82 



CONDUCTIVITY AND VISCOSITY IN MIXED SOLVENTS. 



liquid was raised exactly to the mark above the bulb, by air-pressure. The 

 air was dried over sulphuric acid. The pressure was released by means of a 

 Mohr pinchcock, on a thick-walled rubber tube. By this arrangement the 

 readings agreed to within 0.2 of a second. It was important that the liquids 

 should be given time to drain out of the tube above the upper mark, since, 

 otherwise, a drop of liquid might collect in the upper capillary and impede 

 the entering air, thus introducing large error. 



For the zero-bath a battery-jar was filled with very finely crushed ice 

 moistened with water. The ice was renewed as often as was necessary to 



keep the temperature constant. For the 

 25 bath a 5-liter beaker was employed. 

 The bath was stirred by means of a hot-air 

 engine, the temperature being kept to within 

 0.1 of 25, as in the conductivity method. 

 The room was kept as near this temperature 

 as possible. 



To measure the specific gravities at zero, 

 which was necessary in order to calculate 

 the viscosities, we constructed a pycnometer 

 (fig. 21) which would allow the large ex- 

 pansion of the alcohols and acetone and 

 avoid loss by evaporation. 



PREPARATION OP SOLUTIONS. 



In making up mixtures of solvents, n c. c. 

 of acetone diluted to 100 c. c. was designated 

 FIG. 21. as a mixture of " n per cent acetone." Since 



acetone, especially, has a high coefficient of 



expansion, it was important to have the temperature always the same, 20. 

 The acetone or alcohol was brought to this temperature before making up 

 the mixture. On mixing acetone and water, contraction took place and 

 heat was generated, so that the mixture was brought to the temperature 

 before diluting to the mark. 



The mother-solution was made by weighing into a measuring-flask the exact 

 amount of salt required, and adding the mixed solvent. Since, however, 

 heat was again generated, especially with the calcium nitrate, the solution 

 was again brought to the designated temperature before diluting to the 

 mark. 



From the mother-solution the other solutions were made by successive 

 dilutions. Where this would necessitate the use of small quantities of solu- 

 tion, a new mother-solution was made, and from this successive dilutions 

 prepared. 



