PURCHASE: AND USE OF FERTILIZERS 321 



The desired fertilizer would contain, in 1,000 pounds, 80 

 pounds available phosphoric acid, 20 pounds nitrogen, and 20 

 pounds potash. 



Since i pound cottonseed meal contains 0.07 pounds nitrogen, 

 it would take 20 -- 0.07 = 286 pounds cottonseed meal to furnish 

 20 pounds nitrogen. This 286 pounds would contain also 

 286 X 0.02 = 5.7 pounds phosphoric acid and 286 X i-5 = 4-3 

 pounds potash. 



The 80 pounds available phosphoric acid required, less 5.7 

 pounds, in the cottonseed meal, leaves 74.3 pounds to be secured 

 from the acid phosphate. 74.3 -f- 0.14 = 531 pounds acid phos- 

 phate. 



The 20 pounds potash required, less 4.3 pounds in the cotton- 

 seed meal, leaves 15.7 pounds to be secured from the kainit. 

 15.7 -r- 0.12 = 131 pounds kainit. 



Then the desired ingredients to make 1,000 pounds of the 

 fertilizer, would consist of : 



Pounds 



Cottonseed meal 286 



Acid phosphate 531 



Kainit 131 



Total 948 



Filler 52 



I ,OOO 



It would thus be necessary to add 52 pounds filler to make the 

 desired composition. 



The ingredients for other fertilizer mixtures may be calculated 

 in a similar way. In factory work, it is necessary to allow for 

 variations in the composition of the ingredients by providing for 

 a slight over-run. Otherwise, some of the mixtures may fall be- 

 low guarantee. 



Incompatibles in Fertilizer Mixtures. Certain materials should 

 not be mixed in making fertilizers, for the following reasons : 



( i ) Chemical reactions take place which result in the loss of 

 nitrogen in the form of ammonia. For this reason, ammonium 

 sulphate, guano, or barnyard manure should not be mixed with 

 lime, ashes, or Thomas slag. 



