The lonisation of Dihde Solutions at the Freezing Point 193r 



both the extent and the accuracy of onr experimental knowledge of 

 these relations. Freezing-point determinations for very dilute solu- 

 tions are extremely difficult, owing to the minute differences of tem- 

 peratiu^e to be measured, and the results given by various observers 

 showed great discrepancies. On the other hand, the most satisfactory 

 experiments on the electrical ionisation of corresponding solutions had 

 been made at higher temperatures, instead of at the freezing point, at 

 which they should be obtained for purposes of comparison. The fact 

 that the temperature coefficient of conductivity differs for solutions of 

 different concentration, showed that the values of the ionisation would 

 vary if the temperature was changed. 



]\Ir. E. H. Griffiths therefore undertook the examination of the 

 freezing points by the method of platinum thermometry, and the 

 present paper contains an account of corresponding measurements of 

 the electrical conductivities at 0° C. 



In order to avoid any possible action of glass on the solvent used, it 

 was determined that the water should be obtained from a platinum 

 still and collected in platinum bottles, and that both the freezing 

 point and the electrical measurements should be made in platinum 

 vessels. The structure of the resistance cell is represented in fig. L 

 The walls of the vessel itself are used as one electrode, and an insu- 

 lated platinum cage, suspended inside, forms the other. Within the 

 cage is a platinum screw, mounted on a shaft, which can be turned by 

 means of a hand wheel and cord. This screw is used to insure tem- 

 perature equality throughout the liquid, and to mix the solutions 

 when made. The shaft of the screw is a hollow tube, closed at the 

 bottom, which contains a thermometer. 



Instead of beginning with a strong solution and gradually diluting^ 

 it was thought better to begin with a definite quantity of the pure 

 solvent, and, when its resistance had been observed, to add weighed 

 amounts of stock solution of known strength by means of the platinum 

 vessel shown in fig. 2. This vessel will obviously empty itself if a flow 

 of liquid is started by slightly increasing the air pressure at the neck. 



In order to obtain a definite quantity of solvent, slightly more than 

 the volume needed was placed in the cell, and the level of the liquid 

 was then adjusted by sucking water through a capillary platinum tube 

 into the glass vessel shown in fig. 3. The bottom of the capillary 

 always comes to the same position relatively to the cell, and, if the 

 sucking pressure is kept constant and equal to that of a water column 

 of about a foot in height, it is found that the amount of water left in 

 the cell is constant to within about one-tenth of a gramme. Thus 

 three independent withdrawals left 219'60, 219'63, and 219-59 grammes. 

 Whenever the cell was dismounted and set up again, this measurement 

 was repeated. 



The platinum vessel was surrounded by a brass case, coils of metal 



