342 



VALUATION AND PURCHASE 



[chap. 



the statement merely signifies that the essential 

 element, potassium, is present in such a quantity that 

 if it were combined with oxygen as potash the latter 

 would amount to 50 per cent, of the fertiliser. It is 

 therefore necessary to remember that 14 of nitrogen 

 are equivalent to 17 of ammonia, and that 142 of 

 phosphoric acid are contained in 310 of tri-calcium 

 phosphate (see p. 377), but that necessity of making 

 such calculations is obviated by the fact that in the 

 United Kingdom dealers in fertilisers are now obliged 

 to give the analysis of their wares in terms of nitrogen, 

 tri-calcium phosphate, and potash, on which basis the 

 calculations which follow will be made. 



The prices given are the wholesale prices ruling in 

 London in October 1908; naturally they do not hold for 

 other times and places, and they do not include 

 carriage, but they are comparable among themselves 

 and with due additions for the locality show the range 

 of prices which may be expected at the present time. 



In order to find the price of nitrogen, we can take 

 nitrate of soda and sulphate of ammonia, which contain 

 nitrogen only, and calculate the unit value as follows : — 



Table XCVI. — Price of Unit of Nitrogen. 



In making this calculation the farmer must be 

 careful to base it upon the price per ton delivered 

 at his local station, since freight charges fall more 

 heavily on the less concentrated manures, to such an 

 extent indeed that at distant points the relative cost 



