168 Mr Johnston on the Vanadiate of Lead, fyc. 



masses, in which the crystalline forms are more or less distinct 

 and which appear to be only a developement of the minute 

 mamillae. Isolated and perfect crystals are rare. 



Heated to redness in a platinum crucible it decrepitates and 

 assumes an orange red colour, changing when it cools to a 

 beautiful pale yellow. Before the blow-pipe in a pair of forceps 

 it fuses, and on cooling retains its yellow colour. If kept some 

 time in fusion, however* it is changed into a steel grey porous 

 mass, which upon charcoal gives immediately globules of lead. 

 Alone on charcoal it fuses readily, exhales the odour of arsenic, 

 gives globules of lead, and leaves after heating in the inner 

 flame a steel grey very fusible slag, which exhibits the reactions 

 of chromium. The fusibility is characteristic of Vanadium. 



The sulphuric and muriatic acids decompose the mineral, 

 giving green solutions of the oxide, and forming sulphate or 

 chloride of lead. With nitric acid it forms a beautiful yellow 

 solution. When the latter acid acts upon it, the oxide of lead 

 is first dissolved, leaving the fragments covered with a beauti- 

 ful red coating of the Vanadic acid, which separates occasion- 

 ally in the form of scales, and is afterwards taken into solution- 



II. — The second form of this mineral can hardly be dis- 

 tinguished in external characters from earthy porous peroxide 

 of manganese. It occurs amorphous and in small rounded 

 forms, often powdering the calamine with a thin black coating, 

 and at times scattered about in the cavities. It is steel grey, and 

 porous, as if it had been subjected to heat. Before the blow- 

 pipe it exhibits the same phenomena as the former variety. 



This mineral has hitherto been found only in one mine at 

 Wanlockhead, and only in one spot about six fathoms in length, 

 where the vein had been subjected to a violent disruption. The 

 mine has been unwrought for the last five or six years, and 

 the only specimens to be met with are among the rubbish of 

 the old workings. A supply of these specimens may be ob- 

 tained from Mr Rose, mineral-dealer, South Bridge- 



I have not yet been able to satisfy myself as to the precise 

 composition of these minerals. I hoped to have given a correct 

 analysis in the present, but want of time obliges me to defer it 

 to a future number. 



FoKTOBELLO, 10<7i JllllG 1831. 



