collier.] REDUCTION OF TIN ORES. 53 
la} T ers and burned; the tin was thus reduced, dropping or flowing to 
the bottom of the hole. Remains of many such rude furnaces have 
been found in Cornwall. Afterwards, bellows were introduced to 
force the fire, and still later charcoal was added. In some parts of 
the Malay Peninsula small amounts of tin are produced by reducing 
in this manner, charcoal being used without artificial draft. 
For a long while the shaft furnace was used, but it is now almost 
entirely superseded by the reverberatory furnace. An average fur- 
nace of this kind has about the following dimensions: Bed, 10 by 17 
feet; fire bridge, 2 by 6 feet; space below fire arch, 3 feet, and below 
fire bridge, 15 inches. The bed of the furnace is built over a hollow 
vault and witli the hollow fire bridge is cooled by allowing the air to 
circulate freely beneath it. 
In Singapore water has been used below the bed to catch the tin 
that leaks through, since the metal is very fluid at the high tempera- 
ture of the smelter. 
The bed has a depth of about 6 inches and slopes from ail three sides 
to the tap hole at one end. Opposite the tap hole is a charging 
door, and there are openings for working the charge at both ends of 
the furnace. The average charge is about 2 tons of concentrated ore, 
mixed with from 15 per cent to 20 per cent of powdered anthracite, a 
small amount of slaked lime, according to the quality of the ore, and 
sometimes a little fluorspar. 
A good heat is raised and the charge kept in a reducing atmosphere 
at about the temperature of melting cast iron, and after several rab- 
blings is drawn off at the end of from five to seven hours. At Pen- 
zance, Cornwall, 16 men working twelve-hour shifts run four such 
furnaces. 
The tin from the reverberatory furnace must be refined, and after it 
is run into molds it is placed in a liquating furnace, an inclined table 
under which a fire is built, which raises the temperature just above 
the melting point of tin. The tin trickles slowly through the tap hole 
into the "float" or tank for the molten metal, leaving unmelted the 
more infusible substance in the form of "hardheads," which are alloys 
of tin with baser metals, such as copper and iron, and these are refined 
by other methods. The molten tin in the float is allowed to settle a 
few hours, after which wood is forced down beneath the molten mass, 
and the steam and gases formed create a strong ebullition. Bismuth, 
lead, arsenic, and other impurities, and some tin are oxidized and float 
as a scum on top and are skimmed off to be smelted again with the 
slags. The same result is accomplished by dipping up the tin in ladles 
and pouring it back from a height of 2 or 3 feet, but this involves 
more labor and seems to possess no advantage over boiling. 
After boiling, the tin is allowed to settle for two or three hours, and 
then the uppermost part is ladled into molds and sold as refined tin, 
