PEINCIPAL PHOSPHATE DEPOSITS. 39 



climatic conditions in which they are found in the deposits, or by 

 being carried away in its train by rain water. All phospho guanos 

 resemble each other in their composition. They consist mainly of 

 phosphate of lime, the content of which varies between 65 and 80 

 per cent and about 12 per cent of water. They moreover contain 

 from 1 to 13 per cent of carbonate of lime coming from the coral 

 limestone which serves to them as substratum, and about 1 per cent 

 of nitrogen yielded by the organic matters which imparts to them 

 a colour varying from yellow to dark brown. Finally, small 

 amounts of oxide of iron and alumina, calcium fluoride, and analo- 

 gous bodies, the presence of which, as will be seen further on, is 

 calculated to interfere with the dissolving of the phosphates. 



Phospho Guanos were formerly the most highly esteemed raw 

 material of the manufacture of superphosphates and the most ■ 

 easily preserved. Unfortunately, the greater part of the deposits 

 are partially exhausted, and those which still exist are not wrought, 

 owing to the fall in price and the scarcity of labour. Phospho 

 guanos differ much from each other in their appearance, their form, 

 and their colour. They are met with, most often, in a pulverulent 

 state, mixed with lumps, easy to crush between the fingers. They 

 sometimes consist of masses, amalgamated with coral debris, some- 

 times as crusts, or again in masses as hard as stone. The chief 

 deposits of these phosphates are met w4th in a great number of 

 small islands in the West Indies and the Pacific Ocean, and also 

 in the Bay of Mejillones on the West Coast of South America. 

 A rapid description indicating their characteristics will now be 

 given. 



I. West India Islands. — Eedonda Isles, Sombrero, Navassa, 

 Aruba, Curasao, Los Roques, Alta Vela, Rata. 



II. Islands of the Pacific Ocean. — Baker, Jarvis, Maiden, 

 Fanning, Starbuck, Howland, Phoenix, Sidney, Enderbury, Minerva, 

 Aves, Lacepede, Flint, Brov/se (? Brown), Fluon, Chesterfield, 

 Abrolhos, Mona, Cayman, Clipperton, Nauru, Angaur, and Makatea 

 Isles, etc. 



West India Islands.— 1. Eedonda Phosphate. — This phosphate, 

 like that of Alta Vela, does not contain phosphate of lime, but 

 hydrated phosphate of alumina and phosphate of iron. It is thus 

 unfit for making superphosphate. It is yellovv- in colour, more or 

 less dark with black points. Its composition is as follows : — 



TABLE XXIX.— ANALYSES OF EEDONDA PHOSPHATE. 



Voelcker. Tate. 



Per cent. Per cent. 



Water 24-20 21-50 



Phosphoric acid 38-52 38-50 



Oxide of iron and alumina . . • 35-33 32*50 



Insoluble 1-95 6-50 



