1922.] The Need for Lime : How to Meet It. 873 



Lastly, there are the heat losses due to convection and to 

 radiation from the outside surface of the kiln, which can be 

 minimised by thick walls containing non-conducting layers, 

 but must always represent a very material fraction of the fuel 

 bill. 



When all these things are taken into account it is found that, 

 in a well-designed kiln, it is not possible to produce a ton of 

 lime with less than about 3 J cwt. of coal, and it would be safe 

 to say that the majority of kilns in England are using nearly 

 double this amount. 



When making lime from chalk, the amount of moisture 

 commonly present in the chalk is so great that the necessity 

 for its evaporation has an appreciable effect upon the amount 

 of coal burned. An additional f cw^t. of coal per ton of lime 

 produced is the calculated amount required for this purpose in 

 the case of a normally damp chalk. 



Types of Kilns. — There are innumerable designs of kilns, 

 which have been more or less successfully used since the earliest 

 system of burning lime in open clamps fnot yet quite 

 abandoned in this country) gave place to more economical 

 methods. They range from tiny pot kilns, containing only two 

 ^r three tons of lime, to enormous shaft kilns with a daily 

 output of a hundred tons. 



Pot Kilns. — In the small pot kilns, which have a more or 

 less egg-shaped interior, the limestone and the fuel are put in 

 in alternate layers. The first layer of limestone is laid (domed 

 if there are no iron bars supporting the charge) on top of a thick 

 layer of fuel supported on the kindling. When the kiln is full 

 the fire is started and allowed to burn itself out. This method 

 is very wasteful of fuel, but where only a small quantity of lime 

 is needed, it is often the cheapest way of producing it at the 

 spot where it is required. The chief difficulty that will be 

 encountered in attempting to revive this simple practice is in 

 -obtaining the services of a lime burner who has enough 

 experience to be able to superintend the process. Little kilns 

 'of this type are usually built of limestone or some other local 

 stone and are not lined with fire-brick. The surface of the 

 stone usually spalls off, particularly at first, but a more or less 

 refractory slag then forms and seems to act as a preservative 

 for the deeper layers of the stone. The somewhat ruinous 

 remains of kilns of this type can be seen in almost all parts 

 •of our countryside. 



One source of loss in these kilns is the fact that the kiln, as 



