184 REPOKT — 1871. 



smaller amount of chlorine also shows this. The fact is, that a very largo 

 quantity of subsoil -water is admitted into the sewers. 



The effect of the " extractor " is to reduce the total suspended matters 

 by shghtly more than one third of their amount, the amount of solid 

 matter in solution is slightly lessened, and a quarter of the nitrogenous 

 organic matters in suspension pass into solution ; these arc effects not in any 

 ■way due to the action of the machine except as an agitator. 



The effect on this sewage of a flow over one field of rye-grass, as shown 

 by the analysis of an average sami^le made by mixing twelve samples 

 in the proportions indicated by the amount of flow at the time of collecting, 

 was as follows : — 



The suspended matters, being very small in amount, were not determined. 

 The solid matters in solution were reduced in total amount, the reduction 

 being chiefly due, as in the case of the Tunbridge -Wells farms, to the re- 

 tention by the soil and plants of the more volatile substances, as the amount 

 of solid matters left after ignition is practically the same in the effluent 

 Avater as in the sewage. The lessening of the chlorine by more than one 

 fourth of its original amount would point to the fact, already referred to, 

 that a considerable amount of subsoil water dilutes the effluent water ; but 

 notwithstanding this dilution, the effluent water contains more than half as 

 much " actual " ammonia as the same bulk of sewage (after passing thi-ough 

 the extractor), and a quarter as much "albuminoid" ammonia, while the 

 amount of nitrogen escaping as nitrates and nitrites is insignificant. 



This effluent water is therefore not purified in a satisfactory way at all. 



But the most interesting point about these analyses is the comparison of 

 the effluent water which had passed over two fields of rye-grass with that 

 which had only passed over one. 



On a prima facie view, it would have been expected that the former 

 would have been much purer than the latter ; but in this case, on the con- 

 trary, we find that the effluent water which has passed over two fields 

 contains, in the same bulk, — 



1. More than one fifth more solid matter in solution, 



2. More than one third more fixed solids, 



H. More " albuminoid" ammonia, viz. 0-10 instead of 0*06, 



4. Hather more chlorine, 



5. Very slightly less nitrogen as nitrates &c., 



6. More than one fourth less " actual" ammonia, than the effluent water 

 which had passed over one field of rye-grass. 



This shows us : — 



1. That bypassing over an additional field, the sewngc has been strength- 

 ened instead of Aveakened, except as regards '■' actual " ammonia. 



(That this strengthening is probably due chiefly to evaporation through 

 the agency of the plants, is shown by the increase in albuminoid ammonia, 

 and by the fact that the actual ammonia is the only constituent lessened in 

 amount to any extent.) 



2. That the nitrogenous organic matters, as shown by the amoimt of al- 

 buminoid ammonia, are increased. 



3. That no additional oxidizing action took place. These results are what 

 might have been anticipated from the description of the farm already given. 



The soil, not being underdraincd, is saturated with sewage, and the 

 effluent water flowing off one field on to another, already saturated with 

 sewage, can only concentrate itself by evaporation or by solution of matters 

 in the upper layer of the soil. 



