108 FIRST PRINCIPLES OF AGRICULTURE. 



what it costs; and a comparison of the valuation and 

 selling-price of a number in connection with their com- 

 position indicates which is the best for the money. 



Nitrogen from the same source is worth no more in 

 one brand than in another; the same is true in reference 

 to potash and available phosphoric acid. 



Analyses of Fertilizers. The chemical analysis of 

 a fertilizer should show, as far as possible, both the 

 amount and form of either or all of the three con- 

 stituents contained; viz., nitrogen, phosphoric acid, and 

 potash. Such a complete statement gives considerable 

 information as to the source and quality of the materials 

 from which the constituents have been derived. For in- 

 stance, if the analysis shows that three forms of nitro- 

 gen are present, that the "total available" phosphoric 

 acid is chiefly soluble in water, that the percentage of 

 insoluble phosphoric acid is low, and that the potash 

 is in the form of sulphate, it is good evidence that stan- 

 ard high-grade goods have been used. 



The analysis cannot, however, give definite and positive 

 information as to the source of organic nitrogen, whether 

 from the best form, dried blood, or from the poorest, 

 leather. Neither is it possible to tell absolutely how 

 much of the insoluble phosphoric acid has been derived 

 from organic or mineral sources, when materials from 

 both sources have been used. 



Fertilizer Formulas. A fertilizer formula indicates 

 the kind and quantity of raw materials to be used to 

 secure certain proportions of the fertilizer constituents. 

 If it be desired to secure a mixture containing four per 

 cent nitrogen, eight and eight-tenths per cent available 



