FT. Ill, CH. xii] Unit Prices 207 



In this case the sulphate of ammonia was the cheaper 

 and would have been purchased unless there were any 

 special reason for choosing the nitrate of soda. 



The unit value of phosphate in superphosphate or in 

 basic slag, and of potash in the various potash fertilisers, 

 is obtained in the same way. 



When manures contain two or more fertilising con- 

 stituents it is obviously impossible to proceed entirely 

 in this wsij, and certain conventions have to be adopted. 

 It is assumed that the potash has the same value as in 

 the potash fertilisers but that insoluble phosphate has 

 less value than in superphosphate, an assumption that 

 is probably sound. The actual value assigned to the 

 phosphate before the war was usually about \s. 3d. to 

 Is. 9d. according to the grade of the manure; guanos, 

 fish and meat meal ranking higher than steamed bone 

 flour. After allowing for these two constituents one can 

 proceed to calculate the unit value of the nitrogen : 



A Peruvian guano containing^ 7 per cent, of ammonia 

 {i.e., 5- 8 per cent, of nitrogen), 30 percent, of phosphates 

 and 2 of KoO, was offered at 9. 125. 6c?. per ton f.o.r. 



1 unit of phosphate was worth Is. 9d. s. d. 



.: 30 were worth 2 12 6 

 1 unit of KoO was worth 4*. 6d. 



.". 2 were worth 9 



The phosphate and KoO were worth ... 3 1 6 



.. For 5-8 per cent, of nitrogen the dealers 

 were asking 9. 125. 6d. less 3. Is. U. 6 11 



i.e., unit price asked = 225. Id. 

 The advantage of the unit system is that it at once 



^ The trade expression. See pp. 143 and 150. 



