TEEATMENT OF THE OOMSTOOK OEES. 



227 



bolting to the bottom of the pan a circular plate that is cast with a rim an 

 inch deep. The upper edge of the rim is grooved out and a round piece of 

 rubber packing laid in the groove, which, fitting closely against the pan-bot- 

 tom makes a steam-tight joint and allows for the unequal expansion and con- 

 traction of the metal. The dies are attached to the pan-bottom by means of 

 a wedged-shaped projection as in the pan just described. The driver is cast 

 in one long piece ; its upper part, which is attached to the driving shaft by 

 means of a key or feather, is cylindrical, and furnished on the inside with a 

 long babbited bearing for the shaft ; its lower part consists of three legs or 

 standards, each of which has a square lug or projection at the bottom, which, 

 fitting into a raised clutch on the muller-plate, carries and gives motion to 

 the latter. The space between the legs or standards being open, affords free 

 passage for the circulation of the pulp about the center. In front of each 

 lug on the standards of the driver is an iron plate with a flaring or irregularly 

 concave surface which, when the driver is in motion, tends to force the pulp 

 to the center; while directly in front of this contrivance, that is, in the direc- 

 tion of revolution, a large piece is cut out of the muller-plate, thereby afford- 

 ing free passage to the pulp downward and between the grinding surfaces of 

 the shoes and dies. Wings and guide-plates are thus dispensed with, though 

 the pan-rim is cast with the ordinary means of attaching such plates if 

 desired. 



As the bottom of the pan is flat, and the muller has the plane-circular 

 form, the wearing effect on the grinding surfaces is much greater near the 

 circumference than near the center, owing to the difference in radial velocity. 

 It frequently results from this that the shoes and dies of ordinary plane- 

 circular grinding surfaces wear down much more rapidly at the circumference, 

 leaving the metal thicker near the center, and so producing an uneven 

 bearing of the muller upon the bottom and, consequently, an irregular 

 movement. 



In the Fountain pan the radial spaces between the shoes and between 

 the dies are made wider, horizontally, near the center than they are near the 

 circumference, so that the area of grinding surface at the circumference may 

 be more largely in excess of that at the center than it would be if those 

 spaces were of uniform width ; thereby obviating, at least in part, the 



