120 CONDUCTIVITY AND VISCOSITY 



structed of copper. Gas is employed as a means of maintaining the 

 desired temperature, the heat being applied to a heavy iron pipe (fig. 

 52 A-H) outside the circumference of the bath, and through this pipe 

 water is kept circulating by the propellers. Thus only a small portion 

 of the water in the thermostat comes into immediate contact with the 

 heated surface, being subsequently mixed with the main body of water, 

 thereby securing much more even distribution of heat. 



The improved type of mercury regulator described by Davis and 

 Hughes was used to operate the relays (fig. 52 c) controlling the gas- 

 supply to the micro-burners of the thermostats. A new type of toluene 

 regulator suitable for a wide range of temperature has been constructed 

 (fig. 52 B). With the above improved apparatus, temperature regu- 

 lation to within 0.01 was easily maintained over any length of time 

 throughout the work, and with a reasonable amount of attention regu- 

 lation to 0.005 was attained. (See fig. 52 for details of the system.) 



The hot-air engines formerly used as a source of power for the stirrers 

 have been discarded in favor of the electric motor, which gives greater 

 freedom from vibrations and permits the maintainence of constant 

 temperature in the baths both day and night. Both belt and friction 

 drive were used to transmit power from motor to stirrers, a 1-12 horse- 

 power direct-current motor serving to operate all five thermostats. 



Conductivity Apparatus. The conductivity apparatus used in this 

 investigation was identical with that employed for our recent work in 

 acetone-water mixtures; the methods of obtaining duplicate readings, 

 system of wiring, and similar details remaining exactly the same as in 

 the earlier work. The conductivity cells also were of the type now 

 generally employed here for such work, and have been fully described 

 elsewhere. All the instruments used were carefully calibrated at regu- 

 lar intervals or compared with standards. 



Viscosity Apparatus. The usual type of viscosity apparatus as 

 developed and improved here was used throughout this work. Special 

 care was exercised both in calibrating all the instruments and in guard- 

 ing against external jars and vibrations. 



Volumetric Apparatus. All flasks were carefully calibrated by 

 repeated weighings to hold aliquot parts of the true liter at 20; and 

 solvents and solutions were brought to within 0.1 of this temperature 

 before being diluted to the calibration mark. All pipettes used in 

 making up the solvents were standardized to drain a definite amount 

 of each component at 20, the mean of a number of weighings being 

 taken as the drainage capacity of the respective instruments. 



SOLVENTS. 



The glycerol used in these ternary mixtures was Kahlbaum's 1.26, 

 with a mean specific gravity of 1.257 at 25 and a specific conductivity 

 of 0.6X10' 7 at the same temperature. 



