88 ACCOUNT OF A MINERAL FROM ORKNEY. 



lution took place ; the liquor was poured into a glass capsule, 

 and put aside in a cool place ; no crystals appeared in 12 

 hours ; but after several hours a thin ring of amorphous sul- 

 phate was deposited around the margin of the liquid, probably 

 owing to the absorption of water from the air. The insoluble 

 neutral sulphate was however immediately precipitated from 

 the solution by the addition of water. 



b. Artificial sulphate of barytes was treated in the same 

 manner ; a perfect solution was obtained ; and the liquid soon 

 began to form crystals around the edge of the capsule. When 

 the air of the room is dry, the crystals though small are pretty 

 distinct prisms, promiscuously aggregated. They are super- 

 sulphates, agreeing in their properties with what is stated a- 

 bove [a). 



c. Fragments of a transparent crystal of sulphate of strontia 

 from Bristol, reduced to powder, presented exactly similar re- 

 sults with the artificial sulphate {a) ; and a portion of a co- 

 lourless crystal of sulphate of barytes from Dufton near Ap- 

 pleby, was acted on precisely as the artificial sulphate (b). 



In the mineral from Orkney, the whole of the residue in- 

 soluble in nitric and muriatic acids, was dissolved by boiling 

 sulphuric acid ; which shews that there is no silica present. 



The blue precipitate, by prussian alkali, from the muriatic 

 acid digested on the residue, shews that oxyde of iron is uni- 

 ted to the sulphate. 



The mineral, then, consists of carbonate of strontia, carbonate 

 of lime, sulphate of barytes, and a little oxyde of iron. We have 

 yet to ascertain the proportions in which these ingredients 

 enter into its composition. 



D. 



To ascertain the quantity of carbonic acid is important, as it 

 will enable us to verify the other results. 



100 



