64 SOILS - 



formations occur. In the United States, in South Carolina, 

 Florida, Alabama, Tennessee, Kentucky, Nevada; in South 

 America, on Curagoa island, Venezuela ; in the Antilles on Som- 

 brero, St. Martins and Navassa islands. In Africa, in Algiers 

 and Tunisia; in Europe, in Spain (Estremadura, one of the 

 first deposits known), France, Belgium and the adjacent parts 

 of Germany; in Bohemia and Galicia in Austria; and very ex- 

 tendedly in European Russia. Many islands of Oceanica sup- 

 ply phosphorites derived from the decomposition of bird guano 

 by the coral limestone. 



Unfortunately the percentage of phosphate in a large proportion of 

 these materials is not sufficiently high to make their conversion into 

 water-soluble superphosphate economically possible at the present time ; 

 since all the calcic carbonate present must also be converted into com- 

 paratively worthless sulphate (gypsum ) by the use of sulfuric acid ; 

 and as yet no practicable method for avoiding this difficulty has been 

 found. 



" Thomas Slag." Probably the nearest approach to such a method 

 is indicated by the fact that a compound containing four instead of 

 three molecules of lime to one of P 2 O 5 , such as is contained in the 

 " Thomas slag " of the basic process of steel manufacture, is nearly or 

 in some cases ("sour" soils) quite as effective for the nutrition of 

 plants as the water-soluble superphosphate. This discovery has rendered 

 available for agricultural use the phosphoric acid contained in the 

 enormous deposits of limonite iron ore known as bog ore, which con- 

 tains a large proportion of ferric phosphate and from that cause has 

 until lately been excluded from the manufacture of wrought iron and 

 steel. It is reasonable to hope that by some analogous process the 

 low-grade phosphorites, such as those of Nevada and the plains of 

 Russia, will also in the course of time become available for agricultural 

 use. Extremely fine grinding and washing (producing " floats " ) has 

 been resorted to for the purpose of rendering the raw phosphorites 

 effective in fertilization. But while this is successful on some soils, on 

 others the " floats" remain almost inert ; so that this method has found 

 only limited acceptance. 



Animal bones, which consist of from 24 to 30 % of animal 

 substance and 70 to 76,% of "bone earth," (or when fossil 

 are free from the former), are largely used for the manufac- 



