COMMERCIAL FERTILISERS 373 



4. Look out for re-statements in the fertiliser 

 tags, thus: 



Per cent. 



1. Bearing total bone phosphate . . . . 30 to 35 



2. Yielding phosphoric acid 14 to 16 



3. Soluble bone phosphate 22 to 26 



4. Yielding water-soluble phosphoric acid. . 10 to 12 



5. Total available bone phosphate . . . . 26 to 30 



Statement No. 4 is the only one worth considering; 

 the others are mainly re-statements in another 

 form. "Equivalent to" or "Yielding" usually 

 means that the plant food in the fertiliser has al- 

 ready been stated in the guarantee in another 

 form. To convert one material into another, 

 when there is repetition, use the following table: 



To convert the guarantee of Multiply by 



Ammonia . . . into Nitrogen 82 



Nitrate of soda . " Nitrogen 16 



Bone phosphate . " Phosphoric acid . . . .45 



Muriate of potash " Potash 63 



Sulphate of potash " Potash 54 



5. Pay no attention to anything in the guarantee 

 that is not plant food. The amounts of "mois- 

 ture," "silicic acid," "carbonic acid," "mag- 

 nesia," "alumic oxid," "ferric oxid," and other 

 materials that the fertiliser contains are of no 

 interest or value to the buyer. 



CALCULATING THE VALUE OF A FERTILISER FROM 

 THE ANALYSIS 



The value of a commercial fertiliser is based 

 solely upon the amount of plant foot that it con- 

 tains. Animal and green manures are often quite 

 valuable for their effect upon the condition or 

 "heart" of the soil; but commercial fertilisers 

 have little or no value in this respect. When 



