The Trials of Grist Mills and Disintegrators at Plymouth. 611 
furnished with two pairs of grinding discs, set one above the 
other, so that the grist from the upper falls into the lower mill 
and is there re-ground, necessarily producing a very fine 
sample. This machine received f cwt. of maize only, and made 
excellent work, but the whole arrangement was so obviously 
designed to " butter bacon," and as obviously involved the 
purchase by the farmer of two mills instead of one, that the 
Judges thought it needless to do more than ascertain how finely 
this mill could grind. All Bamfords' mills were well designed 
and well made, but they lost points, in comparison with the 
prize machines, both in time and power. 
Type IV. Roller and breast-grinding. — Messrs. Woodroffe's 
mill (No. 2543) consists of a grooved roller 12 inches in 
diameter and 16 inches long, 
of chilled cast-iron, trued up Woodroffe's Second Prize Grist Mill. 
by grinding in contact with 
an emery wheel. The roller 
turns, at the rate of 300 re- 
volutions per minute, against 
a concave, also of chilled 
iron, which encircles about 
one-third the circumference 
of the grinding roller. The 
flutes of the latter are parallel 
with its axis and |-inch pitch, 
while the concave is fluted 
en zigzag. The concave is 
strongly and truly hinged to 
the mill-frame, and is kept 
up to its work by a pair of 
weighted levers, which give 
way to allow of the passage 
of hard foreign bodies through the mill. Adjustments for 
coarse or fine grinding are made by set screws, which control 
the movement of the concave around its hinges, while a pro- 
vision is made for instantaneously detaching the concave itself 
from the adjusting gear, so that the mill can be " opened " in a 
moment if needful. 
A good deal of interest attaches to mills of this type. As 
already indicated, the principle of breast-grinding was intro- 
duced by Williams in the early part of this century, while later, 
or in 1857, John Hardley, of Shide, Isle of Wight, patented 
a mill consisting essentially of " a drum or cylinder, having a 
furrowed or indented periphery revolving within a concave, the 
inner surface of which is also furrowed or grooved, the former 
