132 



NATURE 



[June 7, 1900 



60 per cent. It has maintained a most satisfactory state 

 of aeration, since the air drawn from the bottom has 

 contained, on an average, 17 per cent, of oxygen. 



About 60 per cent, of the matter which settles from the 

 sewage under ordinary conditions is combustible, and 

 could, therefore, very well be dealt with by a destructor. 



The tendency of the coke bacteria beds is undoubtedly 

 to improve in their purifying power with age, provided 

 they are not overworked. A bed which had given for some 

 time a 50 per cent, purification, gradually increased in 

 efficiency until its purifying effect reached nearly 70 per 

 cent. The effluent from this bed underwent an additional 

 purification of 20 per cent, by treatment in a second 

 similar bed. 



The effluent from a single coke-bed worked on the in- 

 termittent principle was clear and odourless, and remained 

 in this condition when it was kept in open or closed 

 bottles in a warm laboratory. It maintained the life of 

 gold-fish, roach, dace and pike indefinitely : it was there- 

 fore not only well aerated, but was able to maintain its 

 aerated condition. This proves that it was free from any 

 rapidly oxidisable matter. It was undoubtedly, however, 

 undergoing gradually further purification by the action 

 of the bacteria which it contained, and with the assist- 

 ance of dissolved oxygen. Such an effluent would be 

 quite suitable for introduction into the tidal part of the 

 river, where the water is too salt and muddy to be used 

 for drinking purposes. 



Bacteria are present in large numbers in the river- 

 water itself, and undoubtedly exert a most useful purify- 

 ing effect upon the water during its flow. The relation 

 between the number present in the sewage and in the 

 water of the River Thames, below and above locks, is 

 shown by the following estimations made by Dr. Hous- 

 ton. The number of liquefying bacteria included in the 

 total number of bacteria present in one cubic centimetre, 

 and the number of spores of bacteria, are also stated :— 



The results obtained by the experimental bacterial 

 treatment of sewage at Manchester during the last two 

 or three years bears out generally those which have been 

 obtained in London. The treatment has differed in some 

 details from that adopted in London. The particles of 

 coke constituting the coke-beds have been smaller. The 

 coke-beds have been subjected to a larger number of in- 

 termittent fillings per day ; and the preliminary treatment 

 in an open anaerobic tank has been carried out with 

 advantageous results. The scientific experts who have 

 suggested and watched the experiments state their con- 

 viction that bacterial treatment is the treatment which is 

 most suitable for Manchester sewage, but that in order 

 to secure the most effective purification, the coke-beds 



NO. 1597, VOL. 62] 



must have sufficiently frequent and prolonged periods of 

 rest, and must be fed with sewage as free as possible 

 from suspended matter, and as uniform in quality as may 

 be. Preliminary anaerobic treatment is referred to as the 

 best means of securing uniformity in quality of the sew- 

 age, and of adapting it to rapid subsequent aerobic purifi- 

 cation. Four fillings in 24 hours have been found 

 suitable, if one day's rest in seven is given to each coke- 

 bed ; the number of fillings, however, may exceed this 

 without detriment to the bed or to the character of the 

 effluent. 



Town sewage is found to arrive at the outfalls at an 

 almost constant temperature throughout the year. It 

 rarely falls below 13° C. And this temperature not only 

 prevents the possibility of the coke-beds being stopped 

 by the freezing of the sewage, but also secures to the 

 bacteria one condition favourable to their action. When 

 a bed is too freely aerated by the passage of frosty air 

 constantly through the interstices of the coke, this 

 favourable condition is, however, seriously interfered 

 with, and the bed may even become stopped by the 

 freezing of the sewage. 



In the more recent experiments carried out in America 

 by the State Board of Health, Massachusetts, the ten- 

 dency has been to use fine coke, and to allow the effluent 

 from the coke to pass through sand The passage of the 

 liquid has either been allowed to take place with the out- 

 flow widely opened, so that the bed never fills ; or the 

 sewage has been allowed to fill the bed and to remain 

 quiescent in contact with the coke for a time, as in the 

 English experiments. The conclusions arrived at seem 

 to be that the degree of purification obtained by the use 

 of fine coke and sand is very satisfactory, but that the 

 volume of sewage dealt with in a given time is smaller 

 than when larger coke fragments are used, and the ten- 

 dency seems to be to adopt the larger coke in order to 

 expedite the more rapid drainage away of the effluent. 



It will be seen from what has already been said that 

 it is well not to speak of this system of treatment as one 

 of filtration. Filtration ordinarily implies a process of 

 mechanical separation of material suspended in a liquid. 

 The fact that the coke-beds only commence their purify- 

 ing action after they have been " primed " by repeated 

 contact with sewage, and that this purifying action keeps 

 increasing as the bed " matures," is sufficient to show 

 that the action is by no means of a mechanical nature. 

 It would be well, therefore, to speak of it as a process 

 of bacterial treatment, and thus to indicate that the 

 purifying agents are bacteria, which are acting under 

 control, and are placed under conditions favourable to 

 the development of their full activity. 



It would be rash to say that the methods of bacterial 

 treatment have as yet reached their most effective state ; 

 but it is significant that these methods have secured con- 

 verts wherever they have received careful and air trial, 

 and that those are their warmest advocates who have 

 had the widest experience of their working. It is ev^n 

 probable that further improvements will be made in the 

 means of treating sewage bacterially, but it is quite 

 certain that the processes at present in use are able to 

 secure the economical and satisfactory purification of 

 ordinary town sewage. Frank Clowes. 



THE TOTAL ECLIPSE OF THE SUN. 



SINCE the first series of telegrams was received 

 announcing successful observations of the total 

 eclipse of the sun on May 28, all the more detailed 

 reports to hand confirm the universal satisfaction of the 

 various parties at the results. As, however, most of the 

 parties having a definite programme arranged to obtain 

 photographic records, complete details cannot be known 

 until the development of the whole of the plates, and m 



