XIV.—WNotes on the occurrence of Cobalt in connection with the Tin 
Ores of Cornwall.—By RICHARD PEARCE, F.G.8., Member of 
the Institution. 
Read at the Spring Meeting, May 23, 1871. 
OME time ago I had occasion to examine a sample of dressed 
Tin Ore, (Black Tin), from Dolcoath Mine, and was rather 
surprised to find that it contained a very appreciable quantity of 
Cobalt. No correct determination of the quantity was made at 
the time, but from the reactions, I should judge that it could not 
have been much less than 0°5 per cent. 
Cobalt ores have been frequently met with from time to time 
at Dolcoath, but under special conditions, associated with native 
arsenic, bismuth, &c. in isolated patches, and I was quite unpre- 
pared to find it so intimately mixed up with the Tin Ore in that 
mine. 
I have reason to believe, that Dolcoath Tin Ore does not form 
an exceptional case, and that if a careful examination of the ores 
be made from the neighbouring mines, Cobalt will be found inti- 
mately associated with the Tin. 
The Cobalt occurs in combination with arsenic, and in all pro- 
bability enters into the composition of the Mispickel, or Arsenical 
Pyrites, which is always found with the Tin of that district. 
In the calcination of the ore, which forms an intermediate 
process in the dressing of Tin Ores, the Arsenide of Cobalt is 
oxidised and converted into an Arseniate, and this is so intimately 
blended with the tin, that the subsequent process of washing fails 
to extract it wholly. I have no doubt of its presence in the 
dressed tin in an oxidised form, as it can be extracted readily by 
treating the ore with dilute sulphuric acid, which fails to dissolve 
-unoxidised Arsenical Cobalt compounds. 
