COMPLEX SOLUTIONS. ARCHIBALD. 43 



inner tube was therefore retained and an outer tube provided of 

 about the same length and thickness of walls, but with an 

 internal diameter of 2.88 cm., thus leaving an air space of about 

 0.9 mm. between the tubes. This gave complete satisfaction. 

 With uniform stirring no tendency was observed for the ice to 

 form on the walls of the tube or on the bulb of the thermometer, 

 or to freeze in a mass. The inner tube had its lower end 

 re-entrant, as recommended by Lootnis. 



I should like to draw attention to the importance of having 

 the air space between the two tubes of the proper size. If the 

 importance of this point has been noted by former observers it 

 has escaped me. 



The hammer used for tapping the thermometer was part of a 

 small electric bell and was covered with a piece of thick rubber 

 tubing. It was found to be very essential to drive the hammer 

 so that the blows on the thermometer might be of uniform 

 strength. Some difficulty was met with in attaining that end ; 

 but by careful attention to the strength of the current what 

 appeared to be sufficient uniformity was attained. 



The stirrer was of the ordinary ring form, the upright rod 

 passing through a glass tube, the upper end of which was con- 

 stricted, a?id the lower so far from the solution that the wetted 

 portion of the stirrer could not touch it. A stop on the upright 

 rod limited the extent of the stroke so that the ring would not 

 leave the solution, and ensured the equality of the strokes. It 

 was worked by hand as uniformly as possible. 



The over-cooling was seldom over 0.1 degree, owing doubt- 

 less to the low temperature of the room in which the observa- 

 tions were made. There was consequently no need of correcting 

 for over-cooling. 



The freezing point of water was determined each day before 

 determining that of the solutions, and in the event of any 

 appreciable change occurring in the atmospheric pressure during 

 the observations on the solutions, the observation on water was 

 repeated. 



