34 ARTIFICIAL MANURES [OH. 



able to compare their cost, and this is done on the basis of unit 

 values. 



The unit value is the cost of 1 per cent, per ton ; it is got by 

 dividing the cost of the manure by the percentage of nitrogen, 

 phosphate, or potash. Thus, the unit value of nitrogen in sulphate 

 of ammonia containing 20 per cent, of nitrogen is at present: 



Cost of manure _ 17 _ 

 Percentage of nitrogen ~~ 20 



while that of nitrate of soda is rather higher. 



The unit value of soluble phosphate in 30 per cent, super- 

 phosphate is 



g -.. 



The phosphates in guano, fish, meat meal, and basic slag are 

 considered of less value than in superphosphate, and those in 

 bone meal, bone flour, and rape meal still less. The nitrogen is, in 

 peace times, reckoned to be worth more than that in nitrate of 

 soda or sulphate of ammonia, but in war time it ought not to 

 increase much in price, as it is not wanted for munitions ; it can 

 safely be put at 18s. per unit. 



Bone flour containing 2 per cent, of nitrogen and 60 per cent, 

 of phosphates was offered at 6. 10s. delivered. 



2 units nitrogen at 18s. are worth 1. 16s., leaving 4. 14s. to 

 pay for 60 units of phosphate, 



4. 14s. R , 



= = Is. vd. per unit, 



a very reasonable sum, only a trifle over peace prices. The offer 

 therefore was a good one. 



Rape dust containing 5 per cent, nitrogen and 4 per cent, 

 phosphate was offered at 8. 10s. per ton f.o.r. 



4 units phosphate at Is. 6d. = 6s., 

 leaving 8. 4s. to pay for 5 units of nitrogen, 



ro A 



= ' - = 32s. Wd. per unit of nitrogen, 

 5 



a very high price which could hardly be justified except in extreme 

 cases. 



