874 The Need for Lime : How to Meet It. 



well as the stone to be burned, has to be heated afresh for each 

 charge. Despite this defect, there are much larger intermittent 

 kilns of more elaborate design, which are occasionally used for 

 burning special limes, although it is doubtful whether their use 

 can ever be justified for agricultural lime, whatever their merits 

 may be when used for hydraulic. 



Draic Kilns. — The t^^pe of kiln in which the agriculturist is 

 most likely to be interested is the shaft or draw-kiln. Here 

 the process is continuous, not necessarily in the sense that the 

 kiln is worked night and day, but continuous in the sense that 

 the fire is only drawn when repairs are needed. Kilns of this 

 type are frequently more than 50 feet in height, and should 

 never be less than 15 feet, and even at this, the efficiency is not 

 likely to be very high. The kiln is circular in plan and usually 

 slightly bottle-shaped, and considerably smaller at the draw eye 

 at the bottom than it is a little higher up where the greatest 

 heat is developed. It is always lined with 9 in. or more of fire 

 brick. 



The principle upon which these kilns are worked is that, once 

 the kiln is started, alternate layers of limestone and fuel are put 

 in at the top in proportion as cooled burned lime is drawn at 

 intervals from the bottom. As this is done the contents of the 

 kiln slip down and a re-distribution and mixing of stone and fuel 

 takes place. Each successive layer of fuel burns evenly and 

 regularly as the flame and hot combustion gases from the lower 

 layers reach up to it. It will be readily understood that in 

 order to attain the maximum thermal efficiency it is necessary 

 that the bed of burned lime below the reaction zone should be 

 deep enough to enable the air entering the eye of the kiln to 

 take up most of its heat before it is " drawn." In this way 

 the air which reaches the fire is well warmed (on the regenera- 

 tive principle) before it enters the " reaction zone," which is 

 anything from 5 to 15 feet in depth, depending on the size of 

 kiln and rate of working. Above this zone there should be 

 room for a deep bed of mixed fuel and stone, through which the 

 hot gases pass before they leave the kiln. In their passage they 

 impart to it a large proportion of the heat which they carry, 

 with the result that the stone is well heated before the actual 

 burning takes place. 



Coal producing much gas is liable to lose an important part 

 of its calorific value during its passage with the stone through 

 this pre-heating section of the kiln. If this defect be dis- 

 regarded there is probably no type of kiln better calculated to 



