PEINCIPAL PHOSPHATE DEPOSITS. 33 



TABLE XXIV.— ANALYSES OF HARD ROCK BLUE RIVER PHOSPHATE. 



Water ....... 



Phosphate of lime ..... 



Oxides of iron and alumina ... 



The laminated rock, the crevices of which are generally filled 

 with clay, rarely sand, frequently contain 5 to 8 per cent of clay, 

 from which it is partially freed by roasting, grinding, and sifting. It 

 then only contains 3 to 4 per cent of oxides of iron and alumina, 

 and is exported. The material passing through the sieve contains 

 up to 10 per cent of clay, and is utilized in the country itself. 

 This roasting of the phosphate is carried out in a very primitive 

 manner : on a layer of wood 1 foot thick is placed a layer of phos- 

 phate 3 to 4 feet thick, and fire applied. This method is decidedly 

 economical, but it yields a bad product. Whilst the phosphate of 

 the lower layer is roasted, that on the top is barely dried, and the 

 whole mixed with ashes and pieces of charcoal. But the roasting 

 has little effect on the moisture content of the phosphate, for it 

 suffices to expose it to the open air for it to recover 1 to 3 per cent 

 of water. 



Flate Bock or Sheet Bock. — This kind of phosphate is the most 

 interesting of all. It is found near Ocala, especially near Anthony, 

 Spar and Montague. It occurs as small tablets, or as large as the 

 hand, of irregular shape of one to several centimetres thick, of a 

 white or brownish-yellow colour. The heavy, brittle fragments are 

 the richest in phosphoric acid, whilst the soft, light fragments 

 contain the most clay. The sorted pieces contain sometimes as 

 much as 80 per cent of phosphate, and only 1 to 2 per cent of oxide 

 of iron and alumina ; the average is 74 to 78 per cent of phosphate of 

 lime, with 3 to 4 per cent of oxide of iron and alumina. This high 

 iron and alumina content comes from the gravel mixed with it, 

 which forms irregular fragments of phosphate, the crevices of which 

 are filled with clay. The plate rock rests always on the dolomitic 

 limestone which forms columns and irregular cones. The cavities 

 comprised between these columns are filled with phosphate, mixed 

 with sand or clay. In certain places the phosphate bed is very 

 pure and contains 50 to 80 per cent of pure phosphate. The 

 superficial layer of sand is usually not very thick, but it is some- 

 time 45 to 50 feet thick. 



Soft Phosphate. — There is known under this name, in Florida, 

 a phosphatic clay of soft, friable, or kneadable consistency, with a 

 very variable moisture content, which constitutes the filling between 

 the pebbles. As the following analyses show, a small portion of its 

 phosphoric acid is sometimes soluble in water or in citrate : — 



3 



