100 CONDUCTIVITY AND VISCOSITY OF SOLUTIONS 



in our work with Wightman on conductivity and viscosity in alcohol- 

 water mixtures. 1 



With this improved form of apparatus we have maintained a con- 

 stant temperature over any desired length of time to within 0.01, for 

 temperatures from 15 to 40, and at 25 with moderate precautions 

 variations in temperature not more than 0.005 resulted. An ad- 

 ditional advantage of the type of thermo-regulators described above, 

 over the more complicated toluol-mercury and other froms, lies in its 

 simplicity and in the fact that it may be readily constructed by anyone 

 possessing moderate skill in glass manipulation. The lengths of the 

 reservoir tubes need be limited only by the depth of the baths used. 

 In this work tubes 25 cm. long and 7 cm. interior diameter were found 

 to be most satisfactory. The thermometers used were of the Beckman 

 type graduated to 0.02 ; and these were compared at frequent intervals 

 with a thermometer which had been standardized within the year by 

 the United States Bureau of Standards. 



VISCOSITY APPARATUS. 



The viscosity apparatus used throughout this investigation was the 

 same essentially as that described in our work with glycerol. 2 Special 

 precautions were taken to eliminate, as far as possible, several annoy- 

 ing sources of error. Vibrations of the instruments due to external 

 causes were guarded against by making use of a special support for 

 the viscosimeters, consisting of a heavy tripodal leveling base resting on 

 several layers of thick piano felt, and a large bronze standard to which 

 a horizontal arm was rigidly attached by a collar and set-screw. The 

 viscosimeters were supported in the bath against a cork-covered brass 

 plate at the extremity of this arm, by means of a spring clamp, the ten- 

 sion of which was adjusted to different instruments by a thumb-screw. 



Further precautions were taken against vibrations by removing the 

 engine and stirrer brackets from direct contact with the desk supporting 

 the baths and viscosimeter stand. 



It was necessary also to guard against dust particles, which would 

 tend to clog the capillary of the viscosimeter. To this end special 

 precautions were necessary, both in making up solutions and in using 

 them in the viscosimeters. It was found necessary to use silk instead 

 of linen in polishing all weighing vessels, and to wash out all flasks 

 with dust-free water and alcohol, and then dry them by a blast of 

 air filtered through cotton wool. The viscosimeters were thoroughly 

 cleansed with chromic acid before each procedure, washed as above, 

 and dried by aspirating hot, dust-free air through them. For this 

 purpose the air was drawn through glass wool, over calcium chloride in 

 a long drying-tower, then through cotton wool, and finally through a 

 short iron tube heated in an asbestos chamber by means of a flat 

 burner. A final filtration through cotton took place before the air 



'Jour. Chim. Phys. (1913). Chapter IV, this monograph. 

 "Carnegie Inst. Wash. Pub. No. 180 (1913). 



