Phosphatic Materials used for Agricultural Purposes. 15 



tions taken from several blocks, was submitted to a careful 

 analysis, which furnished the following results : 



Moisture 2'39 



*0rganic matter and water of combination .. ' .. 7'93 



Lime 39'48 



Magnesia, 1'17 



Phosphoric acid 41*34 



Sulphuric acid 4-57 



Soluble silica and sand 2'28 



99-16 



* Containing nitrogen '139 



Equal to ammonia '169 



By dissolving this mineral in hydrochloric acid and precipi- 

 tating the solution, filtered from the sand, with ammonia, 76'71 

 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 1 '11 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, PO 5 ). There thus remains 3Jr23 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 



