ON SOMBRERITE. 



443 



It contains no fluoride nor chloride of calcium. Its specific gravity is 2'52. 

 A well-chosen specimen has given me the following composition:- 







Atomic ratio. 





9-00 



. 1-00 . 



Phosphate of lime 3 CaO, PhO 5 



. 65-00 



. 0-41 . 



Phosphate of alumina 3A1 2 O 3 , PhO 5 



17-00 



. 0-05 . 



Carbonate of lime .... 



5-00 





Chloride of sodium. .... 



1-44 





Sulphate of lime . , 



1-36 







1-00 





Crenate of ammonia, &c. . 



0-20 





20 



100-00 



which gives for sombrerite the formula — 



;8 (3 CaO, PhO 5 ) + (3A1 2 2 3 , 2 PhO 5 ) + 20 HO. 



Persons who have seen this rock think that it owes its origin to guano — 

 some looking upon it as " fossil guano," and others as " guano modified by- 

 volcanic action." In order to bring forward, if possible, some proof of these 

 theories, I took a large quantity of the mineral, and sought carefully for 

 uric acid. Though the experiment was repeated several times, I have not 

 been able to find the least trace of that compound, but only a very slight 

 quantity of crenate of ammonia, which I have frequently met with in 

 different minerals, notably in iron-ores of various ages. At the same time, 

 it is possible that sombrerite may have derived its origin from ancient 

 deposits of guano, modified by time and geological phenomena, as we see 

 large beds of limestone and sandstone almost completely formed by the 

 debris of organised beings. However that may be, I look upon this rock as 

 having found its way to the surface at a high temperature, in contact with 

 water or steam, and under great pressure. This would account for its 

 pecidiar appearance. 



As regards the uses of sombrerite, it might be turned to account, and I 

 believe it has been employed, for the preparation of phosphorus, phosphoric 

 acid, and its compounds. But for agricultural purposes, its application 

 meets unfortunately with a drawback ; by converting the rock into what is 

 called " superphosphate of lime," a certain quantity of sulphate of alumina 

 is formed, and this salt, being deliquescent, attracts and retains so much 

 moisture, that the product can be dried only with great difficulty. Som- 

 brerite has, however, the advantage of being easily reduced to powder, and 

 would, doubtless, in that state, be advantageously mixed with certain 

 soils. 



