366 Mr. D. Forbes on the Chemical Composition of 



carbonate, and in two cases the amount of water present in tbe 

 limestone was determined by heating a known weight to 300° F. 

 and considering the loss sustained as water. 



1. Upper Silurian. — Wenlock limestone, Dudley ; very fossili- 

 ferous. The most crystalline part, free from fossils, chosen for 

 analysis. Specific gravity 2*70 at 60° F. 



26'08 grs. were employed for analysis, and furnished — in- 

 soluble matter, 1*35 gr. ; alumina, sesquioxide of iron and phos- 

 phoric acid, 0'72; phosphate of magnesia from phosphoric acid 

 determination, 0*195; ditto from magnesia determination, 0*73; 

 sulphate of lime, 31*95. 



The analysis will therefore stand as follows : — 



Carbonate of lime 9009 



Carbonate of magnesia .... 1*26 



Alumina and sesquioxide of iron. 2"30 



Phosphoric acid 0'46 



Insoluble 5'13 



99-24 

 Water, organic matter, and loss . '76 



100-00 



The insoluble matter appeared to be nothing more than Wen- 

 lock shale entangled in the limestone. 



As this limestone is very largely employed in Staffordshire in 

 the blast-furnaces for smelting iron, the amount of phosphoric 

 acid here present is most important in a metallurgical point of 

 view, and of course highly injurious to the quality of the iron 

 produced. 



2. Lower Silurian. — Bala limestone*, YspuUy Evan, North 

 Wales. 



The specimen analysed did not contain any fossils, and was 

 extremely impure ; it could hardly be termed a true limestone, 

 being rather a shale interlaminated with irregular depositions of 

 calcareous matter, crystalline in texture. On dissolving in acids, 

 the insoluble residue was argillaceous, as might be expected. 



50-18 grs. gave 26-23 insoluble, and 0-37 organic matter ; 

 2-43 sesquioxide of iron and alumina with phosphoric acid; 

 0-12 phosphate of magnesia from phosphoric acid determination, 

 and 1-34 from the magnesia present; and the mean of two de- 

 terminations gave 19-84 carbonate of lime. 48-31 grs., heated 

 to 300° F., lost 0-26 estimated as water. 



The analysis when tabulated stands as follows ; — 



* I have here to thank Mr. Salter and Jlr. Bristow of the Ordnabce Geo- 

 logical Sur\eyj for their kindness in furnishing me with a number of spe- 

 cimens of limestone from various locaUties for the purpose of analysis. 



