444 KEPORT — 1873. 



The sewage, after being screened through a bed of " slag," in which the 

 larger suspended matters are arrested, is turned on to one of the four plots 

 into which the area is divided, and allowed to run on this plot for six hours, 

 when it is turned on to another one. Thus each of these four plots has 

 18 hours for rest and aeration of the soil. The surface of the area is laid 

 up in ridges, and cabbages and other vegetables planted along them, the 

 sewage running in furrows between. 



The main results of the examinations which took place in January and in July, 

 extending over seven and eight days respectivelj-, were : — that the effluent 

 water discharged was very largely diluted with subsoil- water which had per- 

 colated through from the river-bed (this was proved both by the gaugings 

 and by the analyses, and had been already observed by the Elvers' Pollution 

 Commissioners) ; that the effluent water was very satisfactorily purified, the 

 nitrogen in solution appearing in the form of nitrates and nitrites — a suffi- 

 cient proof that a considerable amount of oxidation goes on in the filter-beds, 



Fpon a comparison of the total nitrogen in solution in the sewage, in the 

 effluent water, and in the subsoil-water (which was also analysed), it was 

 found that the amount in the effluent water was almost exactly the amount 

 that would be present in the sewage if diluted with the amount of subsoil- 

 water (rather more than its own volume) with which the analyses and the 

 gaugings showed it to have been diluted ; that is to say, that a quantity 

 of nitrogen equal to the amount in solution in the sewage escaped in the 

 effluent water, and was lost (escaping, however, almost entirely in the 

 oxidized and innocuous form of nitrates, &c.), the amount retained in the soil 

 and by the plants being, therefore, equal to the amount in the suspended 

 matters of the sewage. The effluent water was not quite so pure in the 

 summer as in the winter : in the former case four fifths, and in the latter 

 twelve thirteenths of the nitrogen contained in it was in the form of nitrates 

 and nitrites. 



The sewage was cooled by its percolation through the soil ; in the winter 

 from 48° F. to 46° F. (the temperature of the subsoil-water being 42° F.), 

 and in the summer from 00° F. to 55° F. 



The crops grown on the surface of the filter-beds were successful, and 

 realized veiy good prices. 



Irrigation. 



Iq the First Eeport of the Committee a Hst of fifteen places where irriga- 

 tion was practised was given, and a list of twelve more where it was con- 

 templated ; and it was stated that the areas used for irrigation varied from 

 0-4 of an acre to ten or twelve acres per thousand of the population, the 

 distance of the land from the lowest outfall sewer of the town vaiying from 

 100 yards to upwards of a mile. 



The general result was reported to be as follows : — " At most places the 

 ai^plication of the sewage to land has been found to exercise a most beneficial 

 influence on the condition of the streams and rivers receiving the drainage of 

 the district." 



" Generally speaking no objections appear to have been made to the applica- 

 tion of sewage for irrigation; and where such objections have been urged on the 

 ground that the appHcation was ofi'cnsive and injurious, they do not appear to 

 have been supported by medical authority, and in several instances they have 

 ceased. As regards the sanitary condition of these districts, it appears that 

 in most cases the application of sewage for irrigation has not been attended 

 with any apparent change ; but there is said to be a marked improvement at 

 Braintree.*' 



