REESE LIBRARY OF THE UNIVERSITY OF CALIFORNIA. APR 21 1893 Accessions No, -S~ ^^- z -/ . C/j$s Nn. SEWAGE TREATMENT, PURIFICATION, AND UTILIZATION. THE SPECIALISTS' SERIES. Crown 8vo, } cloth, With many Illustrations, Magneto and Dynamo-Electric Machines. By W. B. ESSON. 7s. 6d. Gas Engines. By W. MACGREGOR. 8s. 6d. Ballooning. By G. MAY. 2s. 6d. Electric Transmission of Energy. By G. KAPP. 7s. 6d. Arc and Glow Lamps. By J. MAIER. 75. 6d. On the Conversion of Heat into Work. By WM. ANDERSON. 6s. Sewage : Treatment, Purification and Utilisation. By J. W. SLATER. 6s. In Preparation, The Telephone and its Practical Applications. By W. H. PREECE, F.R.S., and J. MAIER, Ph. D. (Ready shortly.) Galvanic Batteries. By Professor GEORGE FORBES, M.A., F.R.S. Induction Coils. By Professor A. J. FLEMING, M.A., D.Sc. Manures. By Dr. A. B. GRIFFITHS, F.R.S. Ed., F.C.S., Principal and Lecturer on Chemistry in the School of Science, Lincoln. Hydraulic Motors. By GEORGE R. BODMER, Assoc. M. Inst. C.E. (Others to follow.) SEWAGE TREATMENT, PURIFICATION, AND UTILIZATION. A PRACTICAL MANUAL FOR THE USE OF CORPORATIONS, LOCAL BOARDS, MEDICAL OFFICERS OF HEALTH, INSPECTORS OF NUISANCES, CHEMISTS, MANUFACTURERS, RIPARIAN OWNERS, ENGINEERS AND RATEPAYERS. BY J. W. SLATER, F.E.S. LATE EDITOR OF "JOURNAL OF SCIENCE." AUTHOR OF " MANUAL OF COLOURS AND DYE WARES." Of THE UNIVERSITY OF LONDON: WHITTAKER & CO., PATERNOSTER SQUARE. GEORGE BELL & SONS, YORK STREET, COVENT GARDEN. 1888. (The right of 2'ranslation is reterved.) A' PREFACE. THE importance of the Sewage question may, perhaps, be fairly gauged by the number of patents of which it has been the subject, and its still unsettled state may be concluded from their varied and contradictory character. Freezing and heating, concentration and dilution, electrisation and magnetising, the addition of oxidisers and deoxidisers, of ferments and preventives of fermenta- tion recommended, if not actually tried, show the want of any distinct and generally recognised principle. I have, therefore, thought it my duty to lay before the public in plain language and in a concise form the result of my experience in treating sewage and waste waters. That experience dates back to the year 1868, and except in 1870 my attention has during the whole of that time been almost exclusively directed to this question. I have worked with sewage in every quantity, from a few ounces in a beaker or a hydrometer-jar to a daily flow of ten million gallons. I have had oppor- tunities for examining almost every known process, irrigation, filtration, aeration as well as precipitation in its many variations. I have studied sewage in droughts and in storms, in hot weather and in cold, by day and by vi PREFACE. night, in residential towns and in industrial centres. My conclusion is that there is no one process universally applicable. Unfortunately there is no subject, outside the range of party politics, on which so much envy, hatred, malice, and all uncharitableness prevail as on the treatment of sewage. But I ask people to judge by the evidence of their own senses. Do not read about this or that process, but go and look. I know instances where bitter enemies of chemical processes have been convinced of their error by just one unexpected and unprepared for visit of inspection. A few supplementary remarks and explanations are needful : The list of patents is not by any means as complete as the author could have wished. Under the existing state of the Patent law nearly twelve months may elapse from the date of application to that of the acceptation of the complete specification, and more time elapses before such " complete " is printed and is to be found in its place in the Patent Office Library. In the meantime no one can tell whether a patent has been abandoned or not. The difficulty is increased by the circumstance that provisional specifications, if not proceeded with, are now not printed, as heretofore. This renders it difficult to obtain a correct list of the patents for any given year until about eighteen months have elapsed from its termination. When opposite the number of a patent there appear the words " not published," or a blank space, the reader will understand that the " complete " was not to be found at the dates when the author made his searches. The specification M.L.G.G, Daudinart (A.D. 1886), PREFACE. vii No. 4,203, was misunderstood. The zinc precipitate is not applied as a manure. It should be noted that, if we may judge from the local papers, the process adopted at Hendon (p. 91) gives but a very limited degree of satisfaction to the ratepayers. As regards " germs " or morbific ferments, it is now generally held that these tiny organisms when introduced into the system are not the direct causes of disease and death, but that they generate within the body they invade certain most intense poisons, which do the deadly work. Practically speaking this is not a matter of importance. If we can prevent the entrance of these "germs" into our system, or if we can destroy them after entering, they can have no opportunity to develop poisons. Here comes up another point: In addition to the disease-germs, "pathogenic organisms," as they are technically called, there exist in sewage and in other waters germs of a very different class. These latter it would seem, according to the researches of Dr. Dupre, play a very important part in the purification of waters. If, therefore, we remove all germs, whether by filtration, precipitation, disinfection, or any other process, we may in some cases do more harm than good. Can we, therefore, devise some discriminating means which shall destroy the evil germs and leave the useful ones untouched ? If we can do this we may hope to render sewage potable. Here, then, is scope for the inventor. The action of electric currents upon polluted waters remains to be studied. Laboratory experiments hold out hopes, but on the large scale they may prove too costly. viii PREFACE. The shape, size, and general construction of tanks, (p. in) likewise require further study. I may here record my conviction that, wherever practicable, intermittent working is preferable to continuous treat- ment. The sewage is better dealt with at a less outlay for power, chemicals, and labour. There is surely room and need for that fair co- operation of experts which Dr. DupnS asks for, as quoted on p. 267. Journal of Science Office, Ludgate Hill, B.C. CONTENTS. INTRODUCTION. CHAPTER I. Nature and Composition of Sewage Sewage of Residential Towns of Manufacturing Towns Day and Night Sewage- Sunday Sewage Water Supply Single or Double Sewer- age Pages i6 CHAPTER II. How, When and Where is Sewage Injurious Definition of " Nuisance " Microbia in Sewage Sewage Detrimental to Fish Organic Nitrogen in Sewage Urea, Ammonia, Nitrogen Acids Phosphoric Acid Potash, Common Salt Putrescent Vegetable Matter Sulphur Compounds " Hardness " of Sewage its Temperature Sewer Ventilators Matters Hurt- ful to Fish Hurtful to Plants 924 CHAPTER III. Disposal and Treatment of Sewage The Cesspool The Dry Closet Pneumatic Systems . ... 24 30 CHAPTER IV. Water-carriage in General First use of Water-closet Sewer Gas Dangers of Escape into Houses Proposals for dealing with Sewer Gas by P. Spence and W. A. Gibbs The Dust Bin ... . 30 37 x CONTENTS. CHAPTER V. The Bazalgette System a Failure in London . Pages 3743 CHAPTER VI. Irrigation, its Principle and Conditions Quality of Soil and Climate Italian Rye-Grass convertible into Hay Irrigation at Gennevilliers Soil Water-proofed Manurial Matter in Sewage only Partially Utilised Irrigation does not remove " Germs" Encourages Flies Flies convey Disease-GermsExperiments of Mr. Smee, Jun. 43 67 CHAPTER VII. Modifications of Irrigation Settling-pits Introduction of Disinfectants Irrigation as Supplement to Precipi- tation 67 71 CHAPTER VIII. Filtration Structure of Filter-beds Filtering-materials Spongy Iron Professor H. Robinson's Process Intermittent Down- wards Filtration 71 82 CHAPTER IX. Precipitation " Clarify and Purify " Occlusion or Absorption Organic matters eliminated by Chemical Processes Properties required for Precipitants Lead Condemned Iron Alkaline Effluents Lime condemned Sulphates not Desirable Gypsum condemned Sulphates, Hypochlorites, Salts of Barium condemned Useless Agents Phosphate Pro- cesses Salts of Aluminium Alum not Suitable Sodium Aluminate Salts of Manganese Salts of Zinc and Copper Absorbents, Fatty Clays, Coke, Peat, Charcoals, Gelatinous Silica Joint action of Precipitants and Absorbents Inverse Irrigation Intermittent or Continuous Working Treatment of Sewage Sludge Knostropp Works Clean Tanks Supple- mentary Filtration General Arrangements of Works Bogus Patents and Bogus Working 83113 CONTENTS. xi CHAPTER X. D eodorising Chloride of Lime Manganates Aeration of Effluents and of Sewage Gases patented for Treatment of Sewage Pages 118124 CHAPTER XI. Destruction The Scott Process Sewage Cement . 124126 CHAPTER XII. Promiscuous Methods Distillation Freezing Elec- tricity 127133 CHAPTER XIII. Self-Purification Cellular Chemical Treatment Rivers Self- purifying The Vesle, the Calder and Hebble Navigation The Passaic, the Oder, the Seine 134142 CHAPTER XIV. ]/ Detection of Sewage Pollution in Rivers -Watercress in Polluted Waters Experiments Sewage Fungus Professor Koch on Microbia in Water Dr. Link on the Microscopic examination of Water Pollution of Wells The "Recommendations" Their Shortcomings Rational Scale . . . 143 163 CHAPTER XV. Recognition of Purification in Sewage Tanks Underground Pollution Sampling ... . 164 171 CHAPTER XVI. Precipitation Mud, methods of Drying Stanks Filter Presses- Press Liquor Drying Cylinders .... 178187 CHAPTER XVII. Sewage Manures Errors regarding .... 172 178 xii CONTENTS. CHAPTER XVIII. Sewage Legislation The Act of 1876 Its Defects Proposed Measure of 1885 Pages 186190 CHAPTER XIX. Sewage Patents 191256 CHAPTER XX. Discussion on Dr. Tidy's Paper, read before the Society of Arts May 5th, 1886 . 257267 SEWAGE TREATMENT, PURIFICATION, AND UTILISATION. CHAPTER I. NATURE AND COMPOSITION OF SEWAGE. STRANGE to say, even professed sanitarians, municipal authorities, and the like not to speak of educated and intelligent people in general have often very vague notions concerning the nature of sewage. They know that it is nasty, and that it contains sundry matters unsightly and offensive. But they are little aware of its complexity, and of its liability to vary according to the locality, the season, the weather, and even the hour of the day. Were these points better understood many futile processes for sewage treatment would never have been proposed ; or, if proposed, would never have been entertained. We will take, first, the simplest case, that of a " resi- dential " town. By this term sanitarians mean a town where few, if any, manufacturing operations are carried B 2 SEWAGE TREATMENT. on, and where the liquid refuse is mainly of domestic origin. As examples, we may mention Oxford, Win- chester, Bury St. Edmunds, Keswick, Leamington, and Aylesbury. The sewage of such towns is generally of a concentrated character, and the matters which it holds in solution are, for the most part, of an organic and readily putrescible nature. It contains the solid and liquid excre- tions of the inhabitants, the urine of horses and cattle discharged in the streets, the drainage of stables and piggeries, the blood (more or less) of cattle slaughtered in the town, and the washings of the slaughter-houses. Another important constituent is the water which has served for washing the persons of the inhabitants, their clothing, and their cooking utensils, etc. These " slops," as they are called, are very offensive ; they hold in suspen- sion and solution soap, fatty acids, the juices of meat and vegetables, and the exudations from the human skin. Almost every one must have observed that if a bowl of suds from " washing-day " has been allowed to stand, it gives off in the course of a few hours a most unpleasant odour. There are also certain organic substances not offensive nor readily capable of putrefaction, out which, nevertheless, play a most important part as far as the treatment of sewage is concerned. Thus a very large quantity of waste paper finds its way into the sewers, and is there subdivided into particles, which quite escape the notice of an inexperienced observer. To these are added fine filaments derived from washing linen and cotton articles, and, to a less extent, from woollens. I say to a less extent, not because woollens when washed give off a smaller quantity of fibre, but because the total amount of woollens washed in a residential town is much smaller than that of cotton and linen fabrics. These NATURE AND COMPOSITION OP SEWAGE. 3 filaments of textile materials and of paper are scarcely perceptible on a hasty examination. A glass of sewage held up to the light, if not rendered turbid by suspended clay, road-silt, etc., appears almost as limpid as ordinary river or pond water. But if we try to filter it through the filter-paper used by chemists, we find that the flow, though tolerably rapid at first, quickly slackens, and soon comes practically to an end. If the liquid is then poured carefully away from the filter-paper, and if a small portion of the latter is examined with the microscope, it will be found coated with the above mentioned fila- ments of textile matters, which effectually choke up its pores. If we attempt to filter unprepared sewage through coke, gravel, sand, peat, asbestos, or ordinary arable soil, we encounter the same difficulty, the rapid flow observed at first becoming sooner or later obstructed. Hence, as I shall endeavour to explain more fully below, filtration is not practically successful even for freeing sewage from its suspended impurities. There is another constituent of sewage harmless in itself, but which seriously interferes with most processes of treatment. I mean the sand, gravel, and pulverized stone which are washed into the sewers by every heavy shower, to the greatest extent in towns, where the streets are "metalled" or macadamized. We shall show else- where how this silt, by keeping bad company, acquires offensive properties. Its inconvenience in the various forms of sewage treatment will be duly noticed. In a manufacturing town or district the sewage is of a much more complicated character, and is more un- sightly, though not necessarily more dangerous to public health often, indeed, less so. Its purification is some- times easier than that of the sewage of residential towns. 4 SEWAGE TREATMENT. The pollution reaches its greatest height in places where the textile, tinctorial, and chemical arts are carried on. Here we find in the sewage, in addition to the normal excrementitious matters, sulphuric, hydrochloric, and nitric acids ; alkalies, soap-lyes, solutions of iron, zinc, tin, alum, copper, chrome, antimony, and arsenic ; waste dye liquors, spent dye wares, glue, sizes, dressings, waste tan solutions, etc. It must not be supposed that all these substances will be found in the sewage of a manufactur- ing town at one and the same moment. Many of them, indeed, neutralise and precipitate each other a circum- stance on which is founded a simple process for dealing with liquid industrial refuse. But if we watch the flow of such sewage, we shall find striking changes both in its colour and its odour, according to the kind of waste just emitted from one or other manufacturing establish- ment. I have repeatedly seen some agent proposed for sewage purification fulfill all requirements for several hours in succession, but on the sudden discharge of a new kind of impurity into the sewage it has been found not merely useless, but injurious., actually intensifying the evil. The sewage of such towns, though containing a larger proportion of solid matter, both suspended and dissolved, than that of a residential town, is of far lower agricul- tural value a point to be had in remembrance in select- ing a method for its purification. Some of its possible ingredients, indeed, such as salts of zinc, proto-salts of iron (ferrous salts), are not merely useless, but positively injurious to the land. The sewage of districts engaged in the metallurgical arts, the manufacture of hardware, etc., contains little extra organic impurity. On the other hand, it often ATURE AND COMPOSITION OF SEWAGE. 5 holds in solution iron in considerable amount, derived, e.g.) from " pickling " iron wire. Copper and tin are rarely present, the value of their solutions being a guarantee that they will not be knowingly or wilfully run into the sewer. But certain salts of iron, as ferrous chloride, formerly known as muriate of iron, produced whenever metallic iron is scoured or cleaned from rust by means of hydrochloric acid (muriatic acid, spirit of salt), are abundant in certain kinds of sewage, and are not merely hurtful to crops for the time being, but permanently deteriorate the soil. The sketch of the sewage of manufacturing towns just given is, of course, very general. Each such town, in fact, turns out a special type of sewage, the nature, effects, and treatment of which can be understood only after careful observation and experiment. In all towns there is generally a well-marked diffe- rence between the day and the night sewage. In a residential town the sewage, from midnight till five or six in the morning, is very much reduced in strength, as well as in quantity. Often it consists of little more than the surface-water from the streets and roofs, and of the ground springs, which find their way into the sewers to a- considerable extent. As the day advances the flow of sewage becomes more copious and more offen- sive, and is at its worst from two to eight p.m. In manufacturing towns the difference between the day and the night sewage is often less marked, since certain kinds of waste waters are discharged in the night, if requisite, and refuse which should not rightfully be run into the sewers at all, is often introduced when there is least chance of detection. Hence it is a serious mistake to imagine that the night sewage may be safely neglected 6 SEWAGE TREATMENT. and be allowed to pass into the rivers unwatched and untreated. On Sundays, in a residential town > the sewage differs little from its condition during the rest of the week. In manufacturing towns it is on Sundays more purely excremental in its character, the industrial waste waters being in great part absent. The same holds good with respect to public holidays. In small agricultural centres the sewage on market days is perceptibly stronger than on other days, and requires an extra share of attention. The question has often been raised whether there is any marked difference between the sewage of a " closetted " town and one where a proportion, larger or smaller, of the inhabitants make use of the old- fashioned cesspools or of dry closets and kindred appliances. Certain authorities, on the faith of their analyses, have maintained that there is little or no diffe- rence in the strength of the sewage. Careful considera- tion will show that this is scarcely possible. It may be at once admitted that the liquid excretions of man, and of all analogous animals, contain a larger proportion of nitrogenous matter than do the solid excreta But in a closetted town the whole of the excrements of the popu- lation, liquid and solid, find their way into the sewers. In an unclosetted town, not merely the solid, but the great bulk of the liquid excretions are discharged into the cesspools and dry closets. Very frequently also, in small, straggling towns, public urinals, if they exist at all, are not connected with the sewers. Thus the water running in the latter consists, to a great extent, of soap-suds, the washings of pots and pans, and, in short, what is technically known as " slops." I do not see therefore, how it is possible, all " dilution " notwithstand- NATURE AND COMPOSITION OF SEWAGE. 7. ing, for the sewage of an unclosetted town to contain the same matters as those of a closetted town. A very important consideration is the water supply, known and unknown. By the " known " supply is meant the average quantity per head of the population served out from the water-works. By the " unknown " is meant the quantity which leaks into the sewers from other sources, as well as the surface drainage. Where the sewerage system lies in a wet sub-soil, full of ground springs, and where the sewers themselves are not water- tight, the flow of sewage in dry weather may rise to one hundred gallons per head of the population per twenty- four hours ; whilst in towns where the water supply is scanty, and the sewers well made, it may fall as low as twenty gallons. Another capital distinction is the space covered by a town in respect to its population. Where the streets are wide, where there are few persons to a house, and where there are many gardens, paddocks, vacant spots of building ground, etc., the sewage, especially in wet weather, loses many of its distinguishing properties. This brings us to the question of single or double sewerage. It is suggested by certain engineers that the water-closets, the domestic sinks, the public urinals, etc., should discharge their contents into one set of sewers, whilst the surface drainage is carried off by a distinct system. It must be admitted that this double arrange- ment has some striking advantages : the sewage, pro- perly so-called, would be at all times much more nearly alike in strength and quantity, which would facilitate its treatment, whether by irrigation or precipitation ; its value would also be much greater. On the other hand, the expense of double drainage is a very serious con- 8 SEWAGE TREATMENT. sideration. The water from the street gutters, though receiving nothing from the urinals and closets, will be far from clean, and its admission into the rivers, despite the catch-word " the sewage to the land, and the water to the river," will be a very doubtful question. In manu- facturing towns there are waste liquids such as the rinsing waters from dye-works which, if run into the sewage, will much dilute it ; but if allowed to pass into the rivers will greatly spoil their appearance. Lastly, it is sometimes found, even where the common single system prevails, that the sewers require flushing to prevent solid matter from being deposited in parts where the gradient is insufficient. It is reasonable to suppose that this. will be much more frequently the case in a sewer which carries faecal matters only, undiluted with surface water. Here, then, we should get back, occasionally at least, to that dilution of the sewage which was to be avoided by the double system. HOW IS SEWAGE INJURIOUS CHAPTER II. HOW, WHEN, AND WHERE IS SEWAGE INJURIOUS? BEFORE entering upon these questions I may, perhaps, be asked what is here meant by " injury," or " nuisance " ? In my opinion these terms may fairly be taken in a wider sense than it is usually done. Judge McCarter, in try- ing the Newark case of river pollution, ruled that it was not necessary for the offensive matter complained of to be present in actually poisonous quantity in order to constitute a punishable nuisance. " It is sufficient if it render the water offensive or disagreeable to the taste or smell." Whether this decision be sound law I cannot presume to say, but it is assuredly sound common sense. It is not enough to contend that some particular matter poured into the streams, allowed to diffuse itself into the air, or to soak into the ground, does not directly and palpably cause some definite form of disease, or formally prevent the successful carrying on of some trade or calling. If it occasions discomfort to persons living near if it offends their senses of sight or smell the public have surely a full right to complain, and to demand judicial or, if necessary, legislative interference. My definition of " nuisance " is, therefore, wider than that too commonly accepted. I should include under this head any matter, whether solid, liquid, or gaseous, which io SEWAGE TREATMENT. is in itself injurious to health, or which may become so in contact with other substances, whether the latter may be in themselves hurtful or not ; further, any matter which, though not demonstrably poisonous, is offensive to the senses. There are, of course, certain limitations to be kept in view. Solid, non-volatile matter, on private premises, cannot be regarded as a nuisance so long as it can neither contaminate the air, nor be washed into water- courses, nor out on to public roads, or the lands of other persons. Sewage contains, or rather consists of, in a large proportion liquid, or, at least, soluble matters, which, being liable to rapid chemical changes, give off volatile products vapours and gases in abundance. These vapours and gases are highly offensive to the sense of smell, and, if not directly poisonous, as it is still often maintained, they lower the vital tone of persons who habitually breathe air with which they are mixed. The greatest danger of sewage, and of water to which it has been added, is that it generally, if not always, contains minute living beings, bacteria, bacilli, etc., some of which are found to be casually connected with infectious diseases. These tiny organisms, named collectively microbia, or micro-organisms, are liable to increase and multiply in the water of rivers, wells, or pools into which sewage finds its way. Such water is thus ren- dered unfit for consumption by human beings, probably also by cattle. It may occasion sickness and death if used; e.g., for rinsing out milk-pails, washing cooking utensils, not to speak of watering milk. It may be urged, in opposition, that there are places, many of which I know, where the only water available HOW IS SEWAGE INJURIOUS! 11 for domestic consumption is drawn from shallow wells, separated from cesspools only by a few yards of chalk, gravel, or other open, porous subsoil ; yet the general standard of health in the district remains good. To this it must be replied that the residents of such neighbourhoods have, by a process of "natural selection/' become inured to the effects of polluted waters; whilst a stranger coming to live in such localities is often seriously affected. But, above all, the health of a population using polluted waters depends on what is commonly called accident. If a simple case of typhoid fever, dysentery, or cholera, is introduced into such a district, the disease spreads on all sides, and commits sad havoc. Thus persons who drink impure waters hold their health or their lives at the mercy of chance. But the microbia of contaminated waters find their way also into the air, and may be inhaled with it. In every highly polluted river fermentation is constantly going on. If anyone carefully watches the Aire at Leeds, the Kelvin Water at Glasgow, the Irwell, Irk, and Medlock at Manchester, he will see, especially if the day is warm and the barometer low, bubbles rising to 'the surface and bursting. These bubbles contain sewage gas, a mixture of compounds of carbon, hydro- gen, and, to a less extent, of sulphur. In bursting they carry up with them the microbia, or disease germs, above mentioned, which thus become diffused in the air; whether these microbia are also carried up into the air when polluted waters evaporate quietly, without the escape of bubbles, has been disputed, but it may now be regarded as experimentally demonstrated. There are, of course, cases where the volume of the sewage poured into a river may be very trifling com- 12 SEWAGE TREATMENT. pared with that of the river itself. Even London itself could not suffice to pollute the Amazon. But most of the great cities of the modern world discharge their refuse into comparatively small streams. Seeing, then, that sewage is in the wrong place if poured into waters, we have to ask how does it behave on the land ? Better, perhaps, but not quite free from reproach. It is then spread out over a larger surface than when it flows in a sewer or in a river, and it neces- sarily exposes a larger surface to evaporation in any one locality. However porous the soil, and however com- plete the drainage, a quantity of the evil-smelling liquid rises up into the air, carrying with it disease germs, if such be present. It will be found that if water is allowed to flow, however gently, over the surface of dry soil, bubbles are formed and burst. Thus, whenever sewage is turned on to land which has not been kept constantly damp, disease germs will be carried into the air, just as in the case of the bubbles which form on a polluted river. Further, the putrescent matter and the disease germs will be absorbed by two-winged flies (diptera), and distributed over the food and the persons of human beings. Summing up this part of the subject, it may be safely asserted that sewage is harmful and offensive by its odour and its appearance, and especially by its afford- ing a pabulum and breeding ground for disease germs- It is offensive in the water-courses and rivers by rendering the water unfit, not merely for human con- sumption, but for all delicate manufacturing processes. This last point is often overlooked. It may seem a convenience to the manufacturer to discharge his waste waters into the river, but by so doing he renders it of 110 If 7 IS SE WA GE INJURfO US? 13 little use, save as a sewer, to all establishments lower down stream. The sewage even of a residential town, except in very small proportions, unfits a river for the use of bleach, dye, print, or colour works. The question has been raised by a pseudonymous writer in Ashore or Afloat whether sewage is truly detrimental to fish. We must here remember that there are fish, and fish. Not all species are alike in the conditions under which they can flourish, or even subsist. But one point, at least, is analytically proved. The greater the proportion of organic pollution in a stream, the smaller is the percentage of free oxygen held in solution, such oxygen serving to oxidise in other words, to burn up the impurities, and proving insufficient. Again, we know that certain fish e.g., the trout can live only in well aerated, highly oxygenised waters. Putting these two considerations together, we can have little hesitation in pronouncing sewage pollu- tion to be at least one of the causes which have tended to reduce the fish in our rivers. That in many cases, such as the Thames and the Clyde, other causes are at work, especially steam navigation, is highly probable. We have now to consider what are the compounds or principles which make sewage water unfit for domestic purposes drinking, cooking, washing, bathing, etc., and for the use of cattle. Foremost come the compounds of nitrogen. These are of four kinds. There is nitrogen in organic com- bination, spoken of by chemists as " organic nitrogen " or " albumenoid ammonia." It is contained in albumen, gelatine, and, in general, in all the complex liquid or semi-liquid bodies of animal origin. These substances 14 SEWAGE TREATMENT. are introduced into sewage in the shape of blood, urine, pus, mucus, half-digested animal food, as well as by certain vegetable products. All such substances pass very readily into intense putrefaction, and are not only exceedingly offensive, but serve as nutriment for those low forms of animal and vegetable life which have been already mentioned as especially dangerous. The second state is urea, which foims a very large part of the solids held in solution in urine. Urea is not dangerous in itself, and, in contact with a ferment which is never absent in sewage, it is quickly resolved into ammonium carbonate. It may therefore be regarded as a mere transition compound. The third and fourth states in which nitrogen occurs in sewage are as ammonia and as nitric and nitrous acids, the two latter, in combination either with the ammonia or with potash or soda, forming nitrates and nitrites. Ammonia, with its salts, and the nitrates and nitrites, even in the largest proportions in which they are ever met with in sewage, are harmless in themselves, though, like organic nitrogen, they may afford nourishment for microbia. Moreover, these forms organic nitrogen, ammonia, and the nitrates are constantly passing and repassing into each other. Growing fungi, and other plants, convert ammonia and the nitrates into organic compounds of nitrogen. The only way to render any water absolutely incapable of nourishing low forms of life is to keep it free from combined nitrogen in every shape and state. But, with waters exposed to the air, this, in any absolute sense of the words, is impractic- able. Phosphoric acid is another ingredient introduced into HO W IS SE WA GE INJURIO US? 15 water by contamination with the excrements of animals, or with any other decomposing organic matter. It is no absolute proof of the presence of such pollution, since many natural waters, on careful examination, may be found to contain it in very small quantity. It is, in itself, not merely harmless, but doubtless in most cases beneficial. Yet it may be an indirect source of danger by favouring the multiplication of microbia. Much the same may be said of potash. It is note- worthy that the three constituents combined nitrogen, phosphoric acid, and potash which are most valuable on the land, as being necessary to the growth of our food-crops, should be most dangerous in the water as fostering the growth of disease germs. One and the same kind of matter, accordingly as it is in the right or the wrong place, becomes the source of life or death. Common salt (sodium chloride) is more largely present in sewage than in ordinary natural waters. It is, as every one knows, harmless to human life, even in greater proportions than it is ever known to occur in sewage. In water from a pump in London, now dis- used, it has been found to the extent of 60 grains per gallon. But it tells a tale of animal pollution. If in water there is more than I grain of chlorine per gallon (=nearly if grain common salt), we have good primoi facie reason to suspect that sewage, or at least the blood or the urine of animals, must have found its way in quantity into the river or the well. There are, of course, exceptions, where salt springs and beds of saliferous minerals occur in the district, or if aluminium, iron, tin, etc., chlorides have been intro- duced by industrial waste waters. These latter, how- 1 6 SEWAGE TREATMENT. ever, rarely find their way into a stream unaccompanied by sewage in the stricter sense of the term. Waters containing merely putrefying vegetable matter, such as the drainage of rice-fields, may be positively poisonous. Mr. L. d'Aguilar Jackson, C.E., observed, when in Venezuela, that the result of getting wet in some rivers there, without subsequently rubbing dry, is malignant fever. Thus the absence of chlorine (common salt), save in very trifling proportions, may be accepted as proof that a stream is free from animal pollution but not necessarily that it is a safe drinking water. Soluble compounds of sulphur, especially hydrogen sulphide (commonly known as sulphuretted hydrogen), ammonium sulphide, etc., are very generally present in sewage if at all stale, and are a main cause of its evil odour, though not necessarily of its worst effects. We must here note that, though putrefaction is in certain of its phases accompanied by a disgusting smell, we must not venture on the inverse conclusion that the absence of such a smell is any proof of the absence of the products of putrefaction. The sulphur compounds are in great part derived from the solid excrements of men and cattle, who feed largely upon cabbages, turnips, and other cruciferous vegetables, and from water in which such vegetables have been boiled. Sulphuretted hydrogen is also found in abundance when organic matter undergoes decomposition in pre- sence of sulphates, such as gypsum. This reaction, as we may remark in passing, is a reason against the use of gypsum (sulphate of lime, calcium sulphate) in any form in the treatment of sewage. HO IV IS SE WA GE INJURIO US? 1 7 I once met with an instance of gypsum having been added to sewage mud to aid in solidifying it. Sulphu- retted hydrogen was given off in such plenty that the men employed suffered from temporary blindness, a well-known effect of this offensive gas. Volatile compounds of phosphorus (hydrogen phos- phide, phosphuretted hydrogen) have been popularly supposed to be given off by sewage and sewage deposits, I know of no analytical evidence in proof of this notion, and consider it a pure freak of imagination. Marsh gas (light carburetted hydrogen or methane) is found in abundance in stale sewage, as also in sewers with too small a gradient, in ill-managed subsidence tanks, and in accumulations of sewage mud where de- composition is not checked by proper chemical agents. If such deposits are stirred up, and if a light is held over them, the bubbles of gas ignite and burn with a very pale flame. Marsh gas has no especially injurious action on the animal system. Carbonic acid (carbon dinoxide) is another gaseous product of the decomposition of sewage, and is given off mingled with methane. Workmen have been suffocated by this mixture in ill-ventilated sewers and other under- ground passages. A gas invariably present in natural waters, but prac- tically absent in sewage, and found only in exceptionally small proportions in polluted rivers, is free and uncom- bined oxygen. In sewage it is spent or consumed by acting upon the organic pollution. This negative feature of sewage and of impure streams accounts for a part of their injurious action upon the higher aquatic plants and upon animals. As regards "hardness" (i.e., the presence of the salts 18 SEWAGE TREATMENT. of lime and magnesia), sewage differs little from the ordinary water supply of the district. If anything, it will be softer on account of the introduction of soap and washing soda, and of a considerable proportion of rain water. The sewage of a residential town has generally an alkaline reaction ; that of a manufacturing town may be at times slightly acid, owing to various kinds of indus- trial refuse. It will be at once seen, on considering the extreme complexity of sewage and the unstable character of most of its components, that as it flows it must be continually changing its character ; that a sample taken in the heart of a town will differ in its chemical properties and in its physiological action from another sample which has travelled along the sewers for the distance, say, of two miles. These changes are most decisive where, as in certain manufacturing towns, the sewage has a tempera- ture of 60 to 70 Fahr. It is needless to say that organic matters suspended or dissolved in water at such temperatures must undergo very rapid fermenta- tions. Wherever the sewers are open, as at the grids and ventilation holes, clouds of steam rise up, carrying with them a very sickening odour. Here, I may remark, is a serious flaw in the water carriage of excrementitious matters as at present con- ducted. If there are no ventilators the sewage gas is liable, under certain very possible contingencies, to be forced back into the houses, overcoming the traps of the sinks and water-closets. If there are ventilators of the ordinary kind, i.e., gratings or trap-doors along the streets, all the passers-by are forced to inhale the fumes. In some towns, e.g., in many parts of London, HO IV IS SE WA GE INJURIO US ? 1 9 these trap-doors are constructed in the foot ways, and are opened for a certain time daily to reduce the pressure within. At such times it is a common sight to see a small crowd collect round the opening, craning out their necks as if to lose no chance of inhaling the vile fumes. So far I have been speaking of the ingredients of sewage found to be harmful to men or other animals living near them. But, as far as fish and other animals living in the waters are concerned, several other impuri- ties found in sewage and in polluted rivers must not be forgotten. Foremost must come, perhaps, solutions of free chlorine and of the hypochlorites, such as bleaching lime and bleaching soda. When these liquids find their way into a river the fish are destroyed far and wide. The surface of the Medway, at Maidstone, is sometimes covered with their dead bodies to such an extent that an exceedingly offensive smell is given off. H. H. Saare and Schwab (Archiv fur Hygiene, vol. III., part I, page 8 1) have observed that liquids containing 0*04 to 0*005 per cent, are rapidly fatal to tench, while solutions of 0*0008 per cent, are directly deadly to trout. A change into fresh water did not restore fishes after they had fallen on one side. As the lowest limit of this destruc- tive action may be taken a proportion of 0^0005 per cent, of chlorine acting for two and a half hours. The presence of acids increases the action of the chlorine. Of sulphur compounds I have already made some mention. Sodium sulphide (sulphuret) is, like not a few other substances, the more harmful the higher the temperature. Tench could bear for half an hour the proportion of O.I per cent. ; and for two hours twenty- six minutes the proportion of 0*05 per cent. Their natural colour was, to a great extent, removed by the 20 SEWAGE TREATMENT. experiment, and did not return even on prolonged sojourn in pure water. Sulphuretted hydrogen was regarded fatal in proportion of O'Oi and 0*00 1 per cent, and proved deadly also to tench. Lime in its caustic state, whether introduced into the stream as quick-lime, slacked lime, or lime-water, is well known as a fish destroyer, and has for ages been com- monly employed by poachers. Its application in the treatment of sewage is common, and the attendant dangers are too often overlooked even by professed experts. I should advise riparian owners, lessees of fisheries, etc., to protest against its introduction into their waters. One manner in which lime present in waters destroys fish is by entering their gills, and, being there precipitated by the carbonic acid exhaled, it forms deposits of carbonate of lime, which interfere with respiration. Common salt, even in the proportion of 10 per cent, was found harmless at temperatures ranging from 43" to 68 Fahr. Ten per cent, of chloride of calcium (formerly known as muriate of lime, and by no means to be confounded with chloride of lime) is harmless at 43 Fahr., but becomes hurtful, and even deadly, about 68 Fahr. Sulphate of soda, accidentally escaping into a river in unknown quantity, has proved very widely destructive to fish. Ammonia and ammonium carbonate are inactive in any proportion likely to be met with in rivers. Sulphurous acid, especially if accompanied by another acid, is even more deadly than chlorine. But its normal salts are harmless, and salts of lime diminish its injurious action. Hence the introduction of sulphurous acid is less pernicious in hard than in soft waters. Carbonic HO W IS SE WA GE TNJURIO US? 21 acid at o'l per cent, kills in a few minutes, while at 0*075 per cent, it has no permanent action. Hydrochloric, sulphuric, and nitric acids are injurious. The first-mentioned at I per cent, is invariably fatal both to trout and tench. Sulphuric acid at 0*1 per cent, is fatal to trout in two to six hours ; whilst tench are not seriously affected in eighteen hours. From the duration of the resistance against these three acids, Saare and Schwab infer that the higher the molecular weight of an acid, the less rapid is its action. Oxalic acid ato'i per cent, had no action on a trout in thirty minutes. Tannic acid at 0*1 per cent, is harmless even to trout. Soda at I per cent, is fatal to trout on prolonged exposure. Its occurrence in streams to this extent is exceedingly improbable. At 46 degs. Fahr. a tench remained for twenty-two hours without injury in a 5 per cent, solution of man- ganese chloride, and a trout endured a I per cent, solution for five hours. Iron is a specific poison for fishes, both as a ferrous (proto) and a ferric (per or sesqui) salt ; 0*02 to o'Oi of ferric oxide in a solution is injurious. Ammonia and potash-alum have as acute an action as the salts of iron, the limit of endurance falling between o* I and 0*05 per cent. As the poisonous action is said to depend on the proportion of alumina, it is probable that the simple salts of aluminium will be poisonous also. It must here be remembered that the proportion of aluminium and iron compounds used in the treatment of sewage can be, and practically is, much more completely regulated than that of lime. It is very rare to see an excess of a sulphate or chloride of aluminium passing out into a river. 22 SEWAGE TREATMENT. Arsenious acid in the proportion of OT per cent., whether free or combined with soda, is not poisonous to trout and tench. Mercuric chloride (corrosive sublimate) is at once fatal in proportions of 0*1 to 0*05 per cent. Copper sulphate in O'l and i.o per cent, kills trout in a few minutes if they cannot escape into pure water. Potas- sium cyanide, 0*01 and 0*005 per cent, is also deadly. Ammonium sulpho-cyanide and potassium ferro-cyanide have no effect at I per cent. Carbolic acid is poisonous to trout in proportions between o'Oi and 0*005 P er cent. H. H. Saare and Schwab, in summing up their results, declare every substance soluble in water to be more or less injurious to fishes. Proportions which do not induce acute disease will probably be found hurtful on more prolonged action, and will especially interfere with the multiplication of fish. Many of the results of these authors stand in need of verification, and their experiments have not extended to various substances, such as salts of lead, zinc and tin, chromates, etc., which may easily find their way into industrial waste waters, and which have even been recommended for the treatment of sewage. We have next to consider what constituents of sewage,- if any, are hurtful to plants. In the recent sewage of a residential town there is nothing in the least hurtful to any of our cultivated plants, unless it is either supplied in too large a quantity, or that it is too strong. Very few plants can bear repeated waterings with undiluted urine. But in the sewage of manufacturing towns there are abundance of constituents which destroy or injure trees, HO W IS SE WA GE INJURIO US ? 23 crops, etc., and have, further, even a sterilising effect upon the soil. As such may be mentioned waste bleaching liquors, most sulphur compounds, including the waste of the alkali manufacture, sulphuric and hydrochloric acids, solutions of alumina, iron, tin, lead, zinc, chrome, etc. Further, waters containing tannin, gallic acid, starch, glucose, and many coal-tar products. Thus objection must be taken to the waste waters of paper-mills, bleach-, dye-, print-, and chemical works, electro-plating establishments, and works where wire is " pickled," where the manufacture of tin and tern plates is carried on. On the other hand, the waste waters of soaperies, glue arid gelatine works, and some other establishments are not to be feared. It will be at once seen that the useful disposal of waters injurious to vegetation is an exceedingly difficult task, and that some of the best methods are at once excluded. 24 SEWAGE TREATMENT, CHAPTER III. THE DISPOSAL AND TREATMENT OF SEWAGE. IN the primitive condition of mankind population was necessarily scanty, and, above all, it was nowhere con- gested into dense masses. Hence the offensive products necessarily resulting from animal life in whatsoever form occasioned no trouble. Sewage, as we understand it, was not produced, and consequently no question concerning its dangers and its treatment could arise. Both the liquid and the solid excreta were voided on the ground, and, never accumulating in large quantities, they were easily absorbed by the soil, or were in part consumed by certain insects. Even to the present day there are places in England, not to speak of less populous countries, where this system, if I may so call it, still prevails. So long as the population remains thin, and as no epidemic is present, there is no mani- fest harm. Epidemics, indeed, are the rarer and the less formidable in proportion as a country is sparsely peopled. But so soon as it becomes at all numerously or densely inhabited, excrementitious matter ac- cumulates in the neighbourhood of dwellings and is liable to be washed by heavy rains into wells and other waters used for drinking. Hence in times of any common sickness serious consequences may ensue. THE DISPOSAL AND TREATMENT OF SEWAGE. 25 It is interesting to note how, in so ancient a document as the Pentateuch, it was especially enjoined upon the Israelites that excrements should not be left to lie upon the surface of the soil, but should be covered with earth (Deuteronomy xxiii. 13.) This command evidently implies a knowledge of the sanitary efficacy of the soil possibly also of the danger of exposing faecal matter to be washed into the rivers, or to be the pabulum of flies, which then settle upon human beings and their food, and thus propagate disease. The possession of such knowledge at so early a date is a very remarkable circumstance, if we suppose it to be a dictate of Egyptian civilization. The next step, unavoidable as soon as large villages and towns took their rise, was the cess-pool. This was, and often still is, a mere pit in the soil, not in any way rendered water-tight to prevent the contents from soaking into the earth at the bottom or sides. Nor was it generally covered in so as to minimise the escape of offensive odours. In most places the contents were dug or scooped out from time to time, and conveyed into the gardens or the fields. Here, at any rate, was an attempt to restore to the soil what had been taken from it. But this method is open to very serious objections. Unless the cess-pit is made water-tight with masonry or cement, the liquid portions of the excrement its most valuable part soaked into the earth and were lost. Worse than lost, they not uncommonly found, and still find, their way into chinks and crevices in the sub-soil, especially in chalky districts, or drained through porous formations (gravel, etc.) into wells and water- courses. 25 SEWAGE TREATMENT. A further objection is that the emptying such cess- pools is a very loathsome process, and under certain circumstances it may prove highly dangerous both to the workmen employed and to all persons living in the immediate neighbourhood. To lessen this drawback it became, from a very early age, customary to add to the contents of the cess-pits matters which, it was supposed, might to some extent absorb and neutralise the evil odours. Among such substances the ashes of wood, peat, coal, etc., took a prominent place. The cess-pool became also the general receptacle for all the refuse of the household, some of which was far from tending to render it less offensive or less dangerous. Such is the village cess- pool in our days, tolerable only where it is lined with slabs of slate or flag-stones well cemented together, so as to prevent infiltration into the sub-soil. But in many districts, where room was plentiful and where the soil is, as commonly termed, " light," the cess-pools were not emptied periodically, or indeed at all. When full, they were covered in, not by any means in an air-tight manner, whilst a fresh pit was excavated near at hand and brought into use instead. There are towns where this process has been carried on so long and so generally though now put an end to that the entire subsoil is polluted to an unknown depth, and its sanitation becomes scarcely possible. It is, or was until very lately, common to find in castles and other large mansions old cess-pools, the very existence of which had been quite forgotten. I understand that sub- sequent to the death of Prince Albert not a few such abominations were detected in Windsor Castle. The THE DISPOSAL AND TREATMENT OF SEWAGE. 27 same evil was not wanting in dwellings of much less pretentions. It often happens in country places, when a row of old cottages is demolished to make room for some new buildings, the cess-pits are not cleared out, but simply filled up with any kind of available rubbish, and new houses or manufacturing premises are built over the spot, the occupants being in happy ignorance of what lies beneath their feet. To sum up this part of the subject, it may be said that cess-pools are utterly out of the question in towns. They are permissible, nay, sometimes they may be the best expedient, in the case of villages and detached houses in the country. But the following conditions must be observed : 1. The pit must be lined in a water-tight manner with masonry, flag-stones, etc., so that nothing can leak out into the soil. 2. It must be situate so that a clear current of air can play between it and any dwelling or workshop, etc., and it should be covered in from rain. 3. It must be regularly cleared out and the contents dug into the soil not in the immediate neighbourhood of any well or water-course. 4. Garden mould or fine ashes should be added to the faecal matter liberally. 5. At the time of thus emptying out, it is well to add some active disinfectant. The like should be done if any infectious disease occurs among the persons making use of the convenience, or indeed in the neighbourhood. The emptying should, if possible, never be performed in warm, calm, moist weather. Frost, or, in its absence, drying winds afford the best opportunity. We turn now to various improvements on the cess- 28 SEWAGE TREATMENT. pool system. Foremost among these stands the earth- closet or dry-closet, first proposed by Mr. Goux, and since variously modified. Its principle is that a quantity of dry earth, peat-mould, charcoal, etc., is stored up be- hind and above the seat of a closet much resembling that of an ordinary water-closet. After this has been used a handle is pulled, and a quantity of the dry mate- rial just mentioned falls down so as to cover the excreta and prevent the escape of any offensive fumes. Daily or oftener, the box, pail, or other receptacle, is emptied out either by the inmates of the house or by public servants. This system has very great advantages from a sani- tary point of view. There is, with ordinary care, no nuisance, no danger to health, no generation and escape of sewer gas either in-doors or in the streets and roads ; no pollution of rivers, whilst the liquid and solid excre- ments are restored to the soil undiluted, and before they have had time to enter into fermentation. But, on the other hand, there is considerable trouble and expense in preparing the absorbent material, which must be dry, conveying it into the closet, and emptying the pail or receiving-box. This system, too, like the water-closet scheme, fails to make provision for vege- table refuse, and not only so, but for soap-suds and wash- ing waters, which have still to flow into the sewers, and may easily be the carriers of disease germs. In some cases the dry absorbent matter is omitted, and the excrements are received into tubs or cans capable of being closed air-tight after use. This system has been adopted in some small towns, where carts go round daily to receive the full pails and leave empty ones in their stead. It is, of course, essential that these THE DISPOSAL AND TREATMENT OF SEWAGE. 29 vessels, of whatever shape and material, should be thoroughly cleaned when emptied, or the nuisance would be serious. Hence the working cost is consider- able. Thus, though this system has given satisfaction in some small towns, it is out of the question in larger cities, where the distances to be traversed would require the employment of a ruinous number of carts, horses, and men. In another form, there is in each house a fixed recep- tacle into which all excreta are voided, and which is fitted after use with a (supposed) air-tight cover. From the bottom of this receptacle runs a pipe, which passes through the outer wall of the house, and is closed at its end with a plug. In the night, carts go round to each house. The plug is withdrawn, and a pump is attached to the pipe, which draws the contents of the receptacle into the cart. This operation is not unattended with nuisance, and it is practically impossible for the recep- tacle ever to be thoroughly cleansed from putrescent faecal matter. This is, perhaps, the place to mention the system of Liernur who, unlike prophets, finds honour in his native country, if nowhere else. Here, also, there is no water of dilution. The movable pails and the collecting carts are suppressed, and the excreta are aspirated by power- ful pneumatic machinery out of the recipients through a system of pipes. That either the recipient or the in- terior of the pipes can be entirely sucked clean in this manner, even if a perfect vacuum could be instantly created at the outer extremity of the system, is not to be expected or believed. We thus come to the end of the systems which do not call in the aid of water, but which deal with the excreta 30 SEWAGE TREATMENT. of human beings as a whole, not first forming sewage, in the conventional sense of the word, and then striving to extract some of its constituents for useful purposes. All these dry systems, except the primitive cess-pool, require the dust-bin as an accessory. All of them, as I have briefly hinted, fail to provide for household " slops." Still more completely they are out of the question for industrial waste waters, and even for the washings of slaughter-houses, and the drainage of piggeries and stables. Hence in all towns a system of sewage becomes essential, and the notion of disposing of human excreta also in this manner naturally suggests itself. To this we therefore proceed. WATER CARRIAGE IN GENERAL. 31 CHAPTER IV. WATER CARRIAGE IN GENERAL. THE use of rivers, arms of the sea, and canals as the recipients of faecal matter is not of modern origin. Certain antiquarians consider that the water-closet, as we now have it, was known in ancient Rome, and even that the " summer-parlour " of Eglon, King of Moab (Judges iii. 20), w r as a convenience of this kind. But in modern times it has been common, wherever dwelling- houses or factories stood on the brink of a stream, to have out-shot closets jutting over it, so that the faecal matters might fall at once into the water. The margins of the Fleet Ditch, in London, so long as it remained open, are said to have been lined with such arrange- ments. In the East of Germany they existed about the year 1830. In the North of England they were not uncommon twenty years ago, even on the brink of rivers which were nearly dry in summer, thus occasioning a grievous nuisance. I have seen in a Midland district a contrivance, if possible, still more offensive. A row of cottages stood on a high ground, separated by a public road from a brook, or rather, ditch. Each cottage had a kind of cess-pool, from the bottom of which there ran an ill-made drain under the road. Whenever there was a fall of rain part of the contents of these cess-pools were washed through the drains, down the bank, and 32 SEWAGE TREATMENT. into the tiny brook, which was thus converted into an open sewer. In Melbourne, with an average temperature higher by 10 Fahr. than that of London, cess-pools in houses were allowed to overflow into the surface-water gutters at the sides of the streets. The first systematic use of the water-closet and of the water-carriage of faecal matters began with the suppres- sion of cess-pools in London and other large cities. The excreta of the population were thus compulsorily and by authority diverted into the rivers, no attempt at purification being thought of. Before proceeding to describe the various modifications of, and improvements on, this crude and nasty procedure, I must point out certain initial disadvantages which attend water-car- riage, however the sewage matters may be ultimately disposed of. There is, in the first place, a very serious consumption of water, over and above what would otherwise be necessary for domestic purposes. This increase may, perhaps, be roughly taken as 20 per cent. Thus if a residential town without water-closets requires 100,000 gallons of water daily, if these conveniences are generally introduced the daily demand will rise to 120,000 gallons. This increase may easily mean more than an addition of 20 per cent, to the cost of the water- supply. It is recognised on all hands that the water furnished to a town must be good in quality. But such water is not everywhere t be obtained in sufficient quantity within a reasonable distance. It might happen that a source fully adequate for a town in other respects might not leave a sufficient margin for the water carriage of excreta. WATER CARRIAGE IN GENERAL. 33 It may be contended that a second-rate water is quite good enough for working water-closets and flushing sewers. So it is ; but we are then driven to the trouble- some and costly expedient of a double water supply a good quality for drinking, cooking, etc., and an inferior sort for the closets. This would prove a heavy addition to local taxation a sphere where no one thinks of retrenchment. Another disadvantage is the generation of " sewer gas." This term includes all the volatile products gases or vapours arising from excreta in various stages of decomposition. Such sewage gas may or may not be capable of directly occasioning disease. But few very few competent medical authorities will deny that if persistently inhaled it lowers the tone of the con- stitution, and renders the inroads of fevers, etc., more probable. Above all, this same sewage gas is liable to convey disease germs into our dwellings and into our bodies. It is a serious consideration that we have now this gas " laid on," so to speak, in every house. Not only our water-closets, but our bath-rooms and our very sleeping apartments, are placed, potentially at least, in connection with the sewer. If there is a chink in the piping, a defect in the soldering, or if the valves are out of order, this potential connection becomes actual. Hence, in addition to good plumbing at the beginning and careful management and watching afterwards, the water-closet requires precautions in its position. It may be a luxury or a convenience to have water-closets in the interior of a house, separated, perhaps, from the bed rooms merely by ill-fitting doors. It is very agree- able, doubtless, to have the wash-stand in a dressing- room fitted with a fixed basin from which the water can D 34 SEWAGE TREATMENT. be discharged into the sewer by lifting a plug. But this convenience has to be paid for in the shape of risk. The true situation of the water-closet in a house is in an out-shot annex with two windows on opposite sides, so that it may be ventilated not into the house, but into the air outside. It must also be remembered that water forms no ab- solute barrier between the air of the sewer and the air inside the house. Through the water there is a constant, though slow, interchange of gases going on. As for the plugged wash-basins in bed-rooms and dressing-rooms, despite their convenience, they had better be given up. This change, I understand, has been carried out in many of the principal hotels in America. Another drawback on the water carriage system is that the sewers, if not absolutely water-tight which is scarcely possible allow more or less of their contents to ooze out and saturate the surrounding soil, thus grad- ually forming a bed of poisonous matter. This bed alters the character of the "ground -water," which has been so thoroughly investigated by Professor von Petten- kofer, of Munich, and renders it more harmful. The vapours given off from this polluted "ground-water " will escape in the direction of least resistance, and that direction, in the case of streets paved, flagged, and especially asphalted, will be into the cellars or the sunk ground-floors of the adjoining houses. If a momentary digression is permissible, I would add my protest against the custom, all but universal, of carrying the soil-pipes of water-closets under the floor of the house to join the sewer outside in the street. If the connections are imperfect, or have never been made at all as is sometimes the case -ill-health and WATER CARRIAGE IN GENERAL. 35 death will be the lot of the occupiers of the house. A sewer should never be permitted to pass under any human habitation unless there is a clear, open air-way left between the top of such sewer and the foundations of the house. Another point is the ventilation of the sewers an absolute necessity. If we suppose a system of sewerage perfectly air-tight, and having no inlets, save the trapped openings through which the liquids from sinks, water- closets, etc., find entrance, it would very often happen, from the fermentation of the faecal matters, that the pressure inside the sewer would be greater than the pressure of the external atmosphere. In such cases the sewer gas would force its way through the ordinary sink- traps, and escape in bubbles into the houses. To prevent such a grave inconvenience it is usual in most towns to provide the sewers with trap-doors, which, when opened, act as ventilators, and allow the condensed gases, if any, to come to an equilibrium. But these ventilating trap-doors are placed too often in the foot- ways, with the bad results which I have already pointed out. Surely situations might be found for ventilating traps not open to this objection. It will be perceived that the sewer retains its unpleasant character up to the very point where it discharges its contents for treatment. No system of purification adopted at this point can obviate the nuisance arising from every grid on the way. Disin- fectants of various kinds are sometimes poured into the sewers in an intermittent manner, in the hope of preventing the formation of sewer gas. It sometimes happens that conterminous sanitary authorities use substances which are mutually incompatible, one, for 36 SEWAGE TREATMENT. instance, employing chloride of lime or a permanganate, whilst his neighbour is using some de-oxidising agent, such as carbolic acid or an alkaline sulphite. I can here merely refer to two projects for dealing with sewage gases and the sewer ventilation question. The late Peter Spence, of the Pendleton Alum Works, proposed to connect all chimneys, whether of houses or factories, with the sewers, whilst these, again, were made to vent into one huge central stalk, actuated by a mighty furnace. In this manner all the sewage gases would be aspirated into the central chimney, and, being already to some extent disinfected by the smoke and other products of combustion drawn into them, would be finally dealt with in passing through the furnace and discharged in a harmless state from the central chimney. Thus smoke and sewage gas would be done away with at once. Mr. W. A. Gibbs, of Gillwell Park, Essex, proposes a different scheme for towns situate on the banks of tidal rivers. Huge fans, worked by tidal power, would be erected at the outfalls, say at Barking Creek and Crossness. The air in the streets of London would rush into the sewers, removing fog, sewage gas, and all evil vapours. Whether it would be possible by any power applied at the outfalls to create an in-draught into the sewers at the most remote parts of the metropolis, I am not prepared to decide. But I could wish that both of these schemes might have a fair trial in some town, smaller than London, and conveniently situate. Not the smallest of the defects of the water carriage of excreta is that the excessive dilution reduces their agricultural value, and renders any method of treatment that may be adopted less remunerative, if not less easy. Lastly, we must remember that where water carriage WATER CARRIAGE IN GENERAL. 37 is adopted the dust-bin is indispensable. The solid refuse, household ashes, the bones, skins and shells of fish, the parings and stalks of fruit and vegetables, etc., cannot be passed down the soil-pipe, and hence they find a temporary home in the dust-bin. This receptacle is supposed to be from time to time cleared out by the servants of the local authority, or by contractors an unpleasant operation, in which smells, offensive, if not positively harmful, are diffused. The nuisance is the greater the longer the refuse is allowed to accumulate. Such time may be somewhat long, especially if the householder is not willing to give the men employed a liberal backsheesh. But the worst evil is the subsequent destination of the matter. It is sold by the contractors to building speculators, who use it for all manner of unsanitary purposes, such as filling up hollows, laying out streets, mixing mortar, etc. I have even seen it employed in mending old-established streets, long since in the hands of the local authorities. The unpleasant smells, and the flocks of blow-flies hovering round, proved but too plainly that the "dust" was utterly unfit to be used in street repairing or in building operations. The contractor is supremely indifferent about complaints inserted in the Press, or addressed to the local sanitary department. He has duly " squared " the surveyor, who will, as in duty bound, " make it all right." But in spite of its shortcomings, and of its needful adjunct the dust-bin, the water carriage system is in all large cities simply Hobson's choice. No one has yet suggested any practicable method by which it might be superseded. Our inventors are too busily employed in devising " aerostats," submarine boats, and other devices for taking human life, to turn their attention in this direction. 38 SEWAGE TREATMENT. CHAPTER V. THE BAZALGETTE SYSTEM. CONCERNING the direct discharge of sewage and other waste waters into rivers, nothing further need be said. It has no advocates, and offers no advantages save a fallacious cheapness. The whole vexed question of river pollution is the outcome of this mistake. The first method that we shall discuss is very simple, very costly, and very unsatisfactory. The original responsibility for this process seems to fall upon F. Lipscombe, who proposed it in a patent, A.D. 1857, No. 2168. E. Strangman (A.D. 1861, No. 1040) obtained a patent for a somewhat similar scheme. It may, however, be conveniently called Bazalgettism, from the distinguished engineer to the Metropolitan Board of Works, who has carried it out on a gigantic scale as a means of disposing of the sewage of London. Its essential principle is discharge either directly into an arm of the sea, or into a tidal river, at the time of ebb. In the latter case, the sewage must be received, in the first place, in large reservoirs or store-tanks, in which it is allowed to accumulate during the flow of the tide, and is let out as soon as the ebb commences. The theory of the process is that before the tide again flows, all the THE BAZALGETTE SYSTEM. 3 9 offensive matter will have passed out at the mouth of the river and have been diffused into the sea. It is manifest that this method is available only in a limited class of places. If a city lies on the banks of a river, so far from the sea that the sewage would not have time to reach its mouth whilst the tide is running out, it is met by the next flood tide and carried back again. Thus the lower part of the river becomes a sink of pollution, intensified by constant recruits of filth. Even on the sea-shore this system cannot be safely applied in the case of land-locked harbours, and narrow deep bays. In few situations is sewage pollution more formidable than in the harbours of Marseilles, Bombay, Rio Janeiro, Bahia, etc. Those of Sydney and Mel- bourne will, doubtless, in due time reach the same undesirable condition. The expense of Bazalgettism is exceedingly serious. The construction of the tanks to store up the sewage whilst the tide is running up involves an outlay which for many communities is simply prohibitive. Such tanks cannot, for obvious reasons, be situate in or very near to the city or town in question. They must lie at a lower level than such city, or the sewage cannot be conveyed into them by gravitation. Yet they must be so high that their contents can be run out to the very bottom at low water. These two conditions will generally be found mutually incompatible. Thus, at the two London sewage outfalls, Barking Creek and Crossness, the sewage is first pumped up into the storage tanks. I have seen a calculation what every stroke of the powerful and ornate machinery effecting this task extracts out of the pockets of the ratepayers. It will be at once seen that this system offers not the 40 SEWAGE TREATMENT. slightest set-off against the expenditure. It is all out- lay, with no returns. Nor is the prevention of nuisance by any means com- plete. I will suppose, for argument's sake, that every drop of the discharged sewage is carried out to sea be- fore it can be forced back by the returning flood tide. Yet the lower part of the river is of necessity polluted to the annoyance and danger of persons navigating it or dwelling near its banks. A portion of the finely divided mineral matter which invariably enters into the sewage of a town, especially where the lamentable custom of macadamising or " metalling " the roads is tolerated, is gradually deposited in the bed of the stream, and must, all assertion to the contrary notwithstanding, take rank as one of the agencies which silt up the channel. Each such particle of sand or clay or ground-stone becomes, by surface attraction, coated with a thin layer of the offensive organic matters present in the sewage. Any one who doubts this may soon be convinced to the contrary if he will take a pound of such sewage silt, dry it, and then heat it strongly, when a powerful faecal odour will be given off. Even in those few localities where the outflow can take place directly into the sea, there is still an opening for mischief. The suspended particles of excrementi- tious matter "hug the shore," just as corks or chips floating in a tub of water make their way by attraction to the side. Among the unpleasant results of this phenomenon I may mention that shrimps feed upon the unclean matter, and are then caught and consumed by men before it can be completely assimilated. It has been lately established that mussels found in the open sea are harmless, but if deposited in harbours they be- THE BAZALGETTE SYSTEM. 41 come poisonous, and lose anew their malignant proper- ties on being taken back to the open. It is exceedingly probable that the poisonous properties developed are due to the consumption of sewage matters. Two of the poisons detected in mussels by Dr. Brieger are ptomaines. Where sewers open into the sea without the inter- position of a storage tank, the case is still worse. When the tide rises and covers the mouth of the drain pipes the sewage gas, holding possibly disease germs in sus- pension, is driven back into the town, and into the very houses, overcoming the traps. In the rare cases where a manufacturing establish- ment is situate on an open coast not a tide-way or harbour its liquid refuse may find vent direct into the sea, if no more useful mode of disposal can be devised. But the admission which we made above, for argu- ment's sake, is found, in the case of London, to be quite incorrect. Sewage matters discharged into the river at Barking and Crossness are not pushed out to sea by the combined action of the ebbing tide and of the cur- rent They mingle with the water, and work their way back to points far above the outfalls, thus effecting that pollution which the intercepting sewers and the costly channels running parallel to the river were to have averted. The Bazalgette process, as applied to London, is a total failure. It involves the utter waste of all the manurial matters in the sewage ; it aids in silting up the bed of the Thames ; it occasions a nuisance much com- plained of by the inhabitants of the country below the outfalls on both banks ; its cost is exceedingly serious ; and it does not even guarantee to the inhabitants of London an unpolluted river. Some persons might 42 SEWAGE TREATMENT. think that all these charges against the system being admitted, the Metropolitan Board of Works would hasten to abandon the scheme altogether, and cry peccavimus with the best grace possible. Whoever should form such an expectation would betray a very imperfect knowledge of the official mind. Instead of renouncing the whole scheme as a failure, they seek its extension. It is proposed to convey the sewage down to Thames Haven in a vaulted culvert, that from the south side of the Thames being carried under the river by a tunnel and then pumped up into the culvert on the northern shore. The cost of this gigantic sewer, twenty miles in length, is estimated by Sir Joseph Bazalgette at 4,000,000. Those who have had some experience in engineering estimates will expect this sum to be largely exceeded should the scheme unfor- tunately be carried into execution. The working cost with which the ratepayers of the metropolis are threat- ened is 3 1 7,000 yearly, in addition to interest on the four millions borrowed and the expense of paying off the loan. At Thames Haven the entire sewage will be dis- charged. We will now examine the probable result of this scheme. The annual charges for dealing with the sewage of London, already quite heavy enough, will be seriously increased. The faecal matters of the sewage will still, as at present, be wasted. The dwellers on the shore near the point of outflow will complain of a nuisance, just as now do their neighbours a little higher up stream. Sewage matters will scarcely find their way, as at present, to points above London Bridge, and the silting up process will be suspended. But, on the other THE BAZALGETTE SYSTEM. 43 hand, the Thames will be deprived of a tribute of 120 million gallons of water which are now poured into it daily, at a time when its level is lowest owing to the ebb. Surely it would be far better to pour this volume of water into the river in a purified condition, which, as we shall see, might be effected more cheaply, and with at least a partial utilisation of the manurial matters contained in the sewage. It is well known on the west coast of Africa and in Mauritius that the contact of polluted land waters with the sea is greatly to be dreaded, as far as public health is concerned. 44 SEWAGE TREATMENT. CHAPTER VI. IRRIGATION. THE second method of sewage treatment is irrigation ; a system which has contrived to secure advocates, many, influential and enthusiastic. Its essential principle is the application of the sewage to cultivated land, under the impression that the excrementitious and other offensive and putrescent matters held in solution or suspension will be absorbed by the soil, and utilised by the growing crops ; whilst the water, sufficiently purified, will pass away into the drains, and may be permitted to enter the rivers without fear of pollution. The action is supposed to be two-fold ; on the one hand, the soil itself has an absorbent power. As the sewage soaks down into the ground, it carries with it air, by which certain of its organic impurities are oxidised and destroyed. That such a purifying process really takes place, whatever its theory, may be proved by the simple experiment of rilling a flower-pot with soil, and pouring a little sewage, etc., upon it. The water which oozes out below will, unless the quantity is too great, be to a very considerable extent deprived of its offensive smell. On the other hand, the growing vegetation is supposed to absorb and assimilate a proportion of the organic matter present, just as it does any other manure. The IRRIGA TION. 45 mere filtering action of the soil is thus reinforced, and the impurities are not merely removed, but turned to account Hence, irrigation is, under favourable circumstances, very efficacious. It requires, however, certain con- ditions, which are not everywhere to be met with in combination. The first essential is, of course, a large plot of land, which should be at some distance from the town supplying the sewage, and should not border upon any populous district. The irrigation farm, as such a plot is called, should also be situate at a lower level than the town, as, if the sewage has to be raised to a higher level by pumping, both the first outlay and the annual working cost are necessarily and heavily increased. Now, as nearly all our inland towns lie on the banks of some river, the only ground to which the sewage can flow by gravitation will generally be found at some point lower down the river valley. But in the more populous parts of England and Scotland the river valleys are generally occupied by a string of towns, villages, and factories. Hence, land in such situations is very valu- able, and to acquire a plot suitable for an irrigation farm, if practicable at all, is, necessarily, a costly undertaking. When such a plot has been found, a further outlay is incurred in laying it out, and in conveying the sewage thither. The latter point may be very serious : the authorities of a town in Lancashire, having conveyed their sewage to a plot of land at a certain distance, were sued for heavy damages by the owner of some subjacent coal deposits, on the plea that the working of such deposits would be interfered with by the sewage channel. 46 SEWAGE TREATMENT. Another consideration is that if the sewage has to be conveyed to some distance before it can be applied to the land, the river of the district must be, for a part of the course at least, robbed of no small share of the waters which it would otherwise receive. This point is the more serious, as many streams in the manufac- turing districts are very low in a dry season. Again, the quality of the soil is no less important than the situation. If it is too open and porous in its texture the sewage passes rapidly through it, and emerges, scarcely, if at all, purified. This is especially the case with shallow, sandy, or gravelly soils over- lying rocks. If, on the other hand, it is too compact and retentive, the water cannot escape readily enough, and the soil is rendered swampy. Perhaps the worst case is when the soil, as is not uncommon in chalky districts, is intersected by cracks or crevices which extend far away underneath the surface. Into these the sewage may pass unpurified, and may thus find its way into wells, water-courses, etc., at a very con- siderable distance, thus leading to unsuspected mis- chief. It must next be remembered that not all kinds of sewage are fit and proper to be applied to cultivated land. If there is a notable proportion of industrial refuse, such as acids, metallic salts, dye and tan liquors, etc., it will injure or even destroy the crops, and may sterilize the land for a considerable time. Another point too often overlooked is that a given plot of land cannot go on for ever deodorising and disinfecting an unlimited supply of putrescent or putrescible organic matter. On referring to the chapter on sewage it will be seen that certain of its constituents IRRIGATION. 47 gradually choke" up any porous material, as was shown by an easy experiment. In addition, the soil, as in the case of an old and crowded graveyard becomes ultimately saturated, and would have to be left unused for a con- siderable time probably many years before it could again become capable of disinfecting putrescent matter. Hence in selecting a plot for an irrigation farm the possibility of extension, if needful, has to be taken into account. I must here point out an erroneous assumption in an official document which appeared a few years ago. In speaking of the various towns which have adopted the irrigation process as a means of disposing of their sewage, and of the sums expended and the rates per pound required for paying off the first outlay and defraying the working expenses, it is invariably added, "the cost of acquiring the land will be paid off in so and so many years, and the rate per pound will then be reduced to such-and-such a figure," or words to that effect. But this flattering prospect is based entirely upon the assumption that a given plot of soil will go on for ever absorbing and disinfecting the excretions of an increasing population. This assumption is so contrary to experience in all analogous cases e.g., that of graveyards that until it shall have been demon- strated by actual observation under the strictest test conditions it cannot for a moment be entertained. The next point is that of climate. In some countries the rain fall is too small, either positively, or in relation to the degree of evaporation from the surface of the ground. Or, if not insufficient, it is intermittent, and falls in torrents after long intervals of drought. In all such climates, especially if their average yearly tern- 48 SEWAGE TREATMENT. perature, or even that during the season when vegetation is active, is high, irrigation is the one thing necessary to convert a desert into a garden. Instances may be seen in Italy, Spain, Algeria, Syria, Persia, India, etc. Hence we often find Indian officers enthusiasts in irrigation. But, on calm consideration, we shall find the climate of England differing from that of the countries above mentioned in almost every essential particular. Our average yearly temperature is only about 49 deg. Fahr., and even this small allowance of heat is made up rather by the usual absence of severe frost in winter, than by solar activity in summer. Our rainfall though abso- lutely small as compared with that of some countries, is large if we take into consideration our low tem- perature, our cloudy skies, and frequent fogs, which intercept the direct rays of the sun, and thus check evaporation. Besides, with us, rain descends not in few and violent gushes, but in a very frequent drizzle. So that, in short, with us, moisture is not the one thing needed for agriculture, but the great enemy of our farmers. In a document which appeared some years ago, under the auspices of the Local Government Board, it was admitted that sewage irrigation is not well adapted to white crops and to potatoes, and that even to the ordinary root crops it must be applied with caution. The fact is that, as was brought into distinct pro- minence by H. Lefeldt, a Prussian engineer sent over by his government to examine and report on the various systems of sewage treatment in use in England, sewage can be (to a certain extent) purified by passing through the soil, and it can also serve as a manure. But IRRIGATION. 49 it cannot, under ordinary conditions, combine these two functions. The farmer could, even in England, often use sewage to advantage if he could have it now and again for a few hours in unusually dry weather. But if the sewage of a town is to be purified in this manner, it must flow upon the land day and night, summer and winter, seed-time and harvest, in wet weather and in dry. Nay, just when rain is most plentiful, and is con- sequently least needed, the sewers pour out an increased volume, which must be admitted upon the land. Hence the interests of the farmer and of the sanitary authority are in full opposition. One plant, and, I believe, only one Italian rye-grass answers the conditions of both parties. Its appetite for moisture seems insatiable. Hitherto its cultivation has been checked by the great practical difficulty of convert- ing it into hay, portable, and capable of being reserved for sale when the market was favourable. At Whitley Manor Farm, near Reading, the rye-grass, the produce of ninety-four acres of land irrigated with sewage, has been successfully converted into hay by means of the " Harvest Saver " of Mr. W. A. Gibbs, of Gillwell Park, Essex. This is a very decided advantage for irrigation, and, where that system is otherwise practicable, may render the treatment of sewage self-supporting, even if not positively remunerative ! As regards other crops, the benefits of irrigation are very doubtful from an agricultural or a horticultural point of view. At the celebrated irrigation farm of Gennevilliers, near Paris, where, by the way, all the circumstances are exceptionally favourable, the produc- tion of vegetables and strawberries is very large. But 50 SEWAGE TREATMENT. there is this important drawback these crops come in late in the season, when the market is already glutted, and fetch in consequence the lowest prices. The object of the farmer and the gardener being to bring forward their produce as early as possible, sewage farming is, at least in cold climates, like that of Britain, placed at a disadvantage. The question may be raised, " Why should irrigation, or the application of liquid manure retard a crop ? " I reply, because it lowers the temperature of the soil and of the stratum of air immediately over the soil. Water cannot evaporate without abstracting a portion of heat from any neighbouring bodies. Irrigation, therefore, chills the soil just as a wet coat chills the wearer, or a damp house the inhabitants. But if irrigation is kept up, day by day, the effect is the same as if the field were altogether removed into a colder climate. Few persons will, I think, admit that the soils of England are likely to be benefited by chilling. The next question must be, What is the influence of continuous irrigation upon the texture and condition of a soil ? Have we improvement or deterioration ? The action exerted is twofold. Suppose a quantity of porous soil or of potting-mould is placed in a flower- pot, filled with every appliance to facilitate drainage, and is then continually drenched with pure water. It will soon be found that the soil loses its open, porous character, and becomes compact and sodden, and any ordinary plants which may have been growing therein begin to show marks of declining health. In a sewage irrigation field the same process, of course, takes place. If, for any reason, the supply of water is interrupted, as, e.g. whilst gathering in the crops, the soil bakes together IRRIGATION. 51 into a hard mass, which is afterwards not easily made permeable to air and water. This result may be very well shown in the flower-pot above-mentioned. If the surface, after receiving for some time a superfluity of water is allowed to go dry, such soil becomes most intractable. But when soil is constantly drenched, not with pure water, but with sewage, the action is complicated. As the reader may find on reference to a former chapter, and as, indeed, his own common sense must tell him, sewage holds in suspension finely-divided fila- ments of paper, cotton, linen, etc. These are gradually deposited in the interstices or tiny channels between the granules of the soil, and fill them up with what may be called a kind of papier machk. In fact, the upper layer of such a soil is water-proofed ; the sewage in con- sequence penetrates into it less and less readily, and begins to stagnate upon the surface in small pools. Sewage, further, contains no small amount of fatty matter derived from soap. This also is deposited upon the soil and helps to render it less easily pervious to water. I have heard, on excellent authority, of an instance of a plot of good, dry meadow-land, perfectly free from any tendency to swampiness, which became part and parcel of an irrigation farm. Everything was done according to the rules of art, to promote drainage, and to prevent stagnation. Nevertheless, within a few years the character of the soil was so changed that it became a haunt of snipe. Surely every naturalist, and every sportsman must see the meaning of this fact Industrial waste waters may become especially in- jurious to the land if they contain large proportions of carbo-hydrates, that is of sugary, starchy, an gummy 52 SEWAGE TREATMENT. matters ; such as the drainage of sugar-works, starch- works, distilleries, breweries, and kindred establishments. Such waters ferment and render the soil " sour." Before irrigating with such liquids, the compounds in question should be eliminated or destroyed. A sewage irrigation farm, therefore, if the soil is not to suffer deterioration, must be ample in size so that each field, after being dosed with sewage for a year, may be disconnected from the pipes, ploughed over, and treated in the ordinary manner of farming for at least the next year, or, perhaps, for the next two or more years, whilst the sewage is made to flow over other plots. By such alternate treatment, the land may be kept from swampiness. But it must be admitted that such a farm would, from its size, be very costly, both to acquire and to lay out, and would compel the urban authorities to become farmers on a very large scale. I come now to the question, In how far does sewage irrigation turn to good account the manunal matters ; in other words, the plant-food contained in the sewage ? The great objection to the old custom of running sewage at haphazard into the streams and rivers, as well as to Sir J. Bazalgette's modification, is the waste in- volved. The available and accessible supplies of phos- phoric acid, potash, and combined nitrogen in the world are by no means infinite. If we go on year by year, and century by century, pouring them into the sea, a time must ultimately come when these essentials, if not ex- hausted, must become scarce. For lack of them the yield of the soil will decrease, and human food must in necessary consequence grow scanty. Hence one of the strongest recommendations of any system of sewage treatment would be that it utilises the whole, or prac- IRR1GA TlOtf. 53 tically the whole of the plant-food present in the sewage. This is the more important, since the very kinds of matter which are the most precious when applied to the soil, are the most dangerous and noisome if allowed to find their way into the water. Now Dr. Maercker (Zeitschrift fur Spiritus Indus- trie, vi., p. 371) has recently been making some careful experiments on the waste waters of starch works. These waters are fully as offensive as town sewage,often, indeed, more so, and contain the very same ma nu rial matters, viz., combined nitrogen, potash, and phosphoric acid. Hence their introduction into the rivers, without due pre- vious purification, is in most countries prohibited by law. One of the ways in which their purification has been attempted is by irrigation, applied chiefly to grass-lands. Dr. Maercker, it appears, found the total flow of waste water from a starch works, and by analysing average samples ascertained its composition. He then, in like manner, analysed the grass of the meadows and found its quantity. From these two sets of figures it appeared that of the total plant-food conveyed to the meadows only 2 per cent, of the potash, 3*2 per cent, of the nitrogen, and of the phosphoric acid only 2*9 per cent, were retained and utilized. The residual majority of these three valuable ingredients was there- fore wasted ! This case may, indeed, be considered exceptional ; but even Dr. Frankland, who is certainly not likely to undervalue the good effects of irrigation or to magnify its shortcomings, admits that of the total combined nitrogen distributed upon an irrigation field in the form of sewage, from one-third to one-half may make its escape in the effluent water, and be lost in the rivers. 54 SEWAGE TREATMENT. But there is a further consideration : Is manuria* matter, when dissolved in a large quantity of water, as is the case with sewage, presented to plants in a favour- able form ? I have already shown that irrigation, by lowering the temperature of the soil, delays the maturity of crops. But we may go further. Mr. E. Manson, C.E., in a work entitled Sewage no Value ; the Sewage Difficulty Exploded (E. and F. R. Spon), makes the fol- lowing admission : " Sewage, like water, retards the ripening of the fruit and grain, and develops the leaf. Sewage cannot supersede manure, for it cakes the ground, seals up its pores, and prevents the air from getting at the roots of the crops. It has been found at all times, and in all climates, that irrigation develops the growth of the leaves at the expense of the fruit or grain." These statements, which are fully in harmony with my own experience, are of the greater weight as coming from one who apparently favours sewage irriga- tion, and is no friend of chemical treatment. Entering now upon the sanitary phase of the subject, we have to ask, Does irrigation render sewage, or water contaminated with sewage, sufficiently pure to be introduced without danger into any ordinary river? Does it, in effecting purification, give rise to any nuisance or injury to persons living near the irrigation plots ? Are the vegetables grown on such irrigation plots fit for human consumption and for the food of animals whose flesh or milk may form a part of our diet? To the first question an answer cannot be given in a couple of words. It may be at once granted that, pro- viding always that an irrigation field is properly laid out, that the soil and subsoil are suitable, and have not be- IRRIGATION. 55 come choked by too prolonged and continuous use, and that the sewage is not swept away into the drains and the streams by floods, the effluent water will, on analysis, show but a very small proportion of organic putrescible matter. In colour, transparency, and odour, it will pro- bably not remind the spectator at all of sewage. But it is now contended, on very good grounds, that the chief danger of the introduction of sewage into streams, wells, etc., lies not in dead organic matter, but in living organised matter. In other words, what we have to keep out of our drinking waters is not so much the decomposing residues of plants and animals and the excretions and secretions of the latter, as those minute living beings known scientifically as bacteria, bacilli, micrococci, etc., and called popularly " disease germs," from the fact that certain of them at least, when introduced into the body of a living animal, have the power of setting up morbid changes which may prove fatal. We have, therefore, to ask whether irrigation or any kind of filtration can be depended upon to remove these disease germs ? The answer must be in the negative. Dr. Percy Frankland, though a friend by right of here- dity of sewage irrigation, made the following honest admission in a paper read before the Society of Arts on March I3th, 1884: "There is absolutely no evidence that morbific matter, if present, would be removed," either by irrigation, or by " downward intermittent filtra- tion," of which in a subsequent chapter. " On the con- trary," he proceeded, " there is very strong reason to believe that these processes of purification offer no sort of guarantee that noxious organised matters present in the wage may not pass through into the effluent. For the 56 SEWAGE TREATMENT. removal of organic matter by means either of irrigation or intermittent filtration depends upon the oxidising action which a porous soil exerts upon such matter, and it is quite analogous to the purification of water percolating through a few feet of soil into shallow wells. Now, the instances on record of the percolation of sewage into shallow wells becoming the means of infection are so numerous and so well authenticated, that it is unneces- sary for me to refer to them here At Stuttgart, in Germany, and Winterthur, in Switzerland, some years ago, epidemics of typhoid fever were proved most con- clusively to have been caused by the contamination of the water supply with the effluent from irrigation meadows," At the same meeting, Dr. Jabez Hogg, F.R.M.S., the distinguished microscopist, cited the well-known case of a stream in Switzerland which soaked through an entire mountain of oolitic rocks, yet, on emerging into another valley, was found to have brought with it the infection of typhoid fever. I have seen flocks of sewage fungus (Beggiatoa alba) in the effluent from a large, well-managed irrigation farm on a deep soil. The spores of this fungus must, therefore, have traversed the soil. In passing, I may here mention that this fungus is not, as many persons suppose, a certain indication of the presence of organic pollution. It flourishes where and only where sulphur is present. It is found in streams, into which fall sulphuretted mineral waters, as in the Pyrenees ; it has been observed in the drainage from heaps of " tank-waste," the residue of the Leblanc alkali process, as well as in sewage, and sewage-polluted waters. Nor is its presence in sewage at all universal IRRIGATION. 57 or apparently connected with the degree of pollution. It is sometimes abundant in the sewage of a town in one season, but in the next it may be almost or altogether absent, though no change can be traced in the character of the sewage. Instances of this have been noted in the sewage of Aylesbury as it arrives at the Sewage Works. Hence the presence, the quantity, or the absence of sewage fungus cannot, as it is popularly supposed, be taken as an index of the greater or less degree of impurity of the water. Returning from this digression, we must conclude that if the living microscopic organisms in sewage are its most dangerous feature, and if irrigation is unable to remove such organisms, then the effluent from irrigation fields cannot safely be allowed to escape into wells or streams which supply water for human consumption. It seems not improbable that the chief mischief of excre- mentitious matters, etc., in water, is that they give scope for the multiplication of the " disease germs " in ques- tion. It has next to be asked : Does irrigation effect its object without occasioning annoyance or injury to the inhabitants of the district ? I have never happened to visit or to pass near an irrigation field in warm, still weather without detecting an unpleasant smell. At Gennevilliers, near Paris, the odour, on calm, autumnal evenings may, without exag- geration, be described as abominable. The Prussian Commissioner, Lefeldt, when visiting Romford, found the smells emitted to be " mephitic in the most fearful sense of the word." Now, if I am right in my concep- tion of what constitutes a nuisance, a loathsome odour, even though no definite disease can be traced in those 58 SEWAGE TREATMENT. who inhale it, is something against which the surround- ing population has the clearest right to protest. As regards the production of actual disease in the neighbourhood, diarrhoea, dysentry, typhoid fever, etc., the evidence is somewhat conflicting. In England, enthusiastic irrigationists maintain that e.g., at Croydon no increase of disease or of mortality in districts bordering on an irrigation farm has been observed. But against such negative instances (which somewhat remind us of the thief who brought witnesses to swear that they had never seen him steal a horse) there is to be placed direct, positive evidence. It is well-known that in India irrigation with ordinary river-water is needful in dry seasons ; it is therefore practised on a very large scale. But, according to Mark- ham, it has been found that the health of the irrigated districts is deteriorated, so that a committee appointed to re-consider the question proposed that a double belt of trees should be interposed between the irrigated fields and any adjacent villages. Now, if irrigation is thus recognized as anti-sanitary in India, where ordinary river-water is employed, and where the fields are flooded or moistened only in time of drought, may we not expect at least as great injury from sewage irrigation in England, where the water applied is seriously polluted, containing sometimes disease germs, and where the fields are to be drenched from January to December? It has been all along contended by sanitary authorities that a river polluted with sewage is productive of ill- health, not merely to persons who drink of it, but to those who inhale air which has swept over it. Be it so : I then ask why a plot of sewage-irrigated land, exposing I R RIG A TION. 59 as great as, or perhaps a greater surface than does the river in any one part, and giving evil odours, distinctly recognisable, should not be equally noisome ? However rapidly the sewage may sink into the earth, a certain portion must escape by evaporation, and must rise into the air before it has had the opportunity to be disin- fected. To meet this difficulty, a clever hypothesis has been devised, the only flaw in which is that it lacks founda- tion. We are told that so long as a sheet of water or a stream, however full of disease germs, remains quiet, these germs will not rise up into the atmosphere. But if, as is usually the case in foul ponds or streams, fer- mentation is going on and bubbles of gas are rising to the surface and bursting, these microscopic organisms are flung upwards into the air and are carried away by the wind. But from the surface of a plot of land, wet with sewage, such bubbles do not arise, and consequently the disease germs present do not escape into the air ! In reply to this supposition, I must remind the reader that if we pour any liquid upon a portion of earth somewhat dry for instance, the soil in a flower-pot we see bubbles arise and force their way through the film of liquid, until all the air existing in the interstices or pores of the soil is completely expelled. These bubbles must, of course, on bursting, project any germs present into the air, just as do the bubbles bursting on the surface of a polluted river. But the assertion that germs are not thrown off from the surface of still water without the action of bubbles is denied on the faith of direct experiment. Portions of liquid containing organisms of known kinds, and not undergoing any fermentation, have been 60 SEWAGE TREATMENT. placed in dishes under glass bells. On standing over- night, organisms of the same kind as those present in the liquids have been found in plenty upon glass plates suspended over the dishes, but under the bells. Hence, in accordance with our present state of knowledge, the action of a polluted river, and of a plot of land, frequently or constantly moistened with sewage, must be very similar substantially alike. I must now invite the reader to make a very easy experiment. If he has a garden, let him select a plot of ground, say a square yard, free from vegetation, and, if possible, of a fairly open texture. Let him then pour over this plot a quart of sewage, or, in default of that liquid, a similar quantity of the mixture of urine and soap-water from the chambermaid's slop- pail. Let him then watch the result. If the weather is at all genial a number of two-winged flies (dipterd) of different species will soon settle upon the wet earth, and may be seen sucking up the moisture. As the first comers fly away they will be succeeded by others, and for some hours the damp plot will be a source of attraction to these unclean insects. A similar plot of ground, moistened with clear water by way of a counter-check, will, on the contrary, have very few visitants. This experiment proves that, its admitted deodorising' and disinfecting powers notwithstanding, earth does not immediately absorb and destroy the offensive matters of sewage. Secondly, we learn that soil thus moistened, and, a fortiori, any sewage irrigation field, is an attraction and an encouragement to flies. Let us take the case of a farm receiving the sewage of a town. All the summer long it will be haunted by numbers of blow-flies, dung-flies, house-flies, gnats, IRRIGATION. 6 1 blood-suckers (Stomoxys calcitrans\ and many others. All these will become saturated with the putrescent matter. If the sewage contains, as it conceivably may, the excretions of a cholera or a typhoid patient, the flies imbibe the " germs " of such diseases. Some of the insects will then enter our houses, and crawl over articles of food. Others settle upon our persons and inflict malignant wounds. Fatal illness has not unfrequently been traced to the bite of flies which feed on sewage or carrion. These flies being now recognised as among the greatest agents for carrying putrid poisons and disease germs to the healthy, it is important that all places where they can increase and multiply, and all matters upon which they may feed, should be made offensive to them or destroyed, as the case may admit. Thus, we bury the dead bodies of birds, beasts, and fishes, which are either uneatable or which have perished from disease, as well as all putrid and putrescible solid matter. We do not, if we are prudent, allow blood especially the blood of animals slaughtered by way of stamping out the cattle-plague to stagnate or to soak into the earth. To collections of excrementitious matters, such as the contents of cess-pools, we add such disinfectants as may make them unfit for the habitation of maggots. We do not throw the dejecta of cholera patients, etc., into the gardens and the fields, but treat them with corrosive sublimate. Thus, in all cases where we have to deal with offensive animal matter, especially such as has been the seat of virulent disease, we withdraw it from the reach of dipterous insects by fire, by chemical agents, or by burial. But if we practice sewage irrigation we spread out excrementitious matter, 62 SEWAGE TREATMENT. possibly containing disease germs, over a large extent of surface, and thus throw it fully open to unclean insects. Lest anyone should think that the views above given are exaggerated, we may refer to a recent communi- cation by Dr. Maddox, in a late number of the Journal of the Royal Microscopical Society. This gentleman has proved that the "comma bacillus," now known to be the agent producing cholera, " can pass in a living state through the digestive organs of flies, which may in this manner become carriers of contagion." Dr, Grassi, of Rovellarca, studied this question two years ago. His experiments point to the conclusion that flies may be regarded as veritable promoters of epidemics, and agents in the propagation of other infectious maladies. To prove this, he placed upon a plate in his laboratory some ova of the Trichocephalus, and in a short time these were removed by the flies, and deposited in another place some little distance away. He caught some of the flies, and found that their digestive tubes were full of feculent matter, and of the ova. He also put segments of the tape-worm (Taenia solium) into water. Some of their eggs remained suspended in the water ; the flies drank of the fluid, and in less than an hour he found the eggs of the tape-worm in their intestines, and in their excrements. Flies, he further found, will also transmit the eggs of the small thread- worm Oxyuris, He likewise fed flies on mildewed cream, and after- wards found within them, Oidium lactis. Other flies fed on the "muscardine" of the silkworm voided spores of that pest in their excretions still capable of development. IK RIGA TION. 63 Hence Grassi inferred that these organisms are not destroyed when swallowed by insects, since the germs of mildews and of Schizomycetes pass through their bodies uninjured. Flies are also certain to carry about with them living organisms on their feet and trunk. M. Daraine shows that by feeding flies with infected blood they can be made to convey infection. Dr. Manson has likewise shown that mosquitoes are carriers of the germs of Filaria sanguinis kominis, and that it is quite possible for the dreaded " Tsetse fly " of Central Africa to transmit infections to the animals which it attacks. After many and varied experiments, Dr. Maddox found that the cholera-bacillus can pass through the intestines of a fly in a living state. Hence, surely anything which encourages flies and supplies them with putrid and frequently diseased nutri- ment ought to be carefully avoided. We now come to the third and last question concern- ing the sanitary value of sewage irrigation : Are the vegetables grown on sewage farms fit for human con- sumption or for the food of cattle ? On this subject very conflicting opinions prevail. I must remark that the question probably turns on a point commonly left quite out of consideration. We know that from time immemorial night-soil, the material from cess-pools, including all the constituents to be found in the sewage of a residential town, has been applied to gardens without the production of any known evil effects. At least, if mischief has arisen it has not been recognised. But such night-soil, as far as I am aware, was either dug into the earth some time 64 SEWAGE TREATMENT before the intended crop was planted or else was trenched in between the rows, say, of potatoes, apple- trees, gooseberry-bushes, etc. It was never applied in a fresh state to strawberries, celery, salad-herbs, and the like. Thus the faecal matter never came in im- mediate contact with the roots of plants, nor was the application repeated in the same season. In farming, night-soil was, and doubtless still is, applied to stubble- fields, to be ploughed in, and scattered over pastures and meadows in the late autumn. But I have observed that cattle turned into such pastures next spring would avoid those parts where the night-soil had been applied, and keep, in preference, to any part which had been dressed with farm-yard manure. Now, as regards sewage irrigation all the circumstances of the case are altered. Excrementitious matters suspended or dis- solved in water are passed into the fields not merely during the absence of crops or between the rows of plants, but, practically speaking, throughout the season and in all parts of the land. Suspended excrement, healthy or diseased, as the case may be, comes in direct and constantly renewed contact with the roots and the stems of grasses and other plants, and no matter how close upon perfection the drainage of the field may have been carried, there it will adhere. Of this any candid person may convince himself by observation in such fields, or even by direct experiment. Let him, for instance, fit up a funnel loosely with a grass root and pour sewage upon it. However well the filter acts, he will soon find . the stems and the roots coated with an adhesive matter, concerning the nature of which no doubt can be entertained. If, then, such grass is cut from time to time, without IRRIGATION. 65 any intermission of irrigation, and is given to cows, the faecal matters in question are conveyed into the stomachs of these animals, and their tissues and their secretions may become poisoned. That disease germs may pass into milk and thus reach fresh victims is an established fact. But we have to do not merely with sewage matters clinging to the outer surfaces of plants. The impurities penetrate also into the interior. Herr Lefeldt, to whom I have already referred, in his report on the various systems of sewage treatment as pursued in this country, notices stems of grass from irrigation meadows, full of unassimilated sewage matters (Kloaken-Stoffe). Were the irrigation suspended for a sufficient time these matters would doubtless be assimilated by the plants, which would then be perfectly harmless. But if the sewage flows on day by day, fresh excrementitious matter is absorbed as fast as perhaps faster than the former doses can be assimilated. Surely such grasses or other plants placed in similar conditions must be of very doubtful value as food, whether for man or beast. I now come to the experiments carried out by Mr. Smee, Jun., and published by him in a work entitled, " Milk in Health and Disease." These experiments and their results have been met, I am compelled to say, with something very like the "conspiracy of silence." Certainly, so far as I can learn, no attempt has been made to prove them inaccurate, or to refute the author's conclusions. Two cows were set aside for experiment. The one, which we may call A, was fed on sewage irrigation grass, and the other, B, on grass from an ordinary meadow. The milk obtained from each cow was kept separate, and examined. It was found that 66 SEWAGE TREATMENT. the milk of A became not merely sour, but it putrefied and stank much sooner than that of B. It was noticed that a favourite cat, exceedingly dainty in its tastes* entirely refused to lap the milk of A. The butter from A's milk became rapidly rancid as compared with butter obtained from cows fed on ordinary pasturage. Cream from the milk of A required, in three successive lots, \\ hour, i^ hour, and 2\ hours to churn, and the butter was soft and smeary. Check samples of cream from cows fed on normal food required only thirty-five minutes, i^ hour, and f hour to churn, and the butter was firm. So far, of course, this experiment is open to the objection that the bad quality of the milk and butter from A was due to some morbid condition in herself, rather than in her food. To meet this doubt, Mr. Smee reversed the experiment, feeding B on sewage grass and A on normal herbage. He also tried other cows. Still the results reached were practically the same, the milk from every cow fed on sewage grass was notably more prone to putrescence than that from cows fed on common meadow grass. Mr. Smee made further experiments on the grass itself. He found that the juice of sewage grass became more quickly and more offensively putrid than that of common grass. Hay made from sewage-grass, if kept in a vessel of water in a warm place, quickly set up a putrid fermentation, whilst hay from ordinary grass, treated in the same manner, behaved quite differently. It will, of course, be granted that the application of sewage to fruits and vegetables which are ordinarily eaten raw, such as celery, lettuce, watercress, radishes, strawberries, etc., requires the greatest degree of caution. In connection with this subject it should be remembered IRRIGA TION. 67 that when it not long ago seemed probable that the cholera might visit Paris, the inhabitants were formally warned by the sanitary authorities against consuming vegetables from the sewage irrigation farm at Genne- villiers ! I should suggest that where sewage irrigation is practiced, it should be suspended for the very least a fortnight before the crop is reaped or gathered. Thus, in case of strawberries, it might be well to shut off the sewage from the appearance of the blossoms until the plants have ceased fruiting. I cannot help expressing my regret that the warm friends of irrigation should have shown so little dis- position to investigate this part of the question more closely. Have they a secret misgiving that the truth, if ascertained, may be of an unpleasant character ? In conclusion, I would submit that irrigation, though an excellent method of disposing of, and at the same time utilising, sewage, where suitable land is available, where the climate is warm, and the rainfall scanty or intermittent, is not applicable where these conditions are absent. Any attempt to represent it as the only means of dealing with the sewage difficulty, and to force it upon reluctant communities, is a grave error in fact a crime, the motives for which are in most cases hard to trace. 68 SEWAGE TREATMENT. CHAPTER VII. MODIFICATIONS OF IRRIGATION. IN the last chapter I have understood irrigation as consisting in the direct application to the land of sewage as it flows from the town without any previous preparation. There are, however, modified processes, some of which obviate more or less completely certain of the inconveniences attending upon irrigation " pure and simple." One of these is the introduction of settling-pits, into which the sewage first flows and collects before being passed upon the land. These pits serve, in the first place, to average the sewage. It has been already shown that the sewage of any town varies considerably both in strength and general characters at different parts of the day and night. By averaging the whole, its treatment, on what system soever, is made more convenient. But the settling-pits have a more important task to perform. I have already mentioned, in passing, as among the ingredients of sewage, grit and silt derived from the streets and roads, and I have pronounced this silt as a formidable difficulty in any and every method of sewage treatment. It is, of course, most abundant after heavy rain, but it is also much affected by the character of the streets. If these are asphalted, paved MOD I PICA TIONS OF I R RIG A TION. 69 with wood, or even with stone, the quantity of such silt is relatively trifling. But where the abomination devised by Macadam prevails, as in all parts of London except the City, its quantity is something frightful. Sewage, if allowed to stand even for a few hours in a settling-pit deposits the greater part of this grit. But unfortunately, each grain, by sojourning in the sewer in company with noisome matter, acquires an organic coating of most offensive odour. Hence such settlings cannot be used in mending roads, in making mortar, or in filling up hollows in the ground. The only legitimate use to which they can be put is the improve- ment of heavy clay soils, and if such are not close at hand their disposal is not easy. On the other hand, if sewage is allowed to flow upon the land without having first deposited its silt and grit, the channels are being continually choked up, and the entire level of the ground will be gradually raised. In filtration and pre- cipitation processes the silt is equally an inconvenience. Hence there is a strong temptation to use settling- pits, even when the disposal of their contents is difficult. Their odour is not pleasant, and has, indeed, been described by a foreign authority as being " mephitic, in the most fearful meaning of the term." Still, this difficulty may be got over by the use of some suitable disinfectant. Another modification of the sewage irrigation process is the introduction of some such disinfectant prior to its being allowed to flow over or through the land. This plan has been adopted at Carlisle, the material used being a combination of carbolic and sulphurous acids. By this expedient certain of the objections to crude irrigation are got rid of. Thus the disagreeable 70 SEWAGE TREATMENT. smell often given off by irrigated land is done away with ; the plague of flies is greatly reduced ; and cattle eat the grass with a better relish. Whether the dairy produce obtained from cows fed on such disinfected sewage grass is equal to that of cows pastured on ordinary grass has not, so far as I can learn, been experimentally tested. It is remarkable that attempts in the disinfection, or at least de-odorizing, of sewage prior to use on land have not been more numerous and more varied. It must be remembered that the choice of disinfectants for this purpose is limited. Some are too costly, some poisonous. The use of carbolic acid is not quite free from objections, as fish in rivers into which it is introduced seem to be rendered more liable to parasitic diseases. Experiments on this subject are needed. I should gladly have undertaken this inquiry, but I have been advised that it would be legally unsafe in England without a licence under the " Vivisection Act " ! Irrigation has been occasionally tried as a supplement to some of the precipitation processes to be discussed in a succeeding chapter. Such a combined method is, or was recently, in operation at Coventry. The notion which underlies such schemes is that of a smaller outlay for chemicals and plant than would be required for a thorough precipitation process ; and, on the other hand, that a smaller plot of land would suffice to receive the sewage. Whether there is any real economy in this double working is, however, at least open to question. Just in proportion as a sewage is purified by precipitation, its manurial value for irrigation will decrease down to that of plain water. A certain chemist, now no longer living, did, indeed, once try to argue that the effluent MODIFICA TIONS OF IRRIGA TION. 71 from a precipitation process which he had pronounced well purified was yet better suited and more valuable for irrigation than the original sewage. This attempt at running with the hare and holding with the hounds met with little approval. Sewage freed by some precipitation process from its suspended impurities will, however, have the advantage of not choking up the pores of the land, and thus rendering it liable to become water-logged and ultimately swampy. 72 SEWAGE TREATMENT. CHAPTER VIII. FILTRATION. FILTRATION differs in principle but little from irrigation. During the winter an irrigation field is, in fact, merely an extensive earth-filter. In summer, the difference is greater, as in the irrigation field the growing plants take a certain share in the work, and absorb a part of the impurities existing in the sewage. The duties of a filter are firstly, to remove me- chanically all matters, organic or inorganic, suspended in the sewage. This work is often known as " clarification.'' Secondly, the water, in descending into the pores of the filter bed, draws along with it a certain quantity of atmospheric air, which oxidises, or, in plain language, burns up the animal or vegetable matter present, converting it into substances which are no longer injurious to health. Thirdly, the process of filtration decomposes a number of organic compounds quite irrespective of any oxidation. Lastly, it is supposed, or at least hoped, to withdraw from the liquid to be filtered any disease germs which may be present. These tasks are performed in very varying degrees, according to the kind of material used, to the time the filter has been kept in action, and to the rate at which it is intended to work. Whatever be the material chosen, there are two different kinds of filtration : downwards and upwards ; or FILTRATION. 73 as they are also named, descending and ascending. In downward filtration, which is by far the most common, the liquid to be purified flows upon the surface of the filter bed, passes down through its mass, and is delivered at the bottom. In upward filtration, which is practicable only under peculiar circumstances, the liquid is forced up through the filter bed, and flows out at the top. Down- ward filtration is not only the simplest and oldest kind of filtration, but it is generally the most efficient. In it only is the liquid purified in the second method above- mentioned, that is, by means of atmospheric air drawn down along with it into the pores of the filter. But to this end it is necessary that there should not be any considerable depth of water standing above the level of the filter bed, as otherwise the aeration cannot fully take place. The upper surface should be kept only just wet, a layer of a quarter inch in depth being quite enough. The manner in which the filter is made up is very important ; if the bed is too thin and irregularly thrown together, the water is apt to force its way through in some few places, and thus to escape unfiltered. In building up the filter, the coarsest materials are spread out at the bottom ; over these are placed, regularly and evenly, layers of finer and finer materials, the finest being near the top. But lest the inrush of the water should disturb this fine upper layer, a few large, flattish stones, pieces of slate, or large lumps of coke are laid on the top of all in order to receive the stream at its entrance, and distribute it in thin layers over the surface. It is further desirable that the liquid to be filtered should enter in a shallow sheet over a wide lip. Roughly speaking, for a filter of given size and material, the less rapidly the liquid passes through it, the more thoroughly will- it be purified. 74 SEWAGE TREATMENT. The chief materials used for forming filter beds are gravel, sand, moor-earth, burnt clay, pumice, coke, animal charcoal, wood charcoal, peat (raw or carbonized), seaweed charcoal, spent oil shales, Kimmeridge carbon as obtained from the so-called Kimmeridge blackstone, lignite, spent dye woods and sawdust, especially if slightly carbonised by fire or by the application of acids ; shavings, rushes, faggots, straw, and other hard vegetable matters exposing considerable surface. Further, I must mention spongy iron, magnetic iron ore, black oxide of manganese, scrap iron, and cylinders of unglazed porcelain. These materials are used sometimes alone, sometimes in combinations, which may be varied almost indefinitely. It will be easily seen that for the treatment of sewage many of these materials are out of the question. As it has been already pointed out, the filtration of sewage is far more difficult than that of spring, river, or lake waters for domestic or manufacturing purposes. I lately found that half a litre (about i;i fluid ounces) of the effluent from a certain sewage works took exactly two hours in passing through a 5 -inch paper filter. The same measure of the untreated sewage from the same works took exactly seventy-two hours to pass through a filter of the same size and quality. This simple experiment shows the relative difficulty of filtering sewage. The large quantity of paper pulp and of the fibres from textile goods always present in sewage, even such as appears almost transparent, quickly clogs up the filter beds. The fatty matter derived from soap and from culinary operations combines with these fibrous matters in as it might be called waterproofing the filter, forming an impervious, water-repelling layer not only over the surface, but even within the interstices of the mass. This FILTRATION. 75 choking and clogging process is quite independent of the nature of the materials used, or rather, we may say, that the better the filter was originally, the more thoroughly and quickly it will become choked ; whilst one which allowed the water to run through rapidly will remain in full activity much longer. Hence filters for sewage must be relatively larger than those for river water, etc., and they will require more frequently cleaning or changing. Cleaning a filter bed when it has become dirty is in many cases a most troublesome operation, as the faecal matters which adhere to the sand, coke, etc., will have become very offensively putrid. It is commonly said : take out the soiled and clogged materials, and spread them out to the air. But for this the necessary room is not always to be had, and the smell of the mass thus exposed is liable to raise objections. If we wash the soiled matter, where are we to turn the washings ? If into the river, we occa- sion a pollution nearly as great as if we had all along allowed the sewage to flow in unfiltered ; if we turn it back into the sewage, we have the work to do over again under greater difficulties than at first. Purification by fire is with some materials impossible, and in most cases it requires special kilns or furnaces. A change of filters, to be used alternately, is recom- mended where the room is sufficient. When one filter shows signs of clogging, or allows the sewage to pass through in a foul condition, it is shut off, and the liquid is turned into the other. Sand and gravel, however deep in mass, and however well spread, do little more than remove the suspended, or, I might say, the coarser suspended impurities. But they are relatively cheap, procurable almost everywhere, and when foul they may be easily dealt with. The sand 76 SEWAGE TREATMENT. may serve to improve clay soils, whilst gravel, after due airing, can be used for mending field paths ; but never for filling up hollows upon which houses may subse- quently be built. Moor-earth a mixture of sand and peat where pro- curable, acts better than sand or gravel. When spent, it may be used for farming and gardening purposes. Burnt clay ranks about with gravel. Pumice is toler- ably efficient, but it is too expensive. Animal charcoal, otherwise known as bone-black and as spodium, is also far too costly. This is the less to be regretted since, whilst it purifies polluted waters well at first, it after- wards becomes charged with offensive matter in such a manner that it contaminates water instead of improv- ing. Wood charcoal, if thoroughly burnt, so as to be quite free from oily and tarry matters, acts fairly well in combination with sand, etc. Peat was applied to the filtration of town sewage by the Peat Engineering Company, Limited. It acts well for a time, but when clogged it is difficult to deal with. Peat-charcoal is a promising material, as seaweed charcoal would be also, could it be procured at a lower figure. Mr. S. K. Page, manager of the Aylesbury Sewage Works, has made a series of careful experiments upon the Kimmeridge carbon. Here the results were at first all that could be desired, but the bed soon choked up, and the first cost of the material would not permit it to be frequently exchanged. Unglazed porcelain filters, as proposed by Pasteur and Chambeland, may be considered perfect, as they remove even microscopic organisms. But for dealing with the sewage of a town they are utterly out of the question. Spongy iron bears deservedly a very high character, FILTRATION. 77 and is even said by some authorities to remove bacteria, though this is denied by Mr. Jabez Hogg, M.R.C.S., F.R.M.S., one of our most competent microscopists, and, in this special department, perhaps the most eminent. Be this as it may, spongy iron, like all metallic sub- stances, is inapplicable to the sewage of manufacturing towns, as it would be acted upon and injured by the acids and acid salts rarely absent. It would also, like manganese, soon become mixed with the silt and grit brought down by the current. To separate this refuse matter when the filter-beds require cleaning would be no easy matter without wasting a considerable proportion of the active material. There are two methods, or processes, of filtration which have been especially recommended for dealing with sewage. One is that of Professor Henry Robinson, first made public at the Dublin meeting of the Sanitary Institute, and reported in the Sanitary Record fo r October, 1884. This gentleman an engineer, if I mistake not proposes to adapt clay lands for a some- thing midway between filtration and irrigation by digging ou t the soil to the depth of six feet, burning ib and arranging it in layers interspersed with a stratum of open, alluvial soil, of course unburnt. Such a bed, six feet in depth, will, we are told, continuously clarify it is not said purify the sewage of 1,500 persons per acre. The cost of preparation however, reaches, according to Mr. Robinson's own estimate, the modest sum of ,750 to ,1,000 per acre. Every one knows that such estimates fall far short of the actual cost of these schemeswhen reduced to practice. An observant friendtells me that every 1,000 in an estimate means in reality about ^2,500. But let us accept the estimate, and take 78 SEWAGE TREATMENT. a town with a population of 300,000 persons say, Leeds. At 1,500 persons per acre we should require 200 acres of land, to be prepared at a first cost of .200,000 ! Or, for London, 2,666 acres, costing .2,666,000. I do not find whether in this estimate is included the pur- chase of the land, which anywhere within a moderate distance from a large town must be a heavy item. But this is not all ; Professor Robinson is of opinion that before running the sewage upon this bed the coarser suspended impurities should first be removed by a process of ascending filtration, of course through a separate set of beds, the materials of which, when sufficiently polluted, are to be taken away, and " dug into low-lying land," whilst fresh ascending filters must be brought into action. These ascending filters and the land for digging in the coarser sewage matters will occupy a considerable space ! Even if we are bold enough to assume that the acres stated will go on for ever purifying the flow of sewage, we must admit that the yearly working of this most singular scheme will be no trifle. Nor must it be forgotten that the plots of land thus prepared will be thereby converted into deserts, which neither art nor nature will henceforth be able to reclaim. We come now to the process, designated officially as "intermittent downward filtration," and recommended officially and officiously as the alternative to irrigation, to be used when land of a quality and in a situation suitable for a sewage farm is not to be had. That the term in question is novel must be admitted, but that there is any novelty in the thing itself it might be hard to show. The reader has been already reminded that all ordinary filtration is " downward/' and the term FILTRATION. 79 intermittent merely implies that the filter beds are to be made in duplicate or in triplicate, the one to be in use whilst the others are being cleansed. It may be well to state Professor Frankland's original plan in full. A plot of ground is to be procured, say three times larger than is necessary to receive the en- tire sewage of the town. The soil of this plot, to begin with, must be of suitable quality, and it is prepared (presumably dug up, drained, and rendered uniformly light and open), to the depth of six feet. It is then divided into three plots. Upon one of these the entire sewage is run for eight hours. It is then turned upon the second plot for the next eight hours, and finally upon the third plot for the last eight hours. Thus each plot will have eight hours' action and sixteen hours' rest. I am not aware that there is any sacred- ness in these exact numbers. It would, perhaps, be permissible to divide the plot of land into four parts instead of three, thus giving each part only six hours' action and eighteen hours' rest. From certain labora- tory experiments the distinguished author of this scheme calculated that each acre of land would in this manner purify the sewage of 3,300 persons in saecula saeculorum. In a recent letter to the Times he has reduced his esti- mate to 2,000 persons per acre, and some of his dis- ciples have further varied the figure. Another point of difference is regarding the possible utilisation of the land laid out as filtration beds. Professor Frankland, unless I misunderstand him, holds that it involves the sacrifice of the land from an agricultural point of view, and, of course, of the fertilising matters contained in the sewage. Mr. Bailey Denton who seems to be to Pro- fessor Frankland what AH was to Mahomed and Mr. So SEWAGE TREATMENT. Grant Allen to Charles Darwin thinks that this pecu- liar kind of filtration is the best means of getting a good crop. Now I would ask any practical farmer what crop save, perchance, rye-grass would be the better for hav- ing turned upon it, in addition to the natural rainfall, the sewage of 3,300 persons ; that is, on the average 99,000 gallons of water per acre every day from year end to year end ? Professor Frankland has now essentially modified his views, and recommends that the earth for a " downward intermittent filtration " bed should be prepared to the depth of two feet only, thus tacitly admitting that the lower four feet are of little use, and that his former ex- periments, or at least the conclusions based upon them, were fallacious. It would be a grave error to cavil at a man of science for retracting and modifying opinions which, upon further experiments and observations, are found no longer tenable. But surely a savant who thus openly and honourably confesses his own fallibility might be led to inquire whether some of his other utterances are not quite as much in need of revision ? We have now to ask whether a daily rest of sixteen, or even of eighteen hours will keep the land up to its original degree of permeability ? We have already seen how the soil is waterproofed by the deposit on its sur- face and in its pores of the fibres of paper, linen, cotton, etc. Now these fibres, if exposed to air and moisture, would doubtless in time become disintegrated and oxidised, save for one circumstance. That is, they are coated with greasy matter, as it has been mentioned above, and are thus protected in a very great measure from the action of water and of atmospheric oxygen. Even ordinary clean water applied to soil in such pro- FILTRATION. Si portions as it is recommended for " intermittent down- ward filtration " will ruin its texture. Let any one take a box of soil of one foot square, set in it any kind of plants other than swamp vegetation, and then pour upon it, day by day, two gallons of water (= 90,000 gallons per acre), he will find that its poro- sity will be destroyed, and that the plants will not thrive. How much more must this mischief occur when we have superadded to the water the waterproofing materials above mentioned, and when we have, in addition, the yearly rainfall to contend with ? In proportion as the soil becomes waterlogged (which must ultimately be the case), little pools will begin to stagnate upon the surface, and a larger and larger proportion of the moisture will have to be got rid of by evaporation a result injurious both agriculturally, as chilling the soil, and from a sanitary point of view, as favouring the diffusion of sewage vapours and probably of disease germs. " Digging in " the deposit cannot well be executed whilst any crop is on the ground, and can at most only defer the evil. It must never be forgotten that, whilst irrigation and precipitation present at least the possibility of some return, all the outlay in filtration, as in the Bazalgette system, is pure waste. The object is not utilization but destruction. It must not, however, be supposed that filtration, even as applied to crude sewage, is in all cases to be con- demned. Let us suppose a town or village which is not closetted, and where, consequently, little excrementitious matter finds its way into the sewers. But let there be instead some large manufacturing establishment, emit- ting much liquid refuse, acids, solutions of metals, drain- 82 SEWAGE TREATMENT. age from tank-waste, residual liquors from dye-works, tanneries, paper-mills, etc. If we irrigate with such liquids we kill, instead of nourishing, the crops. If we precipitate we may obtain a clear, colourless, inodorous effluent, but the precipitate will be fit " neither for the land nor for the dunghill." In such cases filtration may prove the least objectionable method of treatment. Further, filtration may often be usefully applied as finale to a precipitation process where extreme purity of effluent is desired. PRECIPITA TION. 83 CHAPTER IX. PRECIPITATION. THE processes for the chemical treatment of sewage are so numerous, so different in their principles, and so varied in their grades of efficiency, that a complete dis- cussion of each is purely impossible. Fortunately, many of them are merely changes rung upon comparatively few agencies, so that they may be dealt with in groups. Before considering the substances used to effect pre- cipitation, we must prepare to meet a cavil which has been uttered with great confidence, not to say rashness, though its first author, like many inventors, is unknown, blushing, perhaps, at the fame which might be his mede. It is said that " chemical agents, though they may clarify i.e., withdraw suspended impurities cannot purify, i.e., they are unable to remove dissolved impurities." It is difficult to understand how any chemist can make such an assertion without placing himself in a very unpleasant dilemma. To begin, it is well known that suspension and solution fade away into each other by scarcely perceptible gradations. It is further evident that suspended organic matters under which head we must include living organisms, the germs of disease, and putrefaction must, in the strictest sense of the word, rank as impurities. If we remove them we/r0 tanto purify the water. 84 SEWAGE TREATMENT. It is also known that there are two methods, if not more, in which dissolved substances can be separated from the solvent liquid : precipitation in the strict sense of the word, and occlusion or aborption. In a well- planned precipitation process these two modes of action are systematically combined. In precipitation proper the dissolved body enters into a definite and more or less stable chemical combination with some other sub- stance introduced, forming a compound which is in- soluble in the liquid, and which then subsides to the bottom. This occurs with organic as well as with in- organic bodies. Thus, if we dissolve a little white of egg (albumen) in water, and add a solution of sugar of lead, the albumen combines with the lead to form an insoluble mass. Or if we take a solution of gelatine in water and add to it a solution of tannin, the gelatine coagulates, and is deposited in combination with the tannin. Everyone acquainted with the arts of dyeing and tissue-printing will know instances where dissolved organic substances are rendered insoluble by contact with metallic salts. These facts are here mentioned, not as in any way novel, but merely to prove the general proposition that dissolved organic compounds are capable of being pre- cipitated. Before passing to instances proving that sewage matters in particular are capable of being thus thrown down, it is proper to refer to occlusion. Here a dissolved substance is withdrawn from solution, not by forming a definite chemical compound with some other body introduced, but by becoming entangled in its pores. Gelatinous silica and hydrated alumina, when freshly precipitated, are capable of thus entangling dis- solved organic matters. PRECIPITATION. 85 We may now pass to an experiment showing the pre- cipitability of dissolved sewage matters. Take a pint of sewage and filter it through the finest filter-paper, which will prove a work of time. The liquid running through may be almost as bright and clear as spring- water. But if there be then added to this liquid a few drops of a solution of alum, or of hydrated aluminium chloride, commonly spoken of as muriate of alumina, or of sugar of lead (all which must be free from any excess of acid), there will soon form a white cloud in the liquid, which will then, before long, settle to the bottom. This is a compound of alumina (or respectively of lead) with the organic matter which was previously in a state of solution. If some of the filtered liquid is analysed before and after the addition of the alum or other pre- cipitant, it will be found that a large proportion of the organic matter previously dissolved in the sewage has been removed. Thus, Professor Dewar, F.R.S., and Dr. Tidy, in the report of their recent prolonged investiga- tion of the sewage of Aylesbury, and its treatment by the "A. B. C. process," state that they found about 60 per cent, of the dissolved organic matter in the sewage was removed, and, further, that the portion not thus removed was precisely that least likely to enter into offensive or dangerous decomposition. Lastly, pure water is a thing which does not occur in nature, and which the majority of those who utter the above-quoted cavil have certainly never seen. If they mean to say that sewage cannot be brought to this state by chemical means or, indeed, by any other they merely utter a gratuitous truism. If under cover of this truism they insinuate that sewage cannot, by precipita- tion processes be so far purified as to be safely admis- 86 SEWAGE TREATMENT. sible into the rivers of a populous and cultivated country, they state at best an opinion which they would find it hard to prove. It is, therefore, sincerely to be hoped that we may have heard the last of the cavil that organic impurities dissolved in water cannot be got rid of by chemical treatment. I find, however, that when I wrote the above para- graph I was paying an undeserved compliment to public intelligence and candour. A few days ago there fell into my hands the prospectus of a new sewage process by aeration. The inventor goes somewhat out of his way to attack precipitation, and writes that the Royal Commission on the Metropolitan Sewage (1883) " admits " note this term ! that the best precipitation processes only clarify, but do not purify ! It is lament- able when a Royal Commission "admits" something very far from the truth. That Commission refused, or neglected and in such a case, these two terms are nearly equivalent to examine fully and fairly into the merits of precipitation. It overlooked the fact that many chemists, engineers, and other experts, who a few years ago were decidedly hostile to chemical treatment, have latterly seen reasons for changing their views. It would not, or at least did not, visit Aylesbury. It was satisfied to condemn precipitation on the faith of the archaic reports of the Royal Rivers Pollution Commis- sion, reports which, if true at the date when written and this is a fairly strong concession are demonstrably false if applied, e.g., to the process now in operation at Aylesbury. It must now be asked, What organic matters are PRECIPITA TION. 87 capable of being eliminated by so-called chemical processes ? We may say that this is the case with albumen and analogous compounds ; with gelatine, mucus, and with peptones. The same holds good with pyin, the albuminoid constituent of pus. Thus we see that the most important portions i.e. t those most likely to occasion mischief on decomposition of blood, urine, and of the soluble part of solid excrements, are amenable to precipitation. That suspended matters can be precipitated has never, probably, been seriously disputed, though some of them, such as fatty particles, are much more difficult to deal with than the bulk of the dissolved impurities. Phosphoric acid is invariably present in sewage, being introduced by urine and by blood. Though not to be called an organic impurity, it is highly objectionable, as it is necessary to the growth and multiplication of disease germs and other microbia. It is satisfactory to know that it may be almost absolutely removed by precipitation. In the waste liquors of industrial establishments there are a vast number of impurities capable of being removed by chemical treatment. Such are the salts of the heavy metals, colouring and tanning matters, etc. Among the substances which resist precipitation are oils and fats, essences, waste products of gas-works, and refuse resulting from the manufacture of india- rubber articles ; ammoniacal salts, salts of the alkalis, especially nitrates, nitrites, and common salt. Con- cerning these various bodies it is to be noticed that gas-works refuse cannot be lawfully run into the sewers at all, and that where soapsuds are abundant they are generally kept back by the manufacturers, and separately treated for the recovery of the fatty matter. 88 SEWAGE TREATMENT. One of the principal animal products which hitherto has not been found practically precipitable is urea. This substance, in contact with a ferment which is never absent in urine, is quickly converted into ammonium carbonate, and never reaches the sewage tanks. The ammoniacal salts and the alkaline nitrates and nitrites are never found either in polluted rivers, or in sewage in such a proportion as to be in themselves a nuisance. At the same time we must regret that they are not precipitable, because : 1. If they could be thus arrested, they would greatly increase the manurial value of the deposit obtained. 2. Though in themselves inodorous, incapable of putrescence, and, in fact, harmless, the nitrogen which they contain may be brought into putrescible conditions by the action of living organisms, and because they will doubtless favour the multiplication of microbia. It must be remembered that in irrigation and filtration nitrites and nitrates occur in abundance in the effluent water. I have now to point out what are the properties, positive and negative, which a precipitating agent ought to have over and above mere efficiency. In the first place it must be cheap cheap, not merely by reason of present small demand, but of abundant, or, rather, unlimited supply. It must not be actively or cumulatively poisonous. Certain salts of lead are well adapted for throwing down organic matter from suspension and from solution. But, on the one hand, the deposit would be unsafe as a manure ; and, on the other, the slightest excess remaining in the effluent water would be deadly PRE CIP1 7 'A T10N. 89 to vegetation, to fish, and to cattle, which might drink of the stream. Antimony is excluded on the same grounds, as are also tin and bismuth, which are, in addition, too costly. The precipitating agent must not have in itself any distinct colour, or generate a colour with substances which it may probably have to encounter. This condition condemns, under most circumstances y compounds of iron. Many of these are in other respects well adapted for precipitation. But waters to which they have been added take a greenish-yellow colour on prolonged exposure to the air, and a yellow, ochreous deposit is formed on stones, brick-work, piles, etc. Though these deposits may be perfectly harmless, yet to the public they convey the notion of an excremen- titious origin, and the process is at once condemned. Iron sediments, if containing sulphur, or if coming in contact with sulphur compounds (mineral or organic), turn intensely black, and have an unpleasant appear- ance. All substances are objectionable which yield an alkaline effluent. This principle, strange as it may sound, at once excludes the commonest agent lime. The reason is that putrefaction is more active in alka- line solutions than in such as are neutral or acid. In all experiments on the culture of the microscopic organisms, to which we have referred so often, and in all attempts to generate life from dead matter, alka- linity is a condition insisted upon. Now lime, if used not merely to neutralise some acid or acid salt, but, as a substantive precipitant, invariably renders the effluent water alkaline, and thus favours decomposi- tion. Whether the lime is applied in a powder, as 90 SEWAGE TREATMENT. cream of lime, or as clear lime water, is merely a question of convenience and cost. According to some recent investigations of Professor Konig and Dr. Boehmer (Landwirth Jahrbiicher, 1885, vol. xiv., part 2, pp. 228-238), lime reduces the total organic matters suspended and dissolved in sewage by 33 per cent, in the tanks, and if the effluent be then allowed to flow over grass-land, by about 25 per cent. more, making thus a total of 58 per cent. But salts of alumina, with the aid of proper absorbents, are found capable of reducing the total organic impurities sus- pended and dissolved by 83 per cent, in the tanks alone, without flowing over grass at all. A lime effluent is well known to be injurious to fish in any stream into which it penetrates. Of course, it will be said that the caustic lime present will soon be rendered inert, and be precipitated by the carbonic acid of the atmosphere. But if the supply of lime is con- tinuous, a considerable tract of water may easily remain deadly to fish. It will have been generally noticed that lime effluents and lime sewage deposits give off a very peculiar and most unpleasant odour. This, I suspect, is due to the volatilisation of some ptomaine (putrefaction alkaloid) present in the sewage. The action of lime upon colouring matters in sewage and in industrial waste waters, discharged, e.g., from tanneries and dye works, is very unsatisfactory. I have seen such waters easy to treat by other agents, but which, if mixed with lime water, were turned from a pale yellow to a dark and very permanent mahogany colour. It is interesting to find that Professor E. Frankland, PRE C I PIT A TION. 9 1 in conjunction with Dr. Stevenson, has recently recom- mended lime as a precipitating agent for the Hendon sewage. The better to appreciate this advice, we turn to vol. i. of the first report of the " Royal Rivers Pollu- tion Commission" of 1868, of which body Professor Frankland was the most active arid prominent member. In this document, published in 1870, we read : "(a). Treatment with Lime. This process was, doubt- less, first suggested by the ingenious operation devised by the late Dr. Clark, of Aberdeen, for softening certain hard waters. " It has been applied to sewage upon an extensive scale at Tottenham, for the manufacture of Tottenham sewage guano ; at Blackburn, and especially at Leicester, in the production of the so-called ' Leicester Bricks ' (the name under which the manure was sold). " In all these places the plan has been a conspicuous failure, whether as regards the manufacture of valuable manure, or the purification of the offensive liquid. " We have witnessed the process at Blackburn, and on two occasions at Leicester, where it is still used, the machinery employed at the latter place being very perfect and efficient. " At both places the method obviously failed in the purification of the sewage to such an extent as to render it admissible into a river. At Blackburn especially, the river below the outlet of the limed sewage was in a most offensive condition of putrefaction, our note, made at the time of our visit, being as follows : ' Horribly offen- sive, turbid, blackish stream, disengaging most offensive gases, with black masses of putrid mud floating on the surface.' " A committee of most eminent chemists, not, perhaps, 92 SEWAGE TREATMENT. remarkable for their special experience in the treatment of sewage, have recently devised and published a palliative process for the London sewage until the culminating extravagance of conveying it down to Thames Haven has been completed. These savants recommend the use per gallon of 37 grains of lime with one grain of copperas. It need scarcely be said that the effluent after the addition of this mixture will possess the defect of being alkaline. It may, indeed, to some extend " clarify," but it cannot " purify," the foul odour not being removed. In hot weather, therefore, it is recommended to add from '5 to I 5 g r ain of manganate of soda, with half its weight of sulphuric acid. This formula will still leave the water alkaline, and in a good condition for the multiplication of micro-organisms. It has been recently alleged by Dr. Percy Frankland that treatment with caustic lime (as in the Clarke process) removes bacteria from water to a considerable extent. The same authority has subsequently materially qualified this statement, informing us that after a few days the micro-organisms become more numerous than ever. Lime is admitted to have a decomposing action upon the suspended organic impurities, in virtue of which the)/ are in part rendered soluble. Among the substances to be as far as possible avoided are further sulphates compounds of sulphuric acid with various metals. The reason is that if brought into con- tact with moist carboniferous matter, such as sewage deposits, they may be gradually reduced to sulphides (sulphurets), which, in turn, if they meet with even the feeblest acids, liberate sulphuretted hydrogen. This result is easily noticed when copperas (ferrous sulphate, protosulphate of iron, or green vitriol) is used as a PRECIPITA TION. 93 precipitating agent. The change is shown in this case by the intense black colour of the mass, which has been mentioned above. Sulphate of lime (gypsum), or any mixture or com- bination by which sulphate of lime can be produced, is exceedingly objectionable. Although there is here no blackening, yet hydrogen sulphide (sulphuretted hydro- gen) is given off in plenty. Instances are on record where men employed in mixing sewage deposits with gypsum to promote solidification have been rendered seriously ill. Even sulphate of alumina of which below is probably one of the least desirable forms in which alumina can be introduced in the treatment of sewage. Sulphurets (sulphides) are very rarely admissible. On no account should any soluble sulphide, or anything which may form such a sulphide, be allowed to pass into a river. Hypochlorites, such as bleaching lime (commonly called chloride of lime), and the corresponding magnesia and soda compounds, must also be excluded. The late Royal Rivers Pollution Commission was fully justified in its protest against these substances as unfitting the water of rivers for almost every conceivable purpose, and especially rendering it deadly to fish. Mr. A. Anthony Nesbit, F.C.S., has shown within what narrow limits this deadly action takes place. Salts of barium, such as barium chloride and baryta water, have been proposed for the treatment of sewage, and even for the improvement of drinking waters. They will, of course, remove from a water any sulphuric acid, free or combined, which may be present in solution, and will also precipitate carbonic and phosphoric acids. But 94 SEWAGE TREATMENT. they are more expensive than lime, the lowest figure for the native carbonate (Witherite) being 505. per ton. Above all, they are very poisonous, and any portion passing out in the effluent or remaining in the deposit in a soluble state may work mischief both to animal and vegetable life. Salts of strontium, if they become cheaper, might be used with more safety. Free acids, at least the hydrochloric (muriatic) and sulphuric, have been proposed. They are first to be run into the sewage, and then neutralised by the addition of an alkali or an alkaline earth, lime as the cheapest having probably been used. It is hard to see what good end can be reached in this manner, the alkali or alkaline earth undoing anything that the acid might have effected, and the final result being merely an 'addition of calcium sulphate or chloride (in older language, sulphate or muriate of lime) to the sewage. Common salt has been used with no definite advantage. This result might be expected if we remember that this same salt, derived from urine, is one of the characteristic features of sewage, and that, if found in any water, it is considered primd facie evidence of contamination with the excreta of animals. Petroleum, coal tar, and similar products have also been recommended. They do not well mix with water ; and> though they may at times mask an offensive smell, they cannot remove putrescent or putrescible matter. Being in themselves a nuisance in water, the Bill intro- duced last year by Mr. Walrond and Earl Percy very rightly proposed to make their emission into streams penal. One of the strangest mixtures ever suggested is ground sulphur and turpentine ! Being insoluble in water, and PRECIPITATION. 95 incapable of mixing with it, the action of this composition would be nil. We come next to a class of systems which cannot fairly be condemned, but which are still not by any means free from objections. Here belong all the many processes which turn on the introduction of phosphates into the sewage. It is highly important that all the phosphoric acid originally existing in sewage should be removed, because such phosphoric acid remaining in the effluent water favours the multiplication of disease germs, and is, in addition, so much loss or waste withdrawn from the manure. The phosphate processes are somewhat varied, the agent selected being either aluminium, iron, calcium (phosphate of lime), or magnesium phosphate. Of these the two first mentioned are generally dissolved in sul- phuric or muriatic acid, avoiding excess. The solution is then run into the sewage and allowed to mix with it in a uniform manner. Lastly, milk of lime, or clear lime-water, is added, so as to neutralise the acid and cause the phosphate of alumina, or of iron, as the case may be, to be reprecipitated, occluding, as it goes down, more or less of the suspended and dissolved impurities. When phosphate of lime is the agent, it has been recom- mended to add to the sewage ordinary superphosphate, and then to precipitate with lime-water as above. Not a few inventors have proposed to remove at once phos- phoric acid and ammonia from the sewage in the form of ammonium-magnesium phosphate, better known as the double phosphate of ammonia and magnesia. All these processes are more suitable for the labora- tory than for actual practice on the large scale. The large quantity of phosphoric acid added must be again 96 SEWAGE TREATMENT. removed, or there occurs not merely loss, but the multiplication of microscopic organisms is promoted. Gelatinous phosphate of lime, in the state in which it exists when freshly precipitated, decidedly promotes decomposition of an unsafe character. If superphos- phate is introduced into the sewage sulphate of lime accompanies it, and if phosphates of alumina and of iron are used dissolved in sulphuric acid, sulphate of lime is thereby formed in the tanks. The objectionable character of this compound in sewage or in sewage mud needs no further demonstration. Further, in all these phosphatic processes the effluent must be kept on the alkaline side. This, except in the magnesia modi- fication, is effected by means of lime. Consequently, all the objections against lime processes come here into force. Further, a per cent, of phosphate of alumina rendered soluble by means of sulphuric acid, and a per cent, of soluble phosphate of lime, costs more than a per cent, of soluble alumina in sulphate of alumina, or in hydrated aluminium chloride. As for the phosphate of magnesia processes, it must be remembered that the double phos- phate of magnesia and ammonia (ammonium-magnesium phosphate) is not a gelatinous mass like hydrated alu- mina, but has a granular texture, and is consequently much less adapted for occluding and entangling the organic impurities of sewage. Every chemist who has used the " magnesia process " for determining phos- phoric acid must be aware that the conditions under which this acid can be entirely removed from a liquid are not such as can be produced in a sewage tank. These considerations, combined with careful and pro- longed experimentation on different scales, have driven PRECIPITATION. 97 me to the very unwelcome conclusion that the phosphate processes are not to be recommended for the treatment of sewage. Having thus glanced at the principal agents which should not be used, we come to those which are more or less free from objection, and which may, therefore, be generally applied. Foremost come the salts of aluminium. They are relatively cheap, inexhaustible, colourless, and harmless in any moderate proportion. As may be seen from their use as mordants, they have what is called a great " affinity " for organic matter. This holds good as well for sewage pollution, dissolved or suspended, as it does for the ordinary colours used by the dyer and the printer. If a solution of a salt of aluminium, say com- mon alum or cake alum (sulphate of alumina), is thrown into a large quantity of water, it is decomposed. A basic sulphate, or as some call it, a subsulphate, is de- posited, and combines with the major part of the impuri- ties present in the water. This action is the more energetic if the water is slightly alkaline, as is usually the case with town sewage when free from industrial waste waters. The decomposition of the salt of aluminium and the precipitation of the impurities is also accelerated if it be added to the sewage hot, as proposed by Mr. W. C. Sillar. It must now be asked, Which is the most suitable salt of aluminium to be applied in the treatment of sewage ? Alum, though used in some of the earlier sewage pro- cesses, such as the original "ABC" process, is not to be recommended. In addition to its high price, it con- tains a considerable proportion of an alkaline sulphate (potassium or ammonium sulphates) which, without 98 SEWAGE TREATMENT. contributing in any degree or shape either to the purification of the sewage or to the agricultural value of the deposit obtained, make the effluent water " analyse worse." This is especially the case with ammonia-alum (double ammonium and aluminium sulphate), which causes the quantity of ammoniacal salts in sewage to be apparently increased by treatment. This fact (the apparent increase of ammonium salts) has been duly noted by certain official opponents of sewage precipita- tion, who have, at the same time, taken good care not to explain its cause. Aluminium acetate, used by dyers and tissue-printers under the name of " red liquor," is a powerful precipi- tant, but its cost is prohibitive. Much the same may be said of the nitrate, which, in addition, increases the proportion of nitrates in the water. The sulphate (cake alum, concentrated alum, or patent alum) is cheaper than alum, more rapidly soluble, and contains 15 per cent, of actual alumina, whilst potash alum contains only 10 and ammonia alum II. If it contains a little iron, as in Spence's "alumino- ferric cake," no disadvantage is occasioned, but, if any- thing, rather an improvement. Basic aluminium sulphates, where easily procurable, are, price for price, preferable to the ordinary sulphate, as they contain a larger amount of alumina, and are more readily decomposed in contact with the dissolved and suspended organic bodies ; but, as it has been already remarked, sulphates are not to be selected except as a matter of necessity. The best of the aluminium salts is the hydrated chloride, familiarly spoken of as muriate of alumina. Until recently this salt could not be prepared at a PRECIPITATION. 99 cost sufficiently moderate to admit of its being used in sewage treatment. Of late, however, a series of pro- cesses have been devised, suitable to different localities, by which a muriate of alumina, sufficiently pure for sewage purposes, can be produced at a very low price. The aluminate of soda was proposed and patented as an agent for sewage treatment by A. J. Vassard, in 1871. More recently it has been patented, in a different combination, by F. Maxwell Lyte. Its pre- cipitating power is indisputable, but the question of relative cost is somewhat doubtful. When used it must be accompanied by some acid salt, otherwise the effluent would, in ordinary cases, be rendered alkaline. The aluminium salts have not merely the property of throwing down dead organic matter (dissolved or suspended) present in water, but they can, to a very great extent, remove disease germs. From time immemorial the Chinese, before using the very ques- tionable water of their rivers for culinary purposes, have been in the habit of adding a pinch of alum to a tub of the water, and allowing it to subside. The French troops in Tonkin have adopted the same expedient, arid have by this simple means almost entirely got rid of the endemic dysentery from which they previously were great sufferers. Dr. Brautlecht has even proposed the use of alum as a means of detecting the microscopic germs present in water. He adds a few drops of a solution of alum to some of the suspected water contained in a test- tube, allows the precipitate to subside, decants off the clear, redissolves the sediment in a few drops of acetic acid, and searches for the organisms in the solution thus obtained. ioo SEWAGE TREATMENT. It should, therefore, appear that the effluent water from any sewage process in which a salt of aluminium is the precipitatingagent should be to a great extent freed from the disease germs in question. An insoluble compound, or alleged compound, of alumina, has recently been recommended for sewage precipitation. This is the so-called carbonate of alumina. The chief authorities, such as Gmelin (" Handbook of Chemistry ") and Watts (" Dictionary of Chemistry") do not admit the existence of such a body, though Mu sprat t (Journal of Chemical Society, ii., p. 210) alleges that he has obtained a true aluminium carbonate by precipitating a solution of alum with ammonium carbonate. The patentee precipitates, it would seem, solutions of cake alum with chalk (or soda-ash ?), obtaining thus a mixture which, at any rate, contains sulphate of lime, undecomposed chalk, and either hydrated alumina (aluminium hydroxide), or the alleged carbonate, or possibly both. However this may be, I have been unable to find this mixture or compound at all more efficacious in purifying sewage, if the same is neutral or alkaline, than the quantity of cake alum from which it was originally obtained. In case of a strongly acid sewage it enables the use of lime water, etc., for neutralising the water to be dis- pensed with. This, however, is a distinction of little moment : if we add sulphate of alumina to acid sewage and neutralise with lime, the final result is the same as if chalk had been added to the sulphate of alumina before putting it into the sewage. The cost of the " carbonate of alumina " is, of course, somewhat higher than that of the cake alum from which it is made. PREC1PITA TION. 101 Carbonates of any kind, or indeed substances which can continue to give off gases after having been mixed with the sewage, are to be condemned. The bubbles of gas disturb the sediment, and cause minute particles to remain in suspension. It is, of course, well known that freshly precipitated hydrated alumina, if well shaken up with the solutions of certain substances e.g., colouring matters is capable of withdrawing them from solution. As far as the mere principle is concerned, this method would be applicable in sewage treatment, but in practice it is scarcely admissible, as the action is not sufficiently rapid and energetic, and the mechanical arrangements would prove too costly. Soluble salts of manganese are excellent precipitants. Not only do they carry down organic substances, dis- solved as well as suspended, but they destroy certain impurities by transferring to them a continual supply of oxygen from the atmosphere, and from the air dissolved in the water. This property is found more or less well marked in the salts of all metals which have two grades of oxidation. Any salt of a higher oxide in contact with organic matter is reduced to the lower oxide, and the oxygen which it gives off oxidises, or, in other words burns up, the organic impurities, whether dissolved or suspended. The lower oxide then takes up fresh oxygen from the air, is reconverted into a salt of the higher oxide, and repeats the former process. It is devoutly to be hoped that the opponents of the chemical treatment of sewage will not seek to deny that in such cases purification and clarification go hand in hand. Oxygen thus trans- ferred to the particles of organic matter in sewage 102 SEWAGE TREATMENT. has a far more energetic action than the oxygen of air driven in by a pump. A manganese process is at present in action in the town of Freiberg. Whether the manurial value of the deposit is reduced by the oxidising action just men- tioned the writer has not been able to learn, though such a result seems likely. Prior to the introduction of the Weldon process, the refuse of the chlorine stills at manufactories of bleach- ing powder was an admirable material for precipitation, either used alone or as an addition to the other precipi- tants. It was, in fact, patented in 1854, by J. A. Man- ning (No. 61). It is now no longer available, save in exceptional cases. This may serve as an instance of the risks of basing an industrial process upon the employ of some waste product ; either an improvement in the primary manu- facture or its decline may render such waste product no longer available. Sulphate of manganese, formed by heating black manganese ore with sulphuric acid, is too expensive an article for sewage purposes. But there has been recently proposed an interesting process by which this difficulty is got over. The inventor designs also to make a joint sulphate of manganese and iron. Zinc, on account of its highly poisonous nature, can- not be applied in the treatment of sewage, though it has been repeatedly claimed. Copper is costly, and is also poisonous, but, according to recent researches, so slightly so in small proportions that it is capable of being used along with other agents as a transferrer of oxygen. Having thus glanced at the principal agents which PRECIPITATION. 103 form combinations with organic impurities and carry them down, we come to a class of substances which act in a different manner, and may be very advantageously combined with the former. The bodies in question act upon impurities by absorption or occlusion. The substances of this kind are for the most part the same as those which are used in irrigation and filtration, but they are applied in an inverse manner. Instead of passing the sewage to be purified through clays, arable soils, grass-roots, etc., or through filter-beds made up of charcoals, coke, sand, peat, lignite, etc., we agitate these bodies in the sewage. Here is the advantage that fresh portions of the purifying material are continually brought into play, so that the annoyance of clogging or saturation never can arise. As the best of these materials may be mentioned fatty clays, as free as possible from sand, grit, and especially from carbonates and sulphates of lime and magnesia. Such clay, in addition to its absorbing, puri- fying action, serves as ballast ; it enables the sediment more readily to subside, and prevents it from being easily buoyed up again to the surface by any escape of gases. Burnt clay, ground clinkers, etc., subside to the bottom, and, like sand, they occlude mere traces of the dissolved impurities. Their presence in the manure is objected to on good grounds. Arable soil is as efficacious in precipitation as in irrigation. But a supply sufficient for use with the sewage of a town even of moderate size is not ordinarily to be procured. This will at once appear if we reflect that such soil is rarely above a foot in depth, and that after its removal io 4 SEWAGE TREATMENT. the land is rendered worthless for the farmer and the gardener for a time practically unlimited. It might, of course, after it has taken its part in a precipitation process, be brought back and spread upon the fields again. All chalky, lime or marl-soils are out of the question, on account of the carbonate of lime they present, which decomposes and wastes the metallic salts used in precipitation. Coke has some absorbent powers, and it has been found by Dr. Percy Frankland very effectual in re- moving microscopic organisms from impure waters. It has been tried in a powdered state in precipitation pro- cesses, but, as it does not improve the resulting manure, the quantity in which it can be used is very limited. Coal ashes have also been applied, but they have little to recommend them. They contain finely- divided silica no better than sand ; alkalies, which impair the effluent, lime, magnesia and sulphur compounds, etc., none of which are desirable. Peat, which in many parts of the United Kingdom is to be had without limit, is an excellent absorbing or occluding agent. It has also, as it is well known, a certain antiseptic action. It must, however, never be used in sewage or waste waters containing compounds of iron, or, of course, where iron is introduced in any shape into the precipitating mixture. We come now to the various kinds of carbon : lignite, peat, and sea-weed charcoal, wood-charcoal, bone-black sawdust, charred by moistening with sulphuric or muriatic acid, the residual carbon from the manufacture of prussiate of potash, as also soot. In selecting any kind of carbon for sewage treatment certain points must be attended to. The carbon must be neither t PRECIPITA TION. 105 dense nor too light. In the former case it settles at once to the bottom without having the time to act upon the dissolved impurities. If too light, it floats on the surface without coming properly into action, and giving the effluent water a very unsightly appearance. Sus- pended charcoal powder may be justly objected to in a stream, whether it is used for industrial or domestic purposes. All charcoals employed must be thoroughly well burnt. If this is not the case they retain fatty and tarry matters, which repel the water and prevent it from penetrating into the pores of the charcoal. On this account soot is very objectionable ; it contains so much fatty matter as to float upon the surface of water without becoming wetted. It contains also a fair proportion of ammonia (r65 per cent), which, without aiding at all in the purification, causes the effluent to contain more ammonia, and, conse- quently, to analyze worse. A very powerful absorbing agent is gelatinous silica. Without forming definite or permanent chemical com- binations with the organic impurities, it entangles them, and carries them down. Its use in various combinations has been repeatedly patented. Cement, Portland or Roman, has been repeatedly proposed as an agent for sewage precipitation. If it has any action at all (which is by no means demon- strated), it will be most likely as an absorbing and occluding substance. I am not aware that it has ever been even tried on a practical scale. That a material which sets or hardens in water can form the basis of a manure seems highly doubtful. In addition to precipitants and absorbents, certain io6 SEWAGE TREATMENT. substances are also occasionally used, which have, or are supposed to have, disinfecting, or, at least, deodo- rising, powers. Among these rank certain gases, such as chlorine, nitric oxide, sulphurous acid, atmospheric air, carbonic acid ; further, carbolic and cresylic acids, carbolic sulphite, creosote, oils of coal and wood-tar, oil of turpentine, ethers, chloroform (!) ; also, chlorides of lime, magnesia and soda, sulphites and bisulphites, manganates and permanganates. Some of these bodies may be applied beneficially ; others are utterly im- practicable, being, e.g., not capable of mixing with water. Some are mutually incompatible, the one undoing what the other has done. Of others, it may be strongly suspected that their chief effect is merely to mask or hide an evil odour, rather than to prevent or destroy it. But of these substances generally it will be more convenient to speak in the chapter on deodoration. If anything approaching to a thorough purification is intended, no one substance will effect the purpose. It is generally requisite to employ conjointly some absorbent body or bodies and a precipitating agent. The absorbents, which are best added to the sewage first, have the task of occluding and entangling in their pores offensive gases and noisome products existing in solution in the sewage. When these materials have become thoroughly incorporated with the sewage, and are saturated with the various nuisances, the precipitant, in the strict sense of the term, is then added. It forms insoluble compounds with much of the remaining dissolved matter, and coagulates both the suspended impurities and the fine particles of the absorbents (now charged with filth), PRECIPITA TION. 107 and carries all to the bottom together. It is generally found that the offensive smell of the sewage is removed as soon as it has been properly mixed up with the absorbents, but that the liquid remains dull and turbid. On the other hand, the precipitant, if added alone, renders the sewage clear and bright, but does not in all cases entirely remove odours and colours. Both conjointly share the task of removing microscopic organisms, "germs," etc., from the sewage. It will be then seen that the systematic conjoint action of precipitants and absorbents or occluders is needed, and that only those sewage processes can be trustworthy in which this co-operation is recognised. It cannot be too clearly impressed upon the mind that a properly managed precipitation process is, or, at least, includes, inverse irrigation, and that this inversion gets rid of almost all the objections which can be raised against irrigation direct. We must come now to the manner in which the chemical agents are brought to bear upon the sewage. The materials, dissolved, if soluble, or, if insoluble, ground to a pulp with water which may be a portion of the sewage are allowed to flow into and become incorporated with the sewage in a channel. This channel should be of such dimensions and construction that every drop of the sewage should have the oppor- tunity to come in contact with the agents used. The channel then delivers the mixture into tanks, where the process of deposition or settlement takes place, whilst the clear water or effluent remains above. This part of the process may be either intermittent or continuous. In the intermittent system we require a number of tanks, arranged side by side, each uncon- io 8 SEWAGE TREATMENT. nected with, and independent of, the remaining. The treated sewage is first let flow into one of these tanks. When that one is full, the current is cut off and turned into the next tank, and so on, tank after tank being filled. As soon as the first tank is found to have settled, the clear liquid is allowed to run off by gravitation, if there is a sufficient fall, or is otherwise pumped off, with due precautions to prevent the mud at the bottom from being disturbed. The mud is then run off through distinct channels, or, if necessary, is pumped into a collecting reservoir, whence it is forwarded to the filter-presses, drying-floors, or other drying apparatus. In the continuous process the treated sewage flows into the first of a series of tanks, all connected together, and from the last of which it passes constantly into the outfall channel. When any one of the tanks is found or judged to contain as much mud as is proper, it is cut off from the series, and pumped or run off, as in the intermittent system, whilst the sewage is let pass through the remainder of the set. It is therefore necessary to have tank room enough to receive and deal with the day's flow even if one tank is temporarily disconnected. In this manner every tank is successively cleaned out. It will be, of course, evident that the tank into which the treated sewage first falls will require emptying much oftener than the rest of the set. Superabundant tank room is essential, as the bulk of the sewage varies greatly according to the weather. The construction of the tanks is a point of capital im- portance. The arrangement shown in the accompany- ing plan has been in use at the Aylesbury Sewage Works for some years, and, except as regards its size, */U. Z f < H \\ c 1L s o CO fe o PRECIPITATION. 109 has given general satisfaction. It is adapted for con- tinuous working. The sewage of the town flows down to the works by gravitation, and is delivered from the sewer at the point marked A, where there is a grating to arrest rags, etc. Here it receives from the trough B a proper proportion of the purifying (absorbent or occlu- sive) mixture, which at once removes all offensive odour, an4i5- Precipitates with sulphate of alumina. 62. /. Linton. 1865. No. 2,626. Adds to sewage solids ground clay, or other suitable refuse, with a small quantity of gypsum (!) as a deodoriser. 63. C. G. Lenk. 1865. No. 2,674. Adds to foul waters alum, "alumnite" neutralised or not, two parts carbonate of soda and solution of iron, or of permanganate of potash. This border very closely upon No. 1,242 of the same year. SEWAGE PATENTS. 199 64. H. Y. D. Scott. 1865. No. 2,808. Deodorises sewage with lime and metallic salts, is chiefly perchloride or persulphate of iron, the former to neutralise the phosphoric and carbonic acid contained in sewage, and the latter to seize upon the sulphuretted hydrogen. The patentee admits that these substances have been already used, but not in the right way ! He causes the lime to act upon the sewage in a separate reservoir and then runs off the effluent into another tank, where it is treated with the solution of iron. It is only necessary to remark ,'that the neutral- isation of carbonic acid is a point of no importance, and that in recent sewage sulphuretted hydrogen is not necessarily present. The patentee adds also some- times sulphate of lime, common salt, and carbolic acid. 65. F. Sutton. 1866. Nc. 101. Treats sewage with sulphate of alumina, alone or in conjunction with clay, sulphate of magnesia, or peroxide of iron. 66. G. E. Moone. 1866. No. 1,163. Treats with lime and distils off the ammonia which is received in hydrochloric acid, forming sal- ammoniac. fy.A.Kithne. 1866. No. 2,107. Treats foul water with chlorine or alkaline perman- ganates, with or without sulphate of iron or other metallic salts ; if excess of permanganate has been used, the inventor neutralises it with hypo-sulphite of soda. 68. R. Irvine. 1866. No. 2,218. Treats sewage with mineral charcoal obtained from the residuum left by the distillation of paraffin oil from shale, and containing silicate of alumina, with lime, mag- 200 SEWAGE TREATMENT. nesia, oxides of iron and carbon in a finely divided state. This specification should be carefully compared with that of Mr. Coleman, of Glasgow, No. 1,954, of 1875. 69. A. H. Bonseville. 1866. No. 2,926. Treats foul waters with lignite coke, charcoal, sul- phate of iron, potter's clay, and slaked lime. 70. Ernst Silvern. 1867. No. 119. Treats sewage, &c., with a mixture of burnt lime, with 5 per cent, of coal tar, and about ten times as much water as lime, with the addition, when necessary, of 10 to 25 per cent, chloride of magnesium. The reader is requested to compare this specification with the subse- quent ones, 1870, No. 3,167 ; and 1876, No. 1,355. 71. W. Parry and J. Fr ear son. 1867. No. 417. Mix with the sewage clay, clay iron ore or manganesic earths, and allow it to settle. 72. A. H. Hart and W. Parry. 1867. No. 788. Use the same materials. 73. E. Guenin. 1867. No. 1,229. Uses waste manganese chloride from the chlorine stills, neutralising acid if needful with dolomite, or other calcareous magnesian substance, or lime / or zinc or iron scrap, or oxidised ores of the same. He also adds 2 or 3 per cent, of raw salts of alumina from the washing of aluminous schists, or a certain quantity of the schists themselves in a natural state. 74. F. Tolhausen. 1867. No. 2,549. Treats urine with plaster, peat, and ashes. 75. T. H. Baker and T. Woodroffe. 1867. No. 2,894. No purifying agent is mentioned beyond baked earth . 76. A. M. Clark. 1867. No. 3,566. Treats sewage with neutral phosphate of magnesia, in order to precipitate ammoniaco-magnesian phos- phate. SEWAGE PATENTS. 201 77- W. C. Sillar, R. G. Sillar, and G. W. Wigner. 1868. No. 1,954. Treat sewage with 4lbs. per 1,000 gals, of the following mixture : Parts, Alum .... Blood .... Clay 600 i c Manganate of potash Burnt clay Chloride of sodium Animal charcoal Vegetable charcoal Magnesian limestone 10 . . 25 10 15 20 2 2,588 This is the original ABC process. It may be sufficient here to remark that the chloride of sodium is certainly injurious, whilst the magnesian limestone, the burnt clay, and the magnesia are, under most circum- stances, inert. 78. W. H. Hughan. 1868. No. 2,883. Mixes the sewage with cement to the consistency of mortar. Acids or salts may be added, e.g. I part of copperas to 6 parts of cement. Describes a special cement made of 4 parts alum and I part of clay or sulphate or phosphate of lime in solution ; a little caustic lime or phosphates may be added, as also charcoal or salt, also bone ash. It is difficult to conceive the quantity of cement which would be needed to solidify the sewage of London. 79. E. H. Prentice. 1868. No. 2,919. Adds to sewage phosphoric acid, or any soluble phos- phate, in the proportion of 12 or 15 Ibs. to 1,000 gals. 202 SEWAGE TREATMENT. sewage, and then precipitates with 20 to 30 Ibs. lime to 4,000 gals, sewage. This is a favourable specimen of the phosphate process. 80. G. Chapman. 1868. No. 3,203. Lets the sewage decompose in large tanks (!) at a temperature of 70 to 80 degs. Fahr. ; then adds caustic lime in a precipitating tank, and passes through the clear liquor steam to extract the ammonia. The first part of this process would be a fearful nuisance. A part of the ammonia would be lost on addition of the lime, if not before. 81. C.Jones. 1868. ^7.3,457. Precipitates sewage with slaked lime and petroleum, or, instead of petroleum, the acid tar obtained in the manufacture of liquid hydro-carbons. To improve the manure, chloride of zinc, or sulphuric acid, or burnt clay, or magnesia may be added. What is to precipitate the petroleum ? Chloride of zinc is a poison to vegetation. 82. T. Smith and J. van Nor den Bazalgette. 1868. No. 3,562. Treat sewage with a mixture of marl, clay, mould, schists, refuse products, ashes, treated by mineral acids. The term refuse products includes substances some of which would be useless, and others positively injurious. 83. A.M. Clark. 1868. No. 3,714. Treats sewage with a double phosphate of magnesia and iron. 84. M.J.Anderson. 1869. No. 3,550. Precipitates with sulphate of alumina (lib. to 100 gals.) followed up by 5 Ibs. slaked lime. This patent became the property of the " Rivers Purification Association," and has been worked for some years at Coventry and Nuneaton, followed up, however, SEWAGE PATENTS. 203 by irrigation. It will be observed that the lime is much more than sufficient to neutralise any acids likely to be present in the sewage, and will therefore act as a substantive precipitant. 85. W. H. Hughan. 1870. No. 67. Uses to sewage natural phosphates, treated with dilute acids, diluted with urine and mixed with night- soil, along with the cement indicated in his former patent, 1,868, No. 2883. 86. D.Forbes and A. J. Price. 1870. No. 607. Add to the sewage phosphate of alumina, previously dissolved in sulphuric acid, and follow up with lime. The proportion of phosphate preferred is 2 Ibs. to 1 ,000 Ibs. of sewage. This process, like the two following, came into the hands of the Phosphate Sewage Company, and was worked at Hertford. 87. D. Forbes and A. P. Price. 1870. No. 1,137. This specification differs very little from that of 1870, No. 607. The inventors now propose to heat the phosphate of alumina in hydrochloric acid or in a mixture of that and sulphuric acid, and they also add deodorising agents, such as animal or vegetable char- coal. 88. A. P. Price. 1870. No. 1,314. This invention, again, borders very closely upon Nos. 607 and 1,137 of the same year. The inventor uses "natural phosphates of iron, lime, and alumina." 89. G. W. Wigner. 1870. No. 1,354. This is an improvement upon No. 1,954 of 1868. The inventor uses : Parts. Alum .... 600 Blood ... i Clay .... 1,900 Magnesia ... 5 204 SEWAGE TREATMENT. Parts Manganate of potash . 10 Burnt clay . . .25 Chloride of sodium . . 10 Animal charcoal . . 15 Vegetable charcoal . . 20 Magnesian limestone . 2 Sulphate of alumina . .169 Sulphate of iron . . 3 Sulphate of lime . . 66 Alumina . . .94 2,920 There is added the proviso that, instead of the last four substances, 488 parts of crude alum may be used, making the entire quantity of alum to be used 1,088 parts. It is certainly strange to find alum and sulphate of alumina combined in the same formula. Alum is not only much more costly and less readily soluble, but has the serious disadvantage of introducing into the effluent water, in pure waste, sulphate of potash or sulphate of ammonia. The useless ingredients of the patent No. 1,954 f J 868 (magnesia, burnt clay, chloride of sodium, and magnesian limestone), are re f ained, and two new ones, sulphate of lime and alumina (unless the hydrate be meant), are introduced. This patent came into the possession of the Native Guano Company, but it has long been abandoned in favour of simpler and more rational processes. 90. B. G. Sloper. 1870. No. 1,706. Mixes fresh sewage with stale sewage to promote fermentation. Then draws off the supernatant water (!), and mixes with the sediment a salt of magnesia and phosphate of soda or lime. To deodorise the sewage he uses sulphate of alumina, sulphate of iron, sulphate of lime, and chloride of lime. SEWAGE PATENTS. 205 To the fermentation process there is a strong objec- tion, mentioned under No. 3,203, A.D. 1868. Sulphates of alumina and iron precipitate, but they have little deodorising power. Sulphate of lime is altogether out of place in sewage treatment, and chloride of lime, if used in sufficient quantity to deodorise sewage, will destroy fish in any river into which the effluent may make its way. gi.J.J.Hays. 1870. No. 2,297. Treats sewage with " ground peat, peat charcoal, or other suitable material." Lets settle, and filters effluent. 92. G. Bischof. 1870. No. 2,516. Passes sewage upwards or downwards through a layer of spongy iron, about a foot thick, at the bottom of a tank or filtering bed. The solids are to be pre- viously filtered out. This process, which involves double filtration is, of course, inapplicable when the sewage contains any sub- stance capable of acting on iron. 93. F. Fenton and S. Hollins. 1870. No. 2,534. Treat sewage with a combination of gypsum, sulphate of lime, bisulphate of iron, soot, chalk, salt, cinder breeze or ashes, or a combination of the bind, clay shale, alum shale, or barren shale of the coal measures, or alum clay or alum shale, either raw or roasted with any or all of the above. For acid waters they use any of the above ingredients, or salt and lime, or salt, lime, gypsum, and chalk, or plaster of Paris, or calcined gypsum, hydrated together or separately, and afterwards mixed. The product may be used " as a substitute for coprolites " (!). The error of using soot, sulphate of lime, chalk, and salt in sewage treatment has been already explained. Most clay shales, raw or roasted, are quite inert. 206 SEWAGE TREATMENT. 94. C. F. Kirkman. 1870. No. 2,653. Seeks to disinfect sewage by treatment with carbonic acid, and by passing through a receptacle in which are a number of zinc and copper plates, by which " a con- tinuous current of electricity is made to pass through the sewage." 95. /. /. Hays. 1870. No. 2,838. Treats sewage with peat charcoal, and filters through a bed of peat charcoal, and afterwards through carbonate or hydrate of lime and sand. (See 1870, No. 2,297.) It is necessary to remark that the actions of carbonate of lime and of hydrate of lime upon sewage are not alike. 96. A . Bryant and S . H. Culley. 1870. No. 3,107. Let sewage deposit in settling tanks, after the addition of deodorising materials, such as carbolic acid, and then filter through sawdust, dried or charred. 97. F. Hille. 1870. No. 3,167. Uses as a disinfectant for sewage, chloride of zinc, calcium and magnesium, lime and gas-tar. (See specification of E. Siivern, 1867, No. 119, in which the use of chloride of magnesium, in combination with lime and coal tar is already mentioned.) 98. H. Y. Darracott Scott. 1870. No. 3,169. Treats sewage with lime, preferably gas-lime (!), to- gether with certain metallic salts, suitable for preci- pitating sulphuretted hydrogen. These agents are to be introduced at different parts in the course of the sewers. This system is objectionable since the deposits produced may accumulate and putrefy in the sewer. The metallic salts best fitted for removing sulphuretted hydrogen are poisonous, and too expensive. 99. C. Rawson y P. Ovenden, James Wylde, W. McCree, andH. Hill. 1870. No. 3,399. Improvements on No. 1,954, A.D. 1868, and on No. 1,354, A.D. 1870. The inventors substitute for blood, SEWAGE PATENTS. 207 <( albuminous, albumenoid, or gelatinous substances." They also propose an alkaline mixture to be added if necessary to the sewage, either before or after the ingredients mentioned in the two former patents. 100. 5. Proctor and J. M. Sutton. 1871. No. 297. Remove large; solids from the sewage by mechanical arrangements ; add then disinfectants such as carbolic acid, and filter. 101. G. B. SloperandF.J.J. Washer. 1871. No. 329. Treat sewage first with an alkali, to decompose nitro- genous matters and convert them into ammonia ; then add salts of magnesia and soluble phosphates to pre- cipitate ammoniacal magnesium phosphate, and complete the 'process by adding " small quantities of lime with sulphate of alumina, or chloride of lime, or protosulphate of iron." Treatment with an alkali fails to decompose some possible nitrogenous compounds altogether, and acts upon others only at very high temperatures. 102. C. Baly. 1871. No. 351. Treats sewage with charcoal from the manufacture of acetic acid and slaked lime ; one part charcoal, two lime to five sewage. 103. A. P. Vassard. 1871. No. 1,211. Treats sewage first with a solution of superphosphate and phosphate of soda, then with sulphate of magnesia, sulphate of alumina and sulphate of ammonia (!). A little lime may also be added. 104. F. Fenton. 1871. No. 1,897. In addition to the processes given in No. 2,534, A - D - 1870, the inventor forces atmospheric air through the sewage. 105. E. Taylor. 1871. No. 1,969. Treats the solids separated from the liquid sewage with 208 SEWAGE TREATMENT. a mixture of chloride of lime, sugar (!) and alum. The same ingredients are apparently to be used also for urine and blood. 1 06. /. T. Lupton. 1871. No. 2,140. Treats sewage with 20 to 40 per cent of carbon, it may be ashes, with a small amount of phosphate of lime. 107. H. Y. Darracott Scott. 1871. No. 2,243. Precipitates sewage with quicklime, dries precipitate and calcines it. Uses the calcined precipitate as manure, or as mortar, or as cement. If used as manure, " super- phosphate may be manufactured therefrom." A substance containing so much lime and so little phosphoric acid cannot prove a very profitable material. 108. /. Banks and W. Walker. 1871. No. 2,495. Filter after settling, and mix sediment with sawdust, straw, etc. 109. /. Hiirrow. 1871. No. 2,659. Treats with an iron, salt and an alkali. HO. /. B.Pow. 1871. No. 2,760. Treats in first tank with copperas ; then filters through i, gypsum, magnesian limestone and charcoal ; 2, aluminium shale from the lias containing sulphates ol aluminium and potassium, with a portion of sulphate of iron combined with vegetable charcoal ; 3, spongy iron, and 4, cocoa-nut fibre or peat charcoal. in. F.L. Hahn Danchell. 1 87 1 . No. 2,903. Treats sewage with a mixture of clay or lime, or both with peat, the mass being charred. 112. A. P. Vassard. 1871. No. 2,926. Treats sewage first with lime ; then adds to the liquid oxide of barium and biphosphate of lime ; then with chloride of lime and aluminate of soda. Instead of oxide of barium, the sulphide or other soluble salt may be used j instead of biphosphate of lime ordinary superphosphate or other phosphate. Also other salts of SE WA GE PA TENTS. 209 magnesia (!) may be used instead of the chloride, and various alkaline re-agents instead of aluminate of soda. The objectionable character of barium compounds has been already noticed ; the sulphide (sulphuret) as giving off sulphuretted hydrogen is the worst. 113. /. Cole and W.Abbott. 1871. No. 2,975. Precipitate the sewage in a tank, but do not state what is the agent employed. 114. H. Smith. 1871. No. 2,997. Reduces the temperature of the sewage and of the air above the tanks, the latter by allowing liquid carbonic acid to evaporate into it. Even if this process could be carried out on the large scale it would be useless, as water, if freezing, is not freed from either its suspended or dissolved impurities. 115. /. F. Fahlman. 1871. No. 3,233. A new mechanical arrangement, where no particular method of disinfecting the sewage is claimed. 116. /. A. Wanklyn. 1871. ^0.3,436. Obtains ammonia from sewage, driving it off either by heat, or by " a current of air of a suitable temperature," and condenses the ammonia by means of acid in a coke tower. 117. H. Y. D. Scott. 1871. No. 3,515. Brings the effluent from, it would seem, any pre- cipitation process in contact with charcoal. When the charcoal is saturated with ammonia it is dried at a gentle heat so as not to expel the ammonia, then heated to redness and the ammonia collected by any suitable means. The power of wet charcoal to absorb and retain ammonia from liquids is not strikingly great. 1 1 8. F. G. Prange and W. Whitthread. 1872. No. 379. Treat sewage with a solution of dicalcic phosphate in an aqueous solution of mono-calcic phosphate, with an p 210 SEWAGE TREATMENT. alkaline earth or alkali, such as lime. If there is an excess of free ammonia, magnesium salts may also be added. 119. A. M. Clark. 1872. No. 388. Fixes the ammonia in sewage by means of bi-magnesian phosphate or calcic magnesian phosphate. 1 20. /. Robey. 1872. ^7.435. Mixes peat and clay, burns the mixture, and uses it in treating sewage. 121. Silvester Fulda. 1872. No. 448. Treats sewage with unslaked lime, sulphate of soda, and, if required, of nitrate of soda, borax, and silica. The uses of sulphate of soda in sewage treatment are almost as hard to imagine as the circumstances under which nitrate of soda and borax can be requisite. Except the original sewage is strongly acid, the effluent from this treatment must be alkaline. 122. F. Hille. 1872. No. 484. Mixes sewage with chloride of magnesium, then passes it into another tank, where it is treated with milk of lime, forces carbonic acid gas into it, or adds instead a small quantity of perchloride of iron, and filters over charcoal. In hot weather, a mixture of lime and tar may be added in a subsequent tank, or in the mixing-tank. It is hard to see the precise novelty in this process. See the inventor's previous patent, No. 3,167 of 1870. 123. 5. W. Rick. 1872. No. 547. Lixiviates aluminous schists, adds to the liquor chloride of sodium and evaporates down. In this manner is obtained a crude chloride of aluminium, fit for treating sewage. 124. W.E.Gedge. 1872. No. 626. Treats sewage and other ammoniacal liquids in a succession of boilers and passes the ammonia into dilute sulphuric acid. SEWAGE PATENTS. 211 125. R.Blackburn. 1872. No. 671. Screens and strains sewage, and treats the liquid portions chemically (how, it is not stated), or uses them for irrigation, or allows them to run into a water-course, As in several patents, the fact that the " liquid portions " of sewage are at once the most valuable, and, if run direct into a watercourse, the most dangerous, is here overlooked. 126. H. Y. D. Scott. 1872. No. 849. Precipitates the suspended impurities with lime, prefer- ably dolomitic ; treats the effluent from first precipita- ting tank with phosphoric acid or a phosphate to preci- pitate lime ; treats then the effluent from the second tank may be treated with phosphate of magnesia to extract the ammonia. Various things are also mentioned which a may " be done. 127. Dugald Campbell. 1872. No. 944. Treats sewage with acid, phosphate of lime, and then adds milk of lime. 128. 5. W.Rich. 1872. No. 1,243. Converts the alumina and peroxide of iron in burnt shales into sulphates by treatment with sulphurous acid. The process is carried on continuously in a kiln, in which the shale is burnt while sulphurous acid gas (from burning pyrites) are introduced below. The product formed is lixiviated, and the liquor used for treating sewage. 129. T. Christy. 1872. No. 1,257. Disinfects foul waters with heavy oils, and then treats them with silica to form a mixture which the inventor terms " silicoid." 130. F.L.H. Danchell. 1872. No. 1,394. Treats sewage with animal or vegetable refuse, mixed with loam, clay, phosphate of alumina, lime, carbonate of lime, or phosphate of lime, and charred. 212 SEWAGE TREATMENT. 131. James Robey. 1872. No. 1,421 Chars arable soil in retorts, and uses the product for treating sewage. 132. James Robey. 1872. No. 2,181. Chars sewage sludge from processes No. 1,954 of 1,868, or No. 1,354 f I ^7o, and uses it for treating sewage. 133. IsaacBrown. 1872. No. 2,279. A mere mechanical arrangement which aims at puri- fying sewage by settling, screening and straining. 134. H. Y.D. Scott. 1872. No. 2,538. Precipitates the sewage with lime, treats the effluent with the " phosphatic precipitants " mentioned in No. 849 of 1872, with or without charcoal. It is very diffi- cult to find any essential difference between the process here described, and that given in No. 849 of 1872. 135. B. W. Gerland and E.Johnson. 1872. No. 2,569. Char fresh turf, and sawdust, spent tan, mixed with loam, and use the product for filtration, with or with- out the addition of phosphoric acid. They divide the sewage into two branches ; to the one is added phos- phoric acid, with or without the charcoal dust, and to the other, milk of lime. The precipitate is let settle, and the effluent filtered through the charcoal above- mentioned. 136. W. Astrop. 1872. No. 2,991. A mechanical method of separating the solids from the liquid portions of sewage. 137. H. Y.D.Scott. 1872. No. 3,028. A method of adding lime to sewage, and a process for drying sewage sludge. 138. /. A. Manning. 1872. No. 3,356. Evaporates sewage to dryness, passing the fumes given off into a furnace (!). The cost of this in the case of a large city ? SEWAGE PATENTS. 213 139. G. Alsing. 1872. No. 3,412. Converts sewage and night-soil into manure by mix- ing with sulphate of lime. 140. C . Hills and B . Biggs . 1872. No. 3,464. Mix sewage in an air-tight tank with lime to liberate ammonia. Force air through the sewage into a second tank containing sulphurous acid. Or they force sul- phurous acid into the sewage instead of air. 141. D. Curran and James Dewar. 1872. No. 3,533. Use peat, either alone or along with chalk, lime, earth, etc., for filtering, disinfecting and absorbing foul waters. 142. H. Y.D.Scott. 1872. -Afo. 3,755. Uses the effluent from a lime-process for working water-closets. 143. H. Y. D. Scott. 1873. No. 154. Treats sewage with lime in excess, and adds to the efflu- ent " soluble salts of cheap metallic oxides." After this, the effluent may be filtered through charcoal, or may be run at once into a stream. 144. /. L. D. Target. 1873. No. 168. Chars sewage solids mixed with sawdust, tar, etc., and uses them as fuel. Boils the sewage along with lime and catches the ammonia. 145. E. C. Hamilton, W. R. Preston, and H. Jones. 1873. No. 187. Mix shoddy with sewage. 146. James Robey. 1873. ^7.230. Chars the sludge obtained under No. 1,954 of 1868, and No. 1,354 of 1870, with or without an admixture of clay, and uses it for treating sewage. As the inventor claimed the use of the same sewage sludge charred, for the same purpose, in patent No. 2,181 of 1872, but abandoned the idea without proceeding to the great seal, the question might be raised, whether he did not, by so doing, anticipate the present patent ? 2i 4 SEWAGE TREATMENT. 147. J.Jacobsen. 1873. No. 266. Treats sewage with phosphate of lime and sulphuric acid, diluted with the liquid sewage itself. 148. H. Y. D. Scott. 1873. No. 296. Precipitates the suspended matters in sewage by lime- water in excess. Treats the effluent with acid solution of phosphatic substances. If this is added in excess, the effluent is again treated with lime. Here we recog- nise a strong family likeness to the inventor's previous processes. 149. Baldwin Latham. 1873. No. 331. Treats the deposits from various sewage processes preferably that from No. 3,650 of 1869 with sulphuric acid to obtain fresh material for treating further portions of sewage. The economy of this process, and of similar processes, is very doubtful, since a portion of sulphuric acid (the expensive article in making sulphate of alu- mina) is wasted by the organic matter and the lime present in the deposit. 150. F.H. Atkins. 1873. No. 556. Filters sewage through ground coke or cinders con- verted by pressure into slabs. He also applies "galvanic, . magnetic, or electric action to filtering apparatus, reservoirs, or tanks, for the purpose of precipitating organic and inorganic matters in suspension or solution." 151. R. S. Symington. 1873. No. 912. An improvement on No. 2,667 of 1868. The effluent water is to be purified by " falling in a broken manner through a sufficient height before passing through the last filtering tank." 152. G. Alsing. 1873. No. 1,319. Mixes sewage sludge with dry gypsum. 153. H. Y. D. Scott. 1873. No. 1,445. The sewage deposit, of course from a lime process, is SEWAGE PATENTS. 215 treated with more lime, and mixed with some material wetted with sulphuric or hydrochloric acid. The com- pound obtained is used for deodorising pail-stuff, and finally employed as manure. Chloride of lime, or chloride of zinc or iron, or sulphates of those metals, may also be added to the compound. Salts of zinc are injurious to vegetation, and cannot, therefore, be safely added to any kind of manure. 154. H. Y. D. Scott. 1873. No. 1,509. Dries sewage deposits from lime processes ; are dried in retorts and used along with lime, chloride of lime and charcoal. 155. Walter Brown. 1873. .Afo. 1,555. Calcines shaly minerals with exclusion of air, quenches them with water, and uses the pieces for mak- ing a filter-bed, or for treating sewage in other ways. It must be remembered that many " shaly minerals " contain nothing capable of yielding a soluble salt of alumina after ignition. 156. E.Moriarty. 1873. No. 1,686. Treats sewage with, per 28 Ibs. : 12 ozs. acid phos- phate of magnesia, 6 ozs. sulphate of iron, 4 ozs. sulphur (!), 4 ozs. ammonia, 4 ozs. phosphoric acid, 4 ozs. nitrate of soda, 3 ozs. nitrate of potash, 4 Ibs. gas tar, 6 Ibs. wood charcoal, and sulphate of lime to bring the whole to a solid state. This process does not aim at producing an effluent, and is intended for cesspool matters rather than for town sewage. \tf.B.Green. 1873. Afo. 1,885. Draws sewage gases through a fire, lets solids deposit as manure, and runs the liquid into a river. 158. Jos. Townsend. 1873. No. 1,967. Treats sewage with any of the three following mix- tures : i. 100 Ibs. of a phosphate containing 40 per cent. 216 SEWAGE TREATMENT. phosphoric acid and 20 per cent, alumina is mixed with 50 Ibs. of lime, and by preference 2 to 5 per cent, of soda or potash, or an equivalent quantity of carbonate, sulphate, or sulphite of soda or potash, " with sufficient lime to set free the alkali." The resulting products are " principally phosphate and aluminate of lime." For the lime may be substituted 36 Ibs. magnesia, or 47 Ibs. lime and 8 Ibs. magnesia. 2. A mixture of alumina with lime or magnesia, or both lime and magnesia. 3. A " substance containing alumina associated with silica " is mixed with lime or magnesia and alkali, or u substances yielding alkali " are added. 1 59- Jo/m Leigh. 1 873 . No. 2,07 1 . Adds a solution of an earthy salt, followed by a solution of silicate of soda or potash. As earthy salt chloride of lime may be used (!). If much gelatinous or aluminous matter is present tannin is also added. For " aluminous " the correct reading is probably " albuminous." 1 60. Jeremiah Marsden and J. Collins. 1873. .#0.2,317. Treat sewage per 200,000 gallons with 12 cwt. lime, 4ocwt. coal ashes, i6cwt. charcoal, "and a small quantity of an acid salt of soda, potash, iron, manganese, or the like." This process is, or has been, at use at Bolton. How manganese can be called " the like " of soda or potash is not apparent. Coal ashes are of very doubtful value. 161. Robert Knott. 1873. .#0.2,442. Treats sewage with a mixture of quicklime and soda .introduced into the sewage in a boiling state. 162. F.Jacobsen. 1873. -#0.2,454. Precipitates sewage with the refuse " obtained after the lye-water of paper-mills has undergone the soda- recovering process." To facilitate precipitation he further adds common salt, sulphate of zinc, chloride of SEWAGE PATENTS. 217 iron, alum, slaked lime, and " the water from electric batteries." Sulphate of zinc is fatal, common salt useless, and the water from batteries very doubtful. 163. F.Jacobsen. 1873. No. 2,455. Treats the waste water from paper-mills and other works with lime. To assist the process he adds " common salt, sulphate of zinc, chloride of iron, and perchloride of iron." 164. William White. 1873. No. 2,532. Neutralises sewage with lime if necessary, and treats with sufficient chloride of calcium to precipitate sulphates, carbonates, and phosphates along with albuminous and other matters. The solution is then treated with sulphate of iron to convert the excess of chloride of calcium into sulphate, setting free chloride of iron, which may be precipitated as oxide by the addition of lime. The final effluent will therefore be alkaline after these four successive treatments. In the deposit there will be sulphate of lime, which, as already explained, is not to be desired. 165. James Robey. 1873. No. 2,534. Treats sewage with raw peat, and adds any suitable precipitating agent. 166. C.Rawson, W. C. Sillar,J. W. Slater, and T. S. Wilson. 1873. No. 2,662. Pass sulphurous acid, chlorine, or other disinfecting gases through sewage, and then precipitate with sul- phate of alumina, etc., if needful. This process was mainly intended for blood. For sewage it is too costly and circumstantial. 167. R. Goodall. 1873. No. 2,791. Adds per i ,000 gallons 2 bushels of fine ashes and 2i 8 SEWAGE TREATMENT. 23lbs. slaked lime. After agitation, I pint sulphate of iron and 7 pints of solution of sulphate of magnesia. 168. W. Whitthread. 1873. No. 3,169. Treats sewage with manganese tetra-chloride. Other haloid salts of manganese may be used. Finally, an alkali is added. 169. A. C. Fraser and W. Watson. 1873. No. 3,632. Treat sewage with calcined schist, which may be saturated with dilute sulphuric acid, and mixed with clay and sulphate of lime. The outflow from the last tank passes into a filter charged with lime, calcined schist, charcoal and sand. 170. H. Y.D. Scott. 1873. No. 3,742. Sewage is precipitated in the " ordinary " manner with lime, and the effluent is treated with "an impure sulphate or chloride of lime and alumina," prepared by " digesting prussiate of potash charcoal with dilute sulphuric or hydrochloric acid." Chloride of lime cannot be obtained at all in the way described. Alumina is present in the charcoal merely as an impurity present in the carbonate of potash used in prussiate-making. The product really obtained will consist mainly of sulphate or chloride of iron, which can be more conveniently or cheaply obtained in other manners. 171. W. White. 1873. No. 3,781. Precipitates sewage with lime-charcoal, a calcined mixture of chalk, peat, and sawdust. Soluble phosphate may be added to the sewage before the treatment with lime-charcoal. " Lime-coke" may also be used, made by burning a mixture of small coal and lime. Ground mineral phosphates may be mixed with peat, or other form of carbon, and used as above. Industrial waste waters unfit for manure may be treated with " lime- SEWAGE PATENTS. 219 clay-charcoal," a calcined mixture of lime and clay with or without carbon. 172. W. White. 1873. No. 3,781. Disclaims the method of preparing the precipitating agents mentioned in the last specification. 173. B. Green. 1873. No. 3,833. Lets the sewage settle in pits, carrying the gases into a furnace, and letting the liquid run into " a river, the sea, or elsewhere." This patent, like certain others, is based on the mistaken notion that sewage, after spontaneously de- positing its " sludge," is harmless, and may be safely run off into rivers. 174. Paul Curie. 1873. ^0.4,181. Treats the sewage with a " disinfectant," sulphate of iron, clay, chalk, etc. The products of combustion from a furnace, mixed with air, are driven through the sewage, which is then apparently evaporated to dryness. 175. A. E. Schmersahl. 1874. No. 160. Treats sewage with a mixture of 2 parts sulphuric acid and I part hydrochloric acid, and then with lime. The result of such treatment will be the formation of sulphate of lime art evil and chloride of calcium. 176. H. M. Synge. 1874. No. 255. A complicated filtration process through successive tanks charged with materials of increasing fineness. 177. E. H. C. Monckton. 1874. No. 265. Purifies sewage by passage through electrified channels, or drives ozonised water into sewage for the purpose of purifying it. Recovers metals in solution from the sewage of manufacturing towns by an electric process. Uses windmills as a power to generate electricity for purifying sewage. Ozone would doubtless prove a powerful deodorising 220 SEWAGE TREATMENT. agent for sewage if its price permitted. It might be interesting to try the action of electricity on sewage where power for driving dynamos could be had free of cost. 178. H. Y. D. Scott. 1874. No. 283. Precipitates sewage by lime, or removes the solids by other means. Passes liquid through filters charged with " phosphate of iron salts," or adds such salts to the liquid. Runs effluent through filters of lime and char- coal. Gives methods for making the phosphate of iron salts, to which, before use, lime refuse from soda or gas- works may be added. The effluent here will apparently be alkaline. It is interesting to note how many changes, capable of being patented, have been rung on the old lime process, in which its cardinal faults are retained, whilst its cheap- ness and simplicity are lost. 179. H. Y.D. Scott. 1874. No. 653. Precipitates sewage by lime mixed with soluble phosphate, or phosphoric acid, or soluble metallic salts. Lime mixed with " soluble metallic salts " will pre- cipitate those most likely to be used for sewage purposes, and render them comparatively inert. It will also render the soluble phosphate or the phosphoric acid insoluble. Phosphoric acid is, further, an agent far too costly to be used in sewage treatment, 1 80. Rupert Goodall. 1874. No. 848. The author places in one vessel a " mixture of calcium and carbon," in another slaked lime and carbon, or slaked lime alone, and in a third vessel a solution of sesqui-persulphate of iron, and delivers these into the sewage. 181. W.R.Lake. 1874. M?. 1,415. Boils the sewage, and receives the volatile matters in a series of Woolf's bottles containing sulphate of SEWAGE PATENTS. 221 iron, lime, sulphuric acid, etc., to fix the ammonia. The residue left in the boilers is cooled and used as manure. How the residue is to be rendered inoffensive we are not informed. Quaere How many boilers would be required to receive the sewage of London ? 182. /. Towle. 1874. No. 1,426. Delivers sewage into pits into which town refuse is also cast. Spent hops and cut straw are also placed in the pits. 183. /. H. Kidd. 1874. No. 1,764. Allows the sewage solids to settle in tanks and runs off the effluent water. Adds, apparently to the deposit, salt or lime and carbonised shale. 184. Rupert Goodall. 1874. No. 1,826. Treats sewage per 1 ,000 gallons with i quart of sesqui- persulphate of iron, and I pint thereof, and I pint of nitrate of iron. There may also be added along with the iron liquors saturated solutions of lead salts, or of ferro-cyanide of potassium. Or a mixture of gas-lime I or 2 parts, slaked lime I or 2 parts, and animal carbon 2 to 4 parts may be added in the proportion of 27 Ibs. per 1,000 gallons. After agitation, iron salts as above are added, or a mixture of 10 parts animal carbon, 2 or 3 brown oil of vitriol, or 3 or 4 nitrosulphuric acid, after which the whole is again agitated. This patent, it is believed, was assigned to the Rivers Clarification Company, Limited, of Leeds. 185. W. H. Hughan. 1874. No. 1,959. Treats the sewage with an "antiseptic" made of Portland cement, sulphates of soda, magnesia and potash mixed in oil, preferably mineral oil, and then precipitates with a mixture of Portland cement, fluor- spar and oil. The effluent is filtered, and the pre- cipitate with the residue from the filtration is mixed 222 SEWAGE TREATMENT. with hot superphosphate. The " antiseptic " may also be made from seaweed, clay and soda -waste treated with sulphuric acid. 1 86. S. Hallsworth and R. Bailes. 1874. No. 2,408. Agitate sewage in a tank with either persulphate of iron made from iron pyrites, or a mixed solution of sulphuric acid and iron from the beds of coal and iron pyrites, or sulphuric acid mixed with the mother- liquor left after crystallisation of copperas, or a mixture of sulphuric acid with other equivalent or suitable solution of iron, or of a solution of copperas and sul- phuric acid. 187. A. E. Schmersakl. 1874. No. 2,439. Treats sewage with a mixture of 2 parts dilute sul- phuric acid and I part hydrochloric acid, enough to make the sewage acid. Or the acids may be added separately, or phospho-muriate of lime, commonly called bone-liquor, may be employed, or chloride of manganese. Sufficient milk of lime is then added to neutralise the acid. See the inventor's previous patent (No 1 60, of 1874). 1 88. W.A.Lyttle. 1874. ^7.2,446. Gives directions for deodorising sludge ; how it is to be precipitated the inventor does not state. 189. H. Y.D.Scott. 1874. No. 2,450. The object of this patent is the recovery of carbonate of ammonia from sewage. If a manure is to be made, magnesia and phosphate of magnesia are agitated with the liquid to be treated. 190. W. Spence. 1874. ^0.2,461. Treats sewage in lead-lined tanks having false bottoms of copper. U A coil of pipes is inserted in such a manner that the half of the pipes are above and the other half below the false bottom." To the first tank acid is added in quantity sufficient to fix the ammonia SEWAGE PATENTS. 223 and dissolve the phosphates of lime. Steam is then admitted into the coils. There is no mention of any phosphate of lime having been added. 191. G. Willett, R. J. Harris, and James Lund. 1874. No. 2,567. Filter through tanks of coal-ashes or coke. 192. H. Y. D. Scott. 1874. No. 2,568. Treats phosphates with acids, adds magnesia, and uses the product to fix the ammonia of urinous or other ammoniacal liquids. 193. /. H. Kidd. 1874. No. 3,199. Lets sewage settle, runs off effluent and dries the solids. 194. JamesMcIntyre. 1874. No. 3,225. Depositing tanks without the use of any precipitant or deodorant. 195. 5. HallsworthandR.Bailes. 1874. No. 3,459. The inventors take per 5,000 gallons of sewage, i| gallons of pyrites liquor and 50 Ibs. of slaked lime, or 100 Ibs. of gas lime. 196. A. F. Paget. 1874. No. 3,613. Treats waste waters with a mixture of sesqui-chloride of iron and aluminium chloride, and afterwards with lime-water. The chloride solution is obtained by dis- solving any argillaceous iron ore containing phosphoric acid in hydrochloric acid. Carbolic acid, permanganate, or other disinfectants may be added as the water leaves the mixing tanks. 197. G. Mackay. 1874. No. 3,751. Treats waste waters with per-salts of iron, preferably the perch loride or persulphate, and thej^ wjrth lime or other suitable alkali. F* Of THt UNIVERSITY 224 SEWAGE TREATMENT. 198. V. B. Halle. 1874. No. 3,784. A mere process of precipitation with lime followed by filtration. 199. F. T. Bond. 1874. ^0.3,799. Uses for disinfection sulphates of iron, aluminium and copper, carbolic acid, terebene potassium, bichromate and permanganate. 200. Rupert Goodall. 1874. No. 4,158. Mixes ashes and gas lime or waste lime from ammonia works with sulphuric acid till effervescence ceases ; adds water and uses one to two gallons of this to 1,000 gal- lons of sewage. The sewage is first treated with slaked lime, or with a mixture of six parts slaked lime and one part animal carbon. Five pounds of lime or 20 Ibs. of the com- pound may be used for every 1,000 gallons of sewage and \ to i gallon of the first described mixture is then stirred in. 20 1. J. C. Morrell. 1874. No. 4,247. Treats sewage with alum, quicklime, or a crystallised chemical substance, which does not appear to be named or described. 202. H. Y. D. Scott. 1874. No. 4,305. Lets sewage deposit in a tank. To the emuent from this he adds milk of lime in a second tank. The lime emuent is then treated in another tank with an acid solution of phosphate of iron, lime, and alumina. Successive precipitations with different agents are bad on account of the great outlay for plant and labour which they involve. 203. W.J.Pughsley. 1,874. A 7 ^ 4,373- Treats .refuse liquor from tin-plate works by filtering first through limestone, then through charcoal, and then through bone-ash. The two latter are separated from each other by a perforated board, and the bones are SEWAGE PATENTS. 225 supported upon an iron plate. The bones are removed from time to time and used as manure. 204. G. Mackay. 1875. No. 91. Treats sewage with mixed solutions of perchloride and persulphate of iron. Salts obtained from alum, alkali, and galvanising works may be mixed with the solution. Lime or other alkali is then added. 205. G.Rydill. 1875. No. 150. Filters through a bed of ashes. 206. /. Box,E. Aubertin, L. Boblique, and H. Leplay. 1875. No. 214. Treat sewage first with a ferruginous phosphate of soda or potash and then with a salt of magnesium. 207. G. Rydill. 1875. No. 399. Treats sewage, etc., with caustic soda or lime. Filters through ashes, and forces air through it from perforated pipes. 208. /. Hallsworth and R. Bailes. 1875. No. 573. Treat sewage with two clarifying mixtures. I. Spent residues of iron pyrites or other ores containing iron as peroxide are ground and mixed with an equal weight of any of the following : Copperas, dry copperas, cop- peras bottoms, copperas sediment, or sediment from the manufacture of nitrate of iron. The mixture is cal- cined and allowed to cool. 2. The pyrites residue or iron ore is saturated with liquor from the pyrite beds at copperas works, or with dilute sulphuric or hydro- chloric acid. The sewage is first treated with slaked lime or with calcium (?) in the proportion of 78 Ibs. of the former or 156 Ibs. of the latter to 5,000 gallons of liquid, and mixed together ; 23 Ibs. of mixture No. I or 46 Ibs. of No. 2 is then mixed with a portion of sewage and then added to the lime sewage. 209. W. M. Brown. 1875. No. 1,335. A kind of filtration process. Q 226 SEWAGE TREATMENT. 210. T. Page. 1875. No. 1,625. A screening arrangement, the deodorising agent is named. 211. P. Spence and F. M. Spence. 1875. No. i ,704. Manufacture of alumino-ferric cake, used in sewage treatment. 212. /. Hill. 1875. No. 1,745. A contrivance for expressing moisture which the inventor applies to separating the solid from the liquid portions of sewage. 213. John Yule. 1875. No. 1,759. A barge for conveying sewage. 214. M.F.Anderson. 1875. No. 1,845. Treats sewage sludge with coprolite, phosphorite, or ground bone, together with sulphuric acid. 215. J. J. Coleman. 1875. No. 1,954. Filters sewage through spent shale from the mineral oil works, or the shale may be added in the sewers and the sewage allowed to settle in tanks. The effluent is passed through beds of shale. See Specification of R. Irvine, 1886, No. 2,218. 216. P. Spence and F. M. Spence. 1875. No. 1,961. Improvements in alumino-ferric cake, rendering it more basic and better adapted for treating sewage. 217. D. Wilks. 1875. No. 1,972. Treats sewage in tanks with powder obtained by car- bonising town refuse. The effluent is filtered. 2 1 8 . /. Odams and R. Blackburn . 1875. ^0.2,358. Revolving screens for separating the solids from sewage. 219. /. Hanson. 1875. No. 2,675. Precipitates sewage with, per 100,000 gallons, slaked lime 20 to 23 Ibs., soot or flue dust J lb., black-ash (by which the inventor means oat waste from the alkali works) 30 Ibs. SEWAGE PATENTS. 227 220. T. Stevens. 1875. No. 2,829. Adds sulphate of lime and common salt to the sewage on its way to the settling tank. Adds milk of lime as it enters the tank, and finally filters. 221. A.M. Clark. 1875. No. 3,162. Treats sewage, according to circumstances, with i. Aluminate of soda, alone or in conjunction with soluble alkaline or earthy phosphates. 2. The same phosphates mixed or combined with oxide or phosphate of iron along with a soluble salt of magnesia. 3. Oxides of nitrogen higher than nitrous oxide but lower than nitric acid. In consequence of this patent, no general claim to the use of aluminate of soda can be maintained by subsequent inventors. 222. /. W. Slater. 1875. No. 3,368. Ignites sewage sludge in retorts, obtaining a carbon which may be used in treating gas. The volatile pro- ducts are condensed and yield ammonia and illuminating gas. The gas thus obtained is of " 8 candle " power. 223. C. Rawson and J. W. Slater. 1875. No. 3,703. Use in place of alum aluminous shales, such as those of Campsie, either in their raw state or artificially weathered by treatment with super-heated steam, or steam and atmospheric air, or hot air charged with moisture, or sulphurous acid gas along with air or steam. 224. A. Le Tellier. 1875. No. 4,061. A mechanical arrangement for treating sewage. 225. James Bannehr. 1875. No. 4,122. A mechanical arrangement. The effluent is filtered and treated with electric currents. 226. H.M.Ramsay. 1875. No. 4,420. Filters sewage first over loose charcoal and scrap metals 228 SEWAGE TREATMENT. and then over " porous-plastic carbon." These filters may be cleansed by reburning or by forcing clean water through them. Where, in the latter case, is this water to go ? 227. John Hanson. 1876. No. 225. Improvement on No. 2,675, f I ^7S- Blast-furnace slag and "Paris white" (i.e., whiting), with or without the addition of sulphuric or hydro-chloric acid, are used to precipitate sewage, either alone or mixed with the ingredients named in the former specification. If the slag is added without acid, it is inert. If acid is used it will be neutralised by the " Paris white." 228. H. Y. D.Scott. 1876. No.$22. A complicated process for treating solid excreta and pail-stuff. 229. F. Hille. 1876. No. 1,355. Slakes lime with sea-water, or with solutions of magnesian salts, or with the refuse liquor from salt works, dried, calcined and re-dissolved in water, with 5 Ibs. gas tar to every 100 Ibs. of lime. This paste is mixed with water, and applied to sewage in tanks. The effluent from this process may be treated with iron- perchloride or with carbonic acid gas. 230. /. Bannehr and S. A. Varley, 1876. No. 1,739. A mechanical arrangement for intercepting solids. Air is then forced through the liquid ; such air may be ozonised by means of electric currents. 231. C. Raw son and J.W. Slater. 1876. No. 1,893. Treat sewage with double fluorides and silico-fluorides. Make an artifical animal charcoal by treating phosphates with carboniferous and nitrogenous matters. 232. W. Clark. 1876. No. 1,930. Mixes sewage with an acid to fix ammonia, draws off clear liquid and evaporates. Or treats sewage with lime, and drives off the ammonia in a " triple effect SE WA GE PA TENTS. 229 evaporator." The ammonia is condensed, and the sludge filtered and pressed. 233 G. Bischof. 1876. No. 2,080. Purifies sewage either by means of spongy iron or manganic dioxide, employed either as filtering media, or added in powder to the sewage. 234. W. Webb. 1876. No. 2,124. A mechanical arrangement for separating the liquid from the solid portions of sewage. 235. Thomas Lovell. 1876. No. 2,387. Merely arrangements for irrigation. 236. F. W. F.Reinhold Goedicke. 1876. No. 2,526. Separation of solids from liquids, the latter being applied for irrigation or other purposes. 237. /. W. Slater. 1876. No. 3,095. Treats sewage with alkaline, alkaline earthy, earthy or metallic salts of hypo-sulphurous, sulphurous and thionic acids. These are obtained by exposing tank-waste to air. They may be used along with aluminium sul- phate or chloride. Claims also infusorial earth in com- bination with salts of alumina, hydrated silica, and clay, or as a filter bed. 238. James Miller. 1876. No. 3,107. Passes sewage through tanks with perforated sides filled alternately with gravel and sand, or lime and sand. 239. Henry Staples. 1876. No. 3,307. Treats natural sulphates of alumina, Campsie shale, etc., with hydrochloric acid in heat, and uses the pro- duct for treating sewage. Adds to the com pound alkali waste to take up moisture, but not to decompose salts of alumina or iron, or to give the mixture on alkaline reaction. 240. Joe Frost. 1876. No. 3,365. Precipitates sewage with sulphides and hydrate of 230 SEWAGE TREATMENT. , barium, hydrates/precipitated hydrates, sulphydrates and sulphides of the same metal, sulphides of soda, slaked lime, carbonate of lime and sulphuric acid. The poisonous character of the salts of barium is well known. 241. W. White. 1876. No. 3,576. Treats sewage with oxychloride or chloroxide of calcium, obtained by boiling lime in a strong solution of calcium chloride, or quicklime may be slaked with dilute hydrochloric acid. Sulphates of aluminium, iron or zinc may be used in connection, as also charcoal and chloride of lime. The poisonous nature of the sulphate of zinc, and the inadmissibility of chloride of lime have been already explained. 242. A. Greenwood, G. E. Davis, and J. J. Speakman. 1876. No. 3,673. Place liquid sewage in a tank, and allow it to remain until the nitrogen has been transformed into ammonia (a great nuisance !), which is then driven off and fixed. 243. J.Watson. 1876. 7V0. 4,203. Treats sewage with hydrochloric acid in a tank, and uses the precipitated sludge for manure. 244. C.D.Abel. 1846. -Afo. 4.516. A complicated system of settling and filtration. 245. G.Rydill. 1876. No. 4,848. Precipitates sewage with waste liquors from the treat- ment of woollen, silk, and other manufactures, also waste acid liquors which have been used for separat- ing animal and vegetable fibres. Treats sewage in a filter-bed made of " extracted vegetable substances, dust and foreign matter," or "vegetable substances con- taining acid ; chemicals are used as a disinfectant, with SEWAGE PATENTS. 231 earth alum, shale, clay refuse, animal carbon, ashes, lime, or salt, the same being strongly impregnated with sulphuric, hydrochloric or nitric acid, or alum along with clay or other chemical agents." In other words, the inventor claims things in general, useful or useless, compatible or incompa- tible. 246. H. D. Y. Scott. 1877. No. 103. Treats pail-stuff and gas liquor for manures. 247. Houzeau and others. 1877. No. 263. Use for sewage, coal-ashes of all kinds from dwell- ings and manufactories ; pyritous, ligneous, or sulphurous ashes, sulphatized or not ; ashes and residues from manufactories of soda, sulphuric acid, sulphate of iron, and waste products from polishing glass; all refuse of products having been used for industrial purposes (!) ; gas from the crystallization of alums, sulphate of alumina, sulphate of iron, and all crystalline salts. These bodies are lixiviated, with or without the aid of an acid, and added to the sewage along with (in most cases) milk of lime. This is, perhaps, the most singular specification ever drawn up as far as sewage treatment is concerned. Among the substances claimed under the head " All refuse of products having been used for industrial pur- poses," there are not a few totally unsuitable, and others which have been used and claimed before. Among the former may be mentioned the highly poisonous re- fuse of the manufacture of magenta, and among the latter a variety of aluminous products. French in- ventors seem, as a rule, utterly to ignore the fact that, according to English law, a bad claim imperils the entire patent, and they re-invent with great calmness processes which are already public property. 232 SEWAGE TREATMENT. 248. /. H. Johnson (Emile Barrault). 1877. No. 488. Claims manufacture of sulphate of alumina by the action of sulphuric acid upon dried or powdered shales, and uses the sulphate thus obtained in treating sewage (! !). 249. G. Lunge. 1877. No. 638. Purifies the drainage from alkali waste. 250. R. Turnbull. 1877. No. 824. Mechanical arrangements only. 251. G. Alsing. 1877. 7V0. 835. Filters through a screen, and treats with a solution of hydrate and sulphide of calcium and gibbside (sic] and filters effluent again. 252. John Hanson. 1877. No. 860. Treats sewage with waste haematite, sulphurous gas, a mixture of alum, soda, and " black ash refuse," i.e., tank waste. Softens water with carbonate of potash and some- times nitre-cake. 25 3. S. Hallsworth and R. Bailes. 1877. No. 952. Treat sewage with (i) 1,000 gallons of liquor from beds of iron pyrites (50 Tw.), mixed with 250 Ibs. sul- phuric acid at 144 Tw. (2) 1,000 gallons of dissolved copperas, or copperas bottoms, or other liquor from copperas at 40 Tw. with 370 Ibs. sulphuric acid at 144 Tw. (3) 1,000 Ibs. solution of iron at 40 Tw. from pickling iron at wire and sheet iron works, along with 250 Ibs. sulphuric acid at 144 Tw. (4) A liquor from iron byrites and sulphuric aci d and water neutralized with scrap iron, set at 75 Twaddle, adding to each 1,000 gallons 250 Ibs. sulphuric acid at 154 Tw. ... (6) tap- cinder from puddling-furnaces, or other slags containing protoxide of iron and dissolved in sulphuric acid. (7) nitrate of iron at 4 Tw. To 10,000 gallons of the SEWAGE PATENTS. 233 sewage they add any of the aforesaid mixtures, followed, or, in some cases, preceded, by milk of lime. This specification might be advantageously studied by inventors who propose copperas and lime as a novelty in sewage-treatment. 254. M. H. Singe. No. 1,619. Filtering and purifying apparatus. 255. H. Y. D. Scott. No. 1,772. A magnesian lime-process. 256. /. Fenton. No. 1,982. A filtering arrangement. 257. W. R. Lake. No. 2,661. Prepares an artificial bone black. 258. /. Hanson. No. 2,725. Treats sewage with six liquids, viz., muriate or nitro-muriate of tin at 50 Tw. ; silicate of soda dis- solved in 7 parts of water ; borax dissolved in 9 parts of water ; " litchen " or Iceland moss boiled in water ; a mixture of the tin solution and of the decoction of Iceland moss, and peracetate of iron in 4 parts of water. In conjunction with the above may be used carbonates or hydrated oxides of iron deposited by water draining from mines and dissolved in sulphuric acid, asbestos ground in water, slaked lime, tank-waste, and sulphurous acid gas. Salts of tin are doubtless good precipitating agents, but they are too costly and too poisonous. Sulphurous acid gas has been already noticed. 259. C.J. Wollaston. ^7.2,841. Uses sulphurous acid or chlorine, or both (!) in con- junction with lime and magnesia. The fact that the actions of sulphurous acid and of chlorine are antagonistic, the former being a de-oxidis- ing and the latter an oxidising agent, is here over- looked. 234 SEWAGE TREATMENT. 260. B. B. Standen. 1877. No. 3,395. No agents for treating sewage are here proposed. 261. H. Y.D. Scott. 1877. No. 3,977. Proposes no means of treating sewage. 262. /. Gray. 1877. No. 3,571. Merely a lime process. The lime is slaked with boiling water, or alum water, and is then used for treating. The alum is, of course, decomposed ! 263. H. Robinson andj. C. Melliss. 1878. No. 12. Treat sewage with the joint addition of copperas and sulphate of alumina, or, if necessary, lime. Quaere, the novelty ? 264. /. Foulis and}, A . Carrick. 1878. No. 75. Treat waste waters with sulphate or chloride of zinc, waste bleach, and soda-limes (?) separately or in conjunction. 265. Walter East. 1878. No. 92. Adds putrescent sewage to hasten fermentation. Con- veys away noxious gases in pipes. Adds iron oxide to remove sulphuretted hydrogen. 266. R. U. Etzensberger. 1878. No. 264. Does not bear upon sewage. 267. /. Adamson and H. Booth. 1878. No. 2,937. A lime process. 268. W. Pochin. 1878. No. 4,270. Treats iron slag with sulphuric acid. No mention of sewage. 269. W. R. Lake. 1879. No. 179. Enriching phosphate of lime. No reference to sewage. 270. W.H.Denham. 1879. No. 437. Burns household refuse and precipitates sewage with the ashes. SEWAGE PATENTS. 235 271. H. Chamberlain. 1879. No. 2,599. A straining process. 272. 1879. Afo. 2,345. Irrelevant. 273. W. L. Wise (Loewig}. 1879. No. 3,195. Prepares " carbonic alkali of alumina." 274. T.H.Cobley. 1879. .#"0.3,312. No reference to sewage. 275. R. Wild. 1879. No. 3,373. Treats with lime and alum and " other suitable pre- cipitant," and filters. 276. R. Wild and H. Ledger. 1879. No. 3,980. Mechanical arrangements. 277. W. F. Mast. 1879. No. 4,402. Method of extracting ammonia from excrement and urine. 278. H. C. Bull. 1879. No. 5,324. No reference to sewage. 279. /. C. Mewbari. 1880. No. 243." Purifies wool-washings with caustic lime, epsoms and copperas, forming insoluble soaps. 280. /. G. Tongue. 1880. No. 742. Destroys organic matter in waste waters by heating them and applying lime white, chloride of magnesium, and other " suitable chemicals." Special mechanical arrangements. 281. /. Duke. 1880. No. 748. Filters through silicates of lime, potash, soda or alumina separately or combined, peat charcoal, and superphosphates. 282. C. Dickinson. 1880. No. 3,898. Proposes mechanical arrangements. Uses for sewage treatment salt-cake, alum and potash, and, if necessary, " well-known deodorising means." 236 SEWAGE TREATMENT. Salt-cake is, of course, useless, and potash, if it answers any good end, is very expensive. 283. E. Parry andT. H. Cobley. 1880. No. 3,554. Prepare earthy silicates, and make no reference to sewage. 284. /. Duke. 1880. No. 2,994. Manufactures soluble silicates by treating Roman and Portland cement, or suitable natural silicates, or kainite, with sulphuric or hydrochloric acid. The re- sulting product is applied to manures, but not to the treatment of sewage. The part which kainite can play in the preparation of silicates is very questionable. 285. /. H. Johnson. 1880. No. 4,603. Treats lavas with sulphuric acid or hydrochloric acid, and uses the resulting mixture, " lava-syrup," as a dis- infectant or for treating sewage. Uses also alumnite calcined in presence of potassium chloride. 286. VV. H. Denkam. 1881.