced death-rate with new intake1 #bag4 ,cholera infantum from impure water1 #bbf4 ,cholera1 in ,hamburg from water1 #bcj4 caused by water1 #bad4 ,clarification1 definition of1 #aac4 ,clark1 ,h4 ,w41 #bd1 #aij4 ,clark's process for softening water1 #ib1 #ade4 ,clay particles1 size of1 #abc4 ,cleaning filters1 #fh4 ,coagulant1 absorption of1 by suspended matters1 #aed4 successive applications of1 #aed4 ,coagulants used in practice1 #aej4 ,coagulation of waters1 #add4 ,cologne1 water-supply of1 from wells1 #bgf4 ,color1 #aac4 amount of coagulant required to remove1 #aec4 amount of1 in various waters1 #aae4 measurement of1 #aad4 ,color1 removal of1 #aag4 ,continuous filters1 #e4 filtration1 nature of1 #hc1 #ib4 ,cost of filters and filtration1 #d1 #dh1 #ajb1 #bjj1 #cad4 ,covered filters1 efficiency of1 #ag4 ,covers for filters1 #ab1 #ae4 at ,albany1 #bie4 in the ,united ,states1 #ag4 omitted at ,lawrence1 #aja4 ,crenothrix1 #aje1 #ahf4 ,diarrha from impure water1 #bbf4 ,dibden1 ,w4 ,j41 #abi4 ,disease from water1 #baj4 ,double filtration at ,schiedam1 #bgc4 ,drainage areas of a number of rivers1 #acc4 ,dresden1 water-supply of1 from filter-gallery1 #bgf4 ,drown1 ,dr4 ,thomas ,m41 #aej1 #aia4 ,effective size of sand1 #ba1 #bch4 ,european sands1 #be4 ,efficiency of filtration1 #hc1 #hh1 #ia4 effect of rate upon1 #ej4 effect of size of sand-grain upon1 #cj4 effect of thickness of sand layer upon1 #cd4 at ,lawrence1 #ajf4 ,european filters1 #ia1 #bfj4 ,effluents1 wasting after scraping1 #gd4 ,fces1 number of bacteria in1 #bae4 ,far ,rockaway1 ,l4 ,i41 filters at1 #aic1 #bec4 ,filling sand with water from below1 #fh1 #cjg4 ,filter beds1 bottoms of1 must be water-tight1 #ab4 covers for1 #ab4 form of1 #aa4 size of1 #aj4 ,filters1 aggregate capacity of1 #bed4 depths of waters on1 #de4 list of cities using1 #bdd4 reserve area required1 #dg4 first constructed at ,london1 #hc4 for household use1 #ahc4 general arrangement of1 #f4 ,filters1 statistics of1 at various cities1 #bda4 ,filtration1 cost of1 #bjj4 degree of purification required1 #e4 general nature of1 #ib4 ,fischer tile system1 #aha4 ,fitz,gerald1 ,desmond1 #gc1 #aaa1 #aif4 ,flood flows not taken for supply1 #aj4 ,frnkel and ,piefke1 experiments on removal of disease germs1 #hf4 ,frankfort on ,main1 water supply of1 from springs1 #bgf4 ,frankland1 ,dr4 ,percy1 #hd4 ,friction of filtered water in pipes1 #bfd4 water in gravel1 #cg4 water in sand1 #bb4 water in underdrains1 #dj4 ,frost1 effect of1 upon filters1 #ab1 #bbi1 #bff4 ,frhling1 on the heating of water by sunshine1 #af4 underdraining at ,knigsberg1 #ci4 ,fuller1 ,g4 ,w41 #aah1 #abc1 #aca1 #aci1 #adj1 #ade1 #aeb1 #aed1 #afa1 #afe4 ,german ,imperial ,board of ,health1 #cd1 #ea1 #ed1 #ge1 #ie4 regulations in regard to filtration1 #bba4 ,gill1 apparatus for regulation1 #ee4 ,glasgow1 water-supply of1 from ,loch ,katrine1 #bge4 ,gravel at ,albany1 #bii4 layers1 #ce4 friction of water in1 #cg4 screening of1 for filters1 #cg4 ,grand ,forks1 ,n4 ,d41 filters at1 #beb4 ,ground-water supplies1 #c4 the use of1 in ,europe1 #bgf4 ,halbertsma1 ,h4 ,p4 ,n41 #ed1 #ei4 ,hamburg1 apparatus for regulating depth of water1 #ei4 health of1 #bbf1 #bga4 regulation of rate of filtration1 #ef4 underdrains of filters at1 #db4 water-supply of1 #bfi4 ,hamilton1 ,n4 ,y41 filters at1 #bec4 ,hardness1 removal of1 #ib1 #ade4 ,harrisburg1 ,penn41 filters at1 #bec4 ,hermany1 ,charles1 #afa4 ,high rates of filtration without coagulant1 #ahb4 ,household filters1 #ahc4 ,hudson1 ,n4 ,y41 filters at1 #bea4 ,ice on filters1 #ac4 ,inlet regulators1 #ei4 ,impounding reservoirs1 #b4 ,intermittent filtration1 #ig4 application of1 #aaa1 #aig4 at ,chemnitz1 #ajg4 at ,lawrence1 #ajj4 of ,pegan ,brook1 #aaj4 ,iron1 compounds of1 as coagulants1 #adf4 in ground-waters1 #ahf4 in ground-water at ,lawrence1 #aje4 metallic1 the ,anderson process1 #adg4 present as ferrous sulphate1 #aia4 removal plants in operation1 #aib4 ,iron waters1 treatment of1 #ahi4 ,jewel filter1 #aea1 #afa1 #afb1 #agb1 #agc4 ,kirkwood1 ,james ,p41 #h1 #cf1 #dg1 #ea1 #ee1 #fa1 #fc1 #fg4 ,kmmel1 #ej1 #ea1 #hf4 ,lambertsville1 ,n4 ,j41 filters at1 #beb4 ,lawrence ,city filter1 description of1 #ajj4 ,lawrence ,experiment ,station1 #ig4 air in water filtered in winter at1 #df4 depth of sand removed at1 #gj4 depth of water on filters1 #df4 effect of loss of head upon efficiency1 #fa4 effect of size of sand-grain upon efficiency1 #cb4 effect of size of sand-grain upon frequency of scraping1 #cb4 efficiency of filters at various rates1 #ej4 efficiency of filtration at1 #hf1 #hi4 experiments with continuous filtration1 #aaj4 filters of fine sand1 #ca4 filters of various sand-grain sizes1 #cb4 gravel for filters at1 #ci4 growth of bacteria in sterilized sand at1 #he4 intermittent filtration investigated1 #ig4 ,lawrence ,experiment ,station1 method of sand analysis at1 #bj4 quantities of water filtered at various losses of head1 #ff4 wasting effluents not necessary1 #ge4 ,lawrence1 typhoid fever at1 #ajb4 ,leipzig1 water-supply of1 from wells1 #bgf4 ,lime in sand1 #bi4 sterilizing effect of1 #adf4 as a coagulant1 #ade4 application of1 to water1 #aeg4 ,lindley1 #dc1 #ea1 #ed1 #eg1 #ha4 ,literature on filtration1 #bgg1 #bhe4 ,little ,falls1 ,n4 ,y41 filters at1 #bec4 ,loam in filters1 #ce4 ,london1 cost of operating filters at1 #bjb4 water-supply of1 #bee4 ,long1 ,prof41 #aca4 ,lorain1 tests of mechanical filters1 #afa4 ,loss of head1 #eb4 limit to1 #fj1 #fg4 reasons for allowing high1 #fe4 ,louisville1 mechanical filters at1 #afa4 ,magdeburg1 filters at1 #bgc4 ,maignen system1 #aha4 ,manchester1 water-supply of1 #bge4 ,manganese1 compounds of1 as coagulants1 #adh4 in ground-waters1 #ahh4 ,massachusetts ,state ,board of ,health1 see ,lawrence ,experiment ,station4 ,mechanical filters1 #aei4 application of1 #aii4 efficiency of1 #agi4 list of1 #bdg4 pressure filters1 #ahj4 rates of filtration used1 #age4 types of1 #agb4 wasting effluent after washing1 #afc4 ,millford1 ,mass41 filters at1 #beb4 ,mills1 ,h4 ,f41 #ig1 #ii1 #ajb4 ,mount ,vernon1 ,n4 ,y41 filters at1 #beb4 ,mud1 see turbidity4 ,muddy waters1 #aac4 ,munich1 water-supply of1 from springs1 #bge4 ,nichols1 ,prof41 suspended matters in ,european streams1 #aca4 ,nitrification1 effect of1 upon bacteria1 #ih4 ,odors1 removal of1 by filtration1 #aab4 ,organic matters in water1 #hc4 removed by intermittent filters1 #ih4 ,paper manufacturing1 filtration of water for1 #e4 ,paris1 ground-water supply of1 #bgf4 ,palmer1 ,prof41 #aca4 ,passages through the sand in filters1 #fg4 ,pegan ,brook1 purification of1 #aaj4 ,period1 how computed and length of1 #gb4 length of1 dependent upon turbidity1 #acg4 ,piefke1 #dh1 #ej1 #ed1 #fc1 #fi1 #gc1 #gd1 #ge1 #hj1 #hd1 #he1 #ij4 ,pittsburgh1 experiments with mechanical filters1 #afb4 ,plgge and ,proskauer1 #hd4 ,plymouth1 ,penn41 typhoid fever at1 #bjh4 ,pollution of ,european water-supplies1 #ic4 ,polluted waters1 utilization of excessively1 #aaa4 ,porcelain filters for household use1 #ahc4 ,poughkeepsie1 ,n4 ,y41 filters at1 #bea4 ,pressure filters1 #ahj4 ,providence1 mechanical filters at1 #aei4 ,rate of filtration1 #dg1 #bbd4 at various places1 #bda4 effect of1 upon cost1 #dh4 effect of1 upon efficiency1 #ej4 lower after scraping1 #gf4 regulation of1 #eb4 ,red ,bank1 ,n4 ,j41 filters at1 #aic1 #bec4 ,regulation of filters1 #eb4 old forms of regulators1 #eb4 modern forms of regulators1 #ed4 at ,albany1 #cje1 #cjh1 #caj4 of mechanical filters1 #agh4 ,reincke1 ,dr41 report on health of ,hamburg for #ahib1 #bbf4 ,reinsch on the cause of poor filtration at ,altona1 #bfg4 ,reserve area required in case of ice1 #ah4 ,reservoirs1 purposes served by1 #acc4 ,rock ,island1 ,ill41 filters at1 #bed4 ,roofs for filters1 #af4 ,rotterdam1 filters at1 #bgb4 ,st4 ,johnsbury1 ,vt41 filters at1 #bea4 ,st4 ,louis1 regulators for proposed filters1 #ee4 ,st4 ,petersburg1 filters at1 #bge4 ,samuelson1 #ea4 ,sand1 #bj4 at ,albany1 #cja4 analysis of ,european1 #be4 analysis of1 from leading works1 #bh4 appliances for moving1 #fh4 compactness of1 in natural banks1 #fa4 depth of1 in filters1 #cd4 depth to be removed from filters1 #fi4 dune1 #bf4 dune1 washing of1 impossible1 #hb4 effect of grain-size upon frequency of scraping1 #cb4 effect of grain-size upon the efficiency1 #cj4 effective size of1 #ba1 #bch4 extra scraping before replacing fresh1 #ga4 for filtration1 #bj1 #cc4 for mechanical filters1 #age4 friction of water in1 #bb4 grain-size of1 #bj1 #bcc4 in ,european filters1 #bd4 in ,lawrence filters1 two sizes of1 #ajj4 lime in1 #bi4 method of analysis of1 #bcc4 quantity to be removed by scraping1 #gd4 replacing1 #ga4 selection of1 #cc4 size of passages between grains of1 #f4 sterilized1 experiments with1 #he4 thickness of layer1 #cd4 uniformity coefficient1 #ba1 #bch4 ,sand washing1 #bf1 #gf1 #cjd4 cost of1 #ha4 water for1 #hj4 ,sandstone filters for household use1 #ahc4 ,schiedam1 double filtration at1 #bgc4 ,scraping filters1 #g1 #fh4 ,scraping filters1 amount of labor required for1 #ha4 depth of sand removed1 #cc1 #ff1 #fi4 frequency of1 #di1 #gb1 #bda4 ,sedgwick1 ,prof4 ,w4 ,t41 #hf4 ,sediment1 removal of1 #ib1 #acc4 ,sediment layer1 #f1 #ca4 influence of1 upon bacterial purification1 #hd4 thickness of1 #cc1 #ff1 #fi4 ,sedimentation basins1 #h1 #acc1 #bic4 effect of1 #acd4 ,sewage1 number of bacteria in1 #bae4 ,simpson1 ,james1 #hc4 ,soda-ash1 application of1 #aeg4 ,somersworth1 ,n4 ,h41 filters at1 #bec4 ,storage for raw water1 #acf4 ,subsidence1 limits to the use of1 #adb4 ,sulphate of alumina1 action of1 upon waters1 #add4 ,surface-waters1 use of1 unfiltered1 #bge4 ,suspended matters1 #aac1 #aag4 in relation to turbidities1 #abb4 in various waters1 #abi4 ,the ,hague1 iron removal at1 #aib4 ,tokyo1 regulation of rate at1 #eh4 ,trenched bottoms for filters1 #cf1 #dj1 #ajj4 ,turbidity1 #ib1 #aac4 amount which is noticeable1 #aba4 amount in several streams1 #abd4 duration of1 #abh4 in relation to suspended matters1 #abb4 measurement of1 #aag4 power of sand filters to remove1 #aci4 preliminary processes to remove1 #acc4 source of1 #abc4 ,typhoid fever in ,berlin and ,altona1 #ab1 #he1 #bfg4 in ,american cities1 #baa4 ,typhoid fever in ,hamburg1 #bga4 in ,lawrence1 #ajb4 in ,london1 #bei4 in ,zrich1 #bge4 ,typhoid-fever germs1 life of1 in water1 #baf4 ,underdrains1 #ce1 #ci4 bacteria from1 #hg4 friction of1 at ,albany1 #bii4 size of1 #da4 ventilators for1 #dd4 ,uniformity coefficient of sand1 #ba1 #bch4 ,ventilators for underdrains1 #dd4 ,vienna1 water-supply of1 from springs1 #bgf4 ,warren filter1 #aea1 #afa1 #afb1 #agb1 #agf1 #agg4 ,warsaw1 filters at1 #bge4 friction in underdrains1 #dc4 regulation of rate at1 #eg4 ,wasting effluents1 #gd4 ,water1 depth of1 on filters1 #de1 #ei4 heating of1 in filters1 #de4 organic matters in1 #hc4 ,water-supplies of ,american cities1 #baa4 ,water-supply and disease1 #baj4 ,waters1 what require filtration1 #bjg4 ,weston1 ,e4 ,b41 #aec1 #aed1 #aei4 ,weston1 ,r4 ,s41 #aec1 #ahi4 ,west ,superior1 iron in ground-water at1 #ahi4 ,winter1 effect of1 upon filtration1 #ab4 temperatures of places having open and covered filters1 #ae4 ,worms tile system1 #aha4 ,zrich1 filters at1 #bgd4 ,,short-,,title ,,catalogue ,,of ,,the ,,publications ,,of ,,john ,,wiley ,,sons1 ,,new ,,york4 ,,london3 ,,chapman ,,hall1 ,,limited4 ,,arranged ,,under ,,subjects4 ,descriptive circulars sent on application4 ,books marked with an asterisk 7997 are sold at net prices only1 a double asterisk 799997 books sold under the rules of the ,american ,publishers' ,association at net prices subject to an extra charge for postage4 ,all books are bound in cloth unless otherwise stated4 ,,agriculture4 ,armsby's ,manual of ,cattle-feeding #abmo1 #a #ge ,principles of ,animal ,nutrition #hvo1 #d #jj ,budd and ,hansen's ,american ,horticultural ,manual3 ,part ,i4 ,propagation1 ,culture1 and ,improvement #abmo1 #a #ej ,part ,,ii4 ,systematic ,pomology #abmo1 #a #ej ,downing's ,fruits and ,fruit-trees of ,america #hvo1 #e #jj ,elliott's ,engineering for ,land ,drainage #abmo1 #a #ej ,practical ,farm ,drainage #abmo1 #a #jj ,green's ,principles of ,american ,forestry #abmo1 #a #ej ,grotenfelt's ,principles of ,modern ,dairy ,practice4 7,woll47 #abmo1 #b #jj ,kemp's ,landscape ,gardening #abmo1 #b #ej ,maynard's ,landscape ,gardening as ,applied to ,home ,decoration #abmo1 #a #ej 99 ,mc,kay and ,larsen's ,principles and ,practice of ,butter-making #hvo1 #a #ej ,sanderson's ,insects ,injurious to ,staple ,crops #abmo1 #a #ej ,insects ,injurious to ,garden ,crops4 7,in preparation47 ,insects ,injuring ,fruits4 7,in preparation47 ,stockbridge's ,rocks and ,soils #hvo1 #b #ej ,winton's ,microscopy of ,vegetable ,foods #hvo1 #g #ej ,woll's ,handbook for ,farmers and ,dairymen #afmo1 #a #ej ,,architecture4 ,baldwin's ,steam ,heating for ,buildings #abmo1 #b #ej ,bashore's ,sanitation of a ,country ,house #abmo1 #a #jj ,berg's ,buildings and ,structures of ,american ,railroads #dto1 #e #jj ,birkmire's ,planning and ,construction of ,american ,theatres #hvo1 #c #jj ,architectural ,iron and ,steel #hvo1 #c #ej ,compound ,riveted ,girders as ,applied in ,buildings #hvo1 #b #jj ,planning and ,construction of ,high ,office ,buildings #hvo1 #c #ej ,skeleton ,construction in ,buildings #hvo1 #c #jj ,brigg's ,modern ,american ,school ,buildings #hvo1 #d #jj ,carpenter's ,heating and ,ventilating of ,buildings #hvo1 #d #jj ,freitag's ,architectural ,engineering #hvo1 #c #ej ,fireproofing of ,steel ,buildings #hvo1 #b #ej ,french and ,ives's ,stereotomy #hvo1 #b #ej ,gerhard's ,guide to ,sanitary ,house-inspection #afmo1 #a #jj ,theatre ,fires and ,panics #abmo1 #a #ej 99 ,greene's ,structural ,mechanics #hvo1 #b #ej ,holly's ,carpenters' and ,joiners' ,handbook #ahmo1 #ge ,johnson's ,statics by ,algebraic and ,graphic ,methods #hvo1 #b #jj ,kidder's ,architects' and ,builders' ,pocket-book4 ,rewritten ,edition #afmo1 mor41 #e #jj ,merrill's ,stones for ,building and ,decoration #hvo1 #e #jj ,non-metallic ,minerals3 ,their ,occurrence and ,uses #hvo1 #d #jj ,monckton's ,stair-building #dto1 #d #jj ,patton's ,practical ,treatise on ,foundations #hvo1 #e #jj ,peabody's ,naval ,architecture #hvo1 #g #ej ,richey's ,handbook for ,superintendents of ,construction #afmo1 mor41 #d #jj ,sabin's ,industrial and ,artistic ,technology of ,paints and ,varnish #hvo1 #c #jj ,siebert and ,biggin's ,modern ,stone-cutting and ,masonry #hvo1 #a #ej ,snow's ,principal ,species of ,wood #hvo1 #c #ej ,sondericker's ,graphic ,statics ,with ,applications ,to ,trusses1 ,beams1 and ,arches #hvo1 #b #jj ,towne's ,locks and ,builders' ,hardware #ahmo1 morocco1 #c #jj ,wait's ,engineering and ,architectural ,jurisprudence #hvo1 #f #jj ,sheep1 #f #ej ,law of ,operations ,preliminary ,to ,construction in ,engineering and ,architecture #hvo1 #e #jj ,sheep1 #e #ej ,law of ,contracts #hvo1 #c #jj ,wood's ,rustless ,coatings3 ,corrosion and ,electrolysis of ,iron and ,steel #hvo1 #d #jj ,worcester and ,atkinson's ,small ,hospitals1 ,establishment and ,maintenance1 ,suggestions for ,hospital ,architecture1 with ,plans for a ,small ,hospital #abmo1 #a #be ,the ,world's ,columbian ,exposition of #ahic ,large #dto1 #a #jj ,,army ,,and ,,navy4 ,bernadou's ,smokeless ,powder1 ,nitro-cellulose1 and the ,theory of the ,cellulose ,molecule #abmo1 #b #ej 99 ,bruff's ,text-book ,ordnance and ,gunnery #hvo1 #f #jj ,chase's ,screw ,propellers and ,marine ,propulsion #hvo1 #c #jj ,cloke's ,gunner's ,examiner #hvo1 #a #ej ,craig's ,azimuth #dto1 #c #ej ,crehore and ,squier's ,polarizing ,photo-chronograph #hvo1 #c #jj 99 ,davis's ,elements of ,law #hvo1 #b #ej 99 ,treatise on the ,military ,law of ,united ,states #hvo1 #g #jj ,sheep1 #g #ej ,de ,brack's ,cavalry ,outposts ,duties4 7,carr47 #bdmo1 morocco1 #b #jj ,dietz's ,soldier's ,first ,aid ,handbook #afmo1 morocco1 #a #be 99 ,dredge's ,modern ,french ,artillery #dto1 half morocco1 #ae #jj ,durand's ,resistance and ,propulsion of ,ships #hvo1 #e #jj 99 ,dyer's ,handbook of ,light ,artillery #abmo1 #c #jj ,eissler's ,modern ,high ,explosives #hvo1 #d #jj 99 ,fiebeger's ,text-book on ,field ,fortification ,small #hvo1 #b #jj ,hamilton's ,the ,gunner's ,catechism #ahmo1 #a #jj 99 ,hoff's ,elementary ,naval ,tactics #hvo1 #a #ej ,ingalls's ,handbook of ,problems in ,direct ,fire #hvo1 #d #jj 99 ,ballistic ,tables #hvo1 #a #ej 99 ,lyons's ,treatise on ,electromagnetic ,phenomena4 ,vols4 ,i4 and ,,ii4 #hvo1 each1 #f #jj 99 ,mahan's ,permanent ,fortifications4 7,mercur47 #hvo1 half morocco1 #g #ej ,manual for ,courts-martial #afmo1 morocco1 #a #ej 99 ,mercur's ,attack of ,fortified ,places #abmo1 #b #jj 99 ,elements of the ,art of ,war #hvo1 #d #jj ,metcalf's ,cost of ,manufactures--,and the ,administration of ,workshops #hvo1 #e #jj 99 ,ordnance and ,gunnery4 #b vols #abmo1 #e #jj ,murray's ,infantry ,drill ,regulations #ahmo1 paper1 #aj ,nixon's ,adjutants' ,manual #bdmo1 #a #jj ,peabody's ,naval ,architecture #hvo1 #g #ej 99 ,phelps's ,practical ,marine ,surveying #hvo1 #b #ej ,powell's ,army ,officer's ,examiner #abmo1 #d #jj ,sharpe's ,art of ,subsisting ,armies in ,war #ahmo1 morocco1 #a #ej 99 ,walke's ,lectures on ,explosives #hvo1 #d #jj 99 ,wheeler's ,siege ,operations and ,military ,mining #hvo1 #b #jj ,winthrop's ,abridgment of ,military ,law #abmo1 #b #ej ,woodhull's ,notes on ,military ,hygiene #afmo1 #a #ej ,young's ,simple ,elements of ,navigation #afmo1 morocco1 #b #jj ,,assaying4 ,fletcher's ,practical ,instructions in ,quantitative ,assaying with the ,blowpipe #abmo1 morocco1 #a #ej ,furman's ,manual of ,practical ,assaying #hvo1 #c #jj ,lodge's ,notes on ,assaying and ,metallurgical ,laboratory ,experiments #hvo1 #c #jj ,low's ,technical ,methods of ,ore ,analysis #hvo1 #c #jj ,miller's ,manual of ,assaying #abmo1 #a #jj ,minet's ,production of ,aluminum and its ,industrial ,use4 7,waldo47 #abmo1 #b #ej ,o',driscoll's ,notes on the ,treatment of ,gold ,ores #hvo1 #b #jj ,ricketts and ,miller's ,notes on ,assaying #hvo1 #c #jj ,robine and ,lenglen's ,cyanide ,industry4 7,le ,clerc47 #hvo1 ,ulke's ,modern ,electrolytic ,copper ,refining #hvo1 #c #jj ,wilson's ,cyanide ,processes #abmo1 #a #ej ,chlorination ,process #abmo1 #a #ej ,,astronomy4 ,comstock's ,field ,astronomy for ,engineers #hvo1 #b #ej ,craig's ,azimuth #dto1 #c #ej ,doolittle's ,treatise on ,practical ,astronomy #hvo1 #d #jj ,gore's ,elements of ,geodesy #hvo1 #b #ej ,hayford's ,text-book of ,geodetic ,astronomy #hvo1 #c #jj ,merriman's ,elements of ,precise ,surveying and ,geodesy #hvo1 #b #ej 99 ,michie and ,harlow's ,practical ,astronomy #hvo1 #c #jj 99 ,white's ,elements of ,theoretical and ,descriptive ,astronomy #abmo1 #b #jj ,,botany4 ,davenport's ,statistical ,methods1 with ,special ,reference to ,biological ,variation #afmo1 morocco1 #a #be ,thom and ,bennett's ,structural and ,physiological ,botany #afmo1 #b #be ,westermaier's ,compendium of ,general ,botany4 7,schneider47 #hvo1 #b #jj ,,chemistry4 ,adriance's ,laboratory ,calculations and ,specific ,gravity ,tables #abmo1 #a #be ,allen's ,tables for ,iron ,analysis #hvo1 #c #jj ,arnold's ,compendium of ,chemistry4 7,mandel ,small #hvo1 #c #ej ,austen's ,notes for ,chemical ,students #abmo1 #a #ej ,bernadou's ,smokeless ,powder4--,nitro-cellulose1 and ,theory of the ,cellulose ,molecule #abmo1 #b #ej 99 ,browning's ,introduction to the ,rarer ,elements #hvo1 #a #ej ,brush and ,penfield's ,manual of ,determinative ,mineralogy #hvo1 #d #jj ,classen's ,quantitative ,chemical ,analysis by ,electrolysis4 7,boltwood47 #hvo1 #c #jj ,cohn's ,indicators and ,test-papers #abmo1 #b #jj ,tests and ,reagents #hvo1 #c #jj ,crafts's ,short ,course in ,qualitative ,chemical ,analysis4 7,schaeffer47 #abmo1 #a #ej ,dolezalek's ,theory of the ,lead ,accumulator 7,storage ,battery74 7,von ,ende47 #abmo1 #b #ej ,drechsel's ,chemical ,reactions4 7,merrill47 #abmo1 #a #be ,duhem's ,thermodynamics and ,chemistry4 7,burgess47 #hvo1 #d #jj ,eissler's ,modern ,high ,explosives #hvo1 #d #jj ,effront's ,enzymes and their ,applications4 7,prescott47 #hvo1 #c #jj ,erdmann's ,introduction to ,chemical ,preparations4 7,dunlap47 #abmo1 #a #be ,fletcher's ,practical ,instructions in ,quantitative ,assaying with the ,blowpipe4 #abmo1 morocco1 #a #ej ,fowler's ,sewage ,works ,analyses #abmo1 #b #jj ,fresenius's ,manual of ,qualitative ,chemical ,analysis4 7,wells47 #hvo1 #e #jj ,manual of ,qualitative ,chemical ,analysis4 ,part ,i4 ,descriptive4 7,wells47 #hvo1 #c #jj ,system of ,instruction in ,quantitative ,chemical ,analysis4 7,cohn47 #b vols #hvo1 #ab #ej ,fuertes's ,water and ,public ,health #abmo1 #a #ej ,furman's ,manual of ,practical ,assaying #hvo1 #c #jj 99 ,getman's ,exercises in ,physical ,chemistry #abmo1 #b #jj ,gill's ,gas and ,fuel ,analysis for ,engineers #abmo1 #a #be ,grotenfelt's ,principles of ,modern ,dairy ,practice4 7,woll47 #abmo1 #b #jj ,hammarsten's ,text-book of ,physiological ,chemistry4 7,mandel47 #hvo1 #d #jj ,helm's ,principles of ,mathematical ,chemistry4 7,morgan47 #abmo1 #a #ej ,hering's ,ready ,reference ,tables 7,conversion ,factors7 #afmo1 morocco1 #b #ej ,hind's ,inorganic ,chemistry #hvo1 #c #jj 99 ,laboratory ,manual for ,students #abmo1 #a #jj ,holleman's ,text-book of ,inorganic ,chemistry4 7,cooper47 #hvo1 #b #ej ,text-book of ,organic ,chemistry4 7,walker and ,mott47 #hvo1 #b #ej 99 ,laboratory ,manual of ,organic ,chemistry4 7,walker47 #abmo1 #a #jj ,hopkins's ,oil-chemists' ,handbook #hvo1 #c #jj ,jackson's ,directions for ,laboratory ,work in ,physiological ,chemistry #hvo1 #a #be ,keep's ,cast ,iron #hvo1 #b #ej ,ladd's ,manual of ,quantitative ,chemical ,analysis #abmo1 #a #jj ,landauer's ,spectrum ,analysis4 7,tingle47 #hvo1 #c #jj 99 ,langworthy and ,austen4 ,the ,occurrence of ,aluminium in ,vegetable ,products1 ,animal ,products1 and ,natural ,waters #hvo1 #b #jj ,lassar-,cohn's ,practical ,urinary ,analysis4 7,lorenz47 #abmo1 #a #jj ,application of ,some ,general ,reactions to ,investigations in ,organic ,chemistry4 7,tingle47 #abmo1 #a #jj ,leach's ,the ,inspection and ,analysis of ,food with ,special ,reference to ,state ,control #hvo1 #g #ej ,lb's ,electrochemistry of ,organic ,compounds4 7,lorenz47 #hvo1 #c #jj ,lodge's ,notes on ,assaying and ,metallurgical ,laboratory ,experiments #hvo1 #c #jj ,low's ,technical ,method of ,ore ,analysis #hvo1 #c #jj ,lunge's ,techno-chemical ,analysis4 7,cohn47 #abmo1 #a #jj ,mandel's ,handbook for ,bio-chemical ,laboratory #abmo1 #a #ej 99 ,martin's ,laboratory ,guide to ,qualitative ,analysis with the ,blowpipe #abmo1 #fj ,mason's ,water-supply4 7,considered ,principally from a ,sanitary ,standpoint47 #c;d ,edition1 ,rewritten #hvo1 #d #jj ,examination of ,water4 7,chemical and ,bacteriological47 #abmo1 #a #be ,matthew's ,the ,textile ,fibres #hvo1 #c #ej ,meyer's ,determination of ,radicles in ,carbon ,compounds4 7,tingle47 #abmo1 #a #jj ,miller's ,manual of ,assaying #abmo1 #a #jj ,minet's ,production of ,aluminum and its ,industrial ,use4 7,waldo47 #abmo1 #b #ej ,mixter's ,elementary ,text-book of ,chemistry #abmo1 #a #ej ,morgan's ,elements of ,physical ,chemistry #abmo1 #c #jj 99 ,physical ,chemistry for ,electrical ,engineers #abmo1 #a #ej ,morse's ,calculations used in ,cane-sugar ,factories #afmo1 morocco1 #a #ej ,mulliken's ,general ,method for the ,identification of ,pure ,organic ,compounds4 ,vol4 ,i4 ,large #hvo1 #e #jj ,o',brine's ,laboratory ,guide in ,chemical ,analysis #hvo1 #b #jj ,o',driscoll's ,notes on the ,treatment of ,gold ,ores #hvo1 #b #jj ,ostwald's ,conversations on ,chemistry4 ,part ,one4 7,ramsey47 #abmo1 #a #ej ,ostwald's ,conversations on ,chemistry4 ,part ,two4 7,turnbull47 #abmo1 #b #jj 99 ,penfield's ,notes on ,determinative ,mineralogy and ,record of ,mineral ,tests #hvo1 paper1 #ej ,pictet's ,the ,alkaloids and their ,chemical ,constitution4 7,biddle47 #hvo1 #e #jj ,pinner's ,introduction to ,organic ,chemistry4 7,austen47 #abmo1 #a #ej ,poole's ,calorific ,power of ,fuels #hvo1 #c #jj ,prescott and ,winslow's ,elements of ,water ,bacteriology1 with ,special ,reference to ,sanitary ,water ,analysis #abmo1 #a #be 99 ,reisig's ,guide to ,piece-dyeing #hvo1 #be #jj ,richards and ,woodman's ,air1 ,water1 and ,food from a ,sanitary ,standpoint #hvo1 #b #jj ,richards's ,cost of ,living as ,modified by ,sanitary ,science #abmo1 #a #jj ,cost of ,food1 a ,study in ,dietaries #abmo1 #a #jj 99 ,richards and ,williams's ,the ,dietary ,computer #hvo1 #a #ej ,ricketts and ,russell's ,skeleton ,notes upon ,inorganic ,chemistry4 7,part ,i4 ,non-metallic ,elements47 #hvo1 morocco1 #ge ,ricketts and ,miller's ,notes on ,assaying #hvo1 #c #jj ,rideal's ,sewage and the ,bacterial ,purification of ,sewage #hvo1 #c #ej ,disinfection and the ,preservation of ,food #hvo1 #d #jj ,rigg's ,elementary ,manual for the ,chemical ,laboratory #hvo1 #a #be ,robine and ,lenglen's ,cyanide ,industry4 7,le ,clerc47 #hvo1 ,rostoski's ,serum ,diagnosis4 7,bolduan47 #abmo1 #a #jj ,ruddiman's ,incompatibilities in ,prescriptions #hvo1 #b #jj 99 ,whys in ,pharmacy #abmo1 #a #jj ,sabin's ,industrial and ,artistic ,technology of ,paints and ,varnish #hvo1 #c #jj ,salkowski's ,physiological and ,pathological ,chemistry4 7,orndorff47 #hvo1 #b #ej ,schimpf's ,text-book of ,volumetric ,analysis #abmo1 #b #ej ,essentials of ,volumetric ,analysis #abmo1 #a #be 99 ,qualitative ,chemical ,analysis #hvo1 #a #be ,spencer's ,handbook for ,chemists of ,beet-sugar ,houses #afmo1 morocco1 #c #jj ,handbook for ,cane ,sugar ,manufacturers #afmo1 morocco1 #c #jj ,stockbridge's ,rocks and ,soils #hvo1 #b #ej 99 ,tillman's ,elementary ,lessons in ,heat #hvo1 #a #ej 99 ,descriptive ,general ,chemistry #hvo1 #c #jj ,treadwell's ,qualitative ,analysis4 7,hall47 #hvo1 #c #jj ,quantitative ,analysis4 7,hall47 #hvo1 #d #jj ,turneaure and ,russell's ,public ,water-supplies #hvo1 #e #jj ,van ,deventer's ,physical ,chemistry for ,beginners4 7,boltwood47 #abmo1 #a #ej 99 ,walke's ,lectures on ,explosives #hvo1 #d #jj ,ware's ,beet-sugar ,manufacture and ,refining ,small #hvo1 cloth1 #d #jj ,washington's ,manual of the ,chemical ,analysis of ,rocks #hvo1 #b #jj ,wassermann's ,immune ,sera3 ,hmolysins1 ,cytotoxins1 and ,precipitins4 7,bolduan47 #abmo1 #a #jj ,well's ,laboratory ,guide in ,qualitative ,chemical ,analysis #hvo1 #a #ej ,short ,course in ,inorganic ,qualitative ,chemical ,analysis for ,engineering ,students #abmo1 #a #ej ,text-book of ,chemical ,arithmetic #abmo1 #a #be ,whipple's ,microscopy of ,drinking-water #hvo1 #c #ej ,wilson's ,cyanide ,processes #abmo1 #a #ej ,chlorination ,process #abmo1 #a #ej ,winton's ,microscopy of ,vegetable ,foods #hvo1 #g #ej ,wulling's ,elementary ,course in ,inorganic1 ,pharmaceutical1 and ,medical ,chemistry #abmo1 #b #jj ,,civil ,,engineering4 ,,bridges ,,and ,,roofs4 ,,hydraulics4 ,,materials ,,of ,,engineering4 ,,railway ,,engineering4 ,baker's ,engineers' ,surveying ,instruments #abmo1 #c #jj ,bixby's ,graphical ,computing ,table ,paper #ai-a_/b #bd-a_/d inches4 #be 9999 ,burr's ,ancient and ,modern ,engineering and the ,isthmian ,canal4 7,postage1 #bg cents additional47 #hvo1 #c #ej ,comstock's ,field ,astronomy for ,engineers #hvo1 #b #ej ,davis's ,elevation and ,stadia ,tables #hvo1 #a #jj ,elliott's ,engineering for ,land ,drainage #abmo1 #a #ej ,practical ,farm ,drainage #abmo1 #a #jj 99 ,fiebeger's ,treatise on ,civil ,engineering #hvo1 #e #jj ,folwell's ,sewerage4 7,designing and ,maintenance47 #hvo1 #c #jj ,freitag's ,architectural ,engineering4 #b;d ,edition1 ,rewritten #hvo1 #c #ej ,french and ,ives's ,stereotomy #hvo1 #b #ej ,goodhue's ,municipal ,improvements #abmo1 #a #ge ,goodrich's ,economic ,disposal of ,towns' ,refuse #hvo1 #c #ej ,gore's ,elements of ,geodesy #hvo1 #b #ej ,hayford's ,text-book of ,geodetic ,astronomy #hvo1 #c #jj ,hering's ,ready ,reference ,tables 7,conversion ,factors7 #afmo1 morocco1 #b #ej ,howe's ,retaining ,walls for ,earth #abmo1 #a #be ,johnson's 7,j4 ,b47 ,theory and ,practice of ,surveying ,small #hvo1 #d #jj ,johnson's 7,l4 ,j47 ,statics by ,algebraic and ,graphic ,methods #hvo1 #b #jj ,laplace's ,philosophical ,essay on ,probabilities4 7,truscott and ,emory47 #abmo1 #b #jj ,mahan's ,treatise on ,civil ,engineering4 7#ahgc47 7,wood47 #hvo1 #e #jj 99 ,descriptive ,geometry #hvo1 #a #ej ,merriman's ,elements of ,precise ,surveying and ,geodesy #hvo1 #b #ej ,merriman and ,brooks's ,handbook for ,surveyors #afmo1 morocco1 #b #jj ,nugent's ,plane ,surveying #hvo1 #c #ej ,ogden's ,sewer ,design #abmo1 #b #jj ,patton's ,treatise on ,civil ,engineering #hvo half leather1 #g #ej ,reed's ,topographical ,drawing and ,sketching #dto1 #e #jj ,rideal's ,sewage and the ,bacterial ,purification of ,sewage #hvo1 #c #ej ,siebert and ,biggin's ,modern ,stone-cutting and ,masonry #hvo1 #a #ej ,smith's ,manual of ,topographical ,drawing4 7,mc,millan47 #hvo1 #b #ej ,sondericker's ,graphic ,statics1 with ,applications to ,trusses1 ,beams1 and ,arches4 #hvo1 #b #jj ,taylor and ,thompson's ,treatise on ,concrete1 ,plain and ,reinforced #hvo1 #e #jj 99 ,trautwine's ,civil ,engineer's ,pocket-book #afmo1 morocco1 #e #jj ,wait's ,engineering and ,architectural ,jurisprudence #hvo1 #f #jj ,sheep1 #f #ej ,law of ,operations ,preliminary to ,construction in ,engineering and ,architecture #hvo1 #e #jj ,sheep1 #e #ej ,law of ,contracts #hvo1 #c #jj ,warren's ,stereotomy--,problems in ,stone-cutting #hvo1 #b #ej ,webb's ,problems in the ,use and ,adjustment of ,engineering ,instruments4 #afmo1 morocco1 #a #be ,wilson's ,topographic ,surveying #hvo1 #c #ej ,,bridges ,,and ,,roofs4 ,boller's ,practical ,treatise on the ,construction of ,iron ,highway ,bridges #hvo1 #b #jj 99 ,thames ,river ,bridge #dto1 paper1 #e #jj ,burr's ,course on the ,stresses in ,bridges and ,roof ,trusses1 ,arched ,ribs1 and ,suspension ,bridges #hvo1 #c #ej ,burr and ,falk's ,influence ,lines for ,bridge and ,roof ,computations #hvo1 #c #jj ,design and ,construction of ,metallic ,bridges #hvo1 #e #jj ,du ,bois's ,mechanics of ,engineering4 ,vol4 ,,ii4 ,small #dto1 #aj #jj ,foster's ,treatise on ,wooden ,trestle ,bridges #dto1 #e #jj ,fowler's ,ordinary ,foundations #hvo1 #c #ej ,greene's ,roof ,trusses #hvo1 #a #be ,bridge ,trusses #hvo1 #b #ej ,arches in ,wood1 ,iron1 and ,stone #hvo1 #b #ej ,howe's ,treatise on ,arches #hvo1 #d #jj ,design of ,simple ,roof-trusses in ,wood and ,steel #hvo1 #b #jj ,johnson1 ,bryan1 and ,turneaure's ,theory and ,practice in the ,designing of ,modern ,framed ,structures ,small #dto1 #aj #jj ,merriman and ,jacoby's ,text-book on ,roofs and ,bridges3 ,part ,i4 ,stresses in ,simple ,trusses #hvo1 #b #ej ,part ,,ii4 ,graphic ,statics #hvo1 #b #ej ,part ,,iii4 ,bridge ,design #hvo1 #b #ej ,part ,,iv4 ,higher ,structures #hvo1 #b #ej ,morison's ,memphis ,bridge #dto1 #aj #jj ,waddell's de ,pontibus1 a ,pocket-book for ,bridge ,engineers #afmo1 morocco1 #b #jj ,specifications for ,steel ,bridges #abmo1 #a #be ,wright's ,designing of ,draw-spans4 ,two ,parts in one volume #hvo1 #c #ej ,,hydraulics4 ,bazin's ,experiments upon the ,contraction of the ,liquid ,vein ,issuing from an ,orifice4 7,trautwine47 #hvo1 #b #jj ,bovey's ,treatise on ,hydraulics #hvo1 #e #jj ,church's ,mechanics of ,engineering #hvo1 #f #jj ,diagrams of ,mean ,velocity of ,water in ,open ,channels paper1 #a #ej ,hydraulic ,motors #hvo1 #b #jj ,coffin's ,graphical ,solution of ,hydraulic ,problems #afmo1 morocco1 #b #ej ,flather's ,dynamometers1 and the ,measurement of ,power #abmo1 #c #jj ,folwell's ,water-supply ,engineering #hvo1 #d #jj ,frizell's ,water-power #hvo1 #e #jj ,fuertes's ,water and ,public ,health #abmo1 #a #ej ,water-filtration ,works #abmo1 #b #ej ,ganguillet and ,kutter's ,general ,formula for the ,uniform ,flow of ,water in ,rivers and ,other ,channels4 7,hering and ,trautwine47 #hvo1 #d #jj ,hazen's ,filtration of ,public ,water-supply #hvo1 #c #jj ,hazlehurst's ,towers and ,tanks for ,water-works #hvo1 #b #ej ,herschel's #aae ,experiments on the ,carrying ,capacity of ,large1 ,riveted1 ,metal ,conduits #hvo1 #b #jj ,mason's ,water-supply4 7,considered ,principally ,from a ,sanitary ,standpoint47 #hvo1 #d #jj ,merriman's ,treatise on ,hydraulics #hvo1 #e #jj 99 ,michie's ,elements of ,analytical ,mechanics #hvo1 #d #jj ,schuyler's ,reservoirs for ,irrigation1 ,water-power1 and ,domestic ,water-supply ,large #hvo1 #e #jj 9999 ,thomas and ,watt's ,improvement of ,rivers4 7,post41 #dd;c4 additional47 #dto1 #f #jj ,turneaure and ,russell's ,public ,water-supplies #hvo1 #e #jj ,wegmann's ,design and ,construction of ,dams #dto1 #e #jj ,water-supply of the ,city of ,new ,york ,from #afeh to #ahie #dto1 #aj #jj ,williams and ,hazen's ,hydraulic ,tables #hvo1 #a #ej ,wilson's ,irrigation ,engineering ,small #hvo1 #d #jj ,wolff's ,windmill as a ,prime ,mover #hvo1 #c #jj ,wood's ,turbines #hvo1 #b #ej ,elements of ,analytical ,mechanics #hvo1 #c #jj ,,materials ,,of ,,engineering4 ,baker's ,treatise on ,masonry ,construction #hvo1 #e #jj ,roads and ,pavements #hvo1 #e #jj ,black's ,united ,states ,public ,works ,oblong #dto1 #e #jj 99 ,bovey's ,strength of ,materials and ,theory of ,structures #hvo1 #g #ej ,burr's ,elasticity and ,resistance of the ,materials of ,engineering #hvo1 #g #ej ,byrne's ,highway ,construction #hvo1 #e #jj ,inspection of the ,materials and ,workmanship ,employed in ,construction4 #afmo1 #c #jj ,church's ,mechanics of ,engineering #hvo1 #f #jj ,du ,bois's ,mechanics of ,engineering4 ,vol4 ,i4 ,small #dto1 #g #ej 99 ,eckel's ,cements1 ,limes1 and ,plasters #hvo1 #f #jj ,johnson's ,materials of ,construction ,large #hvo1 #f #jj ,fowler's ,ordinary ,foundations #hvo1 #c #ej 99 ,greene's ,structural ,mechanics #hvo1 #b #ej ,keep's ,cast ,iron #hvo1 #b #ej ,lanza's ,applied ,mechanics #hvo1 #g #ej ,marten's ,handbook on ,testing ,materials4 7,henning47 #b vols4 #hvo1 #g #ej ,maurer's ,technical ,mechanics #hvo1 #d #jj ,merrill's ,stones for ,building and ,decoration #hvo1 #e #jj ,merriman's ,mechanics of ,materials #hvo1 #e #jj ,strength of ,materials #abmo1 #a #jj ,metcalf's ,steel4 ,a ,manual for ,steel-users #abmo1 #b #jj ,patton's ,practical ,treatise on ,foundations #hvo1 #e #jj ,richardson's ,modern ,asphalt ,pavements #hvo1 #c #jj ,richey's ,handbook for ,superintendents of ,construction #afmo1 mor41 #d #jj ,rockwell's ,roads and ,pavements in ,france #abmo1 #a #be ,sabin's ,industrial and ,artistic ,technology of ,paints and ,varnish #hvo1 #c #jj ,smith's ,materials of ,machines #abmo1 #a #jj ,snow's ,principal ,species of ,wood #hvo1 #c #ej ,spalding's ,hydraulic ,cement #abmo1 #b #jj ,text-book on ,roads and ,pavements #abmo1 #b #jj ,taylor and ,thompson's ,treatise on ,concrete1 ,plain and ,reinforced #hvo1 #e #jj ,thurston's ,materials of ,engineering4 #c ,parts #hvo1 #h #jj ,part ,i4 ,non-metallic ,materials of ,engineering and ,metallurgy #hvo1 #b #jj ,part ,,ii4 ,iron and ,steel #hvo1 #c #ej ,part ,,iii4 ,a ,treatise on ,brasses1 ,bronzes1 and ,other ,alloys and their ,constituents #hvo1 #b #ej ,thurston's ,text-book of the ,materials of ,construction #hvo1 #e #jj ,tillson's ,street ,pavements and ,paving ,materials #hvo1 #d #jj ,waddell's ,de ,pontibus4 7,a ,pocket-book for ,bridge ,engineers47 #afmo1 mor41 #b #jj ,specifications for ,steel ,bridges #abmo1 #a #be ,wood's 7,de ,v47 ,treatise on the ,resistance of ,materials1 and an ,appendix on the ,preservation of ,timber #hvo1 #b #jj ,wood's 7,de ,v47 ,elements of ,analytical ,mechanics #hvo1 #c #jj ,wood's 7,m4 ,p47 ,rustless ,coatings3 ,corrosion and ,electrolysis of ,iron and ,steel #hvo1 #d #jj ,,railway ,,engineering4 ,andrew's ,handbook for ,street ,railway ,engineers #ce inches1 morocco1 #a #be ,berg's ,buildings and ,structures of ,american ,railroads #dto1 #e #jj ,brook's ,handbook of ,street ,railroad ,location #afmo1 morocco1 #a #ej ,butt's ,civil ,engineer's ,field-book #afmo1 morocco1 #b #ej ,crandall's ,transition ,curve #afmo1 morocco1 #a #ej ,railway and ,other ,earthwork ,tables #hvo1 #a #ej ,dawson's 8,engineering0 and ,electric ,traction ,pocket-book #afmo1 morocco1 #e #jj ,dredge's ,history of the ,pennsylvania ,railroad3 7#ahgi7 ,paper1 #e #jj 99 ,drinker's ,tunnelling1 ,explosive ,compounds1 and ,rock ,drills #dto1 half mor41 #be #jj ,fisher's ,table of ,cubic ,yards ,cardboard1 #be ,godwin's ,railroad ,engineers' ,field-book and ,explorers' ,guide #afmo1 mor41 #b #ej ,howard's ,transition ,curve ,field-book #afmo1 morocco1 #a #ej ,hudson's ,tables for ,calculating the ,cubic ,contents of ,excavations and ,embankments #hvo1 #a #jj ,molitor and ,beard's ,manual for ,resident ,engineers #afmo1 #a #jj ,nagle's ,field ,manual for ,railroad ,engineers #afmo1 morocco1 #c #jj ,philbrick's ,field ,manual for ,engineers #afmo1 morocco1 #c #jj ,searles's ,field ,engineering #afmo1 morocco1 #c #jj ,railroad ,spiral #afmo1 morocco1 #a #ej ,taylor's ,prismoidal ,formul and ,earthwork #hvo1 #a #ej 99 ,trautwine's ,method of ,calculating the ,cube ,contents of ,excavations and ,embankments by the ,aid of ,diagrams #hvo1 #b #jj ,the ,field ,practice of ,laying ,out ,circular ,curves for ,railroads4 #abmo1 morocco1 #b #ej ,cross-section ,sheet ,paper1 #be ,webb's ,railroad ,construction #afmo1 morocco1 #e #jj ,wellington's ,economic ,theory of the ,location of ,railways ,small #hvo1 #e #jj ,,drawing4 ,barr's ,kinematics of ,machinery #hvo1 #b #ej 99 ,bartlett's ,mechanical ,drawing #hvo1 #c #jj 99 ,bartlett's ,mechanical ,drawing ,abridged ,ed4 #hvo1 #a #ej ,coolidge's ,manual of ,drawing #hvo1 paper1 #a #jj ,coolidge and ,freeman's ,elements of ,general ,drafting for ,mechanical ,engineers ,oblong #dto1 #b #ej ,durley's ,kinematics of ,machines #hvo1 #d #jj ,emch's ,introduction to ,projective ,geometry and its ,applications #hvo1 #b #ej ,hill's ,text-book on ,shades and ,shadows1 and ,perspective #hvo1 #b #jj ,jamison's ,elements of ,mechanical ,drawing #hvo1 #b #ej ,advanced ,mechanical ,drawing #hvo1 #b #jj ,jones's ,machine ,design3 ,part ,i4 ,kinematics of ,machinery #hvo1 #a #ej ,part ,,ii4 ,form1 ,strength1 and ,proportions of ,parts #hvo1 #c #jj ,mac,cord's ,elements of ,descriptive ,geometry #hvo1 #c #jj ,kinematics2 or1 ,practical ,mechanism #hvo1 #e #jj ,mechanical ,drawing #dto1 #d #jj ,velocity ,diagrams #hvo1 #a #ej ,mac,leod's ,descriptive ,geometry ,small #hvo1 #a #ej 99 ,mahan's ,descriptive ,geometry and ,stone-cutting #hvo1 #a #ej ,industrial ,drawing4 7,thompson47 #hvo1 #c #ej ,moyer's ,descriptive ,geometry #hvo1 #b #jj ,reed's ,topographical ,drawing and ,sketching #dto1 #e #jj ,reid's ,course in ,mechanical ,drawing #hvo1 #b #jj ,text-book of ,mechanical ,drawing and ,elementary ,machine ,design #hvo1 #c #jj ,robinson's ,principles of ,mechanism #hvo1 #c #jj ,schwamb and ,merrill's ,elements of ,mechanism #hvo1 #c #jj ,smith's 7,r4 ,s47 ,manual of ,topographical ,drawing4 7,mc,millan47 #hvo1 #b #ej ,smith 7,a4 ,w47 and ,marx's ,machine ,design #hvo1 #c #jj ,warren's ,elements of ,plane and ,solid ,free-hand ,geometrical ,drawing #abmo1 #a #jj ,drafting ,instruments and ,operations #abmo1 #a #be ,manual of ,elementary ,projection ,drawing #abmo1 #a #ej ,manual of ,elementary ,problems in the ,linear ,perspective of ,form and ,shadow #abmo1 #a #jj ,plane ,problems in ,elementary ,geometry #abmo1 #a #be ,warren's ,primary ,geometry #abmo1 #ge ,elements of ,descriptive ,geometry1 ,shadows1 and ,perspective #hvo1 #c #ej ,general ,problems of ,shades and ,shadows #hvo1 #c #jj ,elements of ,machine ,construction and ,drawing #hvo1 #g #ej ,problems1 ,theorems1 and ,examples in ,descriptive ,geometry #hvo1 #b #ej ,weisbach's ,kinematics and ,power of ,transmission4 7,hermann and ,klein47 #hvo1 #e #jj ,whelpley's ,practical ,instruction in the ,art of ,letter ,engraving #abmo1 #b #jj ,wilson's 7,h4 ,m47 ,topographic ,surveying #hvo1 #c #ej ,wilson's 7,v4 ,t47 ,free-hand ,perspective #hvo1 #b #ej ,wilson's 7,v4 ,t47 ,free-hand ,lettering #hvo1 #a #jj ,woolf's ,elementary ,course in ,descriptive ,geometry ,large #hvo1 #c #jj ,,electricity ,,and ,,physics4 ,anthony and ,brackett's ,text-book of ,physics4 7,magie47 ,small #hvo1 #c #jj ,anthony's ,lecture-notes on the ,theory of ,electrical ,measurements #abmo1 #a #jj ,benjamin's ,history of ,electricity #hvo1 #c #jj ,voltaic ,cell #hvo1 #c #jj ,classen's ,quantitative ,chemical ,analysis by ,electrolysis4 7,boltwood47 #hvo1 #c #jj ,crehore and ,squier's ,polarizing ,photo-chronograph #hvo1 #c #jj ,dawson's 8,engineering0 and ,electric ,traction ,pocket-book #afmo1 morocco1 #e #jj ,dolezalek's ,theory of the ,lead ,accumulator 7,storage ,battery74 7,von ,ende47 #abmo1 #b #ej ,duhem's ,thermodynamics and ,chemistry4 7,burgess47 #hvo1 #d #jj ,flather's ,dynamometers1 and the ,measurement of ,power #abmo1 #c #jj ,gilbert's ,de ,magnete4 7,mottelay47 #hvo1 #b #ej ,hanchett's ,alternating ,currents ,explained #abmo1 #a #jj ,hering's ,ready ,reference ,tables 7,conversion ,factors7 #afmo1 morocco1 #b #ej ,holman's ,precision of ,measurements #hvo1 #b #jj ,telescopic ,mirror-scale ,method1 ,adjustments1 and ,tests ,large #hvo1 #ge ,kinzbrunner's ,testing of ,continuous-current ,machines #hvo1 #b #jj ,landauer's ,spectrum ,analysis4 7,tingle47 #hvo1 #c #jj ,le ,chatelier's ,high-temperature ,measurements4 7,boudouard--,burgess47 #abmo1 #c #jj ,lb's ,electrochemistry of ,organic ,compounds4 7,lorenz47 #hvo1 #c #jj 99 ,lyon's ,treatise on ,electromagnetic ,phenomena4 ,vols4 ,i4 and ,,ii4 #hvo1 each1 #f #jj 99 ,michie's ,elements of ,wave ,motion ,relating to ,sound and ,light #hvo1 #d #jj ,niaudet's ,elementary ,treatise on ,electric ,batteries4 7,fishback47 #abmo1 #b #ej 99 ,rosenberg's ,electrical ,engineering4 7,haldane ,gee--,kinzbrunner47 #hvo1 #a #ej ,ryan1 ,norris1 and ,hoxie's ,electrical ,machinery4 ,vol4 ,i4 #hvo1 #b #ej ,thurston's ,stationary ,steam-engines #hvo1 #b #ej 99 ,tillman's ,elementary ,lessons in ,heat #hvo1 #a #ej ,tory and ,pitcher's ,manual of ,laboratory ,physics ,small #hvo1 #b #jj ,ulke's ,modern ,electrolytic ,copper ,refining #hvo1 #c #jj ,,law4 99 ,davis's ,elements of ,law #hvo1 #b #ej 99 ,treatise on the ,military ,law of ,united ,states #hvo1 #g #jj 99 ,sheep1 #g #ej ,manual for ,courts-martial #afmo1 morocco1 #a #ej ,wait's ,engineering and ,architectural ,jurisprudence #hvo1 #f #jj ,sheep1 #f #ej ,law of ,operations ,preliminary to ,construction in ,engineering and ,architecture #hvo1 #e #jj ,sheep1 #e #ej ,law of ,contracts #hvo1 #c #jj ,winthrop's ,abridgment of ,military ,law #abmo1 #b #ej ,,manufactures4 ,bernadou's ,smokeless ,powder--,nitro-cellulose and ,theory of the ,cellulose ,molecule #abmo1 #b #ej ,bolland's ,iron ,founder #abmo1 #b #ej 8,the ,iron ,founder10 ,supplement #abmo1 #b #ej ,encyclopedia of ,founding and ,dictionary of ,foundry ,terms ,used in the ,practice of ,moulding #abmo1 #c #jj ,eissler's ,modern ,high ,explosives #hvo1 #d #jj ,effront's ,enzymes and their ,applications4 7,prescott47 #hvo1 #c #jj ,fitzgerald's ,boston ,machinist #abmo1 #a #jj ,ford's ,boiler ,making for ,boiler ,makers #ahmo1 #a #jj ,hopkin's ,oil-chemists' ,handbook #hvo1 #c #jj ,keep's ,cast ,iron #hvo1 #b #ej ,leach's ,the ,inspection and ,analysis of ,food with ,special ,reference to ,state ,control ,large #hvo1 #g #ej ,matthews's ,the ,textile ,fibres #hvo1 #c #ej ,metcalf's ,steel4 ,a ,manual for ,steel-users #abmo1 #b #jj ,metcalfe's ,cost of ,manufactures--,and the ,administration of ,workshops #hvo1 #e #jj ,meyer's ,modern ,locomotive ,construction #dto1 #aj #jj ,morse's ,calculations used in ,cane-sugar ,factories #afmo1 morocco1 #a #ej 99 ,reisig's ,guide to ,piece-dyeing #hvo1 #be #jj ,sabin's ,industrial and ,artistic ,technology of ,paints and ,varnish #hvo1 #c #jj ,smith's ,press-working of ,metals #hvo1 #c #jj ,spalding's ,hydraulic ,cement #abmo1 #b #jj ,spencer's ,handbook for ,chemists of ,beet-sugar ,houses #afmo1 morocco1 #c #jj ,handbook for ,cane ,sugar ,manufacturers #afmo1 morocco1 #c #jj ,taylor and ,thompson's ,treatise on ,concrete1 ,plain and ,reinforced #hvo1 #e #jj ,thurston's ,manual of ,steam-boilers1 their ,designs1 ,construction and ,operation #hvo1 #e #jj 99 ,walke's ,lectures on ,explosives #hvo1 #d #jj ,ware's ,beet-sugar ,manufacture and ,refining ,small #hvo1 #d #jj ,west's ,american ,foundry ,practice #abmo1 #b #ej ,moulder's ,text-book #abmo1 #b #ej ,wolff's ,windmill as a ,prime ,mover #hvo1 #c #jj ,wood's ,rustless ,coatings3 ,corrosion and ,electrolysis of ,iron and ,steel #hvo1 #d #jj ,,mathematics4 ,baker's ,elliptic ,functions #hvo1 #a #ej 99 ,bass's ,elements of ,differential ,calculus #abmo1 #d #jj ,briggs's ,elements of ,plane ,analytic ,geometry #abmo1 #a #jj ,compton's ,manual of ,logarithmic ,computations #abmo1 #a #ej ,davis's ,introduction to the ,logic of ,algebra #hvo1 #a #ej 99 ,dickson's ,college ,algebra ,large #abmo1 #a #ej 99 ,introduction to the ,theory of ,algebraic ,equations ,large #abmo1 #a #be ,emch's ,introduction to ,projective ,geometry and its ,applications #hvo1 #b #ej ,halsted's ,elements of ,geometry #hvo1 #a #ge ,elementary ,synthetic ,geometry #hvo1 #a #ej ,rational ,geometry #abmo1 #a #ge 99 ,johnson's 7,j4 ,b47 ,three-place ,logarithmic ,tables3 ,vest-pocket size paper1 #ae #ajj copies for #e #jj 99 ,mounted on heavy cardboard1 #h #aj inches1 #be #aj copies for #b #jj ,johnson's 7,w4 ,w47 ,elementary ,treatise on ,differential ,calculus ,small #hvo1 #c #jj ,johnson's 7,w4 ,w47 ,elementary ,treatise on the ,integral ,calculus ,small #hvo1 #a #ej ,johnson's 7,w4 ,w47 ,curve ,tracing in ,cartesian ,co-ordinates #abmo1 #a #jj ,johnson's 7,w4 ,w47 ,treatise on ,ordinary and ,partial ,differential ,equations ,small #hvo1 #c #ej ,johnson's 7,w4 ,w47 ,theory of ,errors and the ,method of ,least ,squares #abmo1 #a #ej 99 ,johnson's 7,w4 ,w47 ,theoretical ,mechanics #abmo1 #c #jj ,laplace's ,philosophical ,essay on ,probabilities4 7,truscott and ,emory47 #abmo1 #b #jj 99 ,ludlow and ,bass4 ,elements of ,trigonometry and ,logarithmic and ,other ,tables #hvo1 #c #jj ,trigonometry and ,tables published separately ,each1 #b #jj 99 ,ludlow's ,logarithmic and ,trigonometric ,tables #hvo1 #a #jj ,mathematical ,monographs4 ,edited by ,mansfield ,merriman and ,robert ,s4 ,woodward ,octavo1 each #a #jj ,no4 #a4 ,history of ,modern ,mathematics1 by ,david ,eugene ,smith4 ,no4 #b4 ,synthetic ,projective ,geometry1 by ,george ,bruce ,halsted4 ,no4 #c4 ,determinants1 by ,laenas ,gifford ,weld4 ,no4 #d4 ,hyperbolic ,functions1 by ,james ,mc,mahon4 ,no4 #e4 ,harmonic ,functions1 by ,william ,e4 ,byerly4 ,no4 #f4 ,grassmann's ,space ,analysis1 by ,edward ,w4 ,hyde4 ,no4 #g4 ,probability and ,theory of ,errors1 by ,robert ,s4 ,woodward4 ,no4 #h4 ,vector ,analysis and ,quaternions1 by ,alexander ,macfarlane4 ,no4 #i4 ,differential ,equations1 by ,william ,woolsey ,johnson4 ,no4 #aj4 ,the ,solution of ,equations1 by ,mansfield ,merriman4 ,no4 #aa4 ,functions of a ,complex ,variable1 by ,thomas ,s4 ,fiske4 ,maurer's ,technical ,mechanics #hvo1 #d #jj ,merriman and ,woodward's ,higher ,mathematics #hvo1 #e #jj ,merriman's ,method of ,least ,squares #hvo1 #b #jj ,rice and ,johnson's ,elementary ,treatise on the ,differential ,calculus ,sm4 #hvo1 #c #jj ,differential and ,integral ,calculus4 #b vols4 in one ,small #hvo1 #b #ej ,wood's ,elements of ,co-ordinate ,geometry #hvo1 #b #jj ,trigonometry3 ,analytical1 ,plane1 and ,spherical #abmo1 #a #jj ,,mechanical ,,engineering4 ,,materials ,,of ,,engineering1 ,,steam-,,engines ,,and ,,boilers4 ,bacon's ,forge ,practice #abmo1 #a #ej ,baldwin's ,steam ,heating for ,buildings #abmo1 #b #ej ,barr's ,kinematics of ,machinery #hvo1 #b #ej 99 ,bartlett's ,mechanical ,drawing #hvo1 #c #jj 99 ,bartlett's ,mechanical ,drawing ,abridged ,ed #hvo1 #a #ej ,benjamin's ,wrinkles and ,recipes #abmo1 #b #jj ,carpenter's ,experimental ,engineering #hvo1 #f #jj ,heating and ,ventilating ,buildings #hvo1 #d #jj ,cary's ,smoke ,suppression in ,plants using ,bituminous ,coal4 7,in ,preparation47 ,clerk's ,gas and ,oil ,engine ,small #hvo1 #d #jj ,coolidge's ,manual of ,drawing #hvo1 paper1 #a #jj ,coolidge and ,freeman's ,elements of ,general ,drafting for ,mechanical ,engineers ,oblong #dto1 #b #ej ,cromwell's ,treatise on ,toothed ,gearing #abmo1 #a #ej ,treatise on ,belts and ,pulleys #abmo1 #a #ej ,durley's ,kinematics of ,machines #hvo1 #d #jj ,flather's ,dynamometers and the ,measurement of ,power #abmo1 #c #jj ,rope ,driving #abmo1 #b #jj ,gill's ,gas and ,fuel ,analysis for ,engineers #abmo1 #a #be ,hall's ,car ,lubrication #abmo1 #a #jj ,hering's ,ready ,reference ,tables 7,conversion ,factors7 #afmo1 morocco1 #b #ej ,hutton's ,the ,gas ,engine #hvo1 #e #jj ,jamison's ,mechanical ,drawing #hvo1 #b #ej ,jones's ,machine ,design3 ,part ,i4 ,kinematics of ,machinery #hvo1 #a #ej ,part ,,ii4 ,form1 ,strength1 and ,proportions of ,parts #hvo1 #c #jj ,kent's ,mechanical ,engineers' ,pocket-book #afmo1 morocco1 #e #jj ,kerr's ,power and ,power ,transmission #hvo1 #b #jj ,leonard's ,machine ,shop1 ,tools1 and ,methods #hvo1 #d #jj 99 ,lorenz's ,modern ,refrigerating ,machinery4 7,pope1 ,haven1 and ,dean47 #hvo1 #d #jj ,mac,cord's ,kinematics2 or1 ,practical ,mechanism #hvo1 #e #jj ,mechanical ,drawing #dto1 #d #jj ,velocity ,diagrams #hvo1 #a #ej ,mac,farland's ,standard ,reduction ,factors for ,gases #hvo1 #a #ej ,mahan's ,industrial ,drawing4 7,thompson47 #hvo1 #c #ej ,poole's ,calorific ,power of ,fuels #hvo1 #c #jj ,reid's ,course in ,mechanical ,drawing #hvo1 #b #jj ,text-book of ,mechanical ,drawing and ,elementary ,machine ,design #hvo1 #c #jj ,richard's ,compressed ,air #abmo1 #a #ej ,robinson's ,principles of ,mechanism #hvo1 #c #jj ,schwamb and ,merrill's ,elements of ,mechanism #hvo1 #c #jj ,smith's 7,o47 ,press-working of ,metals #hvo1 #c #jj ,smith 7,a4 ,w47 and ,marx's ,machine ,design #hvo1 #c #jj ,thurston's ,treatise on ,friction and ,lost ,work in ,machinery and ,mill ,work #hvo1 #c #jj ,animal as a ,machine and ,prime ,motor1 and the ,laws of ,energetics #abmo1 #a #jj ,warren's ,elements of ,machine ,construction and ,drawing #hvo1 #g #ej ,weisbach's ,kinematics and the ,power of ,transmission4 7,herrmann--,klein47 #hvo1 #e #jj ,machinery of ,transmission and ,governors4 7,herrmann--,klein47 #hvo1 #e #jj ,wolff's ,windmill as a ,prime ,mover #hvo1 #c #jj ,wood's ,turbines #hvo1 #b #ej ,,materials ,,of ,,engineering4 99 ,bovey's ,strength of ,materials and ,theory of ,structures #hvo1 #g #ej ,burr's ,elasticity and ,resistance of the ,materials of ,engineering4 #fth ,edition4 ,reset #hvo1 #g #ej ,church's ,mechanics of ,engineering #hvo1 #f #jj 99 ,greene's ,structural ,mechanics #hvo1 #b #ej ,johnson's ,materials of ,construction #hvo1 #f #jj ,keep's ,cast ,iron #hvo1 #b #ej ,lanza's ,applied ,mechanics #hvo1 #g #ej ,martens's ,handbook on ,testing ,materials4 7,henning47 #hvo1 #g #ej ,maurer's ,technical ,mechanics #hvo1 #d #jj ,merriman's ,mechanics of ,materials #hvo1 #e #jj ,strength of ,materials #abmo1 #a #jj ,metcalf's ,steel4 ,a manual for ,steel-users #abmo1 #b #jj ,sabin's ,industrial and ,artistic ,technology of ,paints and ,varnish #hvo1 #c #jj ,smith's ,materials of ,machines #abmo1 #a #jj ,thurston's ,materials of ,engineering #c vols41 #hvo1 #h #jj ,part ,,ii4 ,iron and ,steel #hvo1 #c #ej ,part ,,iii4 ,a ,treatise on ,brasses1 ,bronzes1 and ,other ,alloys and their ,constituents #hvo1 #b #ej ,text-book of the ,materials of ,construction #hvo1 #e #jj ,wood's 7,de ,v47 ,treatise on the ,resistance of ,materials and an ,appendix on the ,preservation of ,timber #hvo1 #b #jj ,wood's 7,de ,v47 ,elements of ,analytical ,mechanics #hvo1 #c #jj ,wood's 7,m4 ,p47 ,rustless ,coatings3 ,corrosion and ,electrolysis of ,iron and ,steel #hvo1 #d #jj ,,steam-,,engines ,,and ,,boilers4 ,berry's ,temperature-entropy ,diagram #abmo1 #a #be ,carnot's ,reflections on the ,motive ,power of ,heat4 7,thurston47 #abmo1 #a #ej ,dawson's 8,engineering0 and ,electric ,traction ,pocket-book #afmo1 mor41 #e #jj ,ford's ,boiler ,making for ,boiler ,makers #ahmo1 #a #jj ,goss's ,locomotive ,sparks #hvo1 #b #jj ,hemenway's ,indicator ,practice and ,steam-engine ,economy #abmo1 #b #jj ,hutton's ,mechanical ,engineering of ,power ,plants #hvo1 #e #jj ,heat and ,heat-engines #hvo1 #e #jj ,kent's ,steam boiler ,economy #hvo1 #d #jj ,kneass's ,practice and ,theory of the ,injector #hvo1 #a #ej ,mac,cord's ,slide-valves #hvo1 #b #jj ,meyer's ,modern ,locomotive ,construction #dto1 #aj #jj ,peabody's ,manual of the ,steam-engine ,indicator #abmo1 #a #ej ,tables of the ,properties of ,saturated ,steam and ,other ,vapors #hvo1 #a #jj ,thermodynamics of the ,steam-engine and ,other ,heat-engines #hvo1 #e #jj ,valve-gears for ,steam-engines #hvo1 #b #ej ,peabody and ,miller's ,steam-boilers #hvo1 #d #jj ,pray's ,twenty ,years with the ,indicator ,large #hvo1 #b #ej ,pupin's ,thermodynamics of ,reversible ,cycles in ,gases and ,saturated ,vapors4 7,osterberg47 #abmo1 #a #be ,reagan's ,locomotives3 ,simple ,compound1 and ,electric #abmo1 #b #ej ,rontgen's ,principles of ,thermodynamics4 7,du ,bois47 #hvo1 #e #jj ,sinclair's ,locomotive ,engine ,running and ,management #abmo1 #b #jj ,smart's ,handbook of ,engineering ,laboratory ,practice #abmo1 #b #ej ,snow's ,steam-boiler ,practice #hvo1 #c #jj ,spangler's ,valve-gears #hvo1 #b #ej ,notes on ,thermodynamics #abmo1 #a #jj ,spangler1 ,greene1 and ,marshall's ,elements of ,steam-engineering #hvo1 #c #jj ,thurston's ,handy ,tables #hvo1 #a #ej ,manual of the ,steam-engine #b vols41 #hvo1 #aj #jj ,part ,i4 ,history1 ,structure1 and ,theory #hvo1 #f #jj ,part ,,ii4 ,design1 ,construction1 and ,operation #hvo1 #f #jj ,handbook of ,engine and ,boiler ,trials1 and the ,use of the ,indicator and the ,prony ,brake #hvo1 #e #jj ,stationary ,steam-engines #hvo1 #b #ej ,steam-boiler ,explosions in ,theory and in ,practice #abmo1 #a #ej ,manual of ,steam-boilers1 their ,designs1 ,construction1 and ,operation #hvo1 #e #jj ,weisbach's ,heat1 ,steam1 and ,steam-engines4 7,du ,bois47 #hvo1 #e #jj ,whitham's ,steam-engine ,design #hvo1 #e #jj ,wilson's ,treatise on ,steam-boilers4 7,flather47 #afmo1 #b #ej ,wood's ,thermodynamics1 ,heat ,motors1 and ,refrigerating ,machines #hvo1 #d #jj ,,mechanics ,,and ,,machinery4 ,barr's ,kinematics of ,machinery #hvo1 #b #ej 99 ,bovey's ,strength of ,materials and ,theory of ,structures #hvo1 #g #ej ,chase's ,the ,art of ,pattern-making #abmo1 #b #ej ,church's ,mechanics of ,engineering #hvo1 #f #jj ,notes and ,examples in ,mechanics #hvo1 #b #jj ,compton's ,first ,lessons in ,metal-working #abmo1 #a #ej ,compton and ,de ,groodt's ,the ,speed ,lathe #abmo1 #a #ej ,cromwell's ,treatise on ,toothed ,gearing #abmo1 #a #ej ,treatise on ,belts and ,pulleys #abmo1 #a #ej ,dana's ,text-book of ,elementary ,mechanics for ,colleges and ,schools #abmo1 #a #ej ,dingey's ,machinery ,pattern ,making #abmo1 #b #jj ,dredge's ,record of the ,transportation ,exhibits ,building of the ,world's ,columbian ,exposition of #ahic #dto half morocco1 #e #jj ,du ,bois's ,elementary ,principles of ,mechanics3 ,vol4 ,i4 ,kinematics #hvo1 #c #ej ,vol4 ,,ii4 ,statics #hvo1 #d #jj ,mechanics of ,engineering4 ,vol4 ,i4 ,small #dto1 #g #ej ,vol4 ,,ii4 ,small #dto1 #aj #jj ,durley's ,kinematics of ,machines #hvo1 #d #jj ,fitzgerald's ,boston ,machinist #afmo1 #a #jj ,flather's ,dynamometers1 and the ,measurement of ,power #abmo1 #c #jj ,rope ,driving #abmo1 #b #jj ,goss's ,locomotive ,sparks #hvo1 #b #jj 99 ,greene's ,structural ,mechanics #hvo1 #b #ej ,hall's ,car ,lubrication #abmo1 #a #jj ,holly's ,art of ,saw ,filing #ahmo1 #ge ,james's ,kinematics of a ,point and the ,rational ,mechanics of a ,particle4 ,small #hvo1 #b #jj 99 ,johnson's 7,w4 ,w47 ,theoretical ,mechanics #abmo1 #c #jj ,johnson's 7,l4 ,j47 ,statics by ,graphic and ,algebraic ,methods #hvo1 #b #jj ,jones's ,machine ,design3 ,part ,i4 ,kinematics of ,machinery #hvo1 #a #ej ,part ,,ii4 ,form1 ,strength1 and ,proportions of ,parts #hvo1 #c #jj ,kerr's ,power and ,power ,transmission #hvo1 #b #jj ,lanza's ,applied ,mechanics #hvo1 #g #ej ,leonard's ,machine ,shop1 ,tools1 and ,methods #hvo1 #d #jj 99 ,lorenz's ,modern ,refrigerating ,machinery4 7,pope1 ,haven1 and ,dean47 #hvo1 #d #jj ,mac,cord's ,kinematics2 or1 ,practical ,mechanism #hvo1 #e #jj ,velocity ,diagrams #hvo1 #a #ej ,maurer's ,technical ,mechanics #hvo1 #d #jj ,merriman's ,mechanics of ,materials #hvo1 #e #jj 99 ,elements of ,mechanics #abmo1 #a #jj 99 ,michie's ,elements of ,analytical ,mechanics #hvo1 #d #jj ,reagan's ,locomotives3 ,simple1 ,compound1 and ,electric #abmo1 #b #ej ,reid's ,course in ,mechanical ,drawing #hvo1 #b #jj ,text-book of ,mechanical ,drawing and ,elementary ,machine ,design #hvo1 #c #jj ,richards's ,compressed ,air #abmo1 #a #ej ,robinson's ,principles of ,mechanism #hvo1 #c #jj ,ryan1 ,norris1 and ,hoxie's ,electrical ,machinery4 ,vol4 ,i4 #hvo1 #b #ej ,schwamb and ,merrill's ,elements of ,mechanism #hvo1 #c #jj ,sinclair's ,locomotive-engine ,running and ,management #abmo1 #b #jj ,smith's 7,o47 ,press-working of ,metals #hvo1 #c #jj ,smith's 7,a4 ,w47 ,materials of ,machines #abmo1 #a #jj ,smith 7,a4 ,w47 and ,marx's ,machine ,design #hvo1 #c #jj ,spangler1 ,greene1 and ,marshall's ,elements of ,steam-engineering #hvo1 #c #jj ,thurston's ,treatise on ,friction and ,lost ,work in ,machinery and ,mill ,work #hvo1 #c #jj ,animal as a ,machine and ,prime ,motor1 and the ,laws of ,energetics #abmo1 #a #jj ,warren's ,elements of ,machine ,construction and ,drawing #hvo1 #g #ej ,weisbach's ,kinematics and ,power of ,transmission4 7,herrmann--,klein47 #hvo1 #e #jj ,machinery of ,transmission and ,governors4 7,herrmann--,klein47 #hvo1 #e #jj ,wood's ,elements of ,analytical ,mechanics #hvo1 #c #jj ,principles of ,elementary ,mechanics #abmo1 #a #be ,turbines #hvo1 #b #ej ,the ,world's ,columbian ,exposition of #ahic #dto1 #a #jj ,,metallurgy4 ,egleston's ,metallurgy of ,silver1 ,gold1 and ,mercury3 ,vol4 ,i4 ,silver #hvo1 #g #ej ,vol4 ,,ii4 ,gold and ,mercury #hvo1 #g #ej 9999 ,iles's ,lead-smelting4 7,postage #i cents additional47 #abmo1 #b #ej ,keep's ,cast ,iron #hvo1 #b #ej ,kunhardt's ,practice of ,ore ,dressing in ,europe #hvo1 #a #ej ,le ,chatelier's ,high-temperature ,measurements4 7,boudouard--,burgess47 #abmo1 #c #jj ,metcalf's ,steel4 ,a ,manual for ,steel-users #abmo1 #b #jj ,minet's ,production of ,aluminum and its ,industrial ,use4 7,waldo47 #abmo1 #b #ej ,robine and ,lenglen's ,cyanide ,industry4 7,le ,clerc47 #hvo1 ,smith's ,materials of ,machines #abmo1 #a #jj ,thurston's ,materials of ,engineering4 ,in ,three ,parts #hvo1 #h #jj ,part ,,ii4 ,iron and ,steel #hvo1 #c #ej ,part ,,iii4 ,a ,treatise on ,brasses1 ,bronzes1 and ,other ,alloys and their ,constituents #hvo1 #b #ej ,ulke's ,modern ,electrolytic ,copper ,refining #hvo1 #c #jj ,,mineralogy4 ,barringer's ,description of ,minerals of ,commercial ,value4 ,oblong1 morocco1 #b #ej ,boyd's ,resources of ,southwest ,virginia4 #hvo1 #c #jj ,map of ,southwest ,virginia ,pocket-book form1 #b #jj ,brush's ,manual of ,determinative ,mineralogy4 7,penfield47 #hvo1 #d #jj ,chester's ,catalogue of ,minerals #hvo1 paper1 #a #jj ,cloth1 #a #be ,dictionary of the ,names of ,minerals #hvo1 #c #ej ,dana's ,system of ,mineralogy ,large #hvo1 half leather1 #ab #ej ,first ,appendix to ,dana's ,new 8,system of ,mineralogy40 ,large #hvo1 #a #jj ,text-book of ,mineralogy #hvo1 #d #jj ,minerals and ,how to ,study ,them #abmo1 #a #ej ,catalogue of ,american ,localities of ,minerals ,large #hvo1 #a #jj ,manual of ,mineralogy and ,petrography #abmo1 #b #jj ,douglas's ,untechnical ,addresses on ,technical ,subjects #abmo1 #a #jj ,eakle's ,mineral ,tables #hvo1 #a #be ,egleston's ,catalogue of ,minerals and ,synonyms #hvo1 #b #ej ,hussak's ,the ,determination of ,rock-forming ,minerals4 7,smith47 ,small #hvo1 #b #jj ,merrill's ,non-metallic ,minerals3 ,their ,occurrence and ,uses #hvo1 #d #jj 99 ,penfield's ,notes on ,determinative ,mineralogy and ,record of ,mineral ,tests4 #hvo1 paper1 #ej ,rosenbusch's ,microscopical ,physiography of the ,rock-making ,minerals4 7,iddings47 #hvo1 #e #jj 99 ,tillman's ,text-book of ,important ,minerals and ,rocks #hvo1 #b #jj ,,mining4 ,beard's ,ventilation of ,mines #abmo1 #b #ej ,boyd's ,resources of ,southwest ,virginia #hvo1 #c #jj ,map of ,southwest ,virginia ,pocket-book form1 #b #jj ,douglas's ,untechnical ,addresses on ,technical ,subjects #abmo1 #a #jj 99 ,drinker's ,tunneling1 ,explosive ,compounds1 and ,rock ,drills #dto1 hf4 mor41 #be #jj ,eissler's ,modern ,high ,explosives #hvo1 #d #jj ,fowler's ,sewage ,works ,analyses #abmo1 #b #jj ,goodyear's ,coal-mines of the ,western ,coast of the ,united ,states #abmo1 #b #ej ,ihlseng's ,manual of ,mining #hvo1 #e #jj 99 ,iles's ,lead-smelting4 7,postage #i;c4 additional47 #abmo1 #b #ej ,kunhardt's ,practice of ,ore ,dressing in ,europe #hvo1 #a #ej ,o',driscoll's ,notes on the treatment of ,gold ,ores #hvo1 #b #jj ,robine and ,lenglen's ,cyanide ,industry4 7,le ,clerc47 #hvo1 99 ,walke's ,lectures on ,explosives #hvo1 #d #jj ,wilson's ,cyanide ,processes #abmo1 #a #ej ,chlorination ,process #abmo1 #a #ej ,hydraulic and ,placer ,mining #abmo1 #b #jj ,treatise on ,practical and ,theoretical ,mine ,ventilation #abmo1 #a #be ,,sanitary ,,science4 ,bashore's ,sanitation of a ,country ,house #abmo1 #a #jj ,folwell's ,sewerage4 7,designing1 ,construction1 and ,maintenance47 #hvo1 #c #jj ,water-supply ,engineering #hvo1 #d #jj ,fuertes's ,water and ,public ,health #abmo1 #a #ej ,water-filtration ,works #abmo1 #b #ej ,gerhard's ,guide to ,sanitary ,house-inspection #afmo1 #a #jj ,goodrich's ,economic ,disposal of ,town's ,refuse ,demy #hvo1 #c #ej ,hazen's ,filtration of ,public ,water-supplies #hvo1 #c #jj ,leach's ,the ,inspection and ,analysis of ,food with ,special ,reference to ,state ,control #hvo1 #g #ej ,mason's ,water-supply4 7,considered principally from a ,sanitary ,standpoint7 #hvo1 #d #jj ,examination of ,water4 7,chemical and ,bacteriological47 #abmo1 #a #be ,ogden's ,sewer ,design #abmo1 #b #jj ,prescott and ,winslow's ,elements of ,water ,bacteriology1 with ,special ,reference to ,sanitary ,water ,analysis #abmo1 #a #be 99 ,price's ,handbook on ,sanitation #abmo1 #a #ej ,richards's ,cost of ,food4 ,a ,study in ,dietaries #abmo1 #a #jj ,cost of ,living as ,modified by ,sanitary ,science #abmo1 #a #jj ,richards and ,woodman's ,air1 ,water1 and ,food from a ,sanitary ,standpoint #hvo1 #b #jj 99 ,richards and ,williams's ,the ,dietary ,computer #hvo1 #a #ej ,rideal's ,sewage and ,bacterial ,purification of ,sewage #hvo1 #c #ej ,turneaure and ,russell's ,public ,water-supplies #hvo1 #e #jj ,von ,behring's ,suppression of ,tuberculosis4 7,bolduan47 #abmo1 #a #jj ,whipple's ,microscopy of ,drinking-water #hvo1 #c #ej ,winton's ,microscopy of ,vegetable ,foods #hvo1 #g #ej ,woodhull's ,notes on ,military ,hygiene #afmo1 #a #ej ,,miscellaneous4 ,de ,fursac's ,manual of ,psychiatry4 7,rosanoff and ,collins47 ,large #abmo1 #b #ej ,emmons's ,geological ,guide-book of the ,rocky ,mountain ,excursion of the ,international ,congress of ,geologists ,large #hvo1 #a #ej ,ferrel's ,popular ,treatise on the ,winds #hvo1 #d #jj ,haines's ,american ,railway ,management #abmo1 #b #ej ,mott's ,fallacy of the ,present ,theory of ,sound #afmo1 #a #jj ,ricketts's ,history of ,rensselaer ,polytechnic ,institute1 #ahbd-ahid ,small #hvo1 #c #jj ,rostoski's ,serum ,diagnosis4 7,bolduan47 #abmo1 #a #jj ,rotherham's ,emphasized ,new ,testament ,large #hvo1 #b #jj ,steel's ,treatise on the ,diseases of the ,dog #hvo1 #c #ej ,the ,world's ,columbian ,exposition of #ahic #dto1 #a #jj ,von ,behring's ,suppression of ,tuberculosis4 7,bolduan47 #abmo1 #a #jj ,winslow's ,elements of ,applied ,microscopy #abmo1 #a #ej ,worcester and ,atkinson4 ,small ,hospitals1 ,establishment and ,maintenance2 ,suggestions for ,hospital ,architecture3 ,plans for ,small ,hospital #abmo1 #a #be ,,hebrew ,,and ,,chaldee ,,text-,,books4 ,green's ,elementary ,hebrew ,grammar #abmo1 #a #be ,hebrew ,chrestomathy #hvo1 #b #jj ,gesenius's ,hebrew and ,chaldee ,lexicon to the ,old ,testament ,scriptures4 7,tregelles47 ,small #dto1 half morocco1 #e #jj ,letteris's ,hebrew ,bible #hvo1 #b #be ,transcriber's ,notes3-- ,the ,to,c 7,table of ,contents7 has been changed so as to follow the structure of the book more faithfully4 ,the original ,to,c is given here3-- ,,contents4 ,,page ,,chapter ,i4 ,,introduction4 #a ,,ii4 ,,continuous ,,filters ,,and ,,their ,,construction #e ,sedimentation-basins #h ,size of ,filter-beds #aj ,covers for ,filters #ab ,,iii4 ,,filtering-,,materials #bj ,sand #bj ,gravel #ce ,underdrains #ci ,depth of ,water on ,filters #de ,,iv4 ,,rate ,,of ,,filtration ,,and ,,loss ,,of ,,head #dg ,rate of ,filtration #dg ,loss of ,head and ,apparatus for regulating it #eb ,limit to the ,loss of ,head #fj ,v4 ,,cleaning ,,filters #fh ,scraping #fh ,frequency of ,scraping #gb ,sand-washing #gf ,,vi4 ,,theory ,,and ,,efficiency ,,of ,,filtration #hc ,bacterial ,examination of ,waters #ic ,,vii4 ,,intermittent ,,filtration #ig ,the ,lawrence ,filter #ajj ,the ,chemnitz ,filter #ajg ,,viii4 ,,turbidity ,,and ,,color1 ,,and ,,the ,,effect ,,of ,,mud ,,upon ,,sand ,,filters #aac ,color #aad ,turbidity #aag ,preliminary ,processes to remove ,mud #acc ,effect of ,mud upon ,sand ,filters #acg ,,ix4 ,,coagulation ,,of ,,waters #add ,substances used for ,coagulation #ade ,amount of ,coagulant required to remove ,turbidity #aej ,amount of ,coagulant required to remove ,color #aec ,successive ,applications of ,coagulant #aed ,amount of ,coagulant which ,waters will receive #aee ,x4 ,,mechanical ,,filters #aei ,influence of ,amount of ,coagulant on ,bacterial ,efficiency #afe ,types of ,mechanical ,filters #agb ,,xi4 ,,other ,,methods ,,of ,,filtration #aha ,,xii4 ,,removal ,,of ,,iron ,,from ,,ground-,,waters #ahf ,cause of ,iron in ,ground-waters #ahg ,treatment of ,iron-containing ,waters #ahi ,iron-removal ,plants in ,operation #aib ,,xiii4 ,,treatment ,,of ,,waters #aig ,cost of ,filtration #bjj ,,xiv4 ,,water-,,supply ,,and ,,disease #baj ,,appendix ,i4 ,,german ,,official ,,regulation ,,in ,,regard ,,to ,,filtration #bba ,,ii4 ,,extracts ,,from ,,dr4 ,,reincke',s ,,report ,,upon ,,the ,,health ,,of ,,hamburg ,,for #ahib #bbf ,,iii4 ,,methods ,,of ,,sand-,,analysis #bcc ,,iv4 ,,statistics ,,of ,,some ,,filters #bda ,results of ,operation #bda ,list of ,sand ,filters in ,use #bdd ,list of ,mechanical ,filters in ,use #bdg ,notes regarding ,sand ,filters in ,america #bea ,extent of the ,use of ,filters #bed ,v4 ,,water-,,supply ,,of ,,london #bee ,,vi4 ,,water-,,supply ,,of ,,berlin #bfa ,,vii4 ,,water-,,supply ,,of ,,altona #bfe ,,viii4 ,,water-,,supply ,,of ,,hamburg #bfi ,,ix4 ,,notes ,,on ,,some ,,other ,,european ,,supplies #bgb ,x4 ,,literature ,,of ,,filtration #bgg ,,xi4 ,,the ,,albany ,,filtration ,,plant #bhh ,,index #cag ,in the table of 8,,analyses ,,of ,,sands ,,used ,,in ,,water ,,filtration0 the place name 8,owesty0 has been corrested to read 8,oswestry04 ,on page #bgj the statement 8the velocity in the drain will reach #j4ig foot0 should probably read 8#j4ig feet per second04