922.] 



The Need for Lime : How to Meet It. 



860 



THE NEED FOR LIME AND HOW TO 

 MEET IT.— II. 



B. H. Bedell. 



In an article on this subject in the June issue of this Journal, 

 the writer showed in what way the urgent need for more agri- 

 cultural lime could be met by farmers who were so situated that 

 they could utilise a portable limestone grinding plant. It is 

 now proposed to describe, in the briefest outline, the principal 

 features of larger and permanent limestone-grinding plants, 

 and give some particulars of lime kiln construction, and the 

 process of lime burning. 



Permanent Agricultural Limestone Plants. — In cases in 

 which the probable local demand for ground limestone warrants 

 the installation of a fixed plant to be owned by a farmers' 

 co-operative association, or by a company making a business 

 of grinding limestone, it will always be necessary, except when 

 chalk is being dealt with, to elaborate the plant more than was 

 considered expedient in the case of the portable types described 

 in the previous article, and to produce a more finely-ground 

 product. To this end the stone must be broken dow^n to about 

 1-inch cube before it is passed into the mill for fine grinding. 



The lay-out of the plant will therefore be somewhat as 

 follows : — 



(a) Receiving hopper and chute into which quarry skips tip the rough 



stone, dehvering into — 

 (5) Jaw hreaker, reducing stone to 2i-in. cube. 



(c) Elevator, raising broken stone to — 



(d) Small breakei-, or rolls discharging directly into feed hopper of — 



(e) Fine-grinding mill from v/hich the stone dust is raised by an elevator 



into storage bins from which it can b ^ loaded directly into wagons 

 or bagged through properly constructed sacking mouths. 



In the case of small plants, a second jaw breaker or rolls 

 can frequently be omitted by setting the first breaker to pro- 

 duce material fine enough to feed directly into the fine-grinding 

 mill. 



With regard to {h) and (d) little need be said, since these are 

 quite standard pieces of plant with which every quarry manager 

 is familiar. The fine grinding, how^ever, presents many 

 problems, the answers to which are only now being worked 

 out. There are, broadly speaking, three types of mill which 

 in modern practice are considered in connection with this work. 



First, there is the High-Speed Mill in which the stone is ground 

 between steel surfaces somewhat after the principle of a pestle 



