CONDUCTIVITY MEASUREMENTS. 117 



filter bucket, and the intervening space filled with finely crushed ice and 

 water. Such a bath will maintain a temperature of to within 0.1 for 

 hours. The 25 bath was a galvanized-iron tub, lined on the outside with 

 asbestos. The water in it was kept at a uniform temperature by means of a 

 stirrer driven by a small hot-air motor, and could easily be kept to within 

 0.1 of any desired temperature. The thermometers were graduated to 

 0.1 and standardized. The burettes and measuring-flasks were all carefully 

 calibrated by the method of Morse and Blalock. 1 



PREPARATION OF SOLUTIONS. 



The silver nitrate used in this work was obtained from Kahlbaum, and was 

 perfectly neutral. It was finely pulverized, dried for several hours at 100 to 

 105, and kept in a desiccator in the dark. Somewhat more of the salt than 

 was necessary to prepare a N/50 solution was weighed into the solvent, and 

 the exact concentration was determined by titration with a N/25 solution 

 of ammonium sulphocyanate, with ferric ammonium sulphate as indicator. 



The sulphocyanate solution was standardized against a N/25 solution 

 of silver nitrate and weighed quantities of thoroughly dried potassium 

 chloride, which had been especially purified in the physical chemical laboratory 

 of the Johns Hopkins University for use in conductivity work. The solution 

 whose conductivity was to be measured was then made exactly N/50 by the 

 addition of the proper amount of solvent. From this mother-solution the 

 other solutions were prepared by successive dilution. The N/800 and 

 N/1200 solutions were prepared from the N/400. 



CONDUCTIVITY MEASUREMENTS. 



In measuring the conductivity of a solution, readings were always made 

 with three different resistances, and the values given are the mean. Before 

 using, the cells and electrodes were carefully dried and rinsed out with the 

 solution whose conductivity was to be measured. The cell constants were 

 determined with 0.02 N and 0.004 N solutions of pure potassium chloride. 

 The molecular conductivity of the former was taken as 129.7 at 25. 



In tables 66 and 67, under v is given the concentration, expressed in number 

 of liters of the solution containing a gram-molecular weight of the salt; 

 under /* 0, the molecular conductivity at 0; and under ^25, the molecular 

 conductivity at 25. 



The temperature coefficients are obtained by dividing the increase in con- 

 ductivity per degree, by the conductivity at 0. 



The values for the molecular conductivities in water and methyl and ethyl 

 alcohols are obtained, by interpolation, from the measurements of Jones and 

 Bassett, and the temperature coefficients are calculated from these inter- 

 polated values. 



1 Amer. Chem. Journ., 16, 479 (1894). 



