BOOK VIII.

348

they throw it into a copper sieve, and separate the very small pieces whichpass through the sieve from the larger ones ; of these the former are smeltedin a faggot pile and the latter in the furnace. Of such a number then arethe methods of washing.

A— Trough. B— Launder. C—Hoe. D— Sieve.

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One method of burning is principally employed, and two of roasting.The black tin is burned by a hot fire in a furnace similar to an oven 21 ; itis burned if it is a dark-blue colour, or if pyrites and the stone from whichiron is made are mixed with it, for the dark blue colour if not burnt, consumesthe tin. If pyrites and the other stone are not volatilised into fumes in afurnace of this kind, the tin which is made from the tin-stone is impure.The tin-stone is thrown either into the back part of the furnace, or into oneside of it; but in the former case the wood is placed in front, in the lattercase alongside, in such a manner, however, that neither firebrands norcoals may fall upon the tin-stone itself or touch it. The fuel is manipulatedby a poker made of wood. The tin-stone is now stirred with a rake with two

al From a metallurgical point of view all of these operations are roasting. Evento-day, however, the expression “ burning ” tin is in use in some parts of Cornwall, and informer times it was general.