DR T. THOMSON'S Analysis of some Minerals. 453 



So that every integrant particle of the mineral is combined 

 with three atoms of water. 



III. Supersulphuretted Lead. 



The first specimen of this mineral which I had an opportu- 

 nity of seeing, was one said to have been brought from Caith- 

 ness by Sir JOHN SINCLAIR. This was more than twenty years 

 ago. I had no opportunity of analyzing it ; but, when held in 

 the flame of a candle, it burnt with a blue flame, and emitted a 

 strong odour of sulphurous acid. I have been told by the over- 

 seers of the lead mines in the north of England, that this kind 

 of ore is not uncommon in their district ; but I never was so 

 lucky as to get a specimen of it till August 1828, when Captain 

 LEHUNT brought several pieces of it from Ireland, which he got 

 from a mineral-dealer in Dublin ; but unluckily the locality of 

 these pieces is unknown ; though I am in hopes soon of getting 

 some accurate information on the subject. 



The mineral has much the appearance of fine grained galena. 



Colour blue. 



Lustre metallic. 



Texture fine granular ; opaque. 



Scratches common galena ; but, as it is not free from grains 

 of quartz, it may owe its apparent hardness to these grains. 



Sectile. 



Specific gravity 6.713. 



Before the blowpipe, burns with a blue flame, decrepitates, 

 melts, and, on charcoal, is reduced to a button of lead. 



100 grains, when heated, gave out sulphur, and were redu- 

 ced to 98.206 grains. 



20 grains of this mineral, as free from impurities as possible, 

 were digested in nitre-muriatic acid, till every thing soluble was 



3L2 



