362 
Chemical Composition and Commercial Value of 
tions taken from several blocks, was submitted to a careful 
analysis, which furnished the following results : — 
Moisture 2-39 
*Organic matter and water of combination .. .. 7'!)3 
Lime 39-48 
Magnesia 1"17 
Pliosphoric acid 4r34 
Sulpluiric acid 4'57 
Soluble silica and sand 2'28 
U9-1G 
* Containing nitrogen "ISO 
Equal to ammonia 'ICO 
By dissolving this mineral in hydrochloric acid and precipi- 
tating the solution, filtered from the sand, with ammonia, 76"7l 
per cent, of phosphate of lime and magnesia (bone-earth) were 
obtained. The filtrate from the phosphate contained no lime 
whatever, but no less than 4'90 per cent, of phosphoric acid. 
It is thus clear that Monk's Island Guano contains a phos- 
phate which has a different constitution from that of ordinary tri- 
basic or bone-phosphate of lime. On uniting the sulphuric acid 
with lime we obtain I'll per cent, of sulphate of lime, and, de- 
ducting the lime in the sulphate from the total quantity of lime 
found in the analysis, 36'28 per cent, of lime are left, which are 
united with phosphoric acid. The magnesia takes up 2"11 of 
phosphoric acid, and yields 3'28 of phosphate of magnesia 
(2 Ma, O, PO5). There thus remains 39'23 of phosphoric acid 
to unite with 36*28 of lime. 
From these data it appears that this singular and highly valuable 
phosphate consists chiefly of a mixture of pyro-phosphate and 
ordinary tribasic phosphate of lime. Since this substance con- 
tains a phosphate richer in phosphoric acid than ordinary or 
bone phosphate, and is free from carbonate of lime, it is rendered 
soluble with much less sulphuric acid than is required for dis- 
solving bone-ash, apatite, and other phosphates. Monk's Island 
Guano, therefore, is a peculiarly valuable and excellent material 
for preparing artificial manures that are rich in soluble phosphate 
of lime. 
6. Sombrero Rock, or Crust Guano. 
This valuable phosphatic material occurs in one of the West 
Indian Islands, and of late years has been imported into England 
in some quantities. Sombrero Rock, as the name implies, is 
quarried in the islet of Sombrero. A large portion of this islet 
has been quarried away already, and sold both in America and 
in England as Crust or Sombrero Guano. This is not a very 
