MANURE AND FERTILIZERS. 39 



ments sometimes containing as mucli nitrogen as phos- 

 phoric acid, and also a large percentage of potash. 



The chief merit of Pernvian guano is due to the 

 fact that it has been accumulated in a region where it 

 never rains, as upon the Chincha IsUmds, or only occa- 

 sionally upon the Labos Islands, and though fifty per 

 cent, of Peruvian guano is soluble in water it thus 

 remained intact, and did so remain for ages, until 

 the deposits, in some places, accumulated to one hundred 

 feet in thickness, the droppings from birds, and other 

 materials, all derived from the weeds and fish of the sea. 

 There are other bird guanos collected from various 

 islands in other seas, but having been subjected to rains, 

 have lost most of their nitrogen and potash, the phos- 

 phoric acid being retained ; these have been termed 

 phosphatic guanos, while the Chilian grades are termed 

 nitrogenous guanos. The natural sources of phosphoric 

 acid are the rock phosphate, extensively used by the 

 superphosphate manufacturers, large quantities being 

 brought from the island of Navassa, near St. Domingo, 

 and from the South Carolina and Florida phosphate 

 beds. The artificial sources of supply are the vast plains 

 of South America, from whence have been collected and 

 exported the bones of innumerable herds of cattle slain 

 for their hides, and millions of others dying from nat- 

 ural causes, during the past one hundred and fifty years. 



Potash, used commercially as a fertilizer, was at first 

 derived from w^ood ashes, and often from feldspar, and 

 the supply was long insufficient ; but about 1860 the 

 salt miners of Prussia discovered large deposits of potash 

 salts, which have since been the main supply for the 

 manufacture of fertilizers the world over, the damaging 

 chloride of magnesium being first removed. These 

 Prussian mines are vast deposits of saline matter, evi- 

 dently crystalized out of sea water. Before crude salts 

 can be advantageously sold and transported they have to 



