ON THE OSMOTIC PRESSURES OF CALCIUM FERROCYANIDE SOLUTIONS. 327 



Resistance Box. 



The coils of the box were of manganin, and were tested by means of a calibrated 

 platinum bridge wire having a standard-ohm coil joined to each end. Coils of the 

 same nominal value were thus compared and the results calculated in terms of the 

 coil of highest resistance (5000 ohms), thus* giving the value of a box ohm. In no 

 case was the deviation greater than aifooth of the nominal value. 



Resistance Capacity of the Cell. 



The cell was standardised by means of an approximately normal solution of 

 potassium chloride. The specific conductivity of this solution is given by Kolil- 

 rausch (see LANDOLT and BOKNSTEIN'S tables) for temperatures from 0. upwards. 

 The salt used was Merck's purest, and care was taken that it was thoroughly dry 

 before weighing out the necessary quantity. 



Three separate sets of observations were made and the results are tabulated 

 below : 



A normal solution of potassium chloride contains 7'1385 gr. of salt in 100 gr. of 

 solution and has a specific conductivity of 0'06541 at C. ; the specific conductivities 

 given in the table are calculated from this by assuming that the conductivity is 

 proportional to the concentration. 



It is worth noting that on* increasing the speed of revolution of the commutator so 

 that the alternations of current were changed from 36 to 72 per second no appreciable 

 change in the resistance of the solution was engendered. 



Resistance of the Solutions. 



As there was but little salt at our disposal the solutions were made up in the 

 following way : The salt for the strongest solution required was weighed out (a 

 suitable portion from the same bottle being set aside for the analysis of its water 

 content) and the weight of water added determined on the balance. A part of this 

 solution was used for the resistance experiments, and the other part, after weighing, 

 was diluted and again weighed, and so on ; thus the weight concentration of each 

 solution used for the conductivity work was known, and the density corresponding to 



