204 



Fertilisers 



[PT. Ill 



the excrements of the population of the United Kingdom 

 would be: 



This is approximately equal to the value of farmyard 

 manure and all the other fertilisers put together (p. 217). 

 Owing to various losses, however, only a small part of 

 this ever reaches the sewage works. An average 

 quantity of domestic sewage is 33 gallons per head per 

 day, containing 5 parts of nitrogen per 100,000; this 

 corresponds to 6 lbs. of nitrogen per head per annum. 

 Further, only a portion of the population is connected 

 with sewage systems. Unfortunately no practicable 

 means of realising the value of sewage has yet been 

 devised. Broad irrigation and sewage farming answer 

 under certain conditions, but not as general methods of 

 treatment. The only material generally available is the 

 sludge which is prepared by some precipitating or settling 

 process, and therefore contains only the insoluble com- 

 pounds and not the soluble and valuable nitrates, 

 ammonia, etc. This indeed is its weakness: it has been 

 so well washed during the process of formation that it 

 has lost much of its decomposable material. 



Various experiments have frequently been made to 

 ascertain the manurial value of sludge, but the results 



* When sulphate of ammonia =14 per ton; 30% super =3; and 

 sulphate of potash = 12. 



" Tills being the average, the figure is naturally higher for adults. Thus 

 it is estimated that an adult excretes 50 ozs. of urine daily, containing 

 1 % of nitrogen: this alone amounts to 11 lbs. per annum. 



