HORIZONTAL ROTARY RETORT.

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with coal-boxes, (the coal should be spread inthe boxes, in layers two or three inches in depth,)it is obvious that of all the twelve boxes, four onlycan be situated directly over the fire-place, whilethe remaining- eight are placed right and left to-wards the door of the retort. The coal in theformer boxes receives the full effect of the heat,(see the plan of the fire flues of the retort, fig. 1,plate VI.,) while the remaining eight boxes to whichthe fire does not extend, are less heated. The coalin the four boxes which are in the hottest part ofthe retort becomes rapidly decomposed, whilst thecoal in all the other boxes is gradually heated,and consequently deprived only of moisture, pre-vious to being subjected to the greatest heat. Thebox which is situated under the condensing pipeH, plate II., near the entry door, receives thecondensed tar which trickles down the pipe H.

Now let us suppose that the coal in the fourboxes over the fire place is fully decomposed, whichwill be the case if 321 pounds of coal are in eachbox, in two hours, the workman then turns theshaft E, fig. 1, plate II., one-third part of the cir-