THE EXTRACTION OF JUICE BY MILLS. 



speed for mill rollers. The more recent tendency is to design the gearing so 

 that the mills run at a speed up to 25 feet per minute. It has also been the 

 custom to so arrange the gearing that there is an increase in the surface speed 

 from mill to mill ; a thinner blanket of megass is thus obtained, which it is 

 claimed parts with its juice more readily than the thicker blanket obtained if 

 all the mills run at the same speed. 



By a reversal of the calculation given in the preceding section, it follows 

 that, if the volume escribed by the revolution of the rollers is 203-15 cubic 

 feet, the megass consists of 79-96 cubic feet of fibre and 123*19 cubic feet of 

 juice ; let this volume of megass which is derived from 25 tons of cane be 

 passed with the rollers making 2-5 revolutions per minute ; let the speed be now 

 reduced to 2 revolutions per minute ; then the volume now escribed by the 

 rollers in one minute becomes, if the setting remains unaltered, 182-52 cubic 

 feet : since the volume occupied by the fibre is the same in both cases 

 (79-96 c. ft.), there is with the slower speed a volume of (182-52-79-96) 

 or 102-56 c. ft. remaining for the juice; taking this as of density 1*07 as 

 before, the composition of the megass now works out at 50*4 per cent, juice 

 and 49-6 per cent, fibre, as compared with 55 per cent, juice and 45 per cent, 

 fibre when the speed was 2 '5 revolutions per minute. In the opinion of the 

 writer, this argument points to the obtaining of better results with small 

 speeds ; the reasoning is not free from objection since, for example, with the 

 thicker blanket there will be a greater tendency to force the rollers apart and 

 thus to increase the escribed volume. 



Quantity of Fibre in Cane as affecting Composition of 

 Megass. The conception of the escribed volume can be used to show how 

 the percentage of water and of fibre in a megass will vary with the initial 

 composition of the cane. In the example already taken it was shown that, 

 with an escribed volume of 203-15 c. ft., canes containing 12 per cent, of fibre 

 afford a megass of composition fibre 45 per cent, and juice 55 per cent. ; let 

 canes containing 1 per cent, of fibre be now milled, the setting and speed of 

 the mills and the weight of cane remaining unchanged ; the amount of fibre 

 now passing in one hour is 2'5 tons and this quantity will occupy 66*63 c. ft., 

 so that there remains 203-15 66-63=136-52 c. ft. to be occupied by the juice ; 

 this volume of juice, if of density 1*07, will weigh 4*06 tons, and the total 

 weight of megass will be 6-56 tons, so that the percentages of fibre and juice 

 are 38-1 and 61 -9 respectively. 



It follows then, that with a fall in the fibre content of the cane the escribed 

 volume must be decreased to obtain the same results as with the larger quantity 

 of fibre ; this effect can be obtained by running at a slower speed or by 

 decreasing the distance between the rollers ; conversely, megass of the same 

 composition will result by increasing the quantity of cane milled. 



201 



