90 ACCOUNT OF A MINERAL PROM ORKNEY. 



3. The quantity of strontia in the mineral could be ascer- 

 tained by weighing the nitrate ; but there appears to me less 

 certainty in weighing crystals which contain water, and which 

 are very soluble, than in reducing the earthy or other base 

 to the state of an insoluble compound, that may be moderate- 

 ly heated without loss of weight, and the constituents of which 

 are well known. Sulphuric acid was therefore added, in ex- 

 cess, to precipitate all the strontia, and the liquid being eva- 

 porated to dryness in the capsule in which the precipitation 

 was effected, and heated in a platina crucible to expel excess 

 of acid, and water, afforded 84.6 grains of sulphate of strontia, 

 which, by Dr Wollaston's excellent scale, is equivalent to 68.6 

 grains of Carbonate of Strontites. 



4. The alkoholic solution (£. 2.) was evaporated, and afford- 

 ed a tenacious paste, which, when dissolved in water, precipi- 

 tated by carbonate of soda, washed and dried, weighed 2.6 

 grains ; this, then, gives us the quantity of the Carbonate of 

 Lime which enters into the composition of the mineral. 



When we compare these results, with the quantity of car- 

 bonic acid in the mineral, we find an agreement as exact as 

 the nature of such researches will permit : for 



68.(5 carbonate of strontites contains 19-60 carbonic acid ; 



2.6 carbonate of lime contains - 3.14 carbonic acid 



20.74 

 or the difference amounts only to 0.26 per cent. 



F. 



The examination of the insoluble residue was attempted, "by 

 boiling it with carbonate of potassa, in a silver vessel ; but as 

 only a portion was thus decomposed at each boiling, I thought 

 it best to attempt it in the dry way. 



Having 



