ON THE TREATMENT AND UTILIZATION OF SEWAGE. 



67 



This result is no doubt partly due to the concentration of the sewage on a 

 smaller area, and partly to the increased richness of the soil, which was de- 

 monstrated by the analytical results given in the Committee's Fifth Eeport. 



It is necessary to state that the year 1871-72 would, if added, show 

 an apparent exception to this progress, inasmuch as the total amount of pro- 

 duce that year was 2714 tons, an amount that has not been equalled since ; 

 but this exception is only an apparent one, and is caused by the fact that 

 there were then no cereals grown on the farm (whereas in the following 

 years they have formed an important part of the produce), and that a much 

 larger area was under cabbages. 



And notwithstanding the large total weight of crops that year, the rate per 

 acre of produce was less than in 1874-75 ; whilst the amount of nitrogen 

 reckoned as recovered in the crops was less than in either 1873-74 or 

 1874-75, as appears from the figures : — 



Nitroeen 



Nitrogen 



recovered 



per acre. 



lbs. 



1871-72. ... 168 2714 16-2 19,667 117 



The areas given in each case are the total areas of all the crops, of course 

 including sometimes the same land twice. 



The Committee were unable to have samples of sewage and effluent water 

 analyzed regularly every month : but samples were taken three times a week 

 (equal quantities in the case of the sewage, quantities in proportion to the 

 flow in that of the effluent water) and mixed, and a sample of each mixture 

 taken at the end of the month ; thus twelve samples of sewage and twelve 

 of effluent water were obtained. 



As the samples had been kept so long and had not (in the case of the 

 sewage) been taken in proportion to the flow, it was thought sufficient to niix 

 quantities of the samples of sewage proportionate to the monthly quantities 

 of sewage pumped, and to have a sample of this mixture (for the whole 

 period) analyzed : in the case of the effluent waters it was thought better to 

 mix equal quantities (as the monthly total quantities could not be ascer- 

 tained), so as to make four samples, one for each three months, and to have 

 them analyzed. 



The results of these analyses are given in the foUowing Tables : — 



■s2 



