116 



CHEMISTRY OF FARM PRACTICE 



widely distributed in rocks of igneous origin. A typical 

 mineral phosphate is apatite, a double phosphate, and 

 fluoride of calcium with the formula Ca3(PO4)2-Ca2FPCH. 

 Formerly large quantities of this mineral were imported 



FIG. 41. Corn grown on the same area and soil as that of Fig. 40, 

 with the addition of 500 Ibs. acid phosphate and 188 Ibs. dried 

 blood per acre. 



from Canada for manufacture into fertilizer. The expense 

 of mining and transportation does not permit this mineral 

 to enter into competition with rock phosphate as a fertilizer. 

 87. Guano. This material has been a rich source of 

 phosphorus as well as of nitrogen. The standard Peruvian 



