116

DESCRIPTION OF THE

Fig. 12, plate III. exhibits one of the shallowtrays, or coal boxes in perspective.

It will be obvious, that by the motion of theshaft, any number of the trays or coal-boxes canreadily be brought from the coldest, into the hottest,and from the hottest into the coldest part of theretort.

H, tig. 1, plate II., and a, plate III., or H, plateVII., is a perpendicular pipe situated at the margin ofthe retort, close behind the mouth-piece, and conse-quently in the coldest part of the retort. It servesto carry off the distillatory products evolved fromthe coal, and causes part of the vaporous tar, whichbecomes condensed in it, to trickle back againupon the coal in the retort, in order to becomeconverted into gas, when the coal on which it fallsbecomes situated over the fire-place.

This pipe is furnished at its upper extremity witha hydraulic valve, J. fig. 1. plate II. It consistssimply of an inverted cup X, applied over theupper open extremitiy of the perpendicular pipeH, and submersed into a cup formed of a portionof larger pipe, surrounding the pipe II, con-taining tar. The smaller, or inner cup X, is repre-