142 
Improved Kilns for burning Lime. 
"fire-bars pass, and are guided in withdrawing them and driving 
tlicm back. In front of the outer bar is also a cast-iron plate, sup- 
ported on brackets, on wliicli the fire-bars rest when drawn forward. 
The openings to the fire-holes and the withdrawing holes are 
closed by double cast-iron doors, hung in wrought-iron frames. 
Fig. 8. — Ground-plan of Improved Perpetual Kiln. 
Cast-iron skewback plates are laid upon the walls separating 
the fire-holes and withdrawing holes, to prevent the spreading 
of the fire-lumps which cover the fire-holes. These lumps are 
formed in one piece, 30 x 18 X 4 inches, with half-circular 
holes 2 inches diameter on their edges, so as to form draught- 
holes 2 inches diameter when jointed together. Each lump is 
either formed with a tenon or a mortice at the end, so that they 
may joint securely together when fixed in place. 
The centre flue is covered with fire-lumps in a similar 
