260 SORGHUM. 



rollers; and then, by assistance of a returning bar, or knife, as it is 

 termed, the partially crushed cane again passes between the upper and 

 second lower roller. The mills may be classed as upright, or horizon- 

 tal, according to the position of the rolls. All mills of large size are 

 with horizontal rollers. They are also two, three, and four roll mills, 

 generally three. 



In the case of four rolls being used, it is customary to separate 

 them, and, by means of a jet of steam or water, to moisten the partially 

 expressed cane before subjecting it to pressure between the second pair. 



In the construction of mills upon this general principle, it is doubt- 

 ful whether there is left much, if any, room for improvement. 

 The amount of juice expressed varies from 45 to 65 per cent of the 

 weight of the stripped cane, and in exceptional cases, where, as in 

 competition trial of mills, every precaution is taken, the amount of 

 juice may reach 70 per cent, but it is doubtful whether the average re- 

 sults will equal 60 per cent of juice extracted by the sugar mills. 



We have seen that the average of juice present in the cane is at 

 least 90 per cent of its weight; and there is reason, therefore, to con- 

 sider the principle of these mills, to Iparn whether such waste of juice 

 is necessary and inevitable in their use. It appears that such loss is 

 inevitable, owing to the following reasons : 



1. The cells of the cane, which contain the juice, are microscopic in 

 size, and many of them escape rupture, even under the enormous 

 pressure to which the cane is subjected, and it is not unlikely (though, 

 perhaps, this can not be experimentally determined) that the elasticity 

 of the cell walls is such, as to permit a certain degree of j^ressure be- 

 fore they are ruptured. 



2. Owing to capillarity, the bagasse (or pressed cane) rapidly ab- 

 sorbs the juice the instant the pressure is removed; and, since a portion 

 of the juice will follow the cane through the rolls, such portion is at 

 once taken up by the bagasse. It is, of course, mathematically true, 

 that the maximum of pressure exerted, even with the largest rolls and 

 with the slowest revolution, is but instantaneous; and, as the escape 

 of the juice can not be as rapid, a large share of it must be lost. In 

 fact, such is found to be the case. Although, in common language, 

 we often hear the bagasse spoken of as " perfectly dry," it is never 

 found with less than half its weight of water, even after having come 

 from the best mills ; and generally it will be found, that the i^ercentage 

 of water still remaining in the bagasse is equal, approximately, to that 

 present in the cane before it was pressed. With this water is, of 

 course, a lai'ge amount of sugar, estimated as being equal to the half 

 of that expressed in the juice. 



