523 



THE FARMER'S MAGAZINE. 



AGRICULTURAL VALUE OF THE METROPOLITAN DRAINAGE. 



It will be remembered that the First Commiaaioner of her 

 Majesty's works referred to Captain Douglas Galton, K.E., 

 and Messrs. James Simpson, and Tbomas E. Blackwell, cer- 

 tain questions relating to the main drainage of the metropo- 

 lis. Those gentlemen, in the course of their inquiry, deemed 

 it necessary to secure the assistance of Dr. Hofmann, chemist 

 to the Museum of Practical Geology, and Mr. Henry Witt, 

 assistant chemist there, in making the chemical investigations 

 lately connected with the subject. These gentlemen have 

 made their report, which has been presented to Parliament, 

 and is now printed as one of the sessional papers. The expe- 

 riments were continued over a space of four months, during 

 which the influence of the sewage on the Thames water, the 

 composition and value of the sewage, the principal methods 

 proposed for utilization and deodorization of it, and the 

 treatment of sewage in its sanitary aspects, were carefully in- 

 vestigated. The details are given at considerable length, with 

 all the analytical numbers upon which the 'results are based, 

 so that any one interested may examine and interpret for him- 

 self the foundations of the statements made. The following 

 are the conclusions arrived at, under the five heads, as sug- 

 gested in the original letter of reference. The authors sum 

 up the principal results as follow : — 



I.~lNrLUENCE OF THE SEWAGE ON THE COMPOSITION 

 OF THE WaTEK of THE THAMES. 



(a.) Owing to the very great dilution of the sewage by the 

 water of the Thames, chemical analysis indicates but a slight 

 difference in the composition of the river water before and 

 after pollution. 



(6.) Contrary to what might have been expected, the influ- 

 ence of the sewage scarcely increases the qiiuntily of dissolved 

 organic matter. 



(c.) The presence of sewage perceptibly raises the proper- 

 tion of mineral constituents, and especially of common salt. 



(d.) The amount of insoluble organic matter which is pre- 

 sent in the 7nud suspended in the river steadily increases with 

 the degree of contamination. 



(e.) The offensive character of the river wafer, the dis- 

 engagement from it (especially during hot weather) of efflu- 

 via, not only highly offensive, but also exceedingly prejudicial 

 to the health of the inhabitants of the districts lying along the 

 banks, is chiejty caused by the putrefaction of the organic 

 matter dissolved and insoluble, which is diffused through the 

 water. 



(/.) The intensity of this putrefactive decomposition, which 

 the organic matter present in the water undergoes within the 

 metropolitan area, arises from the constant supply of putresci- 

 ble matter, partly by the influx of the sctoage, but more espe- 

 cially by the vast accumulation of the black sewage mud which 

 has gradually collected in the bed of the river. 



II. — Mean Composition and Agricultural Value 

 OF THE Sewage. 



(a.) According to experiments made on specimens which 

 represent its mean composition, the London sewage con- 

 tains on an average, 102 8 grains per imperial gallon of 

 total solid constituents, of which 72 1 grains are mineral, 

 and 30"7 grains organic matter. 



(&.) In these 1028 grains the following quantities of 



substances valuable in an agricultural point of view are 

 present : — 



Nitrogen Q'l 



Phosphoric acid 1 '8 



Potash 1-0 



Organic matter 30-7 



Total 402 



(e.) The total solid matter^ when entirely separated frotn 

 the water with which it is diluted, would have a money- 

 value of £6 Os. 3d. per ton ; that of guano being taken at 

 £11. 



{d.) Of the valuable matter, six-sevenths are present in 

 the liquid portion, on\y one-seventh existing in the insoluble 

 or suspended form. 



(e.) From the knowledge of the quantity of these 

 valuable constituents contained in a given volume of sewage, 

 it has been calculated that the money-value of 100 tons of 

 sewage, supposing all these bodies capable of separation, 

 would be in its original condition 17s. 7d., or 2d. per ton ; 

 and that, therefore, the whole sewage of London is wortli 

 £3,796 per diem, or £1,385,540 per annum. 



(/.) Those numbers are, to a certain extent, confirmed 

 by the calculation of the value of the solid and liquid ex- 

 crements of the whole population of London. 



{g) The foundation of this calculation is, moreover, con- 

 firmed by the anal^'scs of a variety of specimens of sewage, 

 made on different occasions both 'hy ourselves and by others. 



(/i.) The chemical composition of the sewage of Edin- 

 burgh, and also that of Leicester, differs but little from that 

 of the London sewage, 



III.— " Utilization of Sewage for Agricultural 

 Purposes. 



Manufacture of a Manure from Sewage. 



The following, among the many patented processes for 

 the manufacture of manures from sewage, are those which, 

 in accordance with the wishes of the referees, were espe- 

 cially selected for the examination — viz. : 



(A.) Treatment of sewage with lime. 



(B.) Treatment of sewage with a mixture of lime, sul- 

 phate of ammonia, and charcoal (Stothert and Gotto's pro- 

 cess). 



(C.) Treatment of sewage with charcoal (Jasper Rogers 

 and Richard Dover's processes) : 



1. Filtration of sewage through charcoal. 



2. Agitation of sewage with charcoal. 



We were also directed to report our opinion upon— 



(D.) Treatment of sewage with a magnesian salt (Sir 

 James Murray's process). 



The following are the conclusions at which we have 

 arrived under this head : 



(a.) With respect to process (B ), Messrs. Stothert and 

 Gotto's, we find that the cost of the materials employed, 

 irrespectively of working expenses, nearly equals the 

 money value of tkc manure produced ; whilst in process 

 C, 1. Filtration through charcoal, the cost of the ma- 

 terials very considerably exceeds the money value of the 

 manure obtained. These processes cannot, therefore, be 



