COMMERCIAL UMIIIZERS 143 



wholesale prices of these substances at points of supply. 

 For instance, if nitrate of >oda lellfl foi $48 a ton, ami 

 contains 1G per cent of nitrogen, then iti nitrogen ii 

 worth 15 cents a pound. If coitoneeed-meaj Belli for 

 $18 a ton, and contains G.75 per cent of nitrogen, then 

 its nitrogen i- worth 13.3 cents a pound. In the same 

 way, values arc fixed for the phosphoric acid and potash 

 supplied by various substances. • These values are 

 usually fixed once each season, and remain unchanged 

 until the next season. 



When the various substances supplying nitrogen, 

 phosphoric acid and p<>ta-h an- mixed to form a COm- 

 plete fertilizer — that is, a fertilizer containing all of 

 these plant foods — the valuations of the official chem- 

 ists may be used t'> estimate the cost of the raw 

 material.-, as in the example already given. The Belling 

 of the fertilizer is, however, often greater than 

 the estimated value of the raw materials, because the 

 manufacturer charges enough to insure himself a profit 

 after paying the coal of manufacturing and of placing 

 the fertilizer on the market.' 



her the valuation of the official chemist nor the 

 market price indicates, however, the agricultural value 

 of anv fertilizer, for its agricultural value can he deter- 

 mined only by actual tests in the field. The puhlished 

 analyses and the official valuations of fertilizers are, 

 DOWerer, of benefit to the farmer in several ways. 



They show, first, what the composition of a fertilizer 

 is, and whether it fulfills the claims of the manufac- 

 turer. Next, by showing the farmer how to calculate 

 lor himself the market value of the guaranteed con- 



