357 
Tin * 
smelting of tin ores a less intense heat must be given, than 
is sufficient for the scorification of earthy matters, lest the 
tin be oxyded. Tin ores previously bruised, may be 
cleansed by washing, for which operation their great 
weight and hardness render them well adapted. If they 
be intermixed with very hard stones, or ferruginous ores, 
a slight roasting will render these impure matters more 
friable, and, consequently, fitter to be separated from the 
tin ores. Sometimes these operations, the roasting, con- 
tusion, and lotion ; must be repeated. By roasting, the 
ferruginous particles are so far revived, that they may be 
separated by magnets. 
The ore, thus cleansed from adhering heterogeneous 
matters, is to be roasted in an oven, or reverberatory fur- 
nace, with a fire rather intense than long continued, dur- 
ing which it must be frequently stirred to prevent its fu- 
sion. By this operation the arsenic is expelled, and in 
some works is collected in chambers built purposely a- 
bove the oxyding furnace. 
Lastly, the ore cleansed and washed is to be fused, and 
reduced to a metallic state. In this fusion, attention must 
be given to the following particulars : 
1. No more heat is to be applied than is sufficient for 
the reduction of the ore, because this metal is fusible with 
very little heat, and is very easily oxydable. 
2. To prevent this oxydation of the reduced metal, a 
larger quantity of charcoal is used in this than in the other 
fusion. 
3. The scoria must be frequently removed, lest some 
of the tin should be involved in it ; and the melted ore 
must be covered with charcoal powder, to prevent the ox- 
ydation of its surface. 
4. No flu x or other substance, excepting the scoria of 
former smeltings which contains some tin, are to be add- 
ed, to facilitate the fusion. 
