CH. xij Seivage 203 



3. Soot from destructors and boilers, however, is of 

 very much less value, commonly containing about 0-5 

 per cent, of nitrogen, and less than 1 per cent, of potash. 

 On no account should any of these be purchased except 

 on the recommendation of a disinterested analyst. 



Two such samples showed the following percentages : 



Nitrogen Potash (KgO) 



1. 0-5 



2. 0-47 0-80 



These have little or no fertilising value. 



Ash 'pit refuse. This material is naturally very variable 

 in composition. On the whole it is not particularly useful 

 as a fertiliser in spite of its smell: usually it contains 

 only about \ per cent, of nitrogen, 2 per cent, of potash 

 and about 1 per cent, of phosphate. On heavy land it 

 has advantages over and above its fertiliser content, as 

 it makes the soil lighter and more workable. 



Sewage and seivage sludge. 



It is estimated^ that the population of the United 

 Kingdom consumed before the war 1,438,000 metric 

 tons 2 per annum of protein containing 230,000 tons of 

 nitrogen. Most of this is excreted and a considerable 

 part appears in sewage. Assuming the population to 

 have been 45-2 millions, and disregarding the nitrogen 

 in the growth increase, this gives a yearly average of 

 11 lbs. nitrogen excreted per head of the population. 

 Of this 86 per cent, is in the urine and 14 per cent, in the 

 faeces. Data for potash and phosphates do not exist, but 

 assuming that these were about one quarter the value 

 of the nitrogen figures the fertiliser value per annum of 



^ Food Supply of the United Kingdom: Roy. Soc. Repf., 1917, Cd. 8421. 

 ^ A metric ton = 1000 kilos = 2205 lbs. 



