ON THE OSMOTIC PEESSURES OF CALCIUM FERROCYANIDE SOLUTIONS. 325 



as would be likely to give satisfactory osmotic pressures, but without results, as will 

 be seen by the following list : * 



t This experiment was done with an imperfect membrane. 



The Electric Conductivities of the Solutions. 



The cell used for the stronger solutions is shown in fig. 1 ; it was originally designed 

 for another research (the conductivities of saturated solutions), but was found quite 

 satisfactory for the present purpose. A is the cell proper, and B and C its electrodes ; 

 these are covered with platinum black in the usual manner. The solution, which is 

 contained in the beaker D (capacity about 250 c.c.), is sucked up into the cell by 

 means of the tap E, and the resistance is determined by the Fitzpatrick and Whetham 

 commutating method.^ 



As the osmotic pressures were determined at C., it was imperative, for the 

 purpose of comparison, to obtain the conductivities at the same temperature. This 

 was secured in the following way : The whole apparatus was plunged into ice and 

 the stirrer started ; when the temperature was constant at or near C., the solution 

 was sucked up into the cell and its resistance determined ; the cell was then emptied ; 

 after an interval of three or four minutes it was refilled and the resistance 

 re-determined. These operations were repeated until a constant resistance was 

 obtained. The temperature was always noted before and after every operation, and 

 observations in which there had been a change of more than 0'01 C. were rejected; 



* We are now experimenting with the ferricyanides for the same purpose. 

 I ' Phil. Trans.,' A, vol. 194, p. 330. 



