'34 



SCIENCE. 



[Vol. XVIII. No. 44^ 



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THE SELF-PURIFICATION OF RIVERS.' 



We have evidently placed too much confidence in the innate 

 power of rivers to throw ofiE the evil effects of pollution by sewage, 

 which power we now see is largely imaginary. On the other 

 hand, we find, it we may believe the authorities, some coaifort in 

 the fact that the bogy of the present day, the microbe, has not 

 that miraculous vitality which popular belief has attributed to it, 

 and is even to be disposed of by so commonplace a matter as sedi- 

 mentation. Dr. Frankland in the course of his paper refers more 

 than once to the remarkable powers of self-purification of the 

 Thames. Tliat our metropolitan river must practise this virtue to 

 a prominent degree is manifest from the cruel ill-usage to which 

 we subject it ; but we gather that the author referred chiefly to 

 the up-country reaches. Below bridge, especially in the neigh- 

 borhood of Barking and Erith reaches, no self-purification could 

 compensate for the filthy flood that is daily discharged at Cross- 

 ness. There have been reports of various highly paid experts 

 from time to time, the reading of which would lead one to sup- 

 pose that there was nothing, or little, to be desired in regard to 

 the state of the water in this region. But those who live near the 

 banks, or whose duty takes them down the river, know how mis- 

 leading these reports are. At low water especially, the banks are 

 formed by reeking flats of sewage deposit, and when a steamer 

 passes along and churns up the filthy sediment the stench is of a 

 most sickening description. 



To return, however, to Dr. Frankland's paper, which says noth- 

 ing about the unsavory reaches below bridge, the author com- 

 mences by saying that the subject of the self -purification of rivers 

 admits of being considered from two perfectly distinct points of 

 view, viz,, from the chemical and from the biological aspects. 

 Until recently the subject has only been discussed from the chem- 

 cal point of view. The firm conviction possessed by many that 

 rivers undergo spontaneous purification in the course of their 

 flow is generally based upon personal observatidhs made upon 

 streams in which the process appears to be going on in such a 

 striking manner that no analytical evidence is required. All en- 

 gineers are acquainted with streaois which are visibly polluted at 

 one spot, and apparently pure a few miles lower down. When 

 such cases are further submitted to analytical tests, the latter, of 

 course, fully confirm the previous ocular impressions. In fact, 

 such disappearance of organic matter does take place, but when 

 these cases of supposed self -purification are carefully investigated, 

 it becomes very doubtful whether the phenomenon is due to any- 



' Abstract of a paper by Dr. Frankland, read before the Health Congress, 

 London, Aug, 17 (reported in Engineering), 



thing beyond dilution and sedimentation. The careful experi- 

 ments which have been made to test this point are by no means 

 numerous, A series of investigations was made by the Rivers 

 Pollution Commissioners of 1868 to test the point, both as regards- 

 highly polluted streams and comparatively pure ones, but in both 

 cases their results were of a negative character, and pointed to no- 

 real purifications, i,e. , destruction of organic matter, although 

 there was distinct evidence of considerable improvement in the- 

 quality of the water through sedimentation. 



Some years ago Dr. Frankland undertook a series of experi- 

 ments to further test this point in connection with the Thames, 

 which has always been regarded by some as a river possessed 

 of most remarkable self-purifying power, and which un- 

 doubtedly often does reach London after a long flow through 

 a cultivated and fairly populated district in a surprisingly pure 

 state. The experiments in, question consisted in taking samples of 

 the water flowing in the river at difl^erent points on the same day, 

 with a view to establishing whether on the whole the chemical 

 quality of the water was improved or deteriorated during the 

 course of its long flow. Thus, on one day, samples were taken at 

 Oxford, Reading, Windsor, and Hampton; on another day at 

 Chertsey and at Hampton; and on three difl'erent occasions sam- 

 ples were collected both at Windsor and at Hampton on the same 

 day. The results of analysis of these various samples are recorded 

 in a table accompanying the paper. They clearly indicate that, 

 the chemical quality of the water undergoes slight but almost con- 

 tinuous deterioration in flowing from Oxford to Hampton. This- 

 deterioration is in spite of a very large Increase in the volume of 

 the water, a large proportion of which gains access to the river 

 from springs in the chalk, and is of the very highest purity. Thus, 

 Mr, Thornhill Harrison, C,E,, has determined that the total in 

 crease in volume in the Thames between Maidenhead and Thames 

 DItton was (exclusive of the Colne, Wey, and Mole) in April, 1884, 

 249,500,000 gallons per day; on July 8, 1883, 49,000,000 gallons^ 

 July 23 to 26, 131,000,000; November, 1890, 45,000,000, 



After quoting several columns of figures contained in tables, 

 unfortunately too voluminous for us to reproduce, the author goes 

 on to point out that by their study and that of the most recent in- 

 vestigations, we are led to the inevitable conclusion that sedimen- 

 tation is the main cause of any self- purification in river water. Of 

 any oxidation of dissolved organic matter there is still no reliable 

 evidence, although of course dilution, which frequently takes place- 

 on the largest scale, as in the case of the Thames, without being, 

 suspected until made the subject of a most careful scrutiny, will 

 produce a superficial appearance of such a result. This removal 

 of microbes by sedimentation during the flow of a river is unques- 

 tionably of great hygienic importance, and of much greater 

 hygienic importance than the alleged oxidation of dissolved or- 

 ganic matter, which in itself can have no power of communicating: 

 zymotic disease. It is, however, a process which cannot be reliedi 

 upon as furnishing any guarantee that harmful microbes, turned 

 into a stream at a given point, will no longer be present in the 

 water at any point lower down. From the numerous experiments 

 which have been made on the vitality of pathogenic microbes in 

 water, there can be no doubt that many forms which might have 

 subsided, would remain alive for long periods of time, and be car- 

 ried down uninjured when the river was next in flood. Dr. 

 Frankland concludes his paper by saying that we must not allow 

 sedimentation of microbes to cause us to relax our protective 

 measures to e-xclude contamination from our streams, but on the 

 contrary, bacteriological research clearly indicates, on the one 

 hand, the value and importance of purifying by the very best 

 available means all dangerous liquids, such as sewage, before ad- 

 mission into rivers; and, on the other hand, to submit the water 

 drawn from streams for town supply to the most careful subsidence 

 and filtration through sand before delivery. 



The Summer School of Ethics and Sociology at Plymouth, 

 Mass., the first session of which has just been held, is described in 

 a brief illustrated article in the Review of Reviews for September. 

 The article is illustrated with portraits of Professor Felix Adler of 

 New York, Professor Toy of Harvard, and Professor Henry C. 

 Adams of Ann Arbor, 



