STATE GEOLOGIST. 267 
which revolve around a horizontal shaft, this type of machine being 
evolved from the simple chain mills which were used some 20 years ago 
for preparing brick clays in Minnesota and other Western states. The 
chain mills consisted of heavy chains fastened to a revolving shaft which 
Fig. 38. Disintegrator of the hinged-hammer type, as made by Williams. 
whipped the material into small particles. From the standpoint of work 
accomplished these old homemade mills were quite efficient, but the 
construction was imperfect in many cases and gave considerable trouble, 
as was to be expected. The Williams mill, though subject to greater 
wear than the rolls, and also more expensive as to cost of repair, 
is a very efficient machine for limestones which are not too hard and 
dense. When equipped with water-cooled journals, it can work hot 
materials right from the rotary dryer. 
Kent Mill—This mill (see figure 40) consists essentially of a revolv- 
ing ring and three rolls pressing against its inner face. The rolls are 
convex and the ring is concave and tracks on the rolls. Springs support 
the rolls yieldingly and the rolls support the ring so that the four crushing 
parts are free to move. The material falls from the inlets on to the 
inner face of the ring. Centrifugal force holds it there in a layer an 
inch deep. It revolves with the ring and passes under the rolls. The 
latter are pressed by the springs outwardly against the rock on the ring 
with a pressure adjustable to 20,000 pounds, the adjustment being 
accomplished by means of the screws against the springs. As the rolls 
pass over the rock they crush it against the ring, while the crushed rock 
flows off each side of the ring into the casing and falls to the discharge. 
Tt is claimed that 90 per cent. of the rock is abraded on itself in crushing, 
so that the wear on the parts of the machine is quite slight and there is 
