Improved Kilns for hiirning Lime. 
137 
the arch. The l)earing-bars should be of cast iron, 3 inch, square, 
and 1 foot 6 inch, apart from centre to centre. The fire-bars should 
be 3 feet long, 2i x 1 }, and J inch apart. There should b(! a cast- 
iron door filtetl into a wrought-iron frame 3 inch, wide, to close the 
mouth of the fire-holes. The arch over the fire-holes should be \) 
inch, thick, with holes left at the top and sides at intervals of 14 
inch., 3 inch, wide, 4^ inch, long on the inside of the arch, spread- 
ing as they approach the floor of the kiln. Other courses of open 
work are built on the top of these holes, so as to convert the floor of 
the kiln into a chequer of holes with 4^-inch work between them. 
The kiln is filled by packing lumps of chalk or limestone 
over the floor, taking care to leave as wide spaces as possible 
over the holes, so that the fire may draw well through the mass. 
These courses should be about 6 inches thick at the bottom, 
<liminishing to 4 inches after five or six courses have been laid ; 
when the kiln is about two-tliirds full, the remainder of the charge 
may be tipped in from the top, and spread over the surface. 
A kiln of this size requires about thirty-six hours to get to 
the full heat, 12 or 14 hours full heat, and 3G hours to cool 
■down before the lime can be drawn. 
It is better to cover over the top of the kiln with two courses 
of burned bricks, leaving sufficient draught-holes for the heat to 
escape ; but with every precaution it is scarcely possible to burn 
the uppermost 12 inches of the charge to the^ proper pitch, and 
it is usually burnt over again in the next kiln. 
Kg. 5. — Section of Circular Intermittent Kiln with central furnace. 
