Improved Kilns for burning Lime. 
135 
necessitates the construction of two draught-holes, one at each 
end of the ellipse, which are not always easy to arrange when 
the kiln is built in the side of a hill. The same object may be 
obtained by constructing the upper part of the internal walls per- 
pendicular, as above mentioned, and slightly diminishing the 
inclination of the cone just above the fire-bars. 
Fig. 1— Section of Common Perpetual Fig. 3— Section of Common 
Kiln, icith SJiaft of inverted trim- Perpetual Kiln with inner 
cated cone. croion. 
The advantages of the common perpetual kiln may be stated 
to be : — 
1st. The simplicity and economy of its construction. 
2nd. The small amount of skilled labour required in managing 
it, as, after the proportion of fuel to material has been once 
ascertained, the subsequent working is merely a matter of rule. 
3rd. The saving of fuel, by the kiln being kept constantly hot j 
4th. The man who attends to the kiln is only required to 
spend a portion of his time there, and can in the interim attend 
to other business. 
The disadvantages are : — 
1. The difficulty of calcining the lime sufficiently without a 
great additional expenditure of fuel. 
2nd. The impossibility of using wood fuel for the purpose. 
3rd. From the nature and. construction of the kiln, it is only 
applicable when a large quantity of lime is constantly required. 
