NATURAL SCIENCES OP PHILADELPHIA. 97 



2.57 Oxygen in Sulphuric Acid require 0.85 oxygen in Lime, there remains 

 10.19 oxygen of lime, which, if added to the oxygen of the magnesia makes 

 11.69, which stands with the oxygen of the phosphoric acid 23.65 near the 

 ratio 2CaO, PO5. 



A guano rock has recently been brought from a group of Islands called El 

 Roque, in the Caribbean Sea. In composition it resembles very closely that 

 brought from Monk's Island, the specimens that I have analysed, contain how- 

 ever, a much larger quantity of sulphuric acid than has been found in the 

 latter rock. The appearance of the body of the two rocks is also much alike, 

 bat in the specimens which I have seen from EI Roque the exterior ( rust is very 

 different ; it is rarely more than a slight coating ; in some places it has a slight 

 , appearance of the enamel, when examined with a pocket lens; the surface is 

 very irregular, often containing cavities which are lined with the same white 

 coating. It was impossible to obtain sufEcient of this for analysis : the analy- 

 sis of the black portion of the rock was as follows : 



(X.) 



1.8636 grms.loss by ignition 0.1904 grms. water and organic matter 10.22 perct. 



1.4609 " 0.3274 grams. BaO, SO3 gave Sulphuric Acid, 7.70 " 



«' " 1.0066 " CaO, CO2 " Lime, 38 67 " 



" " 0.1118 " 2MgO, PO5 " Magnesia, 2.75 " 



" " 0.0116 " Insoluble 0.78 " 



" " 0.0058 " Fe203 & AI2O3 Iron & Alumina 0.40 " 



1.1680 grams 0.7936 gram. CaO, CO2 gave Lime, 38.12 " 



" " 0.0879 " 2MgO, PO5 " Magnesia, 2.70 " 



" " 0.7383 " 2MgO, PO5 " Phosphoric Acid, 40.49 " 



Organic matter and water, 10.22 per cent. 



Sulphuric Acid, 7.70 Oxygen Ratio, 4.61 



Lime, 38.67 " 10.09 



Magnesia, 2.75 " 1.09 



Phosphoric Acid, 40.49 " 25.93 



Alumina and sesquiox- " 



ide of Iron, 0.40 " 



Insoluble, 0.78 



4.61 oxygen in Sulphuric Acid require 1.54 oxygen in lime; therefore remains 

 3.55 oxygen in lime which stands with the oxygen of Phosphoric Add 25.93 in 

 the ratio 1 : 3, showing that the phosphate in this specimen consists principally 

 of 3CaO PO5. 



A specimen containing no organic matter was examined from Testigoe Island, 

 but the rock was very much disintegrated ; it was very porous, and evidently 

 had been acted upon by some causes which were gradually removing all its com- 

 ponents except the silica. In appearance it was largely a sandstone, as the analy- 

 sis showed. The most compact portion of the specimen was selected, which was 

 readily pulverized ; the results of the analysis differ from all the other speci- 

 mens. The following are the results : 



(XI.) 



1.2910 grams, insoluble silica 0.6722 grams. 



" 0.0085 CaO, CO2 gave 



" 0.0206 2MgO " 



0.8806 grams. 0.1073 loss by ignition 



0.8806 grams, insoluble 0.4600 grams. 



1857.] 



" 0.1158 AI2O3 " gave 



" 2Fe203, 3PO5 0.0318 " " 



2MgO, PO5 0.2394 " " 



