VII MANURES 57 



down into its various constituents, this system was a marked 

 improvement. Baron Liebig, however, to whom agricul- 

 tural science owes so much, found out a cheap and rapid 

 way to prepare the bones for manure. He acted on them 

 by sulphuric acid, producing a dissolved bone manure, and 

 in this condition the phosphate of lime becomes quite soluble 

 and ready to be used as a plant food. 



Miiieral Phosphates. — The demand for phosphatic 

 manures becomes so great, owing to their important action 

 on the soil, that the supply of bones could not keep up with 

 the demand, and other sources of phosphates had to be 

 looked for. Fortunately, large quantities of fossils of ex- Phosphatic 

 tinct organisms, and petrified excrements containing phos- 

 phates, known as coprolites., were found in the Eastern 

 counties of England, and in various parts of the continent 

 of Europe, and they were soon utilized for phosphatic 

 manures. Besides coprolites, deposits of mineral matters 

 rich in phosphates have been discovered in practically in- 

 exhaustible quantities in various parts of Europe and Ame- 

 rica. In the West Indies, mineral phosphates are mined in West Indian 

 the Islands of Sombrero, Redonda, St. Martin, Aruba and ^ °^^ 

 Navassa. Except in the case of the Redonda deposits, the 

 phosphoric acid in the mineral phosphates is combined in 

 various proportions with the metal calcium, and in the Re- 

 donda mineral the acid is combined with alumina, forming 

 phosphate of alumina. The mineral phosphates are usually 

 of a very hard rock-like character, and before being used 

 they are ground to powder ; but, as the phosphates in them 

 are, for the most part, in an insoluble condition, and, there- 

 fore, not easily taken up by the plants, it has been found 

 necessary to dissolve them in sulphuric acid so as to im- 

 prove their manurial value. 



Stipe7-phosphates. — The discovery of the way to convert 

 the insoluble phosphate of lime, or calcium, of bones and 

 minerals into the soluble form has been of immense service 

 to scientific agriculture. The insoluble phosphate is com- 



