OSMOTIC PRESSURES OF AQUEOUS SOLUTIONS OF CALCIUM FEREOCYANIDK 203 



On p. 341 of CASTELL EVANS' ' Phys. Chem. Tables,' the value of ir alt derived from 

 REGNAULT'S measurements is given, together with the value of p a0 , which he has 

 calculated from REGNAULT'S work on the assumption that the partial-pressure law 

 holds.* Using these two values, the results tabulated below are obtained. 



By a similar process of evaluation of the integrals in Prof. PORTER'S equation 

 [equation (1) on p. 177] it is easily seen that it reduces to 



where TT O is the vacuum vapour pressure of water and /a,, its vacuum vapour density, 

 and taking BROCK'S recalculation of REGNAULT'S work on these two quantities in a 

 vacuum, and assuming that they are applicable to the experiments, we obtain the 

 results given below under the head of " unmodified" equation. 



TABLE VI. 



The concordance of these numbers seems to indicate a satisfactory agreement 

 between experiment and thermodynamic theory. 



* Private communication. 



t On turning to Table III., p. 191, it will be seen that a solution of weight concentration 50-184 gave 

 an equilibrium pressure of 131 -04 atmospheres, while one of 49-913 gave 131-38 atmospheres. One of 

 these two observations must evidently be in error. As the value for equilibrium pressure of the 

 strongest solution given in the table is derived from the graph of this pressure against concentration, 

 using the mean of these two observations as the ultimate point, it may be that the value given is 

 0*5 atmosphere too low. 



2 D 2 



