THE FARMER'S MAGAZINE. 



515 



SEWAGE OF THE METROPOLIS. 



,SiR — In my letter of the 21st of Sept. I pointed out a 

 district of the metropolis which has suffered perhaps more 

 than any other, botli in a pecuniary and a sanitary point of 

 view, from the neglect of the Commissioners of Sewers. It 

 is, indeed, a monstrous thing that a course of positive dete- 

 rioration should be allowed to go on year after year for so 

 long a period, when not only a staff of officials are in ex- 

 istence to remedy the evils complained of, but an amount of 

 money has been actually levied upon the inhabitants fully 

 adequate to their removal, but from which they derive no 

 benefit whatever ; the district being now in a far worse 

 condition in every respect, so far as its sanitary arrange- 

 ments are concerned, than it was when, thirty years ago, 

 I first became acquainted with it. Leaving this question 

 to the consideration of your readers, I shall now take up 

 the practical part of the subject, or the way in which it is 

 proposed to dispose of this monster nuisance which is an- 

 nually consigning hundreds of victims to premature graves. 



There are two plans at this time before the Commis- 

 sioners of Sewers. The first is by Mr. Bazelgetti, and 

 embraces the construction of a tank in the Essex marshes, 

 on the bank of the Thames opposite Erith. This reservoir 

 would comprise an area of ten acres in extent, and fourteen 

 feet depth, containing when full upwards of six million 

 cubic feet, or thirty-eight million gallons of sewage ; and 

 Mr. B. estimates that it would be half filled in dry, and 

 quite filled in moderately wet, weather, every tide ; thus 

 being partially filled and emptied twice in every twenty- 

 four hours. This plan, however, independent of serious 

 objections in itself to which it would be liable, has been 

 met by the most determined hostility of the residents of 

 Erith, to whom the nuisance would be intolerable in certain 

 states of the wind or atmosphere. The deposit ( without 

 artificial precipitation) would be about 1,000 tons to every 

 inch of depth, and would comprise the most fetid of the 

 materials of the sewage, which in hot weather would rapidly 

 putrify, and emit an effluvium that , would render a resi- 

 dence in its neighbourhood intolerable. This plan, there- 

 fore, is not likely to be approved by the Commissioners, 

 who will be compelled to have some regard to public opinion 

 in a matter of this kind. 



The second plan is by Mr. M'Clean, and is to the follow- 

 ing effect. After conveying the sewage to West Ham by 

 (as I conclude) a covered conduit, he proposes to continue 

 its course by open cuttings to the valley of the Crutch, a 

 small stream in Essex ; and from thence to the sea, so as 

 to avoid contaminating the Thames, which is an object 

 that must be considered. It would, however, equally 

 ignore the commercial part of the question, by disposing of 

 this immense body of valuable material in the most sum- 

 mary manner. It is, in fact, the enormous quantity of the 

 sewage that renders it so difficult to manage or cope with ; 

 and here .again the folly and negligence of former commis- 

 sioners appears in a striking point of view. They have 

 allowed the metropolis to grow to such an extent, before 

 taking the subject into consideration, that the sewage has 

 become perfectly unmanageable by ordinary means, and 

 requires an outlay and works to get rid of it that now appal 

 them. We fortunately have men still in the country with 

 minds and means large enough to grapple with even the 

 sewage question of the metropolis. 



Desiroi;s of preventing the waste of so much valuable 

 property on the one hand, and with an eye to its commer- 

 cial importance on the other. Sir S. M. Peto has proposed 

 to the Commissioners of Sewers to take the management 

 of the sewage after it has passed from the city sewers, and 

 to furnish the capital to the amox'nt of £600,000, for the 

 construction of the necessary works, on payment of four per 

 cent, per annum interest, and the manure. By this plan the 

 Thames would be saved from pollution, as upon Mr. Bazel- 

 getti's proposal, and the sewage would be economized and 

 rendered productive instead of being discharged into the 

 sea, as Mr. M'Clean's plan would involve. It is proposed 

 to form a company for carrying out the plan of Sir S. M. 

 Peto, and it is to the calculations, &c., which have been 

 made, that I shall now direct the attention of your readers. 



With regard to the value of the sewage, it has greatly 

 increased of late years by the extended use of water-closets, 

 by which all the excreta? of the inhabitants are conveyed 

 into the main sewers. According to Liebeg* the average 

 amount of the liquid and solid excreta of a man is Iglb. per 

 day, or 5471bs, per year, in the proportions of 40Glb3. of the 

 former to Ollbs. of the latter. The whole contains three 

 per cent, of nitrogen, or 1G.41 lbs. per year ; but taking the 

 average of the population, young and old, the quantitj' of 

 nitrogen will probably not exceed 121bs. per head per 

 annum. Mr. Laws has ascertained that the average quan- 

 tity of dried matter is about 4Glbs., which is just half what 

 Liebeg allows to a man. Apportioning, therefore, 81bs. of 

 nitrogen to the solid, and 41bs. to the liquid, part, we bring 

 the result to three-fourths of the average of a man. 



Besides this, there is a part of the excreta of cattle, sheep, 

 horses, pigs, &c., Mvith the blood and offal of the slaughter- 

 houses, the refuse of manufactories, the vegetable garbage of 

 the markets, and a hundred other sources, from which the 

 amount of nitrogen is increased to 201b8. per annum for each 

 of the inhabitants, making, in round numbers, an aggregate 

 of 22,000 tons for the two.anda-half millions of the metro- 

 polis. The value of this, according to Mr. Nesbit, is not less 

 than from £1,500,000 to £1,800,000 sterling; the mean of 

 £1,650,000 being at the rate of £75 per ton! 



Fresh farm-yard manure, according to Dr. Voelcker, con- 

 tains .74, or nearly j per cent, of nitrogen, or about IG^lbs; 

 per ton. The sewage, therefore, of London probably contains 

 as much nitrogen (50 million lbs.) as three million tons of 

 farm-yard manure, which is sufficient to dress 200,000 acres 

 at a rate equal to 15 tons of such manure per acre. It is pro- 

 posed to apply this nitrogen at different dressings, by which it 

 would be more quickly absorbed by the land ; and thus a faj 

 leas loss would accrue from evaporation than in a top-dressing 

 of farm-yard dung, which always loses a large portion of its 

 ammonia, as may be proved any day by the smell. The pro- 

 portion, therefore, retained in the soil from sewage will be 

 greater than from farm-yard manure. It has never been accu- 

 rately ascertained, we believe, what is the maximum quantity 

 of nitrogen a wheat crop would take up without super-satura- 

 tion. An experiment was made at Manchester by which it 

 was found that by applying up to half a ton per acre of guano 

 the production of grass was increased, but that beyond that 

 quantity it was diminished. This allows about ISOlbs. of 



* Agricultural Chemistry, p, 185. 



