November, 1924] fertilizer inspection, 1924 5 



monium sulphate. The per cent of nitrogen is the thing 

 which is important and is the figure which should be used 

 in calculating the value of a fertilizer. The following shows 

 how to calculate the per cent of nitrogen from the per cent 

 of ammonia and vice versa. The nitrogen per cent multi- 

 plied by 1.21584 gives the per cent of ammonia. The per 

 cent of ammounia multiplied by 0.82247 gives the per cent 

 of nitrogen. Do not be misled by thinking that a tag stat- 

 ing 3.29 per cent of nitrogen and nitrogen equivalent to 4 

 per cent of ammonia means that the fertilizer contains the 

 sum of these two. It does not. It means that the fertilizer 

 contains 3.29 per cent nitrogen only. 



For convenience, phosphorus is expressed as per cent 

 of "phosphoric acid" or (P2O5) phosphorus pentoxide. The 

 tag usually gives the total per cent of "phosphoric acid," 

 the "water soluble," "citrate soluble" and "insoluble." For 

 the purpose of figuring out the value of these we can take 

 the sum of the "water soluble" and the "citrate soluble" and 

 call it available phosphoric acid. The per cent of available 

 phosphoric acid is the figure to use in determining the value 

 of the fertilizer. Potassium is expressed as per cent of 

 available (K2 O) or potash. This is water soluble and 

 available to the plant. 



METHOD OF CALCULATING THE RELATIVE 

 COMMERCIAL VALUE. 



Because of the variations in prices during the season 

 and the differences in freight costs, etc. it is difficult to 

 calculate accurately the values of the different brands of 

 fertilizer. The commercial value of a fertilizer is based 

 upon the content of available nitrogen, phosphoric acid, 

 ( P2 O5 ) and potash ( K2O ) If we know the guaranteed 

 analysis and assign approximate commercial values for a 

 pound of each of the plant foods, we can decide the rela- 

 tive values of fertilizers. 



The terms "unit" of nitrogen, "unit" of phosphoric 

 acid and "unit" of potash are sometimes used to express the 



