PHYSICAL CONSTANTS OF SATURATED SOLUTIONS. 



193 



In weighing the pyknometers care was always taken that they should be slung on 

 the balance in such a way that the end of the lower capillary was at a higher level 

 than the level of the liquid in the stem ; this, as a rule, was sufficient to prevent any 

 loss of weight by evaporation, but such observations as did show a loss were rejected. 



Stirring. 



The stirring was obtained by means of a small platinum rod, fitted with a 

 two-bladed screw, suspended vertically in the solution, and rotated by a cord and a 

 small electric motor. The speed of rotation could be varied from 2 to 20 revolutions 

 per second. During the last two years of the course of this work the separate motors 

 were replaced by a shafting driven by an electric motor ; pulleys of various sizes were 

 fixed on it and driving cords taken to the stirrers as required. This shafting also 

 worked the Fleuss pump mentioned above. 



Constant Temperatures. 



At C. the beaker containing the solution was surrounded by ice and water. At 

 15 C. it was placed in a copper vessel, in which was suspended a thermostat, and 

 through which a current of cold water passed. The former actuated a gas burner 



Thermometers 



Tap for closing 

 CSf"~~ pyknometer. 



-Pyknometer. 



-^- -Solution . 



r thermostat, 

 ih. 



Platinum beaker. 

 -SaJb. 



Fig. 4. 



and kept the temperature constant. From 30 C. to 90 C. the solution was placed 

 in a platinum beaker of 300 cub. centims. capacity which formed part of a D'Arsonval 

 thermostat. The platinum beaker (see fig. 4), having a flange welded on to it three- 



VOL. CCIII. A. 



2 c 



