CANE SUGAR. 



165 



each day by the mean barometric pressure for the given 24 hours. But 

 between 30° and 80° the mean daily total pressures are recorded, and the 

 correction for atmospheric pressure is applied by deducting, from the mean 

 of all the mean daily total pressures, the mean barometric pressure of the 

 whole time the cells were under observation. This change in practice 

 was due to the fact that, as the membranes grow older, the duration of 

 barometer effects, as well as of thermometer effects, increases. No con- 

 fusion will result from the change in the form of stating results, if it is 

 remembered that "total" pressure means osmotic plus atmospheric pres- 

 sure, while "osmotic" pressure means total observed minus atmospheric 

 pressure. 



Table 47. — Determinations of osmotic pressure at 0°. 



(Measurements by H. N. Morse, J. C. W. Frazer, and E. G. Zies.) 



[W. N. S. = Weight normal solution. C. G. P. = Calculated gas pressure.] 



It will be seen that the equilibrium pressure was reached in many cases 

 on the second day ; in others, on the third day; and in some, only after sev- 

 eral days. This apparent inconsistency has been explained in a former 

 chapter as due, principally, to the varying ages of the membranes; it hav- 

 ing been observed that, as a membrane grows older, the solvent passes 

 through it more slowly. There are other minor causes of differences in the 



