CHAPTER XI. 



THE EXTRACTION OF JUICE BY MILLS. 



Mills, as row constructed for the extraction of the juice of the cane, 

 consist of heavy iron or steel horizontal rollers, driven by a steam engine 

 through powerful spur and pinion gearing. The rollers are set with their 

 centres at the angles of an isosceles triangle, the verticle angle of which is 

 generally about 83 ; but, sometimes, mills are met with having a vertical angle 

 considerably greater, even reaching up to 90. The rollers draw the cane within 

 their grip, subjecting it in its passage to great pressures and causing the 

 rupture of the cells and the expression of the juice ; the latter falls on to the 

 bed-plate of the mill, whence it flows into a well and is pumped up to the 

 clarifiers for further treatment. 



In almost all recently erected factories, the milling plant consists of not 

 less than nine rollers combined in three mills, the whole combination being 

 driven by one engine. In several instances, notably in the Hawaiian Islands, 

 twelve-roller combinations have been installed; in one case each in the 

 Hawaiian Islands and in Porto Rico, 15-roller combinations are employed, or, 

 including the crusher, 1 7 rollers. This last scheme, which is at work at the 

 well known Ewa and Guanica plantations, is a 15-roller mill in operation but 

 not in construction. At first the Ewa plant consisted of two nine-roller mills 

 placed side by side ; as afterwards arranged the canes pass through one of the 

 original sets, and are then transferred by a cross carrier to the second mill of 

 the other set ; in case of stress the oiiginal method can be used. This scheme is 

 the result of empiricism in regard to the capacity of mills. A number of years 

 ago it was thought that a mill 34 in. X 78 in. was run at its maximum capacity 

 when about 35 tons of cane were ground per hour ; but provided the mills had 

 enough engine power, it was found that much larger quantities could be worked 

 without detriment to the efficiency, and hence came the idea of utilizing the 

 existing train of mills to the best advantage, since the extraction, as is shown 

 later, increases with the number of crushings, the quantity of water added 

 remaining the same. 



In twelve-roller combinations that have been formed by the addition of a 

 three-roller to existing plant the last mill is usually provided with its own 

 engine ; in others that have been laid down to one design a separate engine is 

 provided for each six-roller unit, the earlier one driving also the crusher or 

 shredder. In older plants, especially in those which have been built up 



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