in Cornwall and Devonshire. 421 
value by assaying a sample, carefully taken from the whole quan- 
tity. 
The furnaces for smelting mine tin are all of the common re- 
verberating kind, and are of sufficient size to hold twelve to six- 
teen hundred weight of ore. 
The charge is prepared by mixing it with a proportion of stone 
coal, or Welch culm, to which is added a moderate quantity of 
slaked lime; these are turned over together and moistened with 
water, which prevents the too rapid action of the heated furnace, 
and which would otherwise volatilize some of the metal before 
fusion commenced. 
The heat employed is a very strong one, and such as to bring 
the whole into perfect fusion; it is continued seven or eight 
hours, when the charge is ready to draw. For this purpose, the 
furnace is furnished with a tap-hole leading from the lowest part 
ot the bottom, which, during the process, is stopped with clay 
or mortar, and under which is placed an iron kettle to receive 
the metal. The furnace has also a door at the end opposite the 
fire-place, through which the slag or scoria may be raked out 
from the surface, while the tin is flowing out, by unstopping the 
tap-hole. 
They are thus divided, and the tin is laded into moulds, so as 
to form plates of a moderate size, and put by for a further re- 
fining. The slag, which rapidly hardens into a mass, is re- 
moved to a dressing-floor, where, being broken up and stamped, 
it is washed, and a quantity of tin taken from it, which is called 
Prillion, and which is afterwards smelted again. 
No operation in smelting is more easy than that practised for 
tin ores, nor is there any one in which the reasons for the mode 
of treatment are so obvious. There are but two things to accom- 
plish in this first process ; to obtain perfect fusion of the earths 
so as to suffer the metal to separate easily from them, and to 
decompose the oxide of which the ore uniformly consists, 
The addition of lime contributes to effect the former, and that 
of carbonaceous matter or coal completes the reduction of the 
ore. ‘The separation of the metal from the earths then takes 
place in the usual way during fusion, by the difference in their 
specific gravities, the one precipitating to the bottom of the 
furnace, from whence it is drawn off by the tap-hole, and the 
other, floating on the surface, is removed in the manner I have 
described. 
The plates of tin, which are the produce of this smelting, are 
‘somewhat impure, and are more or less so according to the qua- 
lity of the ore which has been used; they are reserved until a 
sufficient quantity of them is obtained to proceed with the re- 
fining, which is performed either in the same furnace, after ore- 
' smelting 
