ACCOUKT OF A MINERAL FKOM ORKNEY. 83 



Chemical Characters. 



It is insoluble, or nearly so, in water. 



It effervesces briskly with acids, and is partly dissolved. 



It is infusible before the common blowpipe, and resists the 

 ordinary temperature of a smith's forge, when subjected to it 

 in a crucible ; but loses in weight, becomes white, and more 

 hard than before. This process rendered it partly soluble in 

 water, to which it imparted an acrid taste, alkaline qualities, 

 and the odour of sulphuretted hydrogen. 



A fragment of the mineral, thrown into strong sulphuric 

 acid, effervesced, and formed a white powder of little solubi- 

 lity. 



With concentrated nitric and muriatic acids there was, at 

 first, a brisk effervescence, which soon ceased ; but was repeat- 

 edly renewed, on successive additions of small quantities of 

 water. In both cases a portion was dissolved ; the solution 

 was transparent and colourless, and crystallizable on evapora- 

 tion. 



On adding prussiate of potassa and iron to the muriatic 

 solution, no change was at first perceptible ; but after some 

 time, a faint bluish tinge might be distinguished. By digest- 

 ing muriatic acid on the insoluble residue, a deep blue colour 

 was obtained on the addition of the same re-agent. 



Chemical Examination of the Mineral. 



The preliminary experiments by which its chemical charac- 

 ters were ascertained, shewed that it was resolvable by the ac- 

 tion of muriatic acid into gaseous, liquid, and solid substances, 

 each of which became the subject of investigation. 



l2 a. 



