FERTILIZER INSPECTION. 43 



The commercial valuation will be accurate enough as a means 

 of comparison if the following rule is adopted : 



Multiply 3 . 5 by the percentage of nitrogen. 



Multiply 0.8 by the percentage of available phosphoric acid. 



Multiply 0.4 by the percentage of insoluble phosphoric acid. 



Multiply 1 .0 by the percentage of potash. 



The sum of these four products will be the commercial valua- 

 tion per ton on the basis taken. 



Illustration. The table of analyses shows a certain fertilizer 

 to have the following composition: Nitrogen 2.00 per cent; 

 Available phosphoric acid 8.50 per cent; Insoluble phosphoric 

 acid 3 . 50 per cent ; Potash 3 . 25 per cent. The valuation in this 

 case will be computed thus : 



Nitrogen, 3.5X2.00, 7.00 



Available phosphoric acid, .8X8.50, 6 . 80 



Insoluble phosphoric acid, o . 4 X 3 • 50, i . 40 



Potash, 1.0X3-25, 3.25 



Valuation per ton, $18.45 



Since this rule assumes all the nitrogen to be organic and all 

 the potash to be in the form of the sulphate, it is evident that the 

 valuations thus calculated must not be taken as the only guide in 

 the choice of a fertilizer. At best the valuations can only serve 

 to show the approximate cost of the several ingredients contained 

 in the fertilizer in question. In every case the farmer should 

 consider the needs of his soil before he begins to consider the 

 cost. In many instances a little careful experimenting will show 

 him that materials containing either nitrogen, potash, or phos- 

 phoric acid alone will serve his purpose as fully as a "complete 

 fertilizer," in which he must pay for all three constituents, 

 whether needed or not. 



The results of the analyses of the manufacturers' samples of 

 fertilizers are given on the following pages. 



