used for Agricultural Purposes. 
431 
I One sample, No. 3, it will be seen, contained a good deal of 
oxide of iron and alumina, and for this reason was not well 
adapted to the manufacture of superphosphate. The remaining 
samples also contained appreciable quantities of oxide of iron 
and alumina with more or less carbonate of lime. Three of 
the samples contained as high a percentage of phosphate of lime 
as is found in the best samples of Sombrero Rock phosphate, 
which the Aruba mineral resembles closely in its chemical 
composition. 
There are a number of other small islands in the Caribbean 
Sea on which rock phosphates of more or less value occur. For 
instance, on Pedro Keys a phosphatic deposit is found, in a cargo- 
sample of which I found : — 
Composition of a Sample of Pedro Keys Phosphate. 
Moisture and water of combination 9 '34 
'Phosphoric acid 29-69 
Lime 36 '01 
Oxide of iron and alumina, magnesia, carbonic I 19 -gg 
acid, &c -..5 
Insoluble siliceous matter 5 "27 
100-00 
* Equal to tribasic phosphate of lime .. .. 64-81 
This is an inferior mineral phosphate, and not often met with 
in commerce at the present time. 
15. Redonda Phosphate. 
Some years ago a peculiar phosphate, mistaken at the time for 
phosphate of lime, was discovered on the Redonda Island. 
This mineral consists principally of hydrated phosphate ol 
alumina, contaminated with more or less oxide of iron and 
insoluble siliceous matter. Most samples contain no lime 
whatever, and in consequence Redonda phosphate cannot be 
used in the manufacture of ordinary superphosphate of lime. 
It is, however, utilised in chemical works for the production 
of alum, for which several patents have been taken out in Eng- 
land, and it yields, as a by-product in the manufacture of 
alum, impure phosphoric acid, which may be incorporated with 
salts of ammonia and other fertilising materials, and thereby be 
transformed into artificial manures. Redonda, and other kinds 
of crude phosphate of alumina, are also useful after treatment 
with sulphuric acid, as precipitating and clarifying agents of 
town sewage. 
Messrs. Forbes and Price, who have patented the employment 
