the 6 inch diameter housing resulting in a clearance between the rotor pin tips 23 and the housing of 0 125 inch in an initial trial it was found that not more than about 25 grams o d basis of wood pulp at 45 consistency could be agitated in the apparatus 10 at 1050 r p m pin rotor speed when a larger amount of pulp was placed in the apparatus it would stall the 1 5 h p motor which was employed as the prime mover thereafter the diameter of the pin tips 23 was reduced in two steps as shown in the following table allowing somewhat larger amounts of pulp to be run but in all cases the motor was stalled when the machine was loaded with as much as 100 grams of pulp ______________________________________ motor amps clearance pulp weight 7 1 amp f l result______________________________________0 125 inch gt 25 gm stalled0 188 inch 25 gm 6 7 amp pulp circulating 50 gm 6 7 amp pulp circulating 75 gm 7 6 amp pulp circulating 100 gm 33 0 amp stalled0 312 inch 25 gm 0 9 amp pulp circulating 50 gm stalled0 312 inch amp after removing every other pin in each axial row 30 gm 2 0 amp pulp circulating 71 gm 2 2 amp pulp circulating 100 gm stalled______________________________________ in each experiment in which the apparatus stalled after disassembly it was observed that the pin tips 23 were covered with a hard tuft.