TILE ROYAL ARTILLERY INSTITUTION. 
91 
Fig-. 3. Scale iV. 
He found, however, that the strips would not drop horizontally on to the 
second pair of rollers, but that they dropped as often endways as sideways, 
and generally that they fell in all directions, owing to the unevenness of the 
press-cake from which they were cut. 
Mr. Pigou, of Pigou and Wilks', designed a very ingenious pair of rollers 
which performed the work of cutting up the cake into pebbles in one opera¬ 
tion. Both rollers were identical, and had the knives arranged neither 
longitudinally nor circumferentially, but spirally, at an angle of 45° round 
the surface. The knives thus crossed each other perpendicularly at the cutting 
points, and very tolerable granulation was effected. The pebbles, however, 
were very irregular in shape, and by no means so cubical as those cut up by 
knives. The following woodcut of Mr. Pigou's roller is given to show the 
nature of the arrangement:—• 
Fig. 4. Scale i\. 
It had hitherto been supposed that the more uniform the size and shape 
of the grain, the better would be the results at proof; but while Waltham 
Abbey pebble seemed to be failing at proof, Mr. Pigou's pebble gave very 
good results, as shown by the following experiment:— 
Powder. 
Density. 
Experiment. 
M. Y. 
Pressures. 
Date. 
No. 
A. 
B. 
C. 
Lot 826... 
1-765 
28. 3. 71 
to 
00 
1460 
16-5 
16-4 
15-8 
