218 



at the proper times, and under proper conditions of soil and climate, has a won- 

 derfully beneficial effect upon vegetation, so that the above results must be 

 modified, if a true value of sewage as a manure is to be deduced. 



Before closing the subject, there are still some observations to be made 

 upon the theoretical value of sewage, and upon the effects of its use as a 

 manure, upon the health of those living in contiguity to sewaged land. 



By an average of the analyses of several of the most distinguished chemists 

 it has been found that 200 oz. of ammonia are voided annually by an indi- 

 vidual, |-ths of which exists in the fluid matter of sewage, wdiilst the average 

 amount found in one gallon of sewage varies from 9 "7 to 3*91 grains, according 

 to the water supply. This represents a composition in which 1000 tons of 

 sewage is equivalent in ammonia to from 1 6 2-5ths to 6 4-5ths cwts. of guano. 

 Taking guano at 13s. a cwt., the value of sewage varies from 2 - 44d. to Id. per 

 ton. At Barking, from one hundred tons of sewage were derived one ton of 

 grass, of a value of from 15 s. to 20s., which would give the practical value of 

 l"8d. to 24d. per ton, thus approximating, in a striking manner, to the 

 theoretical values. 



As regards the -sanitary points in such a system, it might be reasonably 

 expected that the continued pouring out of such vast quantities of rapidly 

 fermenting manurial matter, the earth would by degrees become saturated, and 

 refuse longer to carry out the powers of deodorization with which nature has 

 endowed her ; such, however, is the case in very rare instances, as it is usually 

 hard to detect any effluvium whatever, and that which exists has nothing 

 particularly disagreeable in its character, being merely like a concentrated 

 essence of soap-suds. This may be partly owing to the extreme dilution, and 

 the absence of any solid matters in the sewage, by the time it arrives at the 

 outfalls, and the rapidity with which it finds itself on the soil before 

 fermentation has set in, and whilst it is in the most fitting state for absorption 

 by the growing crops. In fact, in the sewers and reservoirs themselves, after 

 the first day or two, little inconvenience is experienced whilst the superin- 

 tendent of the lower part of the sewers frequently has to take a walk of some 

 miles up and down the sewers, or a stroll through the reservoirs, before 

 breakfast, without being a bit the worse for it. Upon the tops of both the 

 Bai'king and Crossness reservoirs are several labourers' cottages, where no 

 illness has resulted ; and at the time of the last cholera attack in London, 

 some hundreds of men were drafted down into the author's works from the Isle 

 of Dogs' sewer, w T hei"e several had died, and a panic had arisen. There was not, 

 however, a single fresh case after their removal, though there were many of them 

 daily in probable contact with millions of so-called choleraic germs. It may, 

 therefore, be fairly assumed that no evil effects can result from the use of 

 sewage as a manure, always supposing that it is sufficiently diluted, sufficiently 

 fresh, and sufficiently disintegrated by its passage through the sewers. Also 

 that Italian rye grass is the crop to which it can be most economically applied 

 in large quantities ; the more particularly, as the land upon which it is grown 

 must be re-broken up every three years, so as to ensure a full crop. 



This periodical stirring would also have the effect of preventing the soil 

 becoming too sodden, or giving rise to the generation of noxious gases. 



This paper has been written with a view to lay before the meeting a slight 

 sketch of the value of a system of Main Drainage, which shall ensure a small 

 return to ratepayers upon any sums expended by them in behalf of the health 

 of the general public, as well as to show the value of sewage irrigation 

 generally, where the produce can command a ready market. 



