PHOSPHORUS 



117 



guano contains nearly 40 per cent of bone phosphate, 

 corresponding to about 18 per cent of phosphoric acid 

 (P2O5). Certain small, rocky islands of Peru, owing to 

 the abundance of fish found in the waters of these coasts, 

 have been the habitat for untold ages of enormous numbers 

 of sea birds. Rain seldom falls in these regions and the 

 excrement (Spanish Guano) has collected in thick deposits. 



FIG. 42. Corn grown under the same conditions as that of Fig. 40, 

 but with 160 Ibs. of muriate of potash added per acre. 



From one group of these small islands, the Chincha, guano 

 to the value of $1,000,000,000 has been taken. As a source 

 of phosphorus guano is much more expensive than is rock 

 phosphate and the supply is being exhausted. 



88. Purchase and Application of Phosphorus. The selec- 

 tion of the source of phosphorus to use is largely an economic 

 problem to be determined by the costs of the materials 

 delivered on the farm. Lower prices for fertilizing ma- 



