. -CtEARING OUT THE ARSENIC SOOT. from buff to black, according to the material burnt and type of furnace used. Arsenic soot is also obtained from other industries in the neighbouring districts, coming, for instance, from the roasting of tin ores before the latter can be smelted. The larger smelters recover this by-product in large flues designed for this purpose. Arsenic soot varies greatly in the amount of white arsenic (xlsjOg) it contains, but in any case it is subjected to the refining process before it is placed on the market. The soot is removed from the chambers and returned to a simil
. -CtEARING OUT THE ARSENIC SOOT. from buff to black, according to the material burnt and type of furnace used. Arsenic soot is also obtained from other industries in the neighbouring districts, coming, for instance, from the roasting of tin ores before the latter can be smelted. The larger smelters recover this by-product in large flues designed for this purpose. Arsenic soot varies greatly in the amount of white arsenic (xlsjOg) it contains, but in any case it is subjected to the refining process before it is placed on the market. The soot is removed from the chambers and returned to a similar furnace called a " refiner," where it is again heated and volatilised. Here, however, smoke- less coal is used so that the arsenic may not be con- taminated with particles of carbon from the smoke, and in the case where a round furnace is used it is not'rotated and there is no raking apparatus. The vegetation near the works. The flues are cleaned out about once a year and the arsenic profitably recovered. The chambers where the soot or white arsenic is collected are small vaulted brick rooms connected one with another by an arched opening so placed that the gases, in their passage from one chamber to the next, strike a relatively cool wall before finding their way to the exit placed in the corner diagonally opposed. As the white arsenic vapburs zigzag through these chambers, they condense and deposit in the form of fine white crystals. Along one side of a " set " lies a series of doors, which are closed with clay while the process is proceeding, and are afterwards opened in order to extract the arsenic. This, looking like so much snow, is simply shovelled out into trollies and taken off to the mill.
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