BOOK VIII.

275

to the ore which has been roasted, while it is still hot, in order to makeit softer and more easily broken ; for after fire has dried up the moisturein the ore, it breaks up more easily while it is still hot, of which fact burntlimestone affords the best example.

By digging out the earth they make the areas much larger, and square ;walls should be built along the sides and back to hold the heat of thefire more effectively, and the front should be left open. In these compart-ments tin ore is roasted in the following manner. First of all wood abouttwelve feet long should be laid in the area in four layers, alternately straightand transverse. Then the larger pieces of ore should be laid upon them, andon these again the smaller ones, which should also be placed around the sides ;the fine sand of the same ore should also be spread over the pile and poundedwith shovels, to prevent the pile from falling before it has been roasted ; thewood should then be fired.

A —Lighted pyre. B —Pyre which is being constructed. C —Ore. D —Wood.

E —Pile of the same wood.

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Lead ore, if roasting is necessary, should be piled in an area just like thelast, but sloping, and the wood should be placed over it. A tree trunk shouldbe laid right across the front of the ore to prevent it from falling out. Theore, being roasted in this way, becomes partly melted and resembles slag.