CANE SUGAR. 125 



with twisted shoemakers' thread. The lower end of the stopper, whose 

 introduction through the constricted mouth of the glass tube had pre- 

 viously been so slow and difficult, was thus made much smaller. The 

 effect of the improvement was to reduce, by more than one-half, the 

 time required for closing the cells. It was still further reduced by 

 gradual improvement in the cooperative manipulation of "No. 1" and 

 "No. 2" until finally a cell could be closed in less than one-fifth of the 

 time which was required in the beginning. The effect of rapid and 

 judicious manipulation in diminishing the total loss in rotation was 

 so marked that " quick closing" soon became, and continued to be, one 

 of the principal items in all schemes for the improvement of the method. 



Another method of diminishing initial dilution, which was resorted 

 to in the latter half of the work, consisted in dipping the cells — after 

 filling and before closing them — in a solution of sugar. The concentra- 

 tion of the solutions so employed was at first equal to that of the solu- 

 tions in the cells. Afterward they were made more concentrated. The 

 purpose of the dipping process was, of course, to force the solvent 

 which filled the porous wall outside the membrane to distribute itself 

 between the solution within the cell and that upon the exterior surface. 

 The solution upon the outside of the cell was afterward removed as 

 completely as possible by rinsing, and by soaking the cell, before locat- 

 ing it finally in the bath, in fresh water which was repeatedly renewed. 

 The diminution in the total loss in rotation which followed the introduc- 

 tion of the custom of "dipping" was also considerable. 



The combined effect of shortening the time required for closing the 

 cells, and of the process of dipping them, upon the total loss in rotation 

 sufficed to prove that considerable dilution must have occurred at this 

 period in the case of the earlier series. 



2. The practice of wrapping and tying with twisted and waxed shoe- 

 makers' thread all that portion of the rubber stopper which remained 

 outside the glass tube was followed from the beginning. The object 

 was to confine the exposed part of the stopper within a rigid shell, so 

 that none of the rubber within the glass tube could be forced out of it 

 under pressure. This seemingly simple operation proved to be exceed- 

 ingly difficult. In fact, it was performed with perfect success only 

 in the last four of the eight preliminary series of measurements. The 

 upper part of the stopper suffered, despite the careful winding, con- 

 siderable distortion through a forcing out of some of the rubber between 

 the successive turns of the thread. All such displacements of material 

 represented, of course, an equivalent enlargement of the capacity of the 

 cells and a corresponding dilution of the solutions. A phenonenon 

 which always attended a distortion of the stopper was an upward dis- 

 placement of the manometer while the cell was in the bath. Such dis- 

 placements were recorded in the second and succeeding series and were 

 regarded as a test of some value of the progress which had been made in 



