SOLUTIONS IN MIXTURES OF ACETONE AND WATER. 99 



tested for any appreciable resistance. The two halves of the double 

 system for reading a and 6 were carefully compared, and b was found not 

 to differ from 1 ,000 a by any appreciable quantity , except for resistances 

 smaller than any used in this investigation that is, below 10 ohms. 



Cells. The conductivity cells were of three forms. For the most 

 concentrated solutions two U cells with adjustable electrodes were 

 employed, having constants of about 15,000 and 30,000. The most 

 dilute solutions and the solvents were measured in cells with cylindrical 

 electrodes of the type described by Jones and Schmidt, 1 and by Jones 

 and Kreider, 2 and with constants ranging from 2.9 to 4.3. The inter- 

 mediate dilutions, that is, from N/10 to N/400 solutions, were measured 

 in cells of the plate type described by Jones and Bingham. 3 



Constant-temperature Baths. The constant-temperature baths used in 

 both parts of this investigation were of the same general type employed 

 for such work in this laboratory, and consisted essentially of round, 

 galvanized-iron tubs of about 20 liters capacity, covered with non- 

 conducting material. For the viscosity work the baths were equipped 

 with large glass windows in the upper walls, 180 apart. 



A more efficient form of stirrer provided with double journals and 

 6-bladed propellers was employed, and the brackets supporting these 

 were attached directly to the walls of the building. The stirrers were 

 driven by a round belt, at about 200 revolutions per minute, by a -g^~ 

 horsepower water-cooled hot-air engine. These improvements lessened 

 materially the vibrations due to side-thrust from the propellers, and 

 increased the up-and-down stirring of the water in the bath, at the same 

 time giving less circular motion. 



By means of the pressure from a 2.5 meter stand-pipe, water could be 

 kept flowing through special cooling coils of copper placed in the 

 bottoms of the baths. This facilitated temperature regulation at or 

 below room temperature. An auxiliary coil immersed in an ice-bath 

 was also introduced into the cooling system by means of brass unions, 

 whenever the average temperature of the tap-water approached too 

 closely to the lowest temperature at which the work was attempted. 



Temperature Regulation. Temperature regulation of a high degree of 

 accuracy was obtained by equipping all baths with an approved form 

 of electrically operated gas-valve, consisting essentially of a sensitive 

 150-ohm relay, to the armature of which was attached a device for 

 cutting down the flow of gas whenever the relay was set in action by 

 the thermo-regulator in the bath. The relays were connected in paral- 

 lel on a 2.5-volt circuit from accumulators, and were operated by an 

 improved form of mercury thermo-regulator of the general type de- 

 scribed by Morse, but having 2 to 4 reservoir tubes of special hydro- 

 meter tubing, with walls about 0.25 mm. thick. A maximum surface 

 of mercury was thus secured, in keeping with the stability of the instru- 

 ment. A more detailed description of the above forms is to be found 



'Amer. Chem. Journ., 42, 39 (1909). 2 Ibid., 45, 282 (1911). 3 Ibid., 34, 481 (1905) 



