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BOOK IX.

by agitation ; when taken out they are broken up with a square iron mallet,and then they are re-melted with the fine tin-stone next smelted. Thereare some who crush the slags three times under wet stamps and re-melt themthree times ; if a large quantity of this be smelted while still wet, littletin is melted from it, because the slag, soon melted again, flows from thefurnace into the forehearth. Under the wet stamps are also crushed thelute and broken rock with which such furnaces are fined, and also theaccretions, which often contain fine tin-stone, either not melted or half-melted, and also prills of tin. The tin-stone not yet melted runs outthrough the screen into a trough, and is washed in the same way as tin-stone, while the partly melted and the prills of tin are taken from the mortar-box and washed in the sieve on which not very minute particles remain, andthence to the canvas strake. The soot which adheres to that part of thechimney which emits the smoke, also often contains very fine tin-stone whichflies from the furnace with the fumes, and this is washed in the strake whichI have just mentioned, and in other sluices. The prills of tin and the partlymelted tin-stone that are contained in the lute and broken rock with whichthe furnace is fined, and in the remnants of the tin from the forehearth andthe dipping-pot, are smelted together with the tin-stone.

When tin-stone has been smelted for three days and as many nights in afurnace prepared as I have said above, some little particles of the rock fromwhich the furnace is constructed become loosened by the fire and fall down;and then the bellows being taken away, the furnace is broken through at theback, and the accretions are first chipped off with hammers, and afterwardthe whole of the interior of the furnace is re-fitted with the prepared sand-stone, and again evenly fined with lute. The sandstone placed on the bedof the furnace, if it has become faulty, is taken out, and another is laid downin its place ; those rocks which are too large the smelter chips off and fitswith a sharp pick.

Some build two furnaces against the wall just like those I have described,and above them build a vaulted ceiling supported by the wall and by fourpillars. Through holes in the vaulted ceiling the fumes from the furnacesascend into a dust chamber, similar to the one described before, except thatthere is a window on each side and there is no door. The smelters, whenthey have to clear away the flue-dust, mount by the steps at the side of thefurnaces, and climb by ladders into the dust chamber through the aperturesin the vaulted ceilings over the furnaces. They then remove the flue-dustfrom everywhere and collect it in baskets, which are passed from one to theother and emptied. This dust chamber differs from the other described, inthe fact that the chimneys, of which it has two, are not dissimilar to thoseof a house ; they receive the fumes which, being unable to escape through theupper part of the chamber, are turned back and re-ascend and release thetin ; thus the tin set free by the fire and turned to ash, and the little tin-stones which fly up with the fumes, remain in the dust chamber or else adhereto copper plates in the chimney.