156 Fertilizers 



tions, and because of its mechanical condition or degree of 

 fineness. Different samples of bone derived from the 

 same source, treated in the same way, and ground to the 

 same degree of fineness, would be regarded as standard, but 

 because these conditions differ, bone from different sources 

 cannot be depended upon to act in the same way under 

 the identical climatic and soil conditions. This is also 

 true of tankage, which varies, not only in the total amount 

 of the constituents contained in it, but in the proportion 

 of its two chief constituents, nitrogen and phosphoric 

 acid, and in the rate at which they become available to 

 plants. In this class belong, in addition to the bone and 

 tankage, ground fish, and the various miscellaneous 

 products. They cannot be depended upon, either in 

 respect to their composition or their availability of the 

 essential constituents important advantages possessed 

 by the standard products. 



HIGH-GRADE AND LOW-GRADE FERTILIZERS 



The fertilizers manufactured from these two classes 

 of raw materials will therefore differ. Those made 

 from the first class are always high-grade, both in refer- 

 ence to the quality and quantity of the constituents that 

 may be contained in a mixture. Those manufactured 

 from the second group are not high-grade, so far as the 

 form of the constituent is concerned, though they may 

 be high-grade in the sense that they contain large amounts 

 of them. In the manufacture of fertilizers, too, as a rule, 

 all three of the essential constituents are introduced, and 

 the buying of a fertilizer is really the buying of the three 

 constituents, nitrogen, phosphoric acid and potash. 

 Hence, the more concentrated the product, or the richer 



