270 ANNUAL REPORT 
are often provided with water-cooling arrangement, which enables the 
machine to handle the clinker or material coming from the dryer. The 
machine, as far as known to the writer, has been very successful. 
Ball-Mili.—This mill, in its simplest conception, consists of a 
cylinder revolving around a horizontal axis with die plates around 
Fiq. 41. Ball mill, cross-section. 
the circumference. ‘The grinding is done by steel balls. The die ring 
is composed of perforated chilled iron plates arranged so that each 
laps the next (figure 41). In this manner steps are formed which 
give the balls a drop from one to the other, and at the same time the 
oversize material returned from the screens is admitted into the crush- 
ing space at these points. Outside of the die plates coarse screens 
