8 



HYDRATES IN AQUEOUS SOLUTION. 



In the case of solutions the tendency to undercool was not so marked. 

 Owing to the change in concentration due to the separation of ice, a correc- 

 tion was introduced. The determination of the freezing-point of the solv- 

 ent, as well as of any solution, was repeated several times, and the mean 

 of the results taken as the true freezing-point. 



CONDUCTIVITY METHOD. 



The solution was introduced into the conductivity cell, care being taken 

 to avoid the collection of air-bubbles on the electrodes, and the cell was 

 then placed in the zero-bath where it was allowed to remain for half an 

 hour, this having been found to be sufficient time for the solution to acquire 

 the uniform zero temperature. The conductivity was then determined by 

 the well-known Kohlrausch method. In the more concentrated solutions 

 it was not found necessary to introduce a correction for the slight conduc- 

 tivity of the water. 



BOILING-POINT METHOD. 



Care was taken to use this method only on days when the barometer 

 remained quite constant. The general method of carrying out a boiling- 

 point measurement was employed, care being taken that the solutions 

 boiled evenly, and that the thermometer was gently tapped before reading. 

 The boiling-point as recorded is the mean of a series of readings taken at 

 intervals of thirty seconds. 



REFR ACTIVITY METHOD. 



The determination of refractive indices was made with the refractometer 

 of Pulfrich. Sodium light was employed, and care was taken to have the 

 solutions at uniform temperature. The readings were made to minutes of 

 arc, and by means of the well-known formula n=j/.W 2 -sinV, the indices 

 of refraction were calculated. 



Ca C\ z 



O.I 



0.3 0.5 



m, 



Concentration 

 Fm. 3. 



