86 ACCOUNT OF A MINERAL FROM ORKNEY. 



c. A solid fragment of Carrara marble was attacked and dis- 

 solved by a portion of the same acid, without the addition of 

 water. 



Hence we may consider carbonate of strontia intermediate, 

 in its habitudes with this acid, between carbonate of barytes 

 and carbonate of lime ; and these peculiarities afford an easy 

 method of distinguishing these three native carbonates from 

 each other. 



From the preceding experiments we may conclude, that 

 the portion of the mineral from Orkney, which is soluble in 

 muriatic acid, consists of carbonate of strontia, a little carbo- 

 nate of lime, and a minute trace of iron. 



C. 



The undissolved residue of the former experiments had a 

 yellowish- white colour, and was totally insoluble in water. 

 The calcination of a portion of the mineral had shewn that 

 sulphur entered into its composition, as sulphuretted hydrogen 

 was given out on the addition of water. The probable origin 

 of this had been the decomposition of a sulphate. No trace of 

 a sulphate had appeared in the acid solutions, and therefore 

 we may conclude that the sulphate exists in the insoluble re- 

 sidue. 



1. A portion of this residue was boiled with a concentrated 

 solution of carbonate of potassa in a silver vessel. It was then 

 washed to free it from alkali ; and on finding that it had be- 

 come partly soluble in muriatic acid with effervescence, the 

 process was several times repeated, and thus the greatest part 

 of the residue was rendered soluble in muriatic acid. What 

 remained in the last process, was soluble in boiling sulphuric 

 acid, from which it separated on cooling in acicular crystals. 



2. The 



