,,natural ,,artificial ,,sewage ,,treatment ,,by ,,lieut4-,,col4 ,,alfred ,s4 ,,jones1 ,v4,c4 ,,assoc4 ,m4 ,,inst4 ,c4,e41 ,,fellow ,,and ,,member ,,of ,,council ,,of ,,the ,,sanitary ,,institute1 ,,etc4 ,,and ,h4 ,,alfred ,,roechling ,m4 ,,inst4 ,c4,e41 ,f4,g4,s41 ,,fellow ,,of ,,the ,,sanitary ,,institute1 ,,etc4 ,illustration3 ,printer's ,logo ,london ,e4 ,f4 ,n4 ,,spon1 ,,ltd41 #abe ,,strand ,new ,york ,,spon ,,chamberlain1 #abc ,,liberty ,,street #aijb ,,preface4 ,the ,authors1 some time ago1 read before different ,societies of professional men1 ,papers#a dealing with the ,natural and ,artificial ,purification of ,sewage1 and as these were favourably received1 the thought occurred to them that the time might be opportune for making the information there given available for a wider public4 ,as1 however1 a mere republication of the ,papers would have been against the rules of the ,societies concerned1 the ,authors decided to re-write entirely the subject matter1 and to bring it up to date1 so that the present publication is not a mere repetition of their old ,papers clothed in a new garb1 but an entirely fresh publication1 right up to date4 ,the ,authors hope that they have given the information in such a form as to be readily available for ,district ,councillors1 ,sanitarians1 and all interested in this complicated subject4 ,when considering natural and artificial sewage treatment1 it ought to be borne in mind that in the natural treatment we have to deal with one treatment only1 and that1 in order to bring the results obtained from artificial processes up to the same standard1 the artificial treatment ought to be supplemented by a treatment for the removal of nitrates from the effluent1 and another for the removal of pathogenic micro-organisms1 which means one treatment in natural1 as against three separate treatments in artificial purification4 ,in addition to this it must be understood that1 owing to the great losses by evaporation and by growing plants1 which are continually at work on sewage farms1 especially during the summer months1 when1 as a rule1 the flow of water in the brook that takes the effluent is smallest1 the quantity of the effluent from the natural treatment is probably only from one-half to one-third that resulting from the artificial treatment1 which is a point of very great importance4 ,if it can be proved to them that ,nature is not sure and true enough in its methods1 the ,authors are prepared to assist it with methods and means produced by the inventive brain of man4 ,but if such proof is not forthcoming1 they adhere--in preference to groping in the dark--to ,nature's own methods1 knowing from experience1 that when allowed full scope and fair treatment1 it is most sure in all its ways4 ,that will not prevent them1 however1 from giving in the future1 as they have done in the past1 the question of sewage treatment in all its aspects their most careful consideration4 ,,alfred ,s4 ,,jones4 ,h4 ,,alfred ,,roechling4 ,,london3 ,september #ae1 #aijb4 #a #8,sewage ,treatment3 ,science with ,practice4' ,by ,colonel ,a4 ,s4 ,jones1 ,v4,c41 ,c4,e4 ,read at the ,international ,engineering ,congress at ,glasgow1 #aija4 ,and #8,the ,sewage ,question during the ,last ,century4' ,read by ,h4 ,alfred ,roechling1 ,m4 ,inst4 ,c4,e41 ,f4,g4,s41 ,f4,s4,i41 etc41 on ,december #b1 #aija1 before the ,society of ,engineers1 and awarded the ,gold ,medal of the ,society4 ,,contents4 ,,part ,i4 ,,by ,,lieut4-,,colonel ,,alfred ,s4 ,,jones1 ,v4,c4 ,,page ,,introductory #a ,,the ,,chemist ,,dibdin ,,discards ,,chemical ,,precipitation ,,in ,,favour ,,of ,m4 ,,pasteur',s ,,aerobic ,,organisms #c ,,the ,,cleanly ,,and ,,the ,,dirty 7,,septic7 ,,processes ,,for ,,sludge ,,removal #e ,,the ,,best ,,possible ,,medium ,,for ,,aerobic ,,organisms ,,to ,,work ,,in #e ,,tabular ,,statement ,,derived ,,from ,,the ,,leeds ,,official ,,report ,,of ,,experiments #g ,,the ,,wrexham ,,sewage ,,farm #h ,,the ,,camp ,,farm1 ,,aldershot1 ,,to ,,which ,,six ,,other ,,areas ,,of ,,sewage ,,works ,,have ,,been ,,added ,,from ,,july #bh1 #aijb #i ,,evidence ,,and ,,reports ,,of ,,lord ,,iddesleigh',s ,,royal ,,commission1 #ahih-aijb #ae ,,automatic ,,appliances ,,for ,,sewage ,,and ,,effluent ,,discharge #ag ,,sludge ,,treatment #ai ,,cropping ,a ,,sewage ,,farm #ba ,,importance ,,of ,,having ,,tidy ,,contour ,,carriers ,,accurately ,,levelled #bc ,,summary ,,of ,,the ,,experience ,,of ,a ,,lifetime #bc ,,anticipation ,,of ,a ,,coming ,,reaction ,,against ,,over-,,ridden 8,,fads0 ,,and ,,too ,,much ,,pressure ,,in ,,sanitation #be ,,part ,,ii4 ,,by ,h4 ,,alfred ,,roechling4 ,i4 ,,introductory ,,remarks #bh ,,ii4 ,,the ,,sewage ,,question ,,during ,,the ,,last ,,century3 ,a ,,short ,,retrospect #bi ,,iii4 ,,the ,,subsoil3 #a4 ,mechanical structure of soil #da #b4 ,permeability of soil #db #c4 ,water capacity of soil #db #d4 ,water-retentive power of soil #dc #e4 ,capillary movements of water in soil #dd #f4 ,temperature of soil #de #g4 ,subsoil air #dg #h4 ,movements of water in soil #dg #i4 ,micro-organic life in soil #ej #aj4 ,absorbing powers of soil #ea ,,iv4 ,,self-,,purifying ,,powers ,,of ,,soil4 ,,natural ,,self-,,purification ,,of ,,sewage #eb ,v4 ,artificial ,self-,purification of ,sewage3 #a4 ,general observations #fh #b4 ,artificial self-purification of sewage in intermittent contact beds3 a4 ,name of process #gj b4 ,explanation of process #ga c4 ,water capacity of bed1 and silting up #gc d4 ,absorbing powers of filling material #gh e4 ,consumption of oxygen by the filling material #gi f4 ,formation of carbonic acid #hj g4 ,nitrogen #hj h4 ,formation of nitric acid #hj #c4 ,artificial self-purification of sewage in septic tanks3 a4 ,name of septic tank #ha b4 ,covered or open septic tank #ha c4 ,explanation of process #hc d4 ,velocity of flow through tank #he e4 ,destruction and liquefaction of sludge in septic tanks #hg f4 ,formation of gas in septic tank #hh g4 ,mixing action of septic tank #hi h4 ,micro-organisms in effluent from septic tank #hi #d4 ,continuous contact beds #hi ,,vi4 ,,management ,,of ,,plants ,,for ,,the ,,artificial ,,self-,,purificationof ,,sewage #ij ,,vii4 ,,some ,,observations ,,on ,,the ,,deposition ,,of ,,suspended ,,matters ,,in ,,tanks #ia ,,viii4 ,,concluding ,,remarks #ic ,,postscript #ie ,,natural ,,and ,,artificial ,,sewage ,,treatment4 ,,by ,,lieut4-,,col4 ,,alfred ,s4 ,,jones1 ,v4,c4 ,,assoc4 ,m4 ,,inst4 ,c4,e41 ,,etc4 ,sidenote3 ,introductory remarks4 8,how extremely simple it all is60 was the remark of a recent visitor at a sewage farm--which encourages me to venture on publication of the most recent discussions on a 8problem0 complicated by engineers1 chemists1 bacteriologists and inventors of systems1 who have raised clouds of dust through which it is difficult for ratepayers and district councillors to find their way to 8the best practical and available means of sewage disposal40 ,i have a belief that publication of all attempts to purify the whole of a town's sewage1 rather than small scale experiments with equations founded on such data1 is the desideratum4 ,sidenote3 #ahgb4 ,having begun in the year #ahgb1 with a pamphlet1 8,will a ,sewage ,farm ,pay80#b ,i desire to proceed with the present one thirty years later1 as my humble contribution to a right understanding of the intelligent ,scavenger's business4 ,at the earlier date agriculture was prosperous1 and ratepayers of ,exeter were just as confident that sewage farming would bring large dividends as some of the same city's councillors are at present not in the least sceptical that their engineer's septic system is the true specific for sewage disposal4 ,in adhering to land as the natural and best agent1 ,i have had the support of the ,local ,government ,board with that of many ,royal ,commissions1 notably the one now sitting1 and ,i have naturally chosen cases where suitable land was accessible when ,i desired to demonstrate the efficiency and simplicity with which the powers of ,nature can be applied for the use and convenience of man4 ,nor have ,i failed to study all 8artificial0 substitutes for the best means1 wherever difficulties of obtaining suitable land presented themselves1 e4g4 my ,canvey ,island scheme for dealing with the sewage of ,london on a relatively small area1 and other cases4 ,of late years ,i have welcomed the light thrown on this subject by bacteriologists1 but lamented extravagant statements put forward by those who fail to see that the previously unrecognised microbes can do their work1 as they have always done it1 to most advantage in the upper layers of any porous land4 ,sidenote3 #aijb4 ,an interim report by ,lord ,iddesleigh's ,royal ,commission has1 however1 awakened such theorists to the fact that land is not to be discarded because it may not bring in a profit or because patentees of systems find it to their interest to contrast neglected or badly managed sewage farms with carefully nursed little experimental installations for artificial treatment of selected samples of sewage4 ,recognising the marvellous improvements in arts and manufactures of all kinds due to steam1 chemistry and electricity1 the public has naturally expected similar results from applied science in artificial sewage treatment1 and there has been no lack of study of every imaginable process during the last thirty years4 ,sidenote3 #ahhd4 ,lord ,bramwell's ,royal ,commission establishes principles4 ,but the late ,lord ,bramwell's ,royal ,commission on ,metropolitan ,sewage ,discharge established two very important points of general application1 namely3-- #a4 ,the principle of separation in works of sewerage and drainage2 and #b4 ,the fact that the suspended matters in town sewage can be very effectually removed from its liquid by simple deposition without the aid of any chemical reagent4 ,sidenote3 #ahhg4 ,the chemist ,dibdin discards chemical reagents in favour of ,m4 ,pasteur's aerobic organisms4 ,and ,mr4 ,dibdin three years later began to demonstrate the mistaken policy of adding lime or any other precipitating agent in any quantity likely to arrest the natural agency of abundant bacterial life1 which ultimately disposes of all dead and effete organic matter by forming gases or natural compounds1 with more or less offence to human senses1 according to the supply of oxygen and rate at which these bacteria can carry out their work4 ,sidenote3 ,leeds and ,exeter4 ,it was soon found that the bacteria of two classes1 aerobe and anaerobe1 abound in sewage1 and the latest ,leeds experiment with the continuous or trickling filter show the marvellous rapidity with which the aerobic microbes at any rate1 can accomplish their task where air and liquid sewage are sufficiently diffused in the pores of a filter2 while ,mr4 ,cameron1 ,c4,e41 at ,exeter has shown rapid evolution of gases and considerable solution of organic solids by anaerobic microbes in a septic tank4 ,but the enthusiasm of inventors and their converts has made too much of the benefit to the human race supposed to be conferred by the bacterial discovery of ,m4 ,pasteur as applied by them to sewage treatment4 ,without detracting from the credit due to the great ,french savant and other bacteriologists who have followed up his interesting studies of ferments for the last fifteen years1 the practical man may well ask how much forwarder have we got in the main and pressing business of purifying our rivers--as a consequence of clearer knowledge of minute forms of life8 ,sidenote3 ,intermittent filtration4 ,the late civil engineer ,bailey-,denton demonstrated1 thirty years ago at ,merthyr ,tydvil1 the best conditions of intermittent downward filtration1 and his filters there and at ,kendal1 ,abingdon1 etc41 are still doing their work efficiently to this day1 while the coke1 coal1 clinker1 burnt ballast1 etc41 beds1 so popular of late1 are clogging up after a few years of more careful treatment than was ever accorded to an acre of land under sewage4 ,anaerobic action has also been proceeding in the old sewers of most towns and1 as it has now been proved that there is no advantage in the exclusion of air1 upon which ,mr4 ,cameron laid so much stress when he brought his ,exeter tank to public notice in #ahig1 there can be no novelty except its name attaching to the anaerobic or septic system1 which has thrown many sanitary authorities off their balance of late years4 ,the whole modern system of self-cleansing sewers having been only rendered possible by public recognition of the horrible nuisance arising from middens1 cesspools1 and irregularly built sewers of deposit1 it is hard for those concerned in the cleanly disposal of sewage to be told that because sewage works are usually remote from populous districts they must there put up with the cesspool nuisance and fancy its old smell changed by the new name1 because a preliminary stage in the transmutation of sewage has not taken place1 as was formerly the case in the sewerage system of some modern towns1 before arrival at the works4 ,but in this as in other affairs there is force in the old maxim1 ,medio tutissimus ibis1 and a properly constructed open tank1 for simple deposition of the solids 7frequently washed out71 arrests most of the solids and allows fresh liquid sewage1 after slight anaerobic action1 to pass on to land or filter bed in a perfectly inoffensive condition4 ,sidenote3 ,the cleanly and dirty processes for sludge removal4 ,as an example of this ,i have1 at ,aldershot1 a pair of tanks close to a public high road1 one of which fills with sludge and is emptied every fortnight or so1 and as a contrast there is another pair of larger tanks in a remote quarter of the same farm in use for years as septic tanks1 from which some sludge is drawn off at long intervals1 anaerobic action being allowed its full course as in the ,exeter experiments4 ,it is interesting to compare the results of these preliminary clean1 and dirty1 processes respectively on similar very fresh domestic sewage which enters the clean depositing1 and the septic tanks alike1 and my observations are as follows3-- #a4 ,the manurial result in growth of crop slightly greater with the septic liquid4 #b4 ,labour increased by the greater deposit carried on to the land under septic liquid4 #c4 ,the removal of sludge and washing out the clean tank gives an hour's work with very little smell ten yards to leeward of the site1 but drawing off sludge from the septic tank is a very unpleasant operation1 and1 at all times1 the vicinity of tank and carriers is malodorous for a radius of at least fifty yards from the septic tanks4 ,sidenote3 ,loam on sand and gravel the best medium for aerobic organisms to work in4 ,passing now to the aerobic stage of sewage purification we find it universally admitted1 that a good loam resting on very porous sand or gravel1 affords the best medium for work by the oxygen-loving nitrifying organisms when they are supplied with constantly moving liquid sewage1 and given intermittent periods for the aeration of the pores of the soil4 ,the proportion of sewage to land is of course as variable as the quality of the land itself1 and the best sort of land is rarely available1 while the improvement of natural land is not understood by the engineer or chemist1 who are usually appealed to by sanitary authorities in their sewage difficulties4 ,hence the variety of artificial substitutes of contact beds1 costing from #ejjjl4 to #ab1jjjl4 per acre1 which have been proposed of late years1 with the object of purifying a large volume of sewage on a small area4 ,sidenote3 ,leeds experiments4 ,mr4 ,dibdin first startled the world with the formula #a1jjj1jjj gallons per acre1 but that has long been cut down to #bjj1jjj gallons1 and the life of the contact bed has become the subject of serious concern1 as shown in the annexed table of experiment at ,leeds4 ,others have sought to increase the proportion of sewage to area by arranging for continuous instead of intermittent application2 but the difficulty of sprinkling so that every part of a bed may be kept just moist1 in order that aeration may be continuous as well as the dropping sewage1 is very great1 and increases with every gallon and foot from the scale of a laboratory experiment to that of a practical working for a town's sewage4 ,there was an article published a few years ago in the ,journal ,royal ,agricultural ,society 7,england7 on 8,the ,making of the ,land10 showing how nearly all the value of agricultural land in ,england has been stored up in it by the exertions of our forefathers1 through a process of successive improvements from1 in many cases1 worthless sand and clay1 to a condition of the greatest fertility2 and ,i often think that the #ab1jjjl4 spent at ,birmingham or elsewhere on an acre of contact bed could be expended to better purpose in preparing #ajj acres of the worst land to deal1 for any number of years1 with as much sewage as the contact bed may do for a few years4 ,in the one case we know no limit to the life of the purifier1 and that it must be a very short one in the other case4 ,,table ,,showing ,,the ,,variations ,,in ,,capacity ,,of ,,contact ,,beds4 ---------------------------------------- ------------------------ ,no4 #a ,rough ,no4 #c ,rough ,contact ,bed4 ,contact ,bed4 ---------------------------------------- ---------------------- ,dates4 ,gallons4 ,dates4 ,gallons4 ---------------------------------------- ---------------------- ,original water capacity #ahig4 #ahih4 after putting ,october #a #hc1cjj ,nov4 #ba #ea1hjj in the coke #ahii4 #aijj4 ,after experiment ,may #f #bb1gjj ,march #aj #ad1gjj ---------------------------------------- ---------------------- ,duration of each of above experiments #ai months #fj1fjj #be #cg1ajj and loss in gallons mths4 ,loss in percentage of original capacity #gc per cent4 #ga per cent4 ---------------------------------------- ------------------------ ---------------------------------------- --------------------------------- ,no4 #e ,rough ,no4 #g ,single ,no4 #h ,single ,contact ,bed4 ,contact ,bed4 ,contact ,bed4 ---------------------------------------- ------------------------------ ,dates4 ,gallons4 ,dates4,gallons4 ,dates4 ,gallons4 ---------------------------------------- ------------------------------ ,original water capacity #ahii4 #ahii4 #ahii4 after putting ,feb4 #bh #ec1ajj ,march #ge1jjj ,march #bc #bi1ejj in the coke #bd #aijj4 #aijj4 #aijj4 ,after experiment ,june #a #ac1bjj ,october #ba1fjj ,june #a #i1hjj #bj ---------------------------------------- ------------------------------ ,duration of each of above experiments #ae #ci1ijj #g #cd1ajj #ad #ai1gjj and loss in gallons months months months ,loss in percentage of original capacity #ge per cent4 #fa per cent4 #fg per cent4 ---------------------------------------- --------------------------------- ,n4,b4--,the average duration of the above experiments was #ad months1 and average loss of capacity about #gj per cent4 original water capacity in that period4--,a4 ,s4 ,j4 ,sidenote3 ,wrexham sewage farm4 ,at ,wrexham1 in ,north ,wales1 ,i had nineteen years' management of about #aej acres of good land1 with a mixed residential and manufacturing sewage of some #ae1jjj population1 with large breweries and leather works4 ,the owner of this land at the termination of lease asked so exorbitant a price for the improved freehold1 that the corporation decided to sacrifice the sewage works on his land1 and to carry out a scheme of mine for carrying the outfall sewer two miles further to a site of #bjj acres1 which they could acquire on reasonable terms in the year #ahhi4 ,during my management there was no trouble about the effluent1 although it was carefully watched by the authorities of the city of ,chester1 which takes its water supply from the river ,dee1 some twelve miles below my late farm2 and the fact that the scheme which took the ,wrexham sewage two miles nearer to the ,chester waterworks intake was carried out unopposed is1 ,i think1 strong evidence of well-founded confidence in the efficiency of land treatment where the public have the opportunity of observing such results4 ,it is easy to get up a case with expert evidence against any sewage scheme where the land-owners1 clergy and others have no means of properly informing themselves1 and have a prejudice against sewage which it is very difficult to overcome except by giving the utmost possible publicity to the truth4 ,sidenote3 ,the ,camp ,farm1 ,aldershot4 ,of late years1 while working for the ,war ,department1 ,i have found it expedient to be more reticent1 but the ,camp ,farm restoration has in one way or another become known to the public1 and there can be no great harm in my now referring to the circumstances as neither martial law nor a censorship has yet been proclaimed in ,hampshire4 ,when ,aldershot ,camp was first hutted1 soon after the ,crimean ,war1 a certain ,colonel ,ewart1 ,r4,e41 had imbibed true ideas of the separate system through his association with the work of the late ,mr4 ,menzies1 the ,deputy ,ranger of ,windsor ,forest1 who preached and practised that system in the drainage of ,windsor ,castle and the town of ,eton at a time when every other civil engineer scouted the possibility of keeping rain or subsoil water out of foul sewers--they said it was essential for flushing their big sewers4 ,colonel ,ewart1 at any rate1 impressed his corps1 and after about #ahff one began to see the word ,,foul painted up over gratings into which the soldiers were to pour their slops4 ,a civilian1 ,james ,blackburn1 also a friend of ,menzies1 was employed by the ,war ,office to deal with the camp sewage on about #ajj acres of rough heather-covered land close by1 and he1 knowing his business1 watched what came down the sewers in wet weather and kept the ,royal ,engineers up to the ,menzies standard4 ,sidenote3 ,mr4 ,blackburn's successful management4 ,together with this initial advantage of having a regular volume of sewage not much affected by storm water to deal with1 ,mr4 ,blackburn had many drawbacks in the 8pan10 as it is usually called1 of iron conglomerate underlying the very irregular surface which was pitted all over with holes from which gravel or sand had been dug many years ago2 but he persevered until he had got nearly all the area to bear good crops1 when he entered the ,camp ,farm in competition for the ,royal ,agricultural ,society's #ajjl4 prize in #ahgi for the best managed sewage farm in the ,united ,kingdom4 ,the ,report of the ,judges at that competition is recorded in the ,society's ,proceedings #ahhj1 giving full statistics except financial accounts1 which ,mr4 ,blackburn withheld because he was then in treaty with the ,war ,office for new terms after fourteen years' work on the ,war ,department ,farm4 ,my impression after reading the judges' reports and having seen the farm a year or two previously to its date1 is that1 if the condition as to the production of the financial accounts could have been fulfilled1 the first prize would have been awarded to the ,camp ,farm instead of jointly to those of ,bedford and to ,wrexham4 ,mr4 ,blackburn had built a big wooden shed and sublet it to a man who bought his ryegrass for some fifty cows 7for whose milk there was a great demand in the camp71 so this subtenant made a tempting offer to the ,war ,office and got a fourteen years' lease of the whole farm1 while ,blackburn retired in disgust4 ,i wish to write only from knowledge of facts1 and will therefore take up my narrative again in #ahie1 after an interval of some fifteen years4 ,sidenote3 ,neglected state of1 in #ahie4 ,in the month of ,may #ahie1 ,i was called upon to visit the ,camp ,farm and report to ,mr4 ,henry ,campbell-,bannerman1 the ,secretary of ,state for ,war at that date4 ,i found the whole farm in a deplorable condition of neglected nuisance1 stagnant lakes of sewage retained here and there by banks of earth1 buildings and fences in decay1 and the greater part of the camp sewage passing1 by pipes laid by its tenant1 under a road which forms the lower boundary of ,war ,department land1 to some rough meadows held by their tenant from civilian owners for the purpose of saving him the trouble of spreading the sewage over the sloping surface of the ,war ,department ,farm--work which required the use of a land surveyor's level and staff4 ,in the ditches of these flat meadows the sewage could go through the septic process to its fullest extent as the level of the river ,blackwater kept them nearly full at all times1 and the supernatant liquid could spread over the coarse herbage of these meadows only in winter floods1 with the result of heavy crops of hay1 and sewage disposal conveniently out of sight and outside ,war ,office jurisdiction when a ,royal ,engineer officer might come to inspect the ,camp ,farm from time to time4 ,sidenote3 ,british ,medical ,journal's report4 ,but before my visit an active ,medical ,officer of ,health 7,dr4 ,seaton71 taking an interest in the state of the river bounding his county of ,surrey1 detected the camp origin of the stagnant sewage1 and1 concluding that the meadows must form part of the ,camp ,farm over the road1 made a serious report about 8,government ,sewage ,marshes10 which the ,british ,medical ,journal took as a text for an article1 and the ,thames ,conservancy attacked the ,war ,department as soon as their #ahid ,act gave them jurisdiction in the matter4 ,sidenote3 ,temporary abatement of nuisance4 ,i was told that the ,camp ,farm milk and grass had been condemned1 and that the tenant had consequently sold his cows and was to give up the farm on ,june #bj1 #ahie2 therefore my report was wanted forthwith1 but it was only to take account of anything which could be done temporarily to abate nuisance1 as an agreement was pending with the ,aldershot ,district ,council for the removal of the camp sewage outfall to some site1 at least two miles distant from the camp1 at which the ,district ,council was to become solely responsible for its future disposal1 together with their own ,aldershot town sewage1 and the ,war ,department to be rated for the purpose like any other householder4 ,i found the ,commanding ,royal ,engineer then in office fully alive to the existing nuisance and prepared to support any efforts ,i might make to abate it4 ,accordingly ,i agreed to become manager in control of such labour and material as was necessary for immediate temporary improvement1 and being supplied with army horses1 and any necessary buildings1 tanks1 etc4 to be constructed by the ,royal ,engineers4 ,sidenote3 #ahig4 ,the ,war ,office resolve on permanent improvement4 ,after about two years it became understood that the nuisance could be permanently remedied on the ,camp ,farm1 as ,i had said from the first1 and accordingly the draft agreement1 which had then been in discussion for five years1 was abandoned4 ,i was asked to prepare a scheme and estimate for such permanent works as would enable the sewage to be effectually disposed of on the ,camp ,farm4 ,recollecting that the sewage had to be at once cut off from ,dr4 ,seaton's 8,sewage ,marsh10 and its disposal provided for throughout on ,war ,department land1 it will be observed that the improvement work had to proceed piecemeal with some extra care and arrangement2 but on the whole ,i am satisfied that the work has been completed with greater efficiency and economy than would have been the case if the sewage had been turned into the river and the whole site handed over to a contractor for two years in the usual course4 ,about the same date 7end of #ahig7 about #ac acres of land was handed over to my management with sewage from the ,royal ,military and ,staff ,colleges at ,sandhurst1 about #h miles distant from the ,camp ,farm1 and1 being somewhat better land to begin with1 this part now presents a very pretty example of what a small installation for about #ajjj population may accomplish4 ,but it is worked as part and parcel of the ,camp ,farm1 horses being sent out to ,sandhurst from ,monday to ,saturday when required4 ,it is1 perhaps1 worthy of note that the reform of the ,camp ,farm was initiated in #ahie by the ,secretary of ,state for ,war in a ,liberal ,ministry1 and that it has weathered for seven years all the storms of ,jingoism and the fashionable crazes for artificial sewage treatment4 ,sidenote3 ,sir ,redvers ,buller's period of command at ,aldershot4 ,but whatever may be the rights or wrongs of ,general ,sir ,redvers ,buller's quarrel with the ,press and the ,government1 his reputation as a practical agriculturist is undeniable1 and while in command at ,aldershot it was his custom to stroll over the ,camp ,farm on a ,sunday afternoon1 occasionally leaving a message with cowman or bailiff to warn me of anything he found amiss1 for which ,i was very grateful1 living as ,i do ten miles away4 ,i am proud1 therefore1 to be able to publish the following letter from one who has shown that he is not to be influenced by complaisance to superior or inferior in expressing or modifying his opinions1 and he writes as follows3-- #ag ,,lowndes ,,square1 ,s4,w4 ,july #ad1 #aijb4 ,,my ,,dear ,,jones1 ,i am delighted to hear that you are publishing a book about sewage treatment4 ,the sewage farms at ,aldershot and the ,royal ,military ,college afford ample proof of what a sensible practical man can do4 ,but it is not every one who knows what those farms were before you took charge of them1 nor do ,i think that any one seeing them now could conceive their previous condition4 ,it is to that ,i can testify2 you have turned putrid sewage bogs into fertile fields4 ,you will confer an immense benefit on the country if1 by your book1 you can only teach sanitary authorities generally that the crux of the whole question is the necessity for practical commonsense measures against sewage stagnation1 and if those measures are taken nature will do the work of purification without the assistance of expensive patents or artificial devices4 ,yours very truly1 7,signed7 ,,redvers ,,buller4 ,to ,,col4 ,a4 ,s4 ,,jones1 ,v4,c41 ,c4,e4 ,it must not be gathered from the foregoing account that the ,war ,office authorities are prejudiced in favour of the natural treatment of sewage1 for1 like many other sanitary authorities1 they have been bewildered of late years by the numerous forms of 8artificial0 treatment in vogue1 and ,i know of more than one experimental installation for barracks where good available land has been neglected1 for ,i read last summer of ghastly failures among the bacterial arrangements in some of those4 ,sidenote3 ,success mainly due to activity of farm bailiff1 foremen and other workers4 ,i cannot quit the above account of the vicissitudes of the ,camp ,farm in fourteen years' growth from a sandy waste to a condition which tempted a tenant to pay a rent of #cl4 odd per acre in #ahhj--;its retrogression to its primitive waste during the following fifteen years--and restoration to its present measure of fertility1 without expressing the belief that ,mr4 ,blackburn's success and my own have been mainly due to our good fortune in obtaining the willing services of excellent intelligent foremen and workers who1 one and all1 have taken a real interest in their several tasks4 ,mr4 ,cameron and other engineers may boast of their labour saving 787 automatic appliances for opening and shutting valves on sewage works1 but practical workers1 responsible for dealing with a million gallons a day and upwards average1 in hourly varying flow of town sewage1 will agree with me in hesitation as to placing entire confidence in the substitution of automatic machines for any large proportion of their manual labour4 ,sidenote3 ,education and encouragement of sewage employees advocated4 ,i have for many years advocated education of sewage farm managers and watermen1 to be selected from the rapidly decreasing class of agricultural labourers by the tender of high wages1 houses and good gardens1 with other profit-sharing allowances which it will well pay sanitary authorities to hold out to their sewage employees4 ,in this sense ,i am glad to note the recent formation of 8,the ,association of ,managers of ,sewage ,disposal ,works10 ,secretary1 ,charles ,h4 ,ball1 #e ,fetter ,lane1 ,london1 ,e4,c41 as a ,trades ,union move from within well calculated to raise the status of the class of men upon whose exertions the community must mainly rely if there is to be any hope of improving the condition of our streams and rivers4 ,sidenote3 ,evidence and ,reports of ,lord ,iddesleigh's ,royal ,commission4 ,two large ,blue ,books containing the evidence taken by ,lord ,iddesleigh's ,royal ,commission have been published since the ,interim ,report1 and their contents more than warrant the opinion expressed in the latter2 indeed it must surely be admitted that the case for each of the artificial systems was very fully gone into before that ,commission expressed the guarded conclusion1 8,we doubt if any land is entirely useless40 ,i do not believe that the surface purification obtained by distribution over even the densest of clay lands was effectively put in evidence1 and too much weight was given to the difficulty of increasing the effective top soil on such land2 but on the whole ,i think that the ,interim ,report is very satisfactory to the reasonable advocates of a preference being given to the adoption of a large area of land1 where available1 over any artificial treatment on a small area1 other things being equal4 ,at the time when the ,interim ,report was issued1 however1 a very full and careful examination of a select number of sewage farms was still in progress1 and ,appendix #bb1 with a casual mention by ,dr4 ,m',gowan1 affords the only glimpse to be had in the bulky ,blue ,books1 of any results of that examination having been as yet adduced in evidence4 ,the ,commission's officers1 to my knowledge1 were engaged for many months in examining1 surveying and taking numerous samples of sewage and effluent at the ,camp ,farm1 and1 as they doubtless had equal opportunities of independent observations on the other selected sewage farms1 the further reports of ,lord ,iddesleigh's ,royal ,commission cannot fail to be interesting and instructive4 ,on one point ,appendix #bb to the ,blue ,book abundantly supports an opinion ,i have so often expressed1 namely1 that a good strong loamy surface is a more efficient purifier of sewage than many feet of barren sand4 ,i refer to the curves in ,appendix #bb1 showing the greatly superior purification effected at ,nottingham with the best soil as compared to that of the sandy one at ,aldershot1 which1 in its natural character1 is about the worst for purification and for producing crops to be found in ,england4 ,my experience1 however1 all points to the extreme importance of studying local conditions from the first inception of plans in each particular case1 to their completion with the best available materials4 ,but when the engineer has done his best1 the sanitary authorities1 having borrowed the funds to pay for the work1 will take no further trouble about its sewage1 and will often engage careless ignorant workpeople at inadequate wages to carry on the hourly varying labour1 on efficient performance of which success depends4 ,sidenote3 ,automatic appliances for sewage and effluent discharge4 ,it may seem idle to complain of boards and their employees showing little interest in the work of sewage disposal1 but it is worse to pander to their failings by selling them automatic machines under the pretence that all the thought1 and fertility of resource1 required for efficient sanitary sewage disposal can be supplied by ingenious applications of hydraulics on the principle that sewage is a fluid1 and1 as such1 will behave like clean water4 ,of course1 when the aerobic treatment is carried out on a bare level surface of cinders or coke growing only weeds1 the lack of interest is very excusable1 but in the natural system the growth of crops and contouring a sloping surface with carriers so that every part shall have its trickling water alternating with dry periods for cutting the crops or hoeing out weeds1 should be a matter of constant interest to an agricultural worker1 and1 if he knows his business1 good crops and purity of effluent must go together4 ,sidenote3 ,managers should have a free hand4 ,in order to attain this happy result1 a manager must know his business and be given a free hand1 not pestered by members of a committee 7farmers1 butchers1 gardeners or town tradesmen7 coming to give their advice or orders4 ,the river authority should take samples as often as they like and send the manager as soon as possible the analyses with day and hour of sampling as a guide for future working4 ,he will then have to explain any defect from average purity of effluent1 due to one of the hundred contingencies which may arise in practice1 after he and the river authorities have agreed about what that average analysis should be for his particular farm or works2 and it will be for the advantage of all parties not to try and enforce a fixed standard for a whole district1 as some river authorities usually attempt to do1 because it is easier to lead than to drive a good manager1 and nothing at all can be done with a bad one4 ,it must not be supposed that ,i think river authorities should be easy going1 quite the contrary1 but they should trust their inspectors' reports1 and 8run in0 those sanitary authorities who are careless about the management of their sewage farms and trying to cut down working expenses and capital4 ,in precipitation or other artificial sewage works it is easy to judge this1 but more difficult for any one except the good farm manager to know whether the land is being made the most of for profit or for purification2 still the rivers authority ought to get to know if they and their officers take pains4 ,sidenote3 ,purification and profit4 ,it is a common idea that working a sewage farm for profit1 and for purification of the sewage1 are two incompatible things1 whereas1 the good manager with sufficient working capital 7double or more what would be enough for the same acreage in ordinary agriculture7 and a good market for produce will attain the two together in due proportion in all ordinary seasons1 when a fair allowance has been made him for the necessary sanitary work4 ,it is easy to see how the popular idea of incompatibility has arisen in a case like that above stated of the ,camp ,farm tenant1 eating up year by year all the fertility stored up in the land during the previous period1 and letting nearly all the sewage run to waste1 because its scientific application would cost much in thought and labour4 ,in much the same way district councils have been1 all over the country1 stinting their labour bills and interfering with their managers' purchases and sales in order to make as small a demand on the rates as they can--each year bringing some change of system--to the end that nobody is responsible or has any confidence in master or man4 ,with such a state of things up and down the country the way was prepared for preachers of microbe agency to say1 why should you buy all that land when a septic tank1 a few acres of coke or burnt ballast1 and a patent automatic opener and shutter of valves 7which you see working so nicely with tap water and model at some exhibition7 will give you 8no more troublesome sludge10 and a first class effluent with hardly any labour bill8 if you only agitate against that arbitrary ,local ,government ,board1 which insists upon land6 ,but those gentlemen neglected the fact1 that in a few years' time their filters would have to be pulled to pieces1 washed and put back1 while the land remains as efficient as ever1 and a valuable asset1 in some cases saleable at building value1 if it becomes desirable to move the outfall further at some future time4 ,sidenote3 ,sludge treatment4 ,in the above comparison between natural and artificial treatment reference has been had chiefly to the aerobic branch of the business1 but the anaerobic1 breaking down some of the solid organic matter and the sanitary disposal of the remainder in the state of sewage sludge 7containing fully #ij per cent4 of moisture7 must not be overlooked or shirked as beneath the attention of the scientific bacteriologists and chemists whose analyses of effluents1 and often of what they call crude sewage1 are made from the liquid which has passed through a filter paper in their laboratory before their 8oxygen absorbed0 or 8ammonia processes0 are proceeded with4 ,on the contrary1 ,i have always maintained that sludge1 being the foulest part of town sewage1 ought to receive primary and earnest attention if we desire to improve the condition of our watercourses4 ,when town sewage is pumped through a long rising main1 it can often be spread on the land in its really crude state1 and if the soil is clay ploughed up to receive it the sludge is most beneficial to its texture4 ,but in every other case we must face the nuisance of extracting the sludge1 and its desiccation in one of the following ways4 #a4 ,on a farm at some distance from roads and houses1 the cheapest plan is to form a bank of earth about #ah inches high1 enclosing a rectangular area into which the wet sludge can be run or pumped out of depositing tanks1 and left alone until dry enough for cartage1 when it can be used on the farm or sold to neighbouring farmers for a shilling or two a load4 #b4 ,a wall of farmyard long manure may be used instead of earth1 and trench #e feet wide dug on each side of the longer sides of the rectangle1 leaving #c feet of ground between the wall and trench1 on which men can stand to scoop the sludge over the wall when it has consolidated a little in the trench2 the latter is then ready to receive the sludge from another tank emptying1 which is again scooped over the wall on to a thin coating of farmyard manure1 which has been scattered over the last layer of sludge in the rectangle2 and thus in a year's time a solid mass of the mixture is raised four or five feet high1 and is in capital order for putting in drills for a crop of mangold wurtzel4 ,this is the plan in use at the ,camp ,farm2 it occupies little ground and smells only like rotten dung does during the few days carting to the mangold field4 #c4 ,pressing by compressed air forcing a liquid mixture of sludge and lime into the interstices between cloths supported by vertical iron plates on a horizontal frame2 and such pressing is a very expensive process1 only resorted to when the sewage works are in a confined populated district where no accumulation of sludge can be tolerated4 ,sidenote3 ,expert examination of neighbourhood a very necessary preliminary to any sewage scheme4 ,before any sewage scheme is conceived a very careful survey of the neighbourhood ought to be made by a person who knows the requisites of a site for sewage disposal1 especially if land irrigation is intended1 because natural advantages of site both for tanks1 main carriers1 roads1 etc41 may make all the difference in the world in expense and efficiency not only in first cost of works but also in their use afterwards4 ,and if land is to be acquired for sewage farming it will be very desirable to include in the purchase some neighbouring high lying area1 not required for sewage disposal but for growing straw crops to be used on the farm4 ,,cropping ,a ,,sewage ,,farm4 ,sidenote3 ,vegetation of some kind1 useful or weeds1 will grow from sewage1 and must be frequently removed from land or contact bed4 ,this is a matter of vital importance1 because when sewage is intermittently applied to land of any kind or to coke beds1 vegetation of some kind or other must result and must be removed in order to leave a clear course for the next dose of sewage2 the cost of removal and destruction of weeds will be found very great when contact beds are tried on any working scale and would be quite prohibitive if allowed to grow on irrigated land4 ,hence we must crowd out the weeds as much as possible by useful plants which will bring something towards the cost of their removal2 and as that return from perishable greenstuff is dependent upon its immediate sale or consumption on the farm1 the manager must cast about for demands for his abundant supply2 but as both the sunshine 7in this climate7 and markets are very capricious factors in the problem1 he has no easy task always to make both ends meet4 ,theoretically the town which yields the sewage ought to provide an abundant demand1 but in practice it can rarely be depended upon1 ,edinburgh being the only exception1 where the ,craigentinny sewage meadows are rented at a very high figure by the cow-keepers of a city situated in the heart of an arable district4 ,sidenote3 ,alternative destinations for vegetation thus removed4 ,milk 7everywhere in demand7 or a destructor furnace4 ,fortunately1 however1 there is always an unlimited demand for milk1 and if he has the means of keeping a herd of cows on the farm1 or can arrange with a neighbouring cow-keeper to take all the grass and roots he can supply at a low rate1 it is about the best course a manager can adopt4 ,if he maintains a herd of cows1 tied up in good1 well ventilated stables1 and has them daily brushed and groomed like horses1 they require no exercise and produce milk in perfection for an average period of fifteen months from date of purchase after their third or fourth calving4 ,such a herd will consume rye-grass carted from the field from ,april to ,november1 and mangolds1 kohl-rabi1 and rye-grass hay during the winter1 thus securing a uniform demand for produce of the sewage land throughout the year1 and such cows will only require a little cotton cake and oat straw bedding 7of which latter they eat a good deal7 to fit them for sale to the butcher as soon as they become dry4 ,the advantage of such a steady demand is so great when rye-grass and mangolds1 etc41 are indicated as the main crops of the farm1 owing to the large volume of sewage per acre1 that the system of cow-keeping is forced upon managers1 however reluctant their sanitary authorities may be to provide the necessary working capital1 unless they can find a reliable contractor to receive at a fixed price any quantity of grass and roots the authority may grow and deliver4 ,sidenote3 ,permanent pasture grazed and for hay available in certain cases4 ,when a town has more land in proportion to its sewage1 permanent pasture may take the place of ,italian rye-grass1 and1 with proper precautions1 a part of the permanent pasture may be grazed2 but the saving of labour1 thus supposed to result from letting animals bite and carry their food1 is expended in making up1 in a necessarily imperfect manner1 the carriers trodden in by the cattle4 ,sidenote3 ,importance of neat tidy contour carriers1 correctly levelled4 ,and here ,i would observe that most of the bad odour into which sewage farming has fallen of late years is distinctly traceable to the common absence of sufficient regularly contoured and neatly cut distribution carriers resulting from parsimony about wages bills natural to the ratepayers' representatives in ,council1 and often to the manager's dependence on a borough surveyor's coming to the farm with his level and staff for great measures1 or on his own guesses for smaller works1 instead of using an instrument to peg out every distribution carrier at the right moment4 ,sidenote3 ,attract good labour4 ,there is another important outlay of capital to be provided for in every complete sewage scheme1 which should embrace sufficient good labourers' houses and gardens in order to attract and retain on the spot the best class of workers4 ,sidenote3 ,summary of the experience of a lifetime4 ,to sum up the general conclusions to which my experience points1 and which ,i trust may prove useful to district councillors1 they are as follows3-- #a4 ,in works of sewerage1 limit and regulate1 as far as possible1 the volume of sewage by excluding subsoil water and clean surface water4 #b4 ,where the outfall sewage enters the disposal works provide a pair of open catch-pits 7or grit-chambers71 each twice as wide as1 and #b feet deeper than the sewer1 with sluices allowing the sewage to pass through one pit at a time in its free course1 while the other pit is being dried and the deposited detritus dug out4 ,the depth below sewer invert may be more than #b feet1 and length of catch-pit is immaterial1 but ,i confine its width to twice that of the sewer in order to conserve sufficient velocity in the current to carry forward organic matter1 paper1 etc41 and leave only clean sand and gravel in these catch-pits4 ,continuing the course by open channel 7of same width as outfall sewer71 it should expand to five or six times its width1 forming the screening chamber1 and thence discharge into the #c4 ,depositing tanks4 ,these are best formed in concrete with smooth surface1 with a semicircular level weir from which the liquid overflows into a semicircular collecting open carrier leading to the aerobic process on land or contact bed4 ,the semicircles above referred to are struck from centre of the inlet to depositing tank with a radius of #ej feet or more4 ,the weir level should be at least #a inch below that of invert of inlet1 and the depth of tank immediately under this point should be governed by consideration of the facility of drawing off the sludge by valve at that depth to the sludge drying beds by gravitation if possible1 or pump if necessary1 and from this sludge emptying valve the smooth concrete bottom of tank slopes up to the semicircular weir above described4 ,the bottom and sides of such a tank should be made with the best ,portland cement and finest granite chippings wrought to a smooth surface1 so that the sludge may be easily swept clean away with a squeegee to its outlet valve1 as it is very necessary to have the tank thoroughly washed after each emptying if my view of the clean mode of sewage disposal is to be carried out4 ,but with the dirty mode1 on the contrary1 some of the sludge only should be drawn off and the septic anaerobic action preserved continuously in the tank itself1 whereas ,i prefer that action to have its early and less offensive course in the tank and its completion in a drying bed mixed if possible with farm-yard manure4 #d4 ,the aerobic process4 ,the one essential point in this final process1 whether in land or 8contact beds10 is sufficient aeration 7excess as by blowing has no result commensurate with cost of its introduction71 and it can be attained by intermittence of sewage and rest1 or by continuous passage of sewage through a bed of coarse medium kept always just moist in all its atoms by a rain-like dropping on the surface so carefully adjusted as to moisten all parts and not to form a water-seal in any part of the bed4 ,intermittence is easily arranged on any scale of working1 and continuous filtration1 on the contrary1 is difficult even for a few thousand gallons a day4 ,sidenote3 ,anticipation of a coming reaction against 8fads0 and overpressure in sanitation4 ,since the above was written our grand old philosopher ,herbert ,spencer has published a volume of 8,facts and ,comments0#c containing a chapter on 8,sanitation in ,theory and ,practice10 which points to a coming reaction against the movement begun1 some fifty years ago1 by the late ,sir ,edwin ,chadwick and followed up by many enthusiastic exploiters of the popular dread of 8germs10 which he associated with bad smells4 ,of course the professor's practical acquaintance with ,chadwick's hobby is1 as he says1 very limited1 and his argument1 that because sewage and manure smells are harmless in the open air of the country1 they should be equally innocuous in a town1 falls to the ground when brought to the test of experience1 and ,i trust that ,mr4 ,spencer will forgive me for pointing out that sewer-gas1 drawn into a dwelling room1 in town or country1 through scullery waste pipe or other connection with a sewer in which the air is of lower temperature than that of the dwelling room1 is really prejudicial to health whether accompanied or not by disease germs4 ,and although1 as one of the experts to whom ,chadwick appealed and whose moderate testimony was cast aside because it did not come up to the standard desired by his enthusiasm1 ,i fully endorse ,mr4 ,spencer's caution with regard to the mass of ,blue ,book evidence on sanitation1 ,i venture to express my regret that the dear old man has had an unfortunate experience of sewage treatment1 and my surprise that so deep a reasoner should have published his judgment in this chapter without having taken the pains to extend his acquaintance with sewage treatment in other places than the single instance of ,burton-on-,trent4 ,in thus despising an unsavoury subject ,mr4 ,spencer is not alone1 and ,i am sorry to have to say that general indifference is answerable for the waste of much public health and money1 because it need not be surprising if those following a despised trade are sometimes ready to take advantage of the prejudice and ignorance of their employers4 ,in this sense ,i beg to quote ,professor ,spencer as follows in justification of the reflection with which ,i began the above essay3-- 8,new sanitary appliances are continually being devised1 sanctioned by authority1 and required by surveyors2 and surveyors may have and certainly sometimes do have1 personal interests in pushing the use of them2 either as being shareholders in the companies they are manufactured by or as receiving percentages on the numbers sold through their recommendation40 #b3 ,published by ,longmans1 ,london1 #ahgd4 ,third edition published by ,r4 ,potter1 ,wrexham1 #ahhe4 #c3 #8,facts and ,comments1' by ,herbert ,spencer4 ,williams and ,norgate1 ,london1 #aijb4 ,,natural ,,and ,,artificial ,,sewage ,,treatment4 ,,by ,h4 ,,alfred ,,roechling1 ,m4 ,,inst4 ,c4,e41 ,,etc4 ,i4 ,,introductory ,,remarks4 ,at the request of ,lieut4-,colonel ,a4 ,s4 ,jones1 ,v4,c41 ,assoc4 ,m4 ,inst4 ,c4,e41 who has done yeoman service in this matter1 ,i have great pleasure in putting down some observations on this old but ever controversial question of sewage treatment4 ,colonel ,jones has done more than anyone else living to establish correct views on sewage farming1 and he has lately changed the ,government sewage marshes at ,aldershot into a veritable 8,garden of ,eden10 watered by the waters from ,aldershot ,camp1 growing healthy crops1 and causing not the slightest nuisance4 ,after many struggles1 even the milk from the dairy cows is now recognised as good and supplied to the military hospitals4 ,this is an achievement of which anyone might be proud2 and all those who have been over the farm during the time of the 8deluge10 and can now study the order and system evolved out of chaos by ,colonel ,jones will testify to this6 ,it is pleasant to record that the ,war ,office have recognised ,colonel ,jones' work for them by having appointed him quite recently to manage all the sewage disposal works in the ,aldershot district4 ,this will involve the laying out of irrigation works in eight separate places1 in some of which artificial methods of sewage purification have been tried and found wanting4 ,before commencing with my task proper it may not be out of place to describe here very shortly the various stages through which the sewage question has passed during the century just closed4 ,such a retrospect is of general interest and may throw some further light upon our subject2 it must of necessity be short1 otherwise it would absorb more time and space than is at my disposal1 and any shortcomings in this respect that the reader may discover1 ,i trust he will kindly put down to this cause4 8,the man in the street0 seems year after year more called upon to form an important element in settling questions even of a scientific nature1 and if what ,i am going to say should prove of some service to him my labours will be well repaid4 ,,ii4 ,,the ,,sewage ,,question ,,during ,,the ,,last ,,century4 ,a ,,short ,,retrospect4 ,in dealing with the sewage question during the last century1 it will be an advantage to distinguish between the theory and practice of sewage purification1 as such a division of the subject will render it less complicated and will tend to avoid misconceptions4 ,dealing first with the theoretical side of the question1 it is very doubtful whether at the dawn of the century even a working hypothesis existed to explain the process of sewage irrigation which was then adopted in one or two instances1 notably at ,edinburgh1 where the town sewage was very successfully purified on the ,craigentinny meadows4 ,it is more than likely1 that at this time instinct took the place of theory1 and that sewage irrigation was an instinctive imitation of irrigation with river water employed for many centuries in some eastern countries4 ,later on it is on record1 that ,cagniard de la ,tour in ,france1 about the year #ahbe1 and ,schwann in ,germany1 about the year #ahcf1 expressed the view1 that organised substances--micro-organisms--played some role in fermentative and putrefactive changes4 ,almost diametrically opposed to this were the views authoritatively laid down by the then star in the chemical horizon1 ,justus von ,liebig1 who1 about the year #ahde1 maintained that these changes were brought about by the dead inert matter itself--by molecular movements in the same--and not by organised substances1 the presence of which in fermenting or putrefying substances was purely accidental4 ,so great was ,liebig's authority then1 that many almost blindly adopted his views1 and the strife that commenced around these opposing views was fought with the greatest bitterness4 ,but the stronghold of old ideas1 which were gradually but surely being supplanted by new ones1 could not hold out for ever against combined attacks1 however stoutly it was defended by its designer1 and its final downfall came about the year #ahfj1 when a young ,frenchman1 ,pasteur1 established beyond doubt by his ever classical researches1 that fermentation and putrefaction were1 in the first instance1 due to living organisms and not to dead matter4 ,pasteur further demonstrated that living organisms were also the cause of some and probably of all zymotic diseases4 ,so far1 so good6 ,but unfortunately the methods of biological research employed by ,m4 ,pasteur were very cumbersome and left otherwise much to be desired1 so that his discoveries could not be fully utilised and extended1 until in #ahhb ,robert ,koch of ,berlin published his new methods of investigation4 ,this was the signal of raising the floodgates of biological 7bacteriological7 research throughout the world with this result1 that the flood waters pent up until then inundated practically other branches of scientific investigation and drowned their individual life for some time to come4 ,during this interval1 #ahfj to #ahhb1 investigators who wished to study the organised impurities in sewage had to proceed by indirect methods4 ,they had no means of ascertaining by direct biological experiment the number and character of the micro-organisms contained in sewage3 all they could do1 was to determine chemically the dangerous nature of the sewage by the amount and origin of organic matter it contained1 which would probably act as food to the germs2 and the greater this amount was1 so it was inferred1 the greater would be the number of germs it harboured and the more dangerous its character4 ,this was the condition of things at the time the second ,rivers ,pollution ,commission carried out its investigations1 which in many respects1 and rightly too1 are still considered standard investigations4 ,it cannot be surprising1 therefore1 that1 being without proper means of biological examination1 and having to rely chiefly on chemical methods only1 the ,commissioners came to the conclusion that the changes brought about in sewage purification were due to mechanical and chemical agencies6 ,it is frequently a matter of the utmost difficulty to ascribe1 after the lapse of half-a-century1 a new theory to one special author1 as several investigators may have been trending the same way quite independently of each other1 but may not have been equally successful in the matter of their publications becoming generally known4 ,theories1 as a rule1 do not drop out of the clouds like meteorites1 they force themselves gradually upon men's minds and are elaborated by them until ripe4 ,bearing this in mind1 and subject to further research1 it would appear as if ,alexander ,mller had been the first to apply ,pasteur's general theories as to decomposition1 fermentation and putrefaction to the problem of the self-purification of sewage4 ,he made his experiments in #ahfi and published them in #ahgc4 ,since that date a very large number of investigators have been at work on similar lines1 and whilst it would lead too far to deal with them minutely1 it ought to be stated that the results of their labour confirmed the view of living organisms playing a very important part in the decomposition of sewage4 ,among the many names prominent in this respect are those of ,schloesing1 ,mntz1 ,hatton1 ,warrington1 ,sorby1 ,winogradsky1 ,percy ,frankland1 ,dupr1 ,emich and ,dibdin4 ,that set of researches1 however1 which has done more than any other to consolidate the theory of bio-chemical changes taking place in the self-purification of sewage are the investigations of the ,massachusetts ,state ,board of ,health1 which were commenced in ,november #ahhg1 and are still being continued4 ,since #ahie a large number of additional experiments have been made1 which will be dealt with more in detail later on1 but speaking generally they have not materially increased our knowledge of the processes taking place in sewage purification4 ,summarising the remarks on the theoretical aspect of this question1 it may be said that1 as to the agencies at work1 we know now they are of a mechanical1 chemical and biological nature2 but as to the processes and products brought about by these agencies we know very little beyond the initial and terminal stages1 as will be pointed out in some of the subsequent observations4 ,directing now attention to the practical side of the question1 it has already been stated that the only known sewage treatment at the commencement of last century was land irrigation4 ,then about the middle of the century chemistry seems to have taken the matter in hand and tried to make a lucrative business out of it4 ,it is on record1 however1 that it did not succeed in this attempt1 and the financial loss which this endeavour has caused is a dismal subject to investigate4 ,there is before my mind's eye the case of a gallant officer of ,his ,majesty's land forces who1 after having reached very near the summit of his career1 retired and employed his time in trying to make a fortune out of sewage4 ,so enamoured was he of the subject1 that--so the story goes--he commuted his pension to have all the more ready money2 but fortune did not smile on him1 and his last days were spent under the lengthening shadows of the sorrow of financial difficulties1 having practically lost all he possessed4 ,the emphatic verdict of the first ,sewage ,commission of #aheg1 the first and second ,rivers ,pollution ,commission1 and1 indeed1 of all other authoritative investigations1 was in favour of land treatment2 and it cannot1 therefore1 be surprising to find that the ,local ,government ,board insisted1 save in exceptional cases1 that 8any scheme of sewage disposal1 for which money is to be borrowed with their sanction1 should provide for the application of the sewage or effluent to an adequate area of suitable land before it is discharged into a stream40 ,indeed1 had this body taken any different view and neglected the findings of practically all authoritative inquiries1 it would have been singularly deficient in the discharge of its duties to the ratepayers of this country4 ,but the best of land cannot go on for ever doing its duty if by systematic neglect and ignorance the essential conditions for successful purification are year after year violated2 and the great pity is that the ,local ,government ,board1 after deciding in favour of land treatment1 did not systematically superintend this operation4 ,it may not have had the power1 but it is quite evident that had it done so1 things would not have drifted from bad to worse1 until local authorities1 driven to despair by the apparent failure of land and not discerning the right cause1 refused altogether to be ruled by what seemed to them a very unfair and absurd restriction4 ,it was at this time that ,mr4 ,dibdin1 who1 on behalf of the ,london ,county ,council1 had been carrying out a set of valuable experiments1 came forward with his application of well known theories to sewage operations on a large scale4 ,as ,i pointed out at the time1 ,mr4 ,dibdin's experiments proved beyond a doubt that the application of sewage to suitable land was right in principle and that the failures were brought about by the non-observance of the rules laid down by this gentleman--that1 in fact1 sewage irrigation was the only natural method of sewage purification and that all the other methods were artificial4 ,i described land treatment as the natural self-purification of sewage and the oxidation or contact bed system as the artificial self-purification of sewage4 ,but the swift current of public opinion had set very strongly against sewage farms1 and nothing but the contact bed treatment would do4 ,a large number of experimental plants on this system grew up like mushrooms all over the country1 and the waves of enthusiasm seemed at one time to engulf even the ,local ,government ,board itself with its 8antiquated notions10 until ,parliament came to the rescue and appointed on ,may #g1 #ahih1 a new ,royal ,commission to study the question of sewage purification4 ,this ,commission consists of nine members1#d i4e4 six professional men and three laymen4 ,of the professional men1 one is a biologist1 one a chemist1 two are medical men in administrative positions1 and two are engineers likewise in administrative positions4 ,of the laymen two are members of special boards for the prevention of the pollution of rivers4 ,so far the ,commissioners have issued an ,interim ,report dated ,july #ab1 #aija1 a volume of evidence and a volume of appendices4 ,quite lately1 it is stated1 they have issued a further ,interim ,report1 to which are attached separate reports on some special subjects by their officers1 but this report has not yet come to hand4#e ,at the time of their first ,interim ,report1 ,july #ab1 #aija1 the ,commissioners had held altogether thirty-five sittings1 the first of which was on ,june #bb1 #ahih1 and the last on ,may #bb1 #aija4 ,the period thus covered is nearly two years1 and out of the thirty-five sittings thirty took place in ,london1 and five in the provinces1 viz4 at ,leeds1 ,ripon1 ,manchester1 ,accrington and ,reigate4 ,on these occasions1 all in all1 fifty-eight witnesses were examined1 who may be grouped as follows3 #a ,zoologist #a ,botanist #b ,laymen #c ,bacteriologists #e ,lawyers #g ,medical men #aa ,patentees #ad ,chemists #ad ,engineers #eh witnesses in all4 ,out of this number twenty-five were officials1 viz4 five lawyers1 six medical men1 six chemists and eight engineers4 ,four officials were further managers of artificial sewage purification works1 but not one single manager of natural purification works1 i4e4 a sewage farm manager1 was called1 the term 8sewage farm manager0 being used here to indicate an official whose sole duty it is to manage a sewage farm4 ,the entire absence of this latter class of official is so striking that it cannot be due to accident1 but must be the outcome of a settled policy not to reopen questions conclusively settled by previous inquiries4 ,another point that strikes the observer is that the ,commission only called one zoologist and one botanist1 as it is to these scientists that belongs in the first instance the question of studying the fauna and flora of sewage before the subject is taken up by other branches of natural science4 ,speaking on the whole1 the evidence taken by the ,commissioners forms very interesting reading1 and ought to be carefully studied by those who have to deal with the subject4 ,when now and again opinions are expressed1 which seem directly opposed to each other1 it must be borne in mind that here1 as in other things human1 unanimity of opinion1 though much desired1 is apparently unobtainable4 ,to understand the conclusions fully1 at which the ,commissioners in their ,interim ,report have arrived1 it ought to be pointed out that they had either to accept the recommendations in favour of land passed by all previous ,royal ,commissions and authoritative inquiries1 or they had to show by incontestable evidence that their predecessors had made grievous mistakes1 and where6 ,of these two courses1 the present ,commissioners have adopted1 no doubt for very good reasons of their own1 the first1 and they have started therefore1 in the conclusions to which they have come1 at the point where previous inquiries had left off1 viz4 that land treatment is a very proper method of sewage purification4 ,but before referring more in particular to their observations on land treatment1 it will be necessary to point out that the ,commissioners evidently divide all methods of sewage purification into two main classes1 viz4 natural and artificial methods4 ,into the former they only place land treatment1 whilst they call all other methods artificial4 ,this division seems to have given a great deal of offence to all those who have expressed decided and frequently very one-sided views in favour of the 8bacterial0 treatment of sewage2 but on closer examination it cannot be denied that the ,commissioners were quite right in forming this view1 as the following remarks will show4 ,for main divisions of all methods of sewage treatment two factors seem to be of primary importance1 viz4 the agencies which bring about this purification1 and the way in which these agencies are employed4 ,now1 it will not be denied that all agencies are natural ones1 whether the process employed is a purely chemical one1 a purely 8bacterial0 one1 land treatment pure and simple1 or a combination of these1 and1 at the present time no such thing as an artificial agency is known2 indeed1 it is perhaps not too much to say that there cannot be such a thing as an artificial agency4 ,hence it is impossible to divide sewage purification methods in this respect by the agencies employed1 and one is bound to fall back upon the way in which these agencies are employed4 ,here it is no longer open to argument whether a chemical process or the contact bed system--oxidation bed system--is artificial1 or whether the land treatment is natural6 ,for who would deny that masonry or concrete tanks and the materials contained in the same are artificial products--i4e4 products formed by man--and that land is a natural product--i4e4 formed by nature--and that further the soil is the natural home of bacteria4 ,hence it must be perfectly clear1 even to a casual observer1 that the line of demarcation drawn by the ,commissioners between all known systems of sewage purification is a correct and legitimate one1 and that all objections to such a division are based on misconceptions4 ,concerning land treatment1 the ,commissioners observe1 8,we doubt if any land is entirely useless10 but further on they observe that peat and stiff clay lands are generally unsuitable for the purification of sewage4 ,concerning peat1 nobody acquainted with the subject would probably differ from their conclusions owing to the great amount of moisture contained in this material2 but as to clay soils1 the ,commissioners when making this statement must have known that there are several successful sewage farms on this kind of land in existence1 such as the sewage farms at ,south ,norwood1 ,wimbledon1 ,warwick and ,leicester1 not to mention others4 ,in the case of ,leicester1 although the land is a very dense boulder clay1 the ,corporation of this town have just purchased the freehold of the farm for about #afj1jjjl4 ,dealing with the artificial processes from a chemical point of view1 the ,commissioners are of opinion that it is practicable to produce by these processes alone1 either from sewage or from certain mixtures of sewage and trade refuse1 effluents which might be discharged without fear of creating a nuisance1 and that in consequence the ,local ,government ,board would be justified in modifying1 under proper safeguards1 the present rule as regards the application of sewage to land4 ,the artificial processes referred to in the observations appear to be the following3-- ,closed septic tanks and contact beds4 ,open septic tanks and contact beds4 ,chemical treatment1 subsidence#f tanks and contact beds4 ,subsidence tanks and contact beds4 ,contact beds alone4 ,closed septic tank followed by continuous filtration4 ,open septic tank followed by continuous filtration4 ,chemical treatment1 subsidence tanks1 and continuous filtration4 ,subsidence tanks followed by continuous filtration4 ,continuous filtration alone4 ,the ,commissioners do not say what these safeguards are1 in fact they state that no general rules concerning them can be laid down1 and that in the case of these artificial processes it is necessary to consider every case on its own merits4 ,the next point dealt with is the bacteriological quality of effluents1 and here the ,commissioners observe3 8,we find that1 while in the case of effluents from land of a kind suitable for the purification of sewage there are fewer micro-organisms than in the effluents from most artificial processes1 yet both classes of effluents usually contain large numbers of organisms1 many of which appear to be of intestinal derivation1 and some of which are of a kind liable under certain circumstances at least to give rise to disease40 ,no particulars of effluents from sewage farms are given1 and later on it will be shown that this conclusion of the ,commissioners is not in accord with the results published up to now and available concerning the bacterial purity of effluents from land treatment4 ,the report concludes with some remarks on rivers pollution4 ,the ,commissioners state that it is of the utmost importance to provide the simplest possible means for adequately protecting all rivers1 and they think that this subject is of such grave importance 8as to demand the creation of a separate ,commission or a new department of the ,local ,government ,board1 which shall be a supreme ,rivers ,authority1 dealing with matters relating to rivers and their purification1 and which1 when appeal is made to them1 shall have power to take action in cases where the local authorities have failed to do so40 ,summing up the observations on the practice of sewage treatment1 it may be said that as a result of their extended inquiries1 the present ,royal ,commissioners have at the end of the century re-established land in its position as the first and only natural method of sewage purification1 beside which they have recognised artificial 7biological7 treatments as being under proper safeguards admissible for the purification of sewage4 ,before concluding this portion of the observations1 it is necessary to mention the valuable work done by ,mr4 ,scott-,moncrieff and ,mr4 ,cameron1 who1 contemporaneous with ,mr4 ,dibdin1 but quite independently1 had experimented with sewage and evolved their own artificial methods of sewage treatment4 ,these remarks must suffice for the more historic portion of the subject1 viz4 the progress of sewage purification during the last century1 and it is time now to direct attention first to natural and afterwards to artificial sewage treatments4 #d ,two of these have since retired4 #e ,this report has just been issued 7,august #ah1 #aijb71 and although the special reports it contains are of the greatest interest1 it is not necessary to refer to it again in these observations4 #f ,the expression 8subsidence tanks0 is intended to denote tanks which are used in such way that little or no septic action is produced4 ,,iii4 ,,the ,,subsoil4 ,sidenote3 ,general remarks on subsoil and its properties4 ,before dealing more in detail with the processes taking place in the pores of the subsoil of sewage farms1 it may not be out of place to make here a few general observations on the mechanical structure of soil1 its permeability1 water capacity1 retentive power1 the capillary movements in the same1 its temperature1 the subsoil air1 the movement of water in and through the same1 the micro-organic life in soil1 and its absorbing powers4 #a4 ,,mechanical ,,structure ,,of ,,soil4 ,sidenote3 ,size of grain and pores4 ,here is of interest the size of the grains or particles composing the soil1 the size of the pores and their collective capacity4 ,according to the character of the soil1 its grains or particles will vary from very large in coarse gravel to very fine in fine sand and clay4 ,sidenote3 ,variable size of pores4 ,sidenote3 ,surface attraction4 ,the size of the pores will vary as the size of its grains from large to small1 but frequently a certain kind of soil will contain a mixture of large and small pores4 ,the finer the pores the more energetic will1 as a rule1 be the surface attraction of the grains composing the soil4 ,sidenote3 ,pore-volume4 ,sidenote3 ,with particles of equal size pore-volume amounts to about #ch per cent4 of the total space1 and sinks down to #aj or #ae per cent4 with particles of unequal size4 ,sidenote3 ,with equally sized particles the pore-volume is the same whether the particles are small or large4 ,the collective capacity of the pores or the pore-volume mainly depends on the equal or unequal sizes of the particles4 ,when the same are of equal size the pore-volume amounts to about #ch per cent4 of the total space occupied by the soil1 but when this is not the case it may sink to as low as from #aj to #ae per cent4 of this space4 ,with equally sized particles the pore-volume is the same whether the individual particles are large or small4 ,in nature it will be the exception to find all the particles of equal size1 such a condition of things prevails only when careful sorting by sifting or riddling has taken place1 and in the majority of cases the larger pores will be partly filled up by the smaller particles of the soil4 #b4 ,,permeability ,,of ,,soil4 ,sidenote3 ,permeability depends first on the size of the pores1 and secondly on the pore-volume4 ,the permeability of a soil for the passage of air and water depends1 in the first instance1 on the size of the pores1 and is further to some extent influenced by the pore-volume4 ,sidenote3 ,effect of large and small pores4 ,soil with large pores will offer but little resistance to the passage of air and water1 but when the pores are small these movements will be greatly impeded4 ,sidenote3 ,permeability is proportional to the fourth power of the pore-diameter4 ,it has been ascertained that the permeability of soils is proportional to the fourth power of the diameter of the pores1 so that it decreases very rapidly with the diminishing size of the pores4 ,sidenote3 ,in frozen soil permeability decreases rapidly4 ,in subsoil with small pores all movements of air practically cease when it is half full of water1 and in frozen soil the decrease of the permeability is still more marked4 #c4 ,,water ,,capacity ,,of ,,soil4 ,sidenote3 ,water capacity is equal to the pore-volume4 ,sidenote3 ,air can never be wholly driven out of the pores4 ,the water capacity of a soil is that quantity of water which can be stored in its pores2 it is therefore equal to the pore-volume4 ,for very accurate measurements allowance must be made for a small amount of air1 which even after filling remains in the pores and cannot be dislodged1 but for practical purposes this can be overlooked4 ,sidenote3 #a cubic yard of soil with particles of equal size will hold about #he gallons of water4 ,as has already been stated1 the pore-volume of a soil consisting of equal particles throughout1 amounts to about #ch per cent4 of the space occupied by it1 and #a cubic yard of such a soil--whether we have to deal with coarse gravel or fine sand--will hold about #he gallons of water4 #d4 ,,water-,,retentive ,,power ,,of ,,soil4 ,sidenote3 ,the water-retentive power of soil is a percentage of its water capacity4 ,the water-retentive power of a soil is expressed by that quantity of water which can be retained by it2 it will always be a percentage or portion of the water capacity of this soil4 ,sidenote3 ,soil with a large pore-volume and a large percentage of fine pores retains more water than soil with a small pore-volume and large pores4 ,sidenote3 ,clean gravel retains about #aj gal4 and clean sand about #gj gal4 ,soil with a large pore-volume and with a large percentage of fine pores will retain more water than soil with a small pore-volume and few fine pores4 ,clean gravel will retain about #ab per cent4 of its water capacity1 i4e4 #aj gallons per cubic yard1 whereas fine sand may retain as much as #hd per cent4 of its water capacity1 i4e4 about #gj gallons per cubic yard4 ,sidenote3 ,organically polluted soil retains more water than clean soil4 ,this will explain why a polluted subsoil containing a large amount of organic substances will retain more water than the same soil in a clean condition4 ,sidenote3 ,the retentive power of a soil is due to its surface attractions4 ,the retentive power of a soil is due to the surface attraction of its particles1 and when the space between them is small1 or when1 in other words1 the pores are small1 this attractive power will be all the greater4 ,sidenote3 ,when1 after the limit of the retentive power has been reached1 of water are poured upon the soil1 a portion of the previously stored water is driven out1 and its place in the pores taken up by the fresh supply4 ,it is further of interest to observe here1 that if after the limit of the retentive power has been reached further quantities of water are poured upon the soil1 the water retained in the lower layers will commence to drain away4 ,this means that the water freshly poured upon the soil will drive out a portion of the water previously stored in the pores4 ,it is important to bear this in mind when dealing with polluted water1 as owing to this action the water penetrating into deeper layers will to some extent at least have become purified in the upper layers4 #e4 ,,capillary ,,movements ,,of ,,water ,,in ,,soil4 ,sidenote3 ,capillary attraction causes an upward movement of the water4 ,through capillary attraction an ascending movement of the water is caused in direct opposition to the laws of gravity1 and the height to which water will thus ascend depends mainly on the smallness of the pores2 large pores do not assist in this movement4 ,as the same1 however1 extends over the whole pore-volume the quantity of water thus raised may exceed the water-retentive power of soil4 ,sidenote3 ,capillary attraction also causes lateral and downward movements4 ,in addition to the upward movement brought about by capillary attraction1 this power is also continually at work in a lateral and downward direction2 but for the present purposes only the upward movement will be noticed4 ,sidenote3 ,time occupied by upward movement4 ,height reached by upward movement4 ,in observing the upward movement1 it is interesting to notice the time occupied by it and the total height reached4 ,as to the time occupied1 it has been established that the upward movement in gravel and coarse sand is much quicker than in fine and loamy sand1 but the heights attained are reversed4 ,for whereas the height in a material consisting of coarse or large pores amounts to from #b inches to #d inches2 a height of about #d feet after thirty to thirty-five days has been recorded in fine or loamy sand2 in peaty soil one observer states that the upward movement of the water may reach a height of #bj feet4 #f4 ,,temperature ,,of ,,soil4 ,sidenote3 ,three principal sources of heat4 ,the earth's crust receives its supply of heat from three principal sources1 viz43 #a4 ,from the sun through its rays2 #b4 ,from the interior of the earth through conduction2 and #c4 ,from various physical and chemical processes which take place in it and create heat4 ,sidenote3 ,heat through sun's rays4 ,sidenote3 ,dark soils absorb more heat than light-coloured soils4 ,sidenote3 ,capacity for heat is greater in damp and fine-grained soils4 ,sidenote3 ,evaporation and condensation of aqueous vapour produce the greatest effect in fine-grained soils4 ,dealing with the upper layers of the crust1 it may be said that1 besides the intensity of the sun's rays1 the temperature also depends on a variety of properties possessed by various kinds of soil1 amongst which latter may be mentioned the absorption of heat1 which is much greater in dark than in light-coloured soils2 the heat conductivity and the capacity for heat1 which lead to higher temperatures in damp and fine-grained soils2 and finally the evaporation and condensation of aqueous vapour1 which tend to prevent extremes of heat and cold and which likewise produce the greatest effects in fine-grained soils4 ,sidenote3 ,a fine-grained damp soil does not get so hot1 but retains the heat better4 ,it follows from these observations that a coarse-grained1 dark coloured and dry soil will show the highest and lowest temperatures1 whereas a fine-grained damp soil does not get so hot but retains the heat better4 ,sidenote3 ,the temperature of the surface of the soil may exceed that of the air4 ,it ought to be pointed out in this place that a variety of circumstances may bring about very high temperatures on the surface of the ground which considerably exceed the average temperatures of the air at the same time4 ,sidenote3 ,laws regulating the subsoil temperatures4 ,concerning the laws that have been deduced from careful and long continued observations of subsoil temperatures1 it will not be necessary at this point to deal minutely with them2 it must on the contrary suffice to summarise only the more important ones4 ,with the distance from the surface of the ground1 #a4 ,the differences of temperature become less1 #b4 ,the temperatures are retarded1 and #c4 ,the variations of short durations gradually disappear4 ,sidenote3 ,subsoil temperatures #ah in4 below surface4 ,sidenote3 ,subsoil temperatures at depths of #d ft4 #f in4 and #i ft4 ,at a depth of #ah inches below the surface the daily fluctuations are hardly observable1 the temperature differences of various days become obscured1 the differences between the monthly mean temperatures are less by several degrees1 and the yearly fluctuation amounts only to about #aj ,c4 ,at a depth of #d feet #f inches the latter is only #d ,c41 and at a depth of #i feet it is only #a;,c4 ,sidenote3 ,subsoil temperatures at depths from #i ft4 to #cc ft4 ,between #i and #cc feet1 according to the yearly mean of the surface1 the yearly fluctuation ceases and the temperature remains the same throughout the year4 ,below this point an increase of temperature is observable towards the earth's centre1 which amounts to about #a ,c4 for every #dj feet4 ,sidenote3 ,retardation of temperatures with increase in depth4 ,concerning the retardation of the temperatures with an increase in depth below the surface1 it is interesting to point out that this1 according to ,fodor1 amounts to about three weeks for every yard1 so that the yearly maximum at a depth of #a yard will take place in ,august1 at a depth of #b yards in the beginning of ,september1 and at a depth of #d yards in ,october4 ,this is on the assumption that the maximum temperature of the atmospheric air is reached in ,july4 ,sidenote3 ,frost depth about #c ft4 ,the depth to which frost under ordinary conditions penetrates is about #c feet1 but there are cases on record where water pipes at depths of from #d to #e feet have been frozen up during long continued severe frost4 #g4 ,,subsoil ,,air4 ,sidenote3 ,subsoil air is saturated with aqueous vapour and contains large quantities of carbonic acid4 ,the pores of soil are either partly or wholly filled with air1 which as a rule is saturated with aqueous vapour4 ,this air consists very largely of carbonic acid 7from #jb to #ad per cent41 on an average from #b to #c per cent47 and to a small extent of oxygen1 which has been used up for the formation of carbonic acid4 ,it also contains traces of ammonia and gases of decomposition4 ,the movements of subsoil air need not be considered here1 and beyond these few general observations it will not be necessary to deal with the subject4 #h4 ,,movements ,,of ,,water ,,in ,,soil4 ,sidenote3 ,strata above level of subsoil water4 ,two main strata may here be distinguished in subsoil1 one above the level of the subsoil water and one below this level4 ,the latter strata do not interest us1 and those above the level of the subsoil#g water may again be subdivided into three zones1 which in descending order are as follows3-- ,the evaporation zone2 ,the passage zone2 and ,the capillary zone4 ,sidenote3 ,one-third of the rain-water evaporates4 ,one-third flows off the surface4 ,one-third percolates4 ,all these three zones must be passed by the water in its descent from the surface of the ground to the subsoil water level1 and the quantity of water retained by them will depend on their state of dryness4 ,speaking quite generally and within wide limits1 one-third of the rain-water flows off the surface1 one-third evaporates1 and one-third percolates into the subsoil4 ,sidenote3 ,evaporation zone4 ,the evaporation zone reaches from the surface of the soil to that point below1 which marks the extent of the drying influence of the atmospheric air4 ,in the same the quantity of water stored in the pores may at times sink below the retentive power of the soil1 i4e4 below that quantity which can be retained in the pores owing to the mechanical powers of adhesion1 etc4 ,when it has become very dry through evaporation and other causes the zone1 especially when it extends some way down1 may retain large quantities of water4 ,in a depth of #aj inches1 #a square yard of soil1 with fine pores1 may retain about #aj gallons of water1 and as a rainfall of inch produces only #bc gallons per square yard1 it is clear that subsoil of this nature may retain a number of successive showers4 ,during the height of summer fine porous soil may become so dry that practically no water finds its way into deeper zones2 in this state the evaporation zone can be compared to a large sponge4 ,sidenote3 ,passage zone4 ,the next zone traversed by the water in its downward movement is the passage zone1 which lies beyond the drying influence of atmospheric air4 ,when too far removed from the level of the subsoil water1 its pores will not be completely filled with water1 but will only contain that amount which is due to the retentive powers of the soil4 ,by direct measurement it has been found that on an average a cubic yard of fine porous soil will retain from #cj to #hj gallons of water1 and it can easily be calculated that in a layer from #a to #b yards in thickness the rainfall of a whole year may be retained4 ,the passage zone1 especially if it is of considerable thickness1 represents a very large storage reservoir4 ,sidenote3 ,capillary zone4 ,the last zone before the level of the subsoil water is reached is the capillary zone1 in which the pores are partially or wholly filled by the upward movement--due to capillary attraction--from the subsoil water4 ,the extent of this filling will depend on the size of the pores4 ,sidenote3 ,springs4 ,when the descending water has finally reached the subsoil water it either comes to a standstill altogether on the impervious layer or moves along the same1 if the latter is not horizontal1 until it may eventually leave the subsoil again by issuing therefrom in the form of visible or invisible springs4 ,sidenote3 ,rate of downward movement governed by pores4 ,the rate of movement of any liquid--rain-water1 sewage or other polluting liquid--is largely governed by the size of the pores4 ,where these are large1 as for instance in coarse gravel1 the descent of the water will be comparatively rapid1 but when they are small it may take a very long time before the water reaches the level of the subsoil water1 and in that case it will have undergone material changes as regards its chemical or bacterial composition4 ,sidenote3 ,with a high level of subsoil water zones become indistinguishable4 ,with a high level of subsoil water the zones may become indistinguishable1 one zone reaching into the other1 with the result that the whole of the soil becomes very wet4 ,when subsoil has been artificially drained the amount of water reaching the subsoil water below the general level of the drains will depend on the size of the latter and the distance between them4 ,in such a case the downward movement of the water through undrained soil1 previously described1 may be further interfered with through the ventilation of the subsoil by drains1 and the drying up action caused thereby4 #g ,the term subsoil water is here used to denote that portion of the water in the pores of the soil1 which is either at rest on or moves along the inclined plane of an impervious layer4 #i4 ,,the ,,micro-,,organic ,,life ,,in ,,soil4 ,sidenote3 ,soil probably original home of micro-organisms4 ,sidenote3 ,distribution of micro-organisms in soil4 ,the soil is probably the original home of all micro-organisms1 from which they have emigrated into other media4 ,it contains vast numbers1 and1 according to some observers1 #a ccm4 may hold #ajj1jjj germs4 ,by far the greater number is found on or near the surface1 and in lower layers the numbers gradually diminish1 until at last a depth is reached1 which depends on local conditions1 where the soil is perfectly sterile4 ,the aerobes live near the surface and carry on their work in this region1 whereas the anaerobes are at work lower down in the soil4 ,sidenote3 ,cycle of micro-organic activity during the year4 ,the picture of the cycle of micro-organic activity in the upper layers of the soil during the various seasons of the year is probably the following4 ,in winter1 especially during that period when frost and ice bind the earth1 micro-organic life is apparently at its lowest ebb1 and may in some very cold climates come to a standstill altogether1 when micro-organisms may be said to hold their vegetative winter sleep4 ,with the return of life and the awakening of nature in spring--especially with the approach of higher temperatures and the formation of moisture--micro-organic activity once more makes itself felt all round4 ,during the summer months it is exposed to some injurious influences such as the heating and drying up of the upper layers of the soil1 but1 still gradually increasing1 micro-organisms reach the climax of their activity during the autumnal rains1 to remain in this state until with the advent of the cold season their activity gradually declines again4 ,sidenote3 ,micro-organic life in layers from #c ft4 to #f ft4 in depth4 ,in the lower layers of the soil1 down to #c feet and #f feet1 micro-organisms are more protected against the injurious influences of the atmosphere1 sunlight and drying up1 but the want of oxygen1 together with the greater difficulty of removing such products as carbonic acid1 has an injurious influence4 ,as the temperature in these layers is considerably more uniform1 it may be inferred that the micro-organic activity is there of a more uniform kind1 less influenced by sudden changes1 probably also less intense1 but without pronounced periods of rest4 ,sidenote3 ,micro-organisms probably quickly perish in depths greater than #f ft4 ,in depths greater than #f feet micro-organisms probably perish very quickly owing to unfavourable conditions1 and if found their presence must be explained by emigration from higher layers1 not by actual growth at these depths4 ,on sewage farms the micro-organic activity is without doubt greatly modified1 and proceeds all the year round at a more uniform rate than on ordinary land1 as the sewage always contains the necessary warmth and moisture so beneficial for it4 #aj4 ,,the ,,absorbing ,,powers ,,of ,,soil4 ,sidenote3 ,absorbing powers due to surface attraction of the particles of the soil4 ,sidenote3 ,the finer the pores the greater the absorption4 ,the absorbing powers of soil are due to the surface attraction of its particles or grains1 and these1 as has already been pointed out1 will be all the greater the finer the pores are2 they extend on the one hand to aqueous and other vapours and gases1 and on the other to matters in solution4 ,sidenote3 #a cub4 yd4 of coarse gravel may contain #ej sq4 yds4 of surface and #a cub4 yd4 of fine sand #ibjj sq4 yds4 ,that the attractive force of the surface of the particles is pretty considerable will be at once apparent when it is stated that #a cubic yard of coarse gravel may contain about #adj1jjj grains with a combined surface of #ej square yards1 and #a cubic yard of fine sand #dj million grains with a combined surface of #ibjj square yards1 which is a little under #b acres4 ,sidenote3 ,deodorising action of soil absorption of gases4 ,concerning the absorption by soil of aqueous vapour and gases 7apart from condensation through a fall in temperature71 dry soil with fine pores acts most energetically4 ,the almost instantaneous deodorisation of foul-smelling gases1 such as are formed by decomposing fcal matters 7earth closet7 or coal gas1 through a thin layer of fine dry soil is well known1 and is to be explained in this way4 ,sidenote3 ,absorption of dissolved substances by soil4 ,more interesting still1 and also more important1 is the absorption of dissolved substances by soil4 ,in this way is to be explained the decolorising effect and the retention of dissolved polluting substances such as are contained in sewage4 ,in the same way soil has the power of destroying such poisons as strychnine1 nicotine1 coniine1 etc41 and the experiments of ,falk and others go to show that ptomaines and toxines are likewise retained and rendered harmless by it4 ,this absorbing power of soil is of the utmost importance in agriculture1 and without it soil could not possess purifying powers for polluting liquids4 ,it is quite true that in this process of purification other factors play an important part1 but they could not come into play if this absorption did not exist4 ,the absorbing powers of soil are in some way dependent on the presence of micro-organisms and air1 and in the absence of these they will soon come to a standstill4 ,,iv4 ,,self-,,purifying ,,powers ,,of ,,soil4 ,,natural ,,self-,,purification ,,of ,,sewage4 ,sidenote3 ,self-purifying powers of soil4 ,after these preliminary remarks it becomes necessary now to examine into the self-purifying powers of soil with special reference to sewage farms4 ,generally speaking1 the term 8self-purifying powers powers of soil0 comprises all those processes which go on on the surface and in the pores of the soil of sewage farms1 and by which polluting liquids such as sewage become purified as these take place under natural conditions and in a natural medium1 the process of land treatment of sewage is called--see previous observations--8the natural self-purification of sewage40 ,sidenote3 ,self-purifying powers vary with local conditions4 ,sidenote3 ,soil best suited for sewage farms4 ,it should be stated at the outset that the self-purifying powers of soil will depend largely on the soil itself and the local conditions under which they come into play1 so that observations made in one locality will not be immediately applicable to others without making full allowance for the differences2 this will be clear from the preliminary remarks as to the character and properties of soils made in the previous pages4 ,as will be pointed out more in detail later on1 a subsoil that combines great permeability for air with high retaining and absorbing powers1 is best suited for sewage farms4 ,let us now consider what becomes of water1 sewage or any other polluting liquid containing organic substances after it has been poured out upon the surface of the ground1 and for this purpose we will assume a subsoil of a suitable character and in fair condition for work with proper under-drainage4 ,sidenote3 ,retention of liquid by pores of soil4 ,the liquid thus poured out upon the surface will sooner or later disappear in the soil1 and will at first be retained in the pores of the zone of evaporation1 which may be said to extend to the level of the under-drains4 ,this retention is due to the retentive powers of soil4 ,sidenote3 ,suspended matters retained on the surface1 soil acts like a sieve4 ,sidenote3 ,coating of surface of the land4 ,sidenote3 ,removal of suspended matters generally an advantage4 ,portion of the suspended matters will be retained on the surface and the rest will be strained out in a mechanical manner in the pores1 the soil acting as a sieve more or less fine according to its character4 ,if the suspended matters are present in very large quantities it may happen that they will gradually form a coat on the surface of the land and choke the pores to the exclusion of air1 and as this is a thing to be avoided in sewage farming it is in most cases advisable to remove them out of the liquid before it is poured upon the land4 ,sidenote3 ,the more finely divided the suspended matters are1 the lighter the work of the land4 ,even where such a removal has taken place there will still be left a certain portion of the suspended matters1 and if these are in a finely divided state1 such as is probably the result of their passage through fine strainers or pump valves1 the work of the land will be considerably lightened4 ,sidenote3 ,micro-organisms screened out in a mechanical way4 ,the micro-organisms contained in the liquid will be to a large extent screened out in a mechanical way with the suspended matters and deposited on the surface and in the upper layers of the soil4 ,sidenote3 ,retention of matters in solution after removal out of the liquid is due to physical and chemical agencies4 ,the matters in solution will partly1 after removal out of the liquid1 be retained by the absorbing powers of the soil in the pores1 a process that is due to physical and chemical agencies4 ,sidenote3 ,absorbing powers gradually ripen4 ,it is well known that land which is being treated with sewage for the first time does not purify sewage so well as land that has been under systematic treatment for some time1 and this is probably due to the absorbing powers1 which gradually ripen until they have reached their maximum of efficiency4 ,this process of gradual improvement seems to be due to the formation of a slimy coating round each particle of soil1 which growth does not only assist mechanical filtration1 but also possesses high powers of absorbing oxygen4 ,sidenote3 ,depths to which polluting substances may penetrate into soil4 ,the depth to which polluting substances may penetrate into soil will probably differ in each case1 but the following factors may be said to influence it1 viz4 the velocity of the downward flow1 the nature and degree of the polluting liquid1 and the character of the soil4 ,where1 therefore1 the powers of the soil are over-taxed the polluting substances may reach the level of the underdrains and pass out through them1 in which case the effluent will be but little better than the raw liquid4 ,it must be the aim of careful management to avoid this4 ,sidenote3 ,process of decomposition of organic matters stored in soil during periods of rest4 ,the polluting substances of an organic nature thus stored in the pores undergo here--and that probably chiefly during periods of rest--a process of decomposition or disintegration1 which goes on until the whole of the organic matter has been converted into stable mineral forms4 ,sidenote3 ,explanation of the term 8self-purifying power of soil40 ,this process of retention1 absorption and decomposition of organic impurities is called 8the self-purifying power of soil40 ,sidenote3 ,after conversion substances are removed out of the soil by the plants1 by the subsoil air and subsoil water4 ,the substances thus converted do not remain in the pores1 but they are removed either by the plants1 for which they act as food1 or by the currents of subsoil air1 or by the subsoil water1 and as the removal of fertilising substances by the subsoil water indicates a waste it must be the aim of a careful management to utilise them as much as ever possible for the benefit of the plants4 ,sidenote3 ,process of digestion4 8,sewage sick40 ,the whole of these intricate and very complicated changes may be likened to the process of digestion in animals1 and when these digestive powers are overtaxed signs of sickness may be noticed as the inevitable result1 which increase until1 in sewage phraseology1 the land becomes 8sewage sick40 ,in this condition it remains until the flow of the polluting liquid is stopped1 when after a period of rest--recreative period--the digestive powers gradually return and begin to do their work afresh4 ,sidenote3 ,action of lime4 ,when the soil of a sewage farm has got into this state1 owing to having received heavy doses of sewage1 the application of lime has proved very beneficial by accelerating the process of nitrification1 and in this respect interesting experiments have been made on the ,berlin sewage farms4 ,the action of lime is said to be a twofold one4 #a4 ,it quickly attacks and splits up the organic matters and accelerates afterwards their decomposition and their utilisation by plants2 and #b4 ,it neutralises the excess of acid in the soil1 and causes the latter to part with its carbonic acid4 ,sidenote3 ,decomposition proceeds quickest at or near the surface4 ,the process of decomposition proceeds as a rule at a much quicker rate on the surface and in the upper layers of the soil1 where1 as already mentioned1 the number of micro-organisms is greatest4 ,sidenote3 ,when carefully worked there is no time limit to the purifying powers of the soil4 ,it has been maintained that the soil of sewage farms will after a while silt up and cease to purify sewage1 but the results obtained with carefully managed farms clearly disprove this1 and under these conditions there appears to be no limit as to time to the purifying power of soil4 ,sidenote3 ,depth of soil necessary for purification4 ,concerning the depth of soil--evaporation zone--that is necessary for the successful retention1 absorption and decomposition of sewage1 no generally applicable rule can be laid down1 as this will depend on a variety of factors1 amongst which may be mentioned3 the character and thickness of the top soil 7humus71 the nature and cultivation of the top soil2 the character of the subsoil--its permeability for air and its retaining and absorbing powers2 the surface slopes of the land and the level of the subsoil water4 ,sidenote3 ,greater depths than #d ft4 will be rarely necessary4 ,on some farms a depth of #c feet on an average has proved sufficient1 and on others the drains have been laid at depths ranging between #c and #f feet1 but very special reasons ought to be shown for all depths over #d feet4 ,sidenote3 ,soil best suited for sewage farms4 ,whilst practically no soil is entirely useless for sewage farming1 with the exception perhaps of peat1 owing to the quantity of moisture it contains1 a soil that combines great permeability for air with high retaining and absorbing powers--such as a loamy sand with fairly large grains--is probably the best4 ,sidenote3 ,clay soil not unsuitable for sewage farms1 but it necessitates a greater area of land4 ,it has been maintained that clay1 owing to its impervious character1 is totally unsuitable for sewage farming1 but the experience of such farms as ,south ,norwood1 ,wimbledon1 ,warwick and ,leicester disproves this4 ,it is true1 however1 that as the purifying powers of the soil are restricted in a vertical sense to the upper layers1 it may become necessary in places to extend the area of the farm beyond what would be necessary with a more pervious soil4 ,sidenote3 ,changes observed in the heavy clay land at ,leicester since sewage treatment was commenced4 ,it may not be without interest to draw attention here to some of the changes that have taken place on the ,leicester sewage farm since the land has received regular dressings of sewage4 ,when ,i was engaged in laying it out in #ahhh my powers of locomotion over the land were greatly impeded during wet seasons by the inordinate amount of clay that adhered to the boots2 but when engaged again for some considerable time on the land during the winter #aijj to #aija this unpleasant peculiarity had completely disappeared even on land that had recently been sewaged4 ,through the action of the sewage the very dense clay had been disintegrated and become so pliable that1 when trod upon1 it crumbled to pieces4 ,the colour of the soil had been changed from a yellowish-brown to a greyish-black1 and altogether the land had been greatly improved by the application of the sewage4 ,sidenote3 ,movement of liquid through the passage and capillary zones to the impervious layer4 ,if more sewage is poured upon the land than the effluent drains can deal with--and here it may be well to bear in mind that on sewage farms in our climate on a broad average throughout the year about one-third of the total quantity is lost by evaporation--the excess will pass down between the drains from the evaporation to the passage zone1 and if the flow of the sewage is not discontinued the downward movement in the passage zone may be continued until1 after having traversed the capillary zone1 the level of the subsoil water is reached4 ,sidenote3 ,length of downward movement of water may be very great4 ,what length of time may elapse before this level is reached will entirely depend on local circumstances1 but it will be clear from the preliminary remarks that the completion of this downward movement may in places and under certain conditions take a very long time4 ,sidenote3 ,displacement of sewage held by the pores of the land by the fresh discharge of sewage upon the surface of the land4 ,in connection with this it is of importance to point out that not the fresh sewage which is poured on the surface of the land will at once pass into the lower layers1 but a portion of the old sewage1 which up to then was stored in the pores and is now displaced by the fresh discharge1 so that the fresh raw sewage is retained and only purified sewage allowed to escape into deeper layers1 which means that in its downward movement all sewage undergoes purification4 ,were this not the case the raw sewage might reach the effluent drains4 ,it appears time now to examine somewhat more closely the processes of decomposition and the products elaborated therein4 ,sidenote3 ,factors that influence the process of decomposition4 ,concerning the factors which have a favourable influence upon this process1 some of them1 such as permeability for air1 high retentive and absorbing powers1 have already been mentioned1 and to these can be added moisture and warmth1 the latter of which are always present in sewage4 ,sidenote3 ,advantages of a systematic underdrainage4 ,one word here concerning the systematic under-drainage of the subsoil4 ,its chief function is1 of course1 the carrying away of the effluent water and by doing so to prevent the formation of a swamp1 but after the land has done its work1 and during so-called periods of rest1 the under-drains act as ventilators of the subsoil and thus make it artificially more permeable for air1 with the result that a drying-up action is set up and oxygen supplied for micro-organic life4 ,for the purpose of improving the ventilation of the soil it may become advisable in places to connect the upper ends of the drains with a short upcast shaft4 ,the mouths of the drains should always discharge above water so as to allow of a free circulation of air4 ,sidenote3 ,micro-organisms that carry on the work of splitting up and converting organic compounds4 ,the work of splitting up and converting the organic compounds is primarily carried out by micro-organisms such as yeast fungi1 mould fungi1 alg1 protozoa and even by higher forms of life such as earthworms and insects4 ,to what extent in addition to these other agencies take part in this bio-chemical process is not yet fully elucidated4 ,sidenote3 ,decomposition and putrefaction most complicated processes4 ,fischer in his interesting book1 #8,the ,structure and ,functions of ,bacteria1' observes 7page #ii73 8,the decomposition of dead animal bodies1 of vegetable tissues1 or of substances like stable manure1 is far from being a simple putrefactive process4 ,side by side with the disintegration of nitrogenous bodies there are going on a number of fermentative changes by which non-nitrogenous compounds are being broken up1 besides nitrification and other bio-chemical processes4 ,for this reason it is always difficult and often impossible to determine the respective parts played by the different species of bacteria4''' 8,the phenomena of putrefaction are so complicated that we do not know all of the compounds that arise during the process4''' ,very careful chemical investigations on pure cultures will be necessary before the chaos of phenomena presented by putrefactive bacteria can be arranged in something like order4 ,sidenote3 ,in the decomposition of proteids five or rather six stages may be distinguished4 8,proteids are split up by putrefaction into a large number of simpler compounds both nitrogenous and non-nitrogenous4 ,the substances thus produced are precisely similar to those resulting from the artificial decomposition of proteids by fusion with caustic potash or boiling with hydrochloric acid or barium hydrate4 ,five groups may be distinguished3 ,sidenote3 ,albumoses and peptones4 8#a4 ,albumoses and peptones3 soluble diffusible bodies closely resembling albumen4 ,they are produced by the action on albumen of bacterial enzymes1 similar to the enzymes 7pepsin and pancreatin7 which give rise to peptones in the digestive tract of man4 ,sidenote3 ,aromatic compounds4 8#b4 ,aromatic compounds2 among others indol and skatol1 which give the characteristic odour to human excrement2 also some non-nitrogenous substances such as phenol1 phenylacetic acid1 and phenylpropionic acid4 ,sidenote3 ,amido compounds4 8#c4 ,amido compounds1 all nitrogenous3 leucin1 tyrosin1 aspartic acid1 glycocol4 ,sidenote3 ,fatty and aromatic acids4 8#d4 ,fatty and aromatic acids1 all non-nitrogenous and therefore having no part in the circulation of nitrogen2 acetic1 butyric1 succinic and valerianic acids4 ,sidenote3 ,inorganic end-products of putrefaction4 8#e4 ,inorganic end-products of putrefaction3 free nitrogen1 ammonia1 free hydrogen1 methane1 carbonic acid1 methylmercaptan1 sulphuretted hydrogen4 ,it is probable also1 but not certain1 that phosphuretted hydrogen is formed and is oxidised at once by the free oxygen of the atmosphere4 ,sidenote3 ,ptomaines4 8,most of these substances are formed also by the chemical decomposition of proteids1 but there is a sixth group which may be termed specific putrefactive products4 ,these are the so-called ptomaines or putrefactive alkaloids40 ,some of these bodies are either not poisonous or only poisonous in large doses1 whilst others1 derived from putrid foods of various kinds 7sausages1 cheese71 are highly toxic 7ptomatropine1 tyrotoxine74 ,sidenote3 ,definition of some terms4 ,concerning the work done by micro-organisms1 it may not be out of place here to define the meaning of certain terms1 and to direct attention at the same time to the modifications in the results brought about by the presence or absence of air during the various stages of the process4 ,the terms mineralisation1 disintegration1 oxidation1 hydrolysis1 bacteriolysis1 nitrification1 decomposition1 eremacausis1 putrefaction1 fermentation1 etc41 have by many been used somewhat promiscuously1 and this has led to a good deal of confusion1 bewilderment and misconception4 ,the cause of this has been undoubtedly our small amount of knowledge concerning this process and the changes brought about therein1 but this would appear to be no reason why complication should be made worse4 ,for the purposes of these remarks the undermentioned terms shall have the following meaning4 ,sidenote3 ,mineralisation4 ,the term 8mineralisation0 is used for describing the whole process of the disintegration and conversion of organic into mineral matter1 and no distinction shall be made between organic matter containing nitrogenous and organic matter containing carbonaceous substances4 ,sidenote3 ,aerobic fermentation or decomposition4 ,when this process of mineralisation is carried on in the presence of sufficient quantities of air it is called 8aerobic fermentation10 or 8decomposition10 which is generally characterised by the absence of strong smells4 ,the process may then be called one of complete oxidation4 ,sidenote3 ,anaerobic fermentation or putrefaction4 ,where1 however1 the mineralisation proceeds in the absence of air the process is called 8anaerobic fermentation10 or 8putrefaction10 and it is then that very pronounced foul smells are emitted4 ,the process may then be called one of incomplete oxidation4 ,sidenote3 ,obligatory aerobes and anaerobes4 ,sidenote3 ,facultative anaerobes4 ,that class of micro-organisms which can only live in the presence of oxygen is called 8obligatory aerobes10 and that which can only exist in the absence of this gas 8obligatory anaerobes40 ,between these two is the group of 8facultative anaerobes10 which1 while growing best with a plentiful supply of oxygen1 are nevertheless able to exist with a very small amount1 and even with none at all1 although in this case their vitality is often much impaired4 ,sidenote3 ,organic matters are first split up and then converted into mineral substances4 ,in the process of mineralisation two stages may be distinguished1 viz4 the first or disintegration stage1 and the second or oxidation stage1 i4e4 the organic substances are first split up and afterwards converted into inorganic ones2 and frequently these processes are taking place side by side and not after each other4 ,sidenote3 ,the splitting up of organic substances is frequently carried out in the presence of air4 ,it has been maintained--probably with a view to justifying the necessity of a septic tank--that the preliminary process of splitting up is best carried out in the absence of oxygen1 but sufficient proof does not appear to have been advanced in support of this statement1 and in some cases at any rate it is evidently carried out quite satisfactorily in the presence of air4 ,concerning the presence or absence of oxygen1 ,fischer observes as follows3-- 8,the effects of the presence of oxygen are somewhat better understood4 ,if air have free access1 putrefaction 7decomposition7 may go on without any odour at all1 the evil-smelling gases 7,,nh#c and ,,sh#b1 for example7 being oxidised at once to form nitrates and sulphates4 ,aerobic bacteria1 too1 such as the nitre and sulphur bacteria1 bring about this mineralisation of organic nitrogen4 ,moreover1 when air is circulating freely1 there is no accumulation of intermediate products such as skatol or indol4 ,it occurs on the surface of manure heaps1 on the outer surfaces of carcases1 and in well ventilated soil4 8,in anaerobic decomposition 7putrefaction proper71 as in anaerobic fermentation1 the organic molecules are at first only partly disintegrated1 intermediate products such as leucine1 tyrosine1 skatol and indol being formed4 ,in the absence of air these accumulate1 and hence it is that putrefaction going on in the mud of ponds and ditches1 or inside carcases1 is accompanied by such evil odours4 8,although the details of the process vary considerably1 according to the presence or absence of air1 the ultimate products of decomposition and putrefaction are in both cases the same3 namely1 free nitrogen1 free hydrogen1 ammonia1 methane1 carbonic acid and sulphuretted hydrogen4 ,these are also the end-results of the disintegration of the human body4 8,after the organic nitrogen of decomposing substances has been converted into ammonia1 and to a small extent into free nitrogen1 the latter can at once be utilised by the root-nodule organisms and other bacteria in the soil1 but the ammonia must undergo two further changes and combine with a base to form a nitric salt before it is available for plant life4 ,these two changes are brought about by bacteria1 which convert the ammonia first into nitrous and then into nitric acid2 this process has been called #8nitrification4'0 ,it will be clear from the foregoing remarks that the process of mineralisation is a very complicated one1 which under favourable conditions1 for instance in the pores of an open soil1 may come to an end fairly quickly1 but which under very unfavourable conditions--such as the interior of large heaps of refuse--may last many years4 ,sidenote3 ,chemical purification on sewage farms4 ,concerning the chemical purification effected on sewage farms1 i4e4 the purification of the sewage as revealed by chemical analysis1 it has been put on record over and over again1 and is now fully and universally understood1 that suitable land well managed is capable of changing even the foulest sewage to a perfectly clear water devoid of smell and danger1 so that this point need not be laboured here4 ,for instance1 on the ,berlin sewage farms the degree of purification attained has averaged for a period of #bj years #ig per cent41 and on the farm at ,gennevilliers--one of the ,paris sewage farms--the effluent is so sparkling1 bright and clear that the inhabitants drink it in preference to other available water4 ,sidenote3 ,micro-organic purity of effluent from sewage farms4 ,but in reference to the purity of the effluent as to the products of micro-organic activity and pathogenic micro-organisms1 it will be necessary to make a few observations with a view to remove misconceptions that have from time to time been put forward4 ,sidenote3 ,ptomaines have not been found in effluents from well managed sewage farms4 ,the question whether the specific products of putrefaction1 i4e4 the putrefactive alkaloids 8ptomaines and toxines10 are capable of doing further mischief by escaping with the effluent into the stream1 may be answered as follows4 ,these substances are fortunately very unstable1 and the experiments conducted by ,falk and others seem further to indicate that soil is capable of retaining them and of rendering them harmless4 ,at any rate there is no well authenticated case on record of these bodies having wrought mischief on sewage farms4 7,see here also the remarks made on pages #ea and #eb under the heading 8,the ,absorbing ,powers of ,soil407 ,sidenote3 ,pathogenic germs on sewage farms4 ,it has further been maintained that the presence of pathogenic organisms on sewage farms might in two ways lead to mischief1 viz4 either by transmission through air or by transmission through water4 ,the pathogenic organisms after spreading over the land might rise into the air through the movements of the atmosphere and then be carried about by it1 or they might escape through the land and be conveyed with the effluent into the stream or river that takes the latter4 ,sidenote3 ,pasteur's fears as to mischief likely to be brought about by pathogenic micro-organisms on sewage farms not borne out by facts4 ,in connection with this point it may not be without interest to mention here that even the late ,m4 ,pasteur at one time of his career considered the wholesale spreading of disease germs on sewage farms might prove highly injurious to the public health of the neighbourhood4 ,as he himself admitted1 he based his fears on purely theoretical considerations and opposed1 for this reason1 the extension of the sewage farms in the neighbourhood of ,paris4 ,but when1 later on1 he was made acquainted with the results observed on the ,berlin farms1 he tacitly modified his views and ceased to oppose the extension of the ,paris farms4 ,sidenote3 ,no well-authenticated case is on record where a sewage farm has acted as the focus of a local outbreak of typhoid fever4 ,indeed1 search as ,i might1 ,i have not been able to discover one single instance where a sewage farm has acted as the focus of a local outbreak4 ,on the contrary1 during one or two small epidemics of typhoid fever in ,berlin1 no case of this complaint has been observed on the sewage farms of that city4 ,sidenote3 ,experience on the ,berlin farms4 ,concerning the escape of pathogenic micro-organisms into streams and rivers1 no case is on record where such a thing has actually occurred3 indeed1 the very painstaking investigations on the ,berlin farms have led to negative results4 ,sidenote3 ,observations made at the ,freiburg sewage farm4 ,another sewage farm1 that of ,freiburg in ,baden1 has likewise been made the subject of careful and long-continued investigation by ,dr4 ,korn1 who1 for the twelve months ending ,august #ahig1 made no less than #afe elaborate chemical and bacteriological examinations4 ,summing up his observations on the presence of bacteria in the effluents from subsoil drains1 he remarks3 8,apart from the few exceptional cases of high numbers1 generally speaking my experiments show that the number of germs in the subsoil drain effluents is relatively small1 and even omitting these experiments1 in which a dilution with subsoil water must have taken place1 the number of micro-organisms is still so small that the effects of filtration through soil are clearly perceptible4 ,in addition to this--and this is of considerable importance in forming a judgment--it must be borne in mind that the bacteria in sewage are principally derived from the intestines1 whereas in the subsoil drain effluents the inhabitants of the intestines are either not present at all or only in very small numbers compared with the number of soil and water bacteria1 which are always present4 ,out of #afe examinations ,i only succeeded in #ah cases in proving the presence of bacterium coli40 ,sidenote3 ,bacterium coli no longer a true criterion of sewage pollution4 ,sidenote3 ,dr4 ,weissenfels' conclusions4 ,it may be convenient to point out in this place that bacterium coli can no longer be looked upon as a typical inhabitant of the human intestines after the very elaborate investigations carried out by ,dr4 ,weissenfels1 who arrived at the following conclusions3 #a4 ,the so-called bacterium coli can be cultivated from almost every kind of water1 and its presence can be demonstrated in nearly every case1 provided a sufficient volume of water is utilised4 #b4 ,it is not possible by the result of the experiments upon animals to decide whether the bacterium coli was cultivated from a pure or infected water1 and the discovery of a virulent bacterium coli in any sample of water cannot1 therefore1 be regarded as a criterion that such water has been polluted with fcal bacteria4 ,after these remarks1 it would seem quite possible that the bacterium coli discovered in eighteen cases by ,dr4 ,korn in the ,freiburg effluents was not derived from sewage at all but from the ordinary subsoil water of the land4 ,sidenote3 ,the possibility of further mischief by pathogenic micro-organisms on sewage farms is exceedingly remote1 if it exists at all4 ,bearing these observations in mind1 it is quite clear1 therefore1 that neither theoretical investigations1 as available up to now1 nor practical results1 support the theory that pathogenic micro-organisms may do mischief on sewage farms1 and one is forced to conclude that this possibility--if it exists at all--after systematic treatment on land is an exceedingly remote one4 ,sidenote3 ,sewage farms reduce the quantity of final effluent4 ,before concluding these remarks on the natural purification of sewage it is necessary to draw attention to another considerable advantage which it possesses over artificial sewage treatments1 and that is the reduction in quantity of the effluent1 which at times is very considerable1 whereas in the artificial methods such a reduction is comparatively small4 ,sidenote3 ,loss of liquid by evaporation and by plant life4 ,spread over a large area of land1 well cropped1 evaporation is very active--especially during the summer months1 when the flow of water in the brook that takes the effluent is as a rule at its lowest2 and1 in addition to this1 the growing plants further abstract a considerable amount of the liquid that finds its way into the soil1 so that the quantity of the effluent may not be more than from #cj to #ej per cent4 of the total quantity that was poured over the land4 ,in the artificial treatment the evaporation is considerably smaller1 and as plants are altogether absent the quantity of the effluent is probably about #ij per cent4 and more of the total quantity of the raw sewage4 ,this is a point of very considerable importance so far as the influence of the effluent upon the water in the stream that takes the same is concerned4 ,although the subject of natural purification is by no means exhausted1 it is now time to direct attention to artificial methods4 ,v4 ,,artificial ,,self-,,purification ,,of ,,sewage4 #a4 ,,general ,,observations4 ,sidenote3 ,enumeration of more important experiments4 ,a great many experiments have been made during the last ten years with artificial processes for the self-purification of sewage1 and amongst the more important the following may be mentioned3 ,london experiments4 ,sutton ,exeter ,manchester ,leeds ,sheffield ,leicester ,york ,hamburg ,sidenote3 ,experiments have not been conducted on uniform lines4 ,a casual observer might1 therefore1 consider himself justified in thinking that all these experiments had added a great deal to our knowledge of the intricate changes taking place in these processes1 but such a conclusion would not be justified in reality4 ,for beyond settling questions of local importance by chemical analysis1 the experiments1 owing to a variety of causes1 have not materially enhanced the stores of our information1 indeed not unfrequently the results obtained are apparently contradictory and bewildering4 ,an experiment must be looked upon as a question addressed to nature1 and the answer will depend on the way the question has been put4 ,if this way differs in every case it must be clear that the answer1 too1 will differ in every case1 and it is this absence of uniformity which greatly reduces the general value of these experiments4 ,these remarks must not be misunderstood to convey the impression as if the experiments had not been conducted with care and skill6 ,far from it6 ,some of them have been made with the greatest skill and care and with the very evident desire to arrive at correct conclusions1 and it is only when they are placed side by side with other experiments1 with a view to deducing from them general conclusions concerning the processes at work1 that great difficulties are experienced4 ,the result of each experiment is governed by a large number of factors1 which by slightly different manipulations may attain in this ever-fluctuating process different weights1 so that the results may be contradictory1 and it is only by arranging these factors on a common basis1 as it were1 and by addressing the questions to nature in the same systematic and uniform way1 that good general results may be expected4 ,it is well known1 for instance1 that in some cases septic tanks have not given good results1 whilst in others they have worked very well2 again1 continuous filtration has failed in some experiments1 whilst in others1 notably in the ,york experiments1 it has given good results4 ,if1 therefore1 in future the mistake of the past is to be avoided1 it will be necessary to settle on a common line of action in all experiments4 ,sidenote3 ,attempt to evolve general theory4 ,in spite of all the difficulties which beset such a task1 an attempt will be made in the following observations to evolve some general theory concerning the processes at work in the artificial self-purification of sewage4 ,such a theory1 it is quite clear1 cannot be complete in the present state of our knowledge1 and it is sincerely hoped that the many and serious gaps will be filled up by later investigations4 ,for convenience of reference the different forms of the process1 such as are now employed1 shall be dealt with separately1 commencing with contact or oxidation beds4 #b4 ,,artificial ,,self-,,purification ,,of ,,sewage ,,in ,,intermittent ,,contact ,,beds4 ,at the outset it may not be out of place to make a few remarks concerning the various names given to this form of application4 ,the term 8intermittent contact bed0 is here used to distinguish this kind of bed from the 8continuous contact bed10 frequently called 8continuous filtration40 ,sidenote3 ,names of process misleading4 7a7 ,name of ,process4--,this process has frequently been called 8biological process10 8bacteriological process10 8contact bed system0 or 8oxidation bed system10 but all these terms do not appear to define it sufficiently1 as they do not cover the whole1 but only phases or stages in the same2 hence1 they do not seem appropriate4 ,sidenote3 ,biological process4 ,the name 8biological process0 is decidedly misleading1 for besides biological agencies there are also at work physical 7mechanical7 and chemical ones4 ,sidenote3 ,bacteriological process4 ,the term 8bacteriological or bacterial process0 is likewise erroneous1 for besides bacteria a number of other micro-organisms participate in it--such as yeast fungi1 mould fungi1 alg1 protozoa1 and even higher forms of life1 such as earthworms and insects4 ,sidenote3 ,contact bed system4 ,sidenote3 ,oxidation bed system4 ,the expressions 8contact bed system0 or 8oxidation bed system0 are in so far inappropriate as they describe only portions of the process but not the whole4 ,the term 8contact bed0 describes the first stage1 and the term 8oxidation bed0 portion of the second stage only4 ,sidenote3 ,term most suitable4 ,the term which seems most suitable of all is 8artificial self-purification in contact beds10 as it includes every phase of this lengthy process applied in an artificial form2 the term 8natural self-purification0 being applied to land treatment of sewage1 as it is the only method in which the self-purifying powers are employed under natural conditions4 ,sidenote3 ,working operations4 7b7 ,explanation of ,process4--,the cycle of operations commences with the filling of the bed1 and during the same the sewage comes gradually in contact with the filling material4 ,when the bed is full1 the inflow is stopped and the sewage allowed to remain in contact with the material for some time4 ,the bed is then emptied1 and a period of rest is given it before the filling is commenced again4 ,sidenote3 ,purification of sewage in full bed due to absorbing powers of filling material and only to a small extent due to activity of micro-organisms4 ,it has been held1 that while the sewage is in the contact bed it undergoes a very rapid process of decomposition by bacteria1 but it must be evident1 that as the sewage--including filling--remains only for about two hours in the bed1 the micro-organisms would have to work at an express rate4 ,this fact alone is apt to make this theory very doubtful1 but apart from it1 it has been proved by experiments that the by far greater amount of purification--whilst the sewage is in the beds--is due to the absorbing powers of the filling material1 which are derived from the surface attraction of its component particles4 ,sidenote3 ,retention of suspended matters by bed4 ,sidenote3 ,absorbing powers of filling material4 ,the filling material retains in its upper layers the suspended matters1 which it strains out of the sewage in a purely mechanical manner1 much after the fashion of a screen1 and when the bed is filled its absorbing powers come into play1 which cause the removal of the dissolved matters out of the liquid and their retention on the surface of the particles4 ,this latter process is probably a chemico-physical one assisted by the micro-organic life in the sewage4 ,sidenote3 ,decomposition of organic substances by micro-organisms when bed is empty4 ,it is only after the bed has been emptied that the real activity of the vast number of micro-organisms commences1 which is directed towards converting the organic substances into mineral ones4 ,this process of splitting up1 decomposing1 disintegrating and mineralising organic waste products is an exceedingly complex one1 which ever fluctuates according to the prevailing conditions1 and which does not come to an end until finally stable mineral forms are reached4 ,in the presence of a plentiful supply of oxygen1 the process proceeds as a rule at a more rapid rate1 and the intermediate forms produced are less complex than in the comparative or total absence of this gas2 hence the progress of the process is largely determined by it4 ,the amount of oxygen necessary for bacterial activity is partly abstracted1 and with extraordinary energy1 from the atmospheric air in the pores of the filling material1 and a portion of the substances formed1 such as carbonic acid and nitrogen--in gas form--escape into the atmosphere1 whilst the remaining portions are washed out of the bed with other products1 such as nitric acid1 by the effluent4 ,further remarks upon this process of mineralisation have been made in connection with the subject of natural self-purification of sewage1 and these may be referred to here4 ,sidenote3 ,effluent from bed practically raw sewage as far as its bacterial contents are concerned4 ,the effect of the bed upon the bacterial flora of sewage is1 as was to be expected1 but very slight1 and it is on record now that1 as far as the micro-organic life is concerned1 the effluent is to all intents and purposes raw sewage4 ,sidenote3 ,silting up of bed4 ,some of the substances contained in raw sewage remain in the bed1 no matter how carefully the sewage has been previously strained1 and these1 in combination with the slimy surface coating of the component particles1 the accumulation of mineralised substances in the pores1 the consolidation of the bed1 the disintegration of the filling material1 and the liquid retained1 lead gradually but surely to the silting or sludging up of the bed4 ,sidenote3 ,theoretical original water capacity of bed4 7c7 ,water ,capacity of ,bed and ,silting up4--,the theoretical water capacity of the bed1 previous to commencing operations1 is the aggregate of the cubical space occupied by the pores or small passages between the particles forming the filling material1 and the pores of the filling material itself2 but in practice a certain amount of this space is occupied by air1 which it is impossible to dislodge altogether in filling4 ,the aggregate of the cubical space of the pores may be called the pore-volume4 ,it is difficult to lay down general rules as to what the original water capacity of a bed should be expressed in per cent4 of the space occupied by the filling material1 but speaking within fairly wide limits the following is somewhat near the truth4 ,sidenote3 ,original water capacity with spherical particles of uniform size4 ,when the particles forming the filling material are fairly spherical and of equal size1 the original water capacity of a bed amounts to about #ch per cent4 of the space occupied by the filling material2 but as in practice it is difficult to obtain spherical particles of uniform size1 the original water capacity is found to range from #ce to #de per cent4 of this space4 ,sidenote3 ,original water capacity with particles of different sizes4 ,when1 however1 the particles are of materially different sizes1 and when the smaller ones fill up the spaces between the larger ones1 the original water capacity may sink down to as low as from #e to #aj per cent4 of the space occupied by the filling material4 ,sidenote3 ,size of particles of filling material does1 under certain conditions1 not affect original water capacity of bed4 ,it has been further demonstrated that the water capacity of a bed is not affected by the size of the particles1 provided the latter are spherical and of uniform size4 ,in other words1 the water capacity of two beds filled with material of different sizes is the same1 provided the particles are spherical and of uniform size throughout each bed4 ,sidenote3 ,silting up of bed during regular work4 ,sidenote3 ,rapid initial decrease of capacity4 ,sidenote3 ,consolidation of bed4 ,this original water capacity is1 however1 not maintained in regular work1 as has been pointed out already4 ,basing the observations on regular work only1 the original capacity decreases at first1 after a new bed has been started or after an old reconstructed bed has been taken in hand1 rapidly for some time and afterwards more slowly4 ,graphically expressed1 this decrease is not represented by a straight line but approaches more nearly a parabolic curve4 ,this initial rapid decrease is chiefly due to the consolidation of the bed4 ,sidenote3 ,disintegration of filling material4 ,in connection with the movements in the bed tending towards its consolidation1 it is also clear that the continual filling and emptying operations cause the smaller particles to be washed out of their original position and to be placed in the larger passages between the filling material1 and if this process is assisted by the gradual disintegration of the particles composing the filling material1 it is clear that the pores must become smaller and smaller in time1 i4e4 choked4 ,from these observations it follows that the filling material should be a hard substance1 which will only to a limited extent be subject to this crumbling away process4 ,but besides these there are1 as has already been pointed out1 other silting up agencies at work4 ,sidenote3 ,water-retentive power of filling material4 ,of the total quantity of sewage which has entered the bed a small portion will always remain in it owing to the water retaining power of the material4 ,this power has sometimes been called 8minimum water capacity10 but as this name is liable to be misunderstood1 it is better to adopt here the term 8water-retentive power0 of material4 ,the quantity of the sewage retained by the bed varies with the material and pore-volume1 and is due to adhesion and capillary attraction4 ,the greater the pore-volume1 and the greater the percentage of fine pores1 the greater is the quantity thus retained4 ,clean gravel retains about #ab per cent4 and fine sand about #hd per cent4 of its water capacity--i4e4 expressed per cubic yard of filling material1 one cubic yard of clean gravel will retain about #aj gallons and one cubic yard of fine sand about #gj gallons of water4 ,through draining a bed for several hours through evaporation and other atmospheric influence1 a portion of the sewage retained is lost1 but the quantity so lost will vary continually with the circumstances under which the bed is worked4 ,the water-retentive power of the filling material does not decrease with the working of the bed1 but increases1 which in a large measure is probably due to the slimy coat which forms round the surface of the component particles1 and to which reference is made in the following paragraph4 ,sidenote3 ,slimy surface coating of component particles4 ,a further silting-up agency is the slimy surface coating of the particles of the filling material4 ,this accumulation is well known to all who have had to do with intermittent contact beds1 and has been described as spongy bacterial growth4 ,the ,manchester report for the year ending ,march #bg1 #aija1 contains on page #fb the following passage3 8,this 7spongy bacterial growth7 is at once the cause of increased efficiency in the bed and loss of capacity4 ,on examining the material of a contact bed in active condition1 every piece is seen to be coated over with a slimy growth4 ,if this is removed it soon dries to a stiff jelly1 which can be cut with a knife4 ,under the microscope masses of bacteria and zoogloea will be found to be present40 ,sidenote3 ,accumulations of decomposed substances in the pores4 ,in addition to this slimy surface-coating of the particles1 there are also found in the pores1 especially in the upper layers of the filling material--and in fine beds more so than in a coarse bed--accumulations which are 8akin to humus or garden soil40 ,they contain to a limited extent only putrescible substances1 and appear to be the remains of organic matter decomposed by the activity of micro-organisms4 ,sidenote3 ,periods of rest will not permanently restore portion of the original water capacity of the bed4 ,it was formerly maintained with considerable persistency that periods of rest would permanently restore to a systematically worked bed a portion of its lost water capacity1 but such a contention has been proved to be wrong4 ,it is quite true that immediately after periods of rest an increase of the water capacity is very noticeable1 which is probably due to drying up processes within the bed during the rest1 but such an increase is not permanent and is lost again more or less quickly2 it is therefore only temporary and not permanent4 ,where1 however1 a bed has not been systematically worked1 i4e4 where it has been worked at a greater rate than is suitable1 and where in consequence of this a large quantity of undecomposed substances is stored in it1 a period of rest may permanently restore a portion of the lost capacity2 but this is due to the mineralisation of these undecomposed organic substances during the rest4 ,it follows from these remarks1 as has been stated above1 that when the organic substances are regularly decomposed during systematic work a period of rest cannot materially affect the water capacity1 and that where a considerable permanent restoration of the water capacity takes place the bed has not been properly worked4 ,sidenote3 ,decrease of capacity is accompanied to some extent by increase of efficiency and vice versa4 ,it would1 however1 be incorrect to assume that the silting up of the bed affects its efficiency besides reducing the capacity4 ,on the contrary6 ,to some extent decrease of capacity is accompanied by increase of efficiency and vice versa6 ,sidenote3 ,higher capacity of beds in summer than in winter4 ,at this point it ought to be stated that in the ,manchester experiments 7see page #fa of the report for the year ending #bgth ,march1 #aija7 a higher average capacity is maintained during the summer than during the winter1 which is no doubt due to the greater activity of the micro-organisms during the warm weather of the year4 ,sidenote3 ,raking of beds not advantageous4 ,the raking of the surface does not materially affect the capacity of the bed1 and it is better to scrape off the matters retained on the surface than to rake them into the body of the bed4 ,sidenote3 ,renovation of filling material either partially or wholly4 ,it will be clear from these observations that1 no matter how carefully the bed has been worked1 sooner or later a time will come when the decrease of capacity becomes so pronounced as to render it impossible any longer to treat the daily flow of sewage with the available plant2 and when this point has been reached a renovation1 either partially or wholly1 of the filling material becomes an inevitable necessity4 ,sidenote3 ,minimum capacity of beds to be provided for4 ,to provide for this at the outset1 and thus avoid the difficulties of reduced capacity1 it seems advisable to lay down1 when designing the works1 a minimum capacity1 which will just allow the daily volume of sewage to be treated by the plant1 and which when reached will necessitate the cleansing of the bed4 ,the idea1 formerly frequently expressed1 that the filling material when rationally worked need not be renewed or renovated1 can no longer be maintained and is outside the reach of practical possibilities4 ,sidenote3 ,underdrainage of intermittent contact beds4 ,at this place a word or two about the under drainage of intermittent contact beds may not be out of place4 ,it is of the greatest importance that all drains should work well1 and that the entrance of the sewage into them should not lead to disturbance in the filling material1 especially should the tearing of portions of the filling material into the drain pipes be avoided4 ,by carefully arranging the position1 number1 size and fall of the master drains and branch drains1 it is possible to reduce the resistance so as to allow of a fairly even flow of sewage through all the drains1 and to prevent a great rush of water through the drains near the outlet end4 ,sidenote3 ,the presence of lime is of no consequence4 ,in passing it may not be out of place to point out that the view1 formerly expressed1 that an admixture of lime in some form would prove advantageous to the purification of sewage1 is not supported by the experience gained4 ,sidenote3 ,absorbing effect increases with the time of contact4 7d7 ,absorbing ,powers of ,filling ,material4--,the absorbing effect of any filling material seems to increase with the time of contact4 ,sidenote3 ,absorbing powers increase until bed has become ripe4 ,it ought further to be pointed out that the absorbing powers of the filling material gradually increase until the bed has become ripe4 ,this fact was formerly stated to be due to the development of the proper micro-organisms within the bed1 but it would seem to be chiefly due to the slimy surface coating of the particles of the filling material1 or spongy bacterial growth1 as it has frequently been called1 which does not only assist mechanical filtration but also possesses high powers of absorbing oxygen4 ,sidenote3 ,absorbing powers soon cease in the absence of micro-organisms and air4 ,but it cannot be open to doubt that the absorbing powers of the filling material are dependent in some way or other on the presence of micro-organisms1 for ,dunbar has shown that in the absence of micro-organisms and without periods of aeration these powers soon cease4 ,sidenote3 ,oxygen is absorbed from air in the pores with great energy4 7e7 ,consumption of ,oxygen by the ,filling ,material4--,the oxygen necessary for the proper work of an intermittent contact bed is abstracted with great energy from the atmospheric air1 with which the pores become filled during periods of rest4 ,through diffusion1 and through the vacuum created by the processes of absorption1 further quantities of oxygen are taken from the atmospheric air1 even under difficult conditions1 and1 as pointed out in the ,manchester report for the year ending #bgth ,march1 #aija1 8there is1 therefore1 little need to force air into a bed40 ,sidenote3 ,the oxygen taken up during aeration is not imparted to the sewage at the next filling and does not escape in the effluent4 ,the oxygen thus taken up is not imparted in gas form to the sewage during the next filling1 and the effluents from intermittent contact beds are not saturated with oxygen4 ,dunbar states that the effluents of a satisfactorily worked bed frequently only contain one cubic centimetre of free oxygen per litre4 ,clowes reports a similar result in his third report on the ,london experiments4 ,sidenote3 ,the greatest quantity of oxygen is consumed during the oxidation of the products formed by micro-organisms4 ,there can be no doubt that by far the greatest quantity of oxygen is consumed during the process of oxidation of the products formed by micro-organisms from putrescible organic substances4 ,sidenote3 ,consumption of oxygen and formation of carbonic acid not solely due to biological agencies4 7f7 ,formation of ,carbonic ,acid4--,dunbar has shown by his experiments that the consumption of oxygen and the formation of carbonic acid is not solely due to biological agencies1 but is to some extent the result of physico-chemical processes4 ,sidenote3 ,more free carbonic acid contained in the effluent than in the raw sewage4 ,sidenote3 ,by far the greatest portion of carbonic acid escapes into the air4 ,he further reports that in his experiments the effluents contained on an average #ajj milligram per litre more free carbonic acid than the raw sewage1 and that the quantity contained in the effluents represents only a small portion of the total amount of carbonic acid formed during the whole process4 ,the by far greatest portion of carbonic acid escapes into the air4 ,concerning the air in the pores of the filling material during periods of aeration1 ,dunbar states that it contains sometimes not less than from #f to #aj per cent4 carbonic acid4 ,sidenote3 ,nitrogen escapes in gas form into the air4 7g7 ,nitrogen4--,it is quite clear from all experiments that a considerable amount of the total nitrogen contained in raw sewage is abstracted by the filling material of intermittent contact beds1 and it is interesting to ascertain what becomes of it6 ,does it accumulate in the bed8 ,in that case1 one has a right to assume that the satisfactory work of the bed would gradually cease6 ,as this is1 however1 not the case1 and as1 further1 the sludge formed in the bed1 whether it be fairly fresh or very stale1 only contains a very small amount of total nitrogen1 we must surmise that the nitrogen after its retention by the bed escapes in gas form--like the carbonic acid--into the atmosphere4 ,sidenote3 ,the presence of nitric acid is not an unfailing guide for determining the satisfactory character of the effluent4 7h7 ,the ,formation of ,nitric ,acid4--,concerning the presence of nitric acid in the effluents from intermittent contact beds1 ,dunbar is of opinion that it offers certain means for forming an opinion of the processes taking place in the same1 but that it is only in a subordinate sense an indication of the degree of purification attained and must not be taken as an unfailing guide for determining the satisfactory character of the effluent4 ,sidenote3 ,nitrifying bacteria always present in town's sewage4 ,sidenote3 ,nitric acid is formed very rapidly1 but only during periods of rest4 ,nitrifying bacteria are always present in ordinary town's sewage1 but it would appear that other micro-organisms besides ,winogradsky's bacteria assist in the process of nitrification4 ,nitric acid is formed very rapidly1 but only during periods of rest1 and besides aeration other less powerful influences are at work4 ,sidenote3 ,reduction of nitric acid when bed is filled from bottom with an upward flow4 ,it is further interesting to note that1 according to ,dunbar1 the greater portion of nitric acid which has been formed during periods of aeration becomes completely reduced in a very short time1 when the bed is filled with an upward flow from the bottom1 and that only a small portion remains in the form of nitrous acid4 #c4 ,,artificial ,,self-,,purification ,,of ,,sewage ,,in ,,septic ,,tanks4 ,sidenote3 ,septic tanks only used in combination with contact beds4 ,although it has never been claimed1 and is further not open to doubt1 that a septic tank alone and unaided by subsequent treatment in intermittent or continuous contact beds does not sufficiently purify the sewage1 in these remarks the work of the septic tank only will be considered1 as the treatment in contact beds will be dealt with separately4 ,sidenote3 ,septic tank a suitable name4 7a7 ,name of ,septic ,tank4--,a good many names have been suggested by different observers--such as 8anaerobic fermentation tank10 8putrefying tank10 8liquefying tank10 8cess-pit10 etc4--but there appears to be no reason why the name 8septic tank0 should not be adhered to1 as it describes sufficiently correctly the work done by the tank1 which is chiefly of a septic nature4 7b7 ,covered or ,open ,septic ,tank4--,before dealing with the processes taking place in a septic tank1 it will not be out of place to consider here1 shortly1 whether a closed septic tank confers advantages over an open septic tank sufficiently great to justify the considerably greater expenditure necessitated by its construction4 ,it is well known1 that at ,exeter in the first experimental installation of this process1 the septic tank was covered in by an arched roof2 but subsequent experiments made elsewhere do not seem to support the theory then advanced1 that such a tank should be a closed one4 ,this is chiefly due to the thick skin which1 after a few months' work1 forms on the surface of closed or open tanks1 and which according to locality and season may reach a thickness of from #a to #b feet2 it is maintained then that this cheap natural cover does away with the expensive artificial cover4 ,in the report on the treatment of the ,manchester sewage1 by ,messrs4 ,baldwin ,latham1 ,percy ,f4 ,frankland and ,w4 ,h4 ,perkin1 it is stated on page #ed1 amongst the conclusions and recommendations1 as follows3--8,the anaerobic or septic process is found to take place as effectively in an open tank as in a closed one40 ,this conclusion does not appear to have been modified by the experiments made subsequent to the issue of this report4 ,in the ,leeds experiment a similar result was obtained4 ,sidenote3 ,closed septic tanks possess generally speaking no advantages over open ones4 ,whilst it would1 therefore1 appear to be correct to say1 generally1 that closed septic tanks afford no material advantages over open ones1 so far as the purification of the sewage is concerned1 they may become necessary in special cases1 when the smells emanating from open ones might create nuisances in crowded neighbourhoods4 ,the following remarks refer1 therefore1 equally to open as well as to closed septic tanks1 and no distinction will be made between them4 ,sidenote3 ,the work in the septic tank is chiefly done by obligatory anaerobes4 7c7 ,explanation of ,process4--,although the processes taking place in septic tanks are at present but imperfectly understood1 they may be said to be in the main due to anaerobic micro-organisms1 i4e4 due to such micro-organisms which carry on their life's work in the absence of oxygen4 ,they split up or peptonise the organic compounds in the absence of air1 and the group of changes brought about by them has been termed 8anaerobic fermentation0 or 8putrefaction40 ,during the same1 it is claimed that a considerable amount of the sludge retained in the tank is liquefied or destroyed1 and that the rest becomes so changed as to be denser than ordinary sludge1 and to contain less moisture4 ,sidenote3 ,dissolved matters entering and leaving the septic tank4 ,concerning the amount and nature of the dissolved matters entering and leaving an open septic tank1 the following is taken from the ,manchester report for the year ending ,march #bg1 #aija3-- ,sidenote3 ,manchester observations4 8,a series of determinations have been made of the amount of dissolved matter entering and leaving the tank1 by evaporating known volumes of the sewage and effluent after filtration through paper and weighing the solid residue4 8,an average of six determinations 7confirmed by similar observations in connection with the closed septic tank7 gave the following results3-- ---------------------------------------- -------------------------- ,raw ,sewage4 ,open ,septic ,tank ,effluent4 ,dissolved matter1 grains ,dissolved matter1 grains per gallon4 per gallon4 ---------------------------------------- ----------------------- ,organic and ,organic and ,mineral4 ,volatile4 ,total4 ,mineral4 ,volatile4 ,total4 ---------------------------------------- ---------------------- #ccj #ccj #ffj #cjh #bej #eeh ,reduction1 in per cent4 #ffg #bdbd #aede ---------------------------------------- ---------------------- 8,a certain amount of loss of ammonia1 as ammonium carbonate1 will take place on evaporation in both cases1 and this will probably be greater with septic tank effluent4 8,an examination of the residue obtained by evaporating large quantities of open septic tank effluent 7filtered through paper71 shows that the mineral matters largely consist of iron oxide1 from the decomposition of organic compounds of iron1 and calcium sulphate4 ,among the volatile constituents have been detected ammonium carbonate1 mercaptan-like compounds of very offensive smell1 acetic and butyric acids4 ,no evidence of the presence of amines could be found in the residue on evaporation1 but by distilling large volumes of the liquid and carefully analysing the platinum salts obtained from the distillate1 the presence of amines is indicated4 8,research in this direction is being continued2 careful comparison especially will be made of the products obtained by evaporation and distillation of crude sewage and septic tank effluent respectively4 8,the evidence1 however1 points to a breaking down of albuminoid and cellulose matter in the septic tank into simpler and to some extent volatile compounds4 ,the reactions are probably hydrolytic in character1 ammonia1 amines1 carbonic acid1 water1 and possibly alcohol1 being produced4 8,a further quantity of organic matter also disappears as methane1 nitrogen and hydrogen40 ,sidenote3 ,must aerobic fermentation in all cases be preceded by anaerobic fermentation8 ,it will be clear from the foregoing1 that the changes going on in a septic tank are entirely different from those brought about in contact beds1 and the question whether a septic tank is a necessity for the subsequent contact bed treatment1 or whether it is a distinct disadvantage1 can only be definitely settled when we know whether aerobic fermentation1 i4e4 decomposition1 must in all cases be preceded by anaerobic fermentation1 i4e4 putrefaction1 and to what extent1 or whether such a succession of changes is not necessary4 ,sidenote3 ,at ,manchester contact beds accustomed to septic tank effluent did not at once purify raw sewage4 ,it is interesting to note in connection with this point1 that during the ,manchester experiments it was established that contact beds1 which have become accustomed to septic tank effluent1 will not at once purify comparatively fresh sewage4 7d7 ,velocity of ,flow through ,tank4--,the velocity of flow through the septic tank is of great importance1 as on it depends the size of the installation4 ,it seems to have become a habit to express this velocity by the length of the sojourn of the sewage in the septic tank--for instance1 8the flow of sewage through the tank was such that it would fill it in twenty-four hours02 but as all tanks vary in size1 and as in consequence the distance which has to be traversed by the sewage from the entrance to the exit in twenty-four hours is different in nearly every case1 such a habit is1 to say the very least1 very misleading4 ,it will not be disputed that the deposition of the suspended solids in sewage is dependent on the rate of movement of the liquid1 and that in a quickly moving liquid there will be less deposition than in a very slowly travelling liquid4 ---------------------------------------- -------------------- ,town4 ,length4 ,width4 ,depth4 ,contents4 ---------------------------------------- -------------------- feet4 feet4 ft4 in4 gallons4 ,manchester tanks #cjj #ajj #f #j #a1abe1jjj ,leeds 8 #ajj #fj #g #g #bej1jjj ---------------------------------------- -------------------- ,bearing this in mind it will not be without interest to examine the velocities employed during the ,manchester and ,leeds experiments4 ,the tanks employed in these have the dimensions given in the table on the preceding page4 ,now assuming that each tank is to be filled once in twenty-four hours we obtain the following velocities3 ,manchester 7#cjj #j #ab7_/addj #be per minute4 ,leeds 7#ajj #j #ab7_/addj #jhd per minute4 ,which means that in the ,manchester experiments the velocity would have been three times as large as in ,leeds2 and it is clear that if the sewage of both towns was identical the results1 so far as the retention of the suspended matters in the tanks are concerned1 could not have been identical4 ,as a matter of fact1 considerably greater velocities have been used in the ,manchester experiments1 as will be shown later on4 ,sidenote3 ,rate of flow through septic tanks should not be expressed by the length of sojourn in tank but by some linear measurement in a stated time4 ,it will be clear from this1 that it is most misleading and erroneous to express the rate of flow by the length of the sojourn of the sewage in the tank1 and that the velocity should in each case be expressed by some linear measurement in a stated time--probably inches per minute4 ,the next point to consider is the velocity to be employed in septic tanks2 and here it is not without interest to refer to the various experiments enumerated with their results in the next table4 ,the difference in the results obtained1 so far as the suspended matters are concerned1 is probably due to the different character of the various sewages experimented with2 but so low a velocity as #jeb inch1 as used in the ,exeter experiments1 does not appear to be necessary4 ,in the ,leeds experiments1 it was found that the filling of the tank once in twenty-four hours gave the best results2 and as the velocity then was #jhd inch per second it will be somewhat near the mark to recommend generally a velocity of #a inch per minute4 ,on the assumption that the sewage shall remain twenty-four hours in the tank1 this gives a length of tank of #abj feet1 which is a very suitable one4 ,,septic ,,tank ,,experiments4 ,rate of ,flow and ,deposition of ,suspended ,matters4 ---------------------------------------- ,rate of ,flow4 ----------------------- ,no4 ,name of ,length of ,velocity ,town4 ,sojourn of ,flow of ,sewage per in ,tank4 minute4 --------------------------------------- days4 inches4 #a ,exeter #aj #jeb #b ,manchester #jdd #eeh #c 8 #jef #ddd #d ,leeds #je #afh #e 8 #aj #jhd #f 8 #bj #jdb --------------------------------------- ---------------------------------------- ------------ ,suspended ,matters in ,sewage4 ---------------------------------------- ---- ,no4 ,remaining ,destroyed ,leaving in and ,tank ,total4 ,tank4 ,liquefied in in ,tank4 ,effluents4 ---------------------------------------- --------- per cent4 per cent4 per cent4 #a #ag #ci #dd #ajj #b #da #bb #cg #ajj #c #bc #cc #dd #ajj #d 44 44 44 44 #e average #bh 44 44 say #f 44 44 44 ---------------------------------------- --------- ,sidenote3 ,septic tanks reduce the sludge difficulty to some extent1 but do not altogether remove it4 7e7 ,destruction and ,liquefaction of ,sludge in ,septic ,tanks4--,it was formerly maintained that the employment of a septic tank did away with all sludge difficulties1 and one sees even now advertisements to that effect1 that there is 8no sludge0 with a septic tank2 but experience everywhere does not bear out this contention4 ,on the contrary1 there must be sludge with a septic tank1 and the only question one has to consider is1 to what extent does a septic tank reduce the quantity of sludge8 ,the table above contains the results obtained in the various experiments1 and from these it would appear as if on an average1 with a velocity of #a inch per minute1 #be per cent4 of the total sludge would be destroyed or liquefied in a septic tank4 ,generally speaking1 therefore1 the following figures will be somewhat near the mark1 where the plant is worked systematically and carefully supervised4 ,per cent4 ,suspended matters remaining in tank #ce 8 8 destroyed or liquefied in tank #be 8 8 escaping in effluent #dj --- ,total #ajj ,these figures mean that #ce per cent4 of the total suspended matters will have to be dealt with as sludge1 #be per cent4 will be destroyed or liquefied in the septic tank1 and the remaining #dj per cent4 will be deposited on and in the contact beds4 ,it has already been pointed out that it is claimed that the septic tank sludge is denser and contains less moisture than ordinary sludge1 and that about half of it is mineral matter4 ,as previously stated1 at ,manchester a reduction of about #af per cent4 in the dissolved matter has been observed in the open septic tank4 7f7 ,formation of ,gas in ,septic ,tank4--,it was at one time suggested that the gases formed in septic tanks during anaerobic fermentation might be utilised for lighting or heating purposes1 but anyone well acquainted with the subject will admit that such a use is outside the range of practical possibilities4 ,at ,manchester1 #ajj gallons of sewage evolved in twenty-four hours about a cubic foot of gas1 which on an average contained3 ,per cent4 ,marsh gas1 ,,ch#d #gc ,carbon dioxide1 ,,co#b #f ,hydrogen1 ,h #e ,nitrogen1 ,n 7by difference7 #af --- ,total #ajj ,at this rate #a million gallons of sewage will evolve #aj1jjj cubic feet of gas1 or #jb tons of gas1 in twenty-four hours4 ,sidenote3 ,septic tank effluent more suitable for nitrification4 7g7 ,mixing ,action of ,septic ,tank4--,there is one advantage possessed by a septic tank which cannot be disputed1 and that is the mixing action going on within it4 ,the fresh sewage on its arrival becomes mixed with stale sewage1 and1 owing to the rising of lumps of sludge from the bottom1 and other causes1 the contents of the tank become of a more uniform composition1 which must entail a corresponding advantage for the subsequent contact bed treatment4 ,sidenote3 ,the septic tank effluent is so far as bacterial purity is concerned practically raw sewage4 7h7 ,micro-organisms in ,effluent from ,septic ,tank4--,although the available number of experiments on the micro-organisms contained in the effluent from a septic tank is not large1 yet they support the conclusion which one would form by analogous reasoning1 that so far as the bacterial flora is concerned the effluent is practically raw sewage4 #d4 ,,continuous ,,contact ,,beds4 ,sidenote3 ,continuous contact beds still in an experimental stage4 ,it is necessary to make at this point a few short observations on the artificial self-purification in continuous contact beds4 ,this method of artificial purification has frequently been called 8continuous filtration10 but it will be much better to reserve the term 8filtration0 for the percolation of water through fine material1 such as sand1 and to call the continuous flow of sewage through coarser material continuous contact bed treatment1 as the processes going on during the same are more analogous to those going on in an intermittent contact bed than to those taking place in a waterworks filter4 ,formerly it was attempted to use the same kind of contact bed for continuous treatment as is used for intermittent treatment1 but1 as was to be expected1 the results obtained were so unsatisfactory that the experiments had to be discontinued4 ,now somewhat different forms are utilised1 which are mostly protected by patent rights1 and the mode of distribution has also been altered by the introduction of patent distributors or sprinklers1 which cause the sewage to fall in very thin streams upon the filling material4 ,in the ,manchester experiments1 the proprietary continuous contact bed does not appear to have given satisfactory results4 ,better effluents were obtained at ,leeds1 and at ,york the results obtained are said to have been very good4 ,on the whole1 however1 it is but right to say that the experience gained so far is not sufficient to entitle us to form definite opinions1 and for this reason it will be better to await further results4 ,,vi4 ,,management ,,of ,,plants ,,for ,,the ,,artificial ,,self-,,purification ,,of ,,sewage4 ,sidenote3 ,plants for the artificial self-purification of sewage require very careful handling4 ,it was formerly frequently concluded that neither septic tank nor contact beds required careful superintendence1 but that they could be worked by automatic machinery and left to themselves4 ,it was therefore maintained that the working expenses of plants of this nature would be next to nil4 ,this was1 however1 not ,mr4 ,dibdin's view1 who1 after years of careful study1 came to the conclusion that they were delicate pieces of mechanism which required careful watching4 ,since1 ,mr4 ,dibdin's conclusions have been amply confirmed by all careful experimenters4 ,for instance1 ,mr4 ,fowler1 the chemist in charge of the ,manchester experiments1 observed before the ,royal ,commission on ,sewage ,disposal as follows3 8,it is a delicate operation 7the management of septic tank and contact beds71 which requires careful watching6 ,there is no doubt whatever about that60 7,question #efea47 ,again1 the conditions of successful working of contact beds1 laid down by the same gentleman on page #fd of the ,manchester report for the year ending ,march #bg1 #aija1 are ample proof of this1 and they show very clearly how extremely careful the supervision of such a plant ought to be1 and that in the hands of inexperienced men it will soon come to grief4 ,professor ,percy ,frankland stated in his evidence before the ,royal ,commission1 that in his opinion land required less skilled supervision than contact beds4 7,see ,questions #iicg1 #ajjga-gd47 ,a similar view was expressed by ,mr4 ,h4 ,m4 ,wilson1 the chief inspector of the ,west ,riding of ,yorkshire ,rivers ,board4 7,question #fchj47 ,,vii4 ,,some ,,observations ,,on ,,the ,,deposition ,,of ,,suspended ,,matters ,,in ,,tanks4 ,sidenote3 ,definition of the term 8deposition40 ,the term 8deposition0 shall here be held to mean the precipitation of the suspended matters without chemicals or other artificial means1 i4e4 the unaided subsidence of these matters at such a rate of flow that septic action is not set up within the tanks4 ,the question that is of interest here1 is3 ,which is the most favourable rate of flow of the sewage through the tank1 so far as the deposition of the suspended matters is concerned8 ,to some extent the answer to this question will depend on the special characteristics of the particular sewage under consideration1 but for general purposes the following observations will not be without interest4 ,although of very great importance1 this question does not appear to have received very general consideration1 as the available number of careful experiments is but small4 ,sidenote3 ,tank velocity at ,barking4 ,it appears that the calculated velocity in the channels of the precipitation tanks at ,barking is about #d feet per minute1 and that with this velocity about #gg per cent4 of the suspended matters were deposited in the year #ahid4 ,sidenote3 ,tank velocity at ,manchester4 ,at the ,manchester tanks it is stated that a velocity of #c feet #d inches per minute is employed4 ,sidenote3 ,velocity frequently adopted4 ,a rate of velocity now frequently adopted in this country for new works is #f inches per minute4 ,sidenote3 ,frankfort experiments4 ,in the settling tanks at ,frankfort on the ,main there are deposited about #hd per cent4 of the suspended matters1 with velocities ranging from #i inches to #af inches per minute4 ,sidenote3 ,cassel experiments4 ,with a velocity of #g inches per minute1 it is stated that at the ,cassel sewage works #ig per cent4 of the suspended matters are retained in the tanks4 ,sidenote3 ,hanover experiments4 ,at ,hanover a set of interesting observations has lately been made1 on tanks #bdf feet long1 with a view to ascertaining the most advantageous rate of flow4 ,with a velocity of #idd inches per minute1 #fbg per cent4 of the suspended organic matters were precipitated1 with a velocity of #adag inches per minute #fag per cent4 were deposited1 and with a velocity of #cedc inches per minute #egc per cent42 from which figures it will be clear that there is not much difference in the result on the suspended matters between these velocities4 ,against these results must be placed the results obtained with septic tanks1 where1 as has frequently been stated1 a velocity of #a inch per minute and a sojourn of twenty-four hours in the tank may be expected to lead to a deposition of about #fj per cent4 of the suspended matters4 ,sidenote3 ,reduction of cost4 ,where1 therefore1 a previous septic treatment of the sewage by anaerobes is not necessary1 it is clear that the substitution of ordinary settling tanks for septic tanks will be accompanied by a very considerable reduction of cost4 ,,viii4 ,,concluding ,,remarks4 ,since the foregoing observations were penned1 the ,chairman of the ,royal ,commission on ,sewage ,disposal has delivered a very interesting inaugural address1 in ,august last1 at the ,congress in ,exeter of the ,institute of ,public ,health1 to which attention ought to be drawn at this point4 ,according to ,the ,times he is reported to have stated as follows3 8,he regretted that he could not give some idea of the probable date at which the ,commission would issue its final report and recommendations4 ,they would soon1 he hoped1 be able to publish the results of a prolonged investigation into the treatment of sewage on land2 and their experts were now making elaborate parallel examinations of some of the processes of filtration by artificial means4 ,but he feared that they would ultimately be obliged to bring their proceedings to an arbitrary close2 for1 however much they could learn1 he was quite certain they could never come to a point at which they could say there was nothing more to be learned4 ,the subject was inexhaustible40 ,these very guarded observations are almost in direct contrast with the very positive assurance of some enthusiastic supporters of artificial treatments1 who a year or two ago did not hesitate in proclaiming throughout this country that the panacea for all sewage difficulties had been discovered1 and that the investigations of the ,royal ,commission were a mere matter of form and a foregone conclusion4 ,to all those who did not share these very sanguine expressions of faith1 and who were painfully aware of the great gaps in our knowledge of the processes taking place in sewage purification1 these words of ,lord ,iddesleigh will prove an assurance that the commissioners are not swayed by popular likes and dislikes1 however fascinating they may be1 but that they are earnestly endeavouring1 in an impartial manner1 to throw such light upon this abstruse question as will enable them to arrive at correct conclusions4 ,for a like purpose the foregoing remarks have been written2 and if the facts recorded in the previous pages1 and the opinions expressed therein1 should prove of assistance to anyone in forming correct views1 the labour spent on them will be amply repaid4 ,,postscript4 ,since the foregoing remarks were written1 ,i have been somewhat struck with the views expressed at one or two meetings by some of those who ought to have the full facts of the case at their fingers' ends4 ,there seems to be a considerable vagueness as to the sanitary results to be obtained by either the natural or one of the artificial methods of sewage treatment1 and with a view to making this point quite clear ,i have prepared the following comparative statement 7see next page71 which1 ,i trust1 will show at a glance what one may expect from either system4 ,this statement has not been prepared from experimental installations1 where1 as a rule1 better results are obtained than in actual every-day work2 but it refers to fairly large works dealing from day to day with the whole town's sewage4 ,it has further been assumed1 that the plant both for the natural as well as for the artificial treatment is suitable1 and managed carefully and on intelligent lines4 ,as in all sewage treatments the sanitary results have first to be considered1 ,i have only dealt with them in the statement1 but even if ,i had extended it to economic considerations the result would have been practically the same4 ,from a careful examination of the facts recorded in the statement it follows that with natural treatment we get five distinct advantageous results1 against which we have to place only two on the side of the artificial treatments2 but this means1 that if we wish to bring up the results of these treatments to those obtained by the natural treatment1 we have to supplement them by three further treatments for the extraction of pathogenic germs1 and of the manurial elements1 and for the reduction of the liquid4 ,it is these facts which ought to be carefully considered by all those who wish to study the comparative advantages of these two systems1 or who have to decide on a definite method to be employed in a particular case1 and no step ought to be taken before every one of these five points has been very carefully weighed4 ,generally speaking1 that system will be preferred which confers the greatest number of advantages4 ,,statement4 ,results to be obtained from 7,a7 ,natural ,treatment4 7,b7 ,artificial ,treatment4 #a4 ,removal of suspended #a4 ,removal of suspended matters4 matters4 #b4 ,removal of from #ge to #ie #b4 ,removal of from #ej to #ge per cent4 of the dissolved per cent4 of the dissolved organic matters4 organic matters4 #c4 ,removal of pathogenic #c4 ,nil4 ,effluent bacterially germs4 practically raw sewage4 #d4 ,utilisation of large portion #d4 ,nil4 ,all manurial elements of manurial elements4 escape into the rivers4 #e4 ,great reduction of quantity #e4 ,no appreciable reduction of liquid4 of quantity of liquid4 ,,london3 ,,printed ,,by ,,william ,,clowes ,,and ,,sons1 ,,limited1 ,,great ,,windmill ,,street1 ,w41 ,,and ,,duke ,,street1 ,,stamford ,,street1 ,s4,e4 ,transcriber's ,note3 ,words and phrases in italics are surrounded by underscores1 like this4 ,chemicals are displayed with the numbers surrounded by braces1 e4g4 ,,co#b4 ,footnotes were numbered sequentially and moved to the end of the section in which the related anchors appear4 ,wide tables were split for easier viewing on small screens4 ,an unprinted letter 8,s0 was added to sidenote1 8,springs40 ,obsolete and alternate spellings were not changed4