THE EXTRACTION OF THE JUICE BY MILLS 245 



of water than in the single schemes. The position of the maximum is 

 indicated by a dotted ordinate. 



In the case selected as unfavourable, the profits are very small, and it is 

 easy to see that there will sometimes be occasions where any extraction 

 beyond that obtained with the dry crushing will be attended with loss. 

 The discussion above has purposely neglected two points, the mathematical 

 treatment of which presents difficulty. In many cases the bagasse alone 

 will of itself afford fuel for a substantial imbibition, in which case the only 

 expense to be charged is the interest on the prime cost of additional heating 

 surface in the evaporators. In a case such as this, the theory given above is 

 applicable, if and when it is possible to determine the point in the process 

 where purchased fuel becomes necessary. 



In the second place no account has been taken of the cost of installing 

 the additional mills required in the more complete schemes. This item can- 

 not be expressed as a function of the added water, but will be a constant 

 charge against the process. If such a constant be introduced into the econ- 

 omic equations given above, its differential coefficient will be zero, and the 

 position of the maximum point in the economic curve will not be affected. 

 As has been shown elsewhere in this chapter, the installation of additional 

 mills has a great effect in increasing capacity while maintaining efficiency, 

 and this effect, combined with the superior advantage of long trains on the 

 grounds of the economic use of the water, would still more accentuate the 

 economic position of multiple milling when capacity and efficiency are 

 jointly considered. This last point is only concerned with the economics 

 of the installation of a new factory, or of the extension of an old one. It 

 does not enter into the policy of an executive regarding the operation of the 

 machinery as it actually exists. 



Composition of the Cane as affecting the Economic Extraction. The 



juice of the cane contains from the engineering standpoint two distinct 

 juices, one in the pith, of high sugar content, and the other in the rind and 

 nodes of low. The pith juice is that first expressed, and it hence follows 

 that there must be a continuous fall in the quality of the juice with the 

 expression of each successive fraction. If, however, all the pith juice has 

 been expressed there will be observed no further fall in quality, since the 

 remaining fractions will consist of rind juice only. As has been shown by 

 Savage 12 , such a condition does actually occur in the very high extractions 

 obtained in the Hawaiian Islands, where he found that successive operations 

 on last mill bagasse with an hydraulic press gave a juice of uniform com- 

 position. The selective extraction of the pith juice may be traced in the 

 following experiments due to the writer 13 who separated mill bagasse into 

 pith tissue and rind tissue, analysing each separately. The results given 

 below show that the pith tissue, originally the sweeter, finally contains much 

 less sugar than does the rind tissue, and that, while the extraction as regards 

 the pith juice is nearly complete, the rind tissue is very imperfectly treated. 



Pith bagasse. Mill I. Mill II. Mill III. Mill IV. 



Weight per 100 bagasse 53-33 '48 -62 50 -oo 51 -25 



Sugar per cent. ... 11-33 7 PI 9 3 *7 8 2-87 



Fibre percent. ... 33 -58 41-58 45-63 46-91 



Rind bagasse. 



Weight per 100 bagasse 46 -67 51 -38 50 -oo 48 -75 



Sugar per cent. ... 0-12 7-13 4-34 4-06 



Fibre percent. ... 35-15 41 -54 44-90 46-67 



