ttO 



CHEMICAL MANURES. 



2. Sombrero Phosj)hate. — Two sorts are to be differentiated : 

 one of oolitic structure and variegated in colour, which contains 

 besides tribasic phosphate of lime, phosphate of magnesia, phos- 

 phate of iron, phosphate of alumina, silica, and alumina ; the other 

 has a more homogeneous structure, a white or yellowish colour, is 

 rich in phosphoric acid and contains in addition carbonate and 

 sulphate of lime. This deposit was known in 1814, but it was only 

 in 1858 that it was begun to be worked, and since then there has 

 been drawn from it during long years excellent phosphate of lime, 

 containing 75 to 80 per cent of CagP^O^^, 10 per cent of carbonate of 

 lime, and 2 per cent of oxides of iron and alumina. But for the 

 quality of the product since it began to be extracted below the sea- 

 level, Voelcker gives the following analysis: — 



TABLE XXX.— ANALYSIS OF SOMBRERO PHOSPHATE. (VOELCKER.) 



^Yatel• . 

 Phosphoric acid 

 Lime . 

 Oxide of ir )n 

 Alumina 

 Magnesia 

 Sulphuric acid 

 Carbonic ac.d 

 Fluorine 



Per cent. 

 2-94 

 85-52 

 47-99 

 3-70 

 7-55 

 0-58 

 0-36 

 0-96 

 0-43 



3. Xavassa Phosphate. — The isle of Navassa is of coral origin, 

 with escarpments in some places, and beaten by the waves in 

 others. Phosphate was worked here as far back as 1856, but it 

 was soon seen that it was rich in oxides of iron and alumina, and 

 was abandoned. It is mostly granular, or in the form of grains, 

 the size of which varies from that of a pin -head to that of the fist, 

 and which are often agglomerated into big lumps of almost pure 

 phosphate of lime. Its composition is the following according to 

 Bretschneider (I) and Gilbert (II) : — 



TABLE XXX. (a)— ANALYSES OF NAVASSA PHOSPHATE. 



Wat-r 



Combined water and organic matter 



Phosphoric acid 



Lime .... 



Oxide of iron . 



Alumina 



Sulphuric acid and fluorine 



Cirbonic acid 



Insoluble 



4. Aruba Phosphate. — This phosphate occurs as yellowish stones 

 traversed sometimes by dark-coloured veins and spots. It contains 



