VARIOUS METHODS FOR THE EXTRACTIOX OF JUICE. 283 



from the slices of stalks or beets. This result is due to the principle of 

 diffusion, dialysis, or osmose, as it is termed. It has been found that 

 certain substances, when in solution, •will thus pass through animal or 

 vegetable membranes, as bladder, animal or vegetable parchment, 

 "when such solution is separated from water by the intervention of either 

 of these materials. The cells of plants are composed of matter, which 

 also permits the passage of such materials under similar conditions. 

 The process will continue, until the amount of the material in solution 

 outside is equal to that inside the containing vessel. 



But, while certain substances will thus readily diffuse, another class 

 of substances Avill not. To the former the name crystalloids has been 

 given, because it is found that those substances which crystallize, as 

 sugar, salt, and similar bodies, are diffusible ; to the latter class the 

 name colloids has been given (a word meaning glue-like), because those 

 substances Avhich, like glue, do not crystallize, are also found not to be 

 diffusible. 



It is now interesting and important to observe that, in the cells of 

 the cane, sorghum, or beet, there are found in the juice substances be- 

 longing to both these classes, and also that, while the desirable sub- 

 stance sugar is quite diffusible, those substances which are most trouble- 

 some to the manufacturer of sugar, as the nitrogenous matter, the gum, 

 and the starch, are not diffusible. These substances existing together 

 in the juice are expressed by the common mill, and, in addition, there 

 is ahvays a considerable amount of mechanical impurity, as dirt, frag- 

 ments of cane, and so f >rth, all of which add to the difficulty of secur- 

 ing the sugar in a commercial condition. 



Besides the sugar, there are several other constituents of the juice 

 which are also diffusible, as the many salts. Owing to the large quan- 

 tity of these relatively in the beet, the advantage of this system for 

 beets does not appear to be so decided as it seems that it might prove 

 if applied to sorghum and cane. But, while this sj'stem is in almost 

 universal use in the production of beet sugar, it appears as yet scarcely 

 to have made other than an experimental advance in the working of 

 cane or sorghum. 



It is possible, by this system, to remove practically all the sugar from 

 the stalks or beets ; and we have seen that, by the roller mill, it is es- 

 timated that fully one-third the juice is left in the bagasse ; and many 

 experiments show that the juice remaining in the bagasse is equally 

 rich in sugar with that expressed. 



A review of the attempts to apply this system to sugar-cane will, 

 therefore, be of interest. The methods are practically the same, and 

 consist in cutting the cane in slices from one-sixteenth to one-eighth of 



