CANE SUGAR. 187 



The half of Table 62 which lies to the right of the heavy vertical line is 

 divided into two areas by a heavy zig-zag line, which begins at the top 

 between 25° and 30°, and ends at the bottom between 70° and 80°. All 

 the ratios between the vertical and the zig-zag lines are greater than 

 unity, but decrease continuously with rising temperature. The ratios 

 to the right and above the zig-zag line are unity within necessary experi- 

 mental errors. 



The situation disclosed in Table 62 may be summed up as follows: 

 Between 0° and 25°, the ratios of osmotic to gas pressure are all greater 

 than unity, but constant for each concentration. At some temper- 

 ature between 25° and 30°, these ratios begin to decline, but relatively 

 more rapidly in the dilute than in the concentrated solutions. At 

 some temperature (30° for 0.1 ; 50° for 0.2; 60° for 0.3 and 0.4; 70° for 

 0.5, 0.6, and 0.7 ; and 80° for 0.8, 0.9, and 1.0) the ratio becomes unity for 

 every concentration. 



The decrease in the ratios of osmotic to gas pressure at temperatures 

 above 25° suggests an increasing dilution of the solutions through the 

 dissociation of unstable hydrates; and it serves to strengthen the 

 impression that the excessive but constant ratios below 25° are due to 

 the presence of stable hydrates. 



However the excessive-constant and the excessive-declining ratios 

 may be explained, it is clear that at 30°, 40°, 50°, and 60° the osmotic 

 pressure of the 0.1 weight-normal solution obeys both of the gas laws. 

 The same may safely be affirmed of the 0.2 normal at 50° and 60°; of 

 the 0.3 and 0.4 at 60°; of the 0.5, 0.6, and 0.7 at 70°; and of the 0.8, 0.9, 

 and 1.0 at 80°. It is now important to ascertain whether the ratios, 

 having once declined to unity, maintain that value at all higher tem- 

 peratures ; hence the work of measuring the osmotic pressure of cane 

 sugar at 70° and 80°, and at still higher temperatures, will be resumed 

 as soon as the new cells, previously referred to, have been sufficiently 

 developed for use at those temperatures. The development of mem- 

 branes from a satisfactory condition at 30° to an efficient state at 70° 

 or 80° will probably require about one year. 



Special attention is again called to experiment 2 with the 0.5 weight- 

 normal solution at 15°, where the full osmotic pressure was maintained 

 by the cell for 60 days without any evidence, at the end of that time, of 

 a weakening of the membrane. The experiment is important, not only 

 because it proves the membrane to have great endurance, but also 

 because of the light which it throws upon the question of the deteriora- 

 tion of the membranes while in contact with a solute. The cell (C 5 ) 

 which was used in the experiment in question was brought again into a 

 usable condition within the time ordinarily required for that purpose, 

 and was subsequently employed for eight more determinations which 

 are recorded in the present chapter. A membrane which had been a 

 longtime in contact with a 0.4 weight-normal solution of lithium chloride 

 required for its restoration more than 20 months of soaking in water. 



