ROLL MLLLS. 



279 



Mill 



OldmiU.. 

 Kew mill 



57 16 



1058 

 1087 



15 18 

 20.29 



By comparing the percentage of juice obtained and the specific grav- 

 ity of the juice in the first and last experiments, it will be seen that 

 the former results are to the latter as 100 to 175 ; while, if we com- 

 pare the percentage of juice obtained and the percentage of syrup 

 in the juice, the former experiments in .their results are to the latter 

 as 100 is to 156. This apparent discrepancy is due to the fact that, 

 when the latter experiments were made, it was possible to carry the 

 concentration of the 'syrup to a greater density than in the former 

 cases, and hence a given amount of syrup in this latter case represents 

 a far higher content of sugar than in the former ; but these results 

 clearly indicate that, with a good mill, results from 50 to 75 per cent 

 greater than those obtained in the first experiments could be confidently 

 relied upon. 



As has been said above, this matter is too important to rest upon 

 other than repeated and well established experimental results. 



The Speed of the Bolls. 



This is a matter of extreme importance. We have already seen 

 that the maximum pressure exerted by any mill is instantaneous, but 

 the length of time during which the pressure upon the cane is approx- 

 imately at its maximum, will depend upon the diameter of the rolls 

 and their velocity of revolution. Careful experiments have shown 

 that, without any change in the relative position of the rolls; a greatly 

 increased amount of juice may be secured by diminishing their speed. 

 It is generally true that the speed of the mill is too great. 



Repeated experiments have all tended to prove that, while only 46 

 per cent of the juice is extracted by a speed of 8 revolutions per min- 

 ute, as much as 70 per cent is obtained by the same mill when the 

 speed is reduced to 2^ revolutions per minute. 



Comparative trials were made witli a mill, the rollers of which were 

 22 inches in diameter and 48 inches long, the average speed being 24 



