THE EXTRACTION OF THE JUICE BY£MILLS 209 



unit of time. Converseh', with an increase in the speed, the fibre passing 

 being constant, the pressure on the trash turner will decrease. If, however, 

 the fibre increases and the speed remains constant, the pressure will increase 

 in accordance with the relation H^-^P = C ; for H, the quantity of fibre 

 passing may be substituted, and, if the quantity of cane is constant, the per- 

 centage of fibre in the cane. For example, if with 12 per cent, fibre a pressure 

 on the trash plate of 15 lbs. per sq. in. is computed, with 15 per cent, fibre 



the pressure will be 



Cf 



X 15 = 26-2 lbs. per sq. in. 



The power absorbed b}^- the passage of the bagasse over the trash plate 

 may also be computed. Let the pressure of the bagasse on the trash plate 

 be 28-6 lbs. per sq. in., and let the area of the plate be 1,200 sq. ins. 

 The total pressure on the plate is then 35,500 lbs. The coefficient of 

 friction of bagasse on iron is about o • 4 ; then, if the speed of the bagasse 



Fig. Ill 



be 25 ft. per min., the foot-pounds necessary to draw the bagasse over the 

 plate are 35,500 x 0-4 X 25 = 355,000, and the horse-power necessary is 

 10-7. 



These results obtained by the writer are open to criticism, and have been 

 criticised by Bolk,^ not unjustl}', and it may be remarked : — 



1. The numerical values obtained in the calculation wiU vary with every 

 mill, and especially are controlled by the value taken for the vertical angle 

 of the mill. 



2. The use of one constant for the bagasse in all the mills after a varying 

 number of pressings is too broad. 



3. No account is taken of the slipping action of the top roll when moving 

 over the layer of bagasse. 



4. The occasional fracture of trash turners shows that pressures much 

 greater than those computed do occur. 



5. Any choking of the bagasse on the plate entirely invalidates any 

 conclusions that can be drawn. 



Q 



