THE VALUATION OF FERTILIZERS 191 



and b to vary according to season from about 125. to 135. 

 If simplicity of calculation is considered a point of great 

 necessity, it would be better to give the J % of ammonia 

 an even number of shillings, say 35., since the error of 

 J % is actually allowed in the guaranteed analysis ; this 

 system would allow the zero price a to fluctuate from 

 us. to 2 is., according to season. It will be seen, therefore, 

 that even in such a simple case as the question of sulphate of 

 ammonia, the calculation of values is far more complicated 

 than has usually been allowed for in the text-books. 



The orders for 1919-20 for sulphate of ammonia give a 

 zero price of minus i I2s. a ton, and a unit price for 

 ammonia of i6s., which is equal to a unit price for 

 nitrogen of 195. $d. In other words, the interests of the 

 farmer are here predominant, and the point of view of the 

 producer is not considered. 



Nitrate of Soda. The Board of Agriculture recently 

 (May, 1919) fixed the price of nitrate of soda at 10 a 

 ton, corresponding to i 55. for i % of nitrogen, as against 

 rather under i6s. for i % of nitrogen in sulphate of 

 ammonia. Mr. Kellaway stated in the House of Commons 

 that there is at present no appreciable demand for nitrate 

 of soda from farmers in this country. At such an increased 

 price over sulphate of ammonia, it would not be worth the 

 farmer's while to purchase nitrate of soda. 



Ammonium nitrate has been offered by the Board 

 of Agriculture (March, 1919) at 25 a ton for about 

 33a % nitrogen. This is equal to 155. per unit of nitro- 

 gen, or much below the unit price of nitrogen in sulphate of 

 ammonia. 



The Valuation of Basic Slag. Similar statistical 

 treatment enables one to draw a curve of the prices charged 

 in the case of basic slag. In treating any unknown curve, 

 one can attempt to solve it by a formula of the form of 

 V = a -f- bp + cp z , etc., where the meanings of the symbols 

 are the same as before, with the addition that c is a new 

 constant. If this equation is solved for the basic slag 

 prices, we find that a = 475., b = 785. and c = 0*01745. 



