WORK OF J. SAM GUY. 



EXPERIMENTAL. 

 APPARATUS. 



In this investigation the Kohlrausch method of measuring conductivity has been 

 employed, the improved Kohlrausch slide-wire bridge, resistance box, induction coil, 

 and telephone receiver being used. The entire apparatus was made and carefully 

 calibrated by Leeds, Northrup & Co., Philadelphia, and, in addition, the standard 

 resistance was standardized by the United States Bureau of Standards, Washington, 

 D. C. The new form of bridge is a great improvement over the ordinary Wheat- 

 stone bridge, both in convenience and accuracy. By means of such a bridge readings 

 may be duplicated, under favorable conditions, to 0.1 mm. 



The conductivity cells were of the same type as those described by Jones and 

 Schmidt 1 and by Jones and Kreider. 1 Such cells, as has been stated, have very small 

 constants, and hence are well adapted to measuring the conductivity of solutions with 

 high resistances. In every case the cell constants were determined by means of a 

 potassium chloride solution which was fiftieth normal, repeated determinations made 

 at frequent intervals showing only slight variations in the cell constants throughout 

 the entire investigation. The molecular conductivity of the fiftieth-normal potas- 

 sium chloride solution was taken as 129.7 reciprocal Siemens units at 25. 



The constant-temperature baths were regulated by electrically controlled regu- 

 lators, devised by Reid, 2 and were kept to within 0.02 of the desired temperature. 

 The thermometers were carefully standardized against a certificated Reichsanstalt 

 instrument. All flasks, burettes, and other apparatus were carefully calibrated, by 

 weighing, to hold aliquot parts of the true liter at 20. 



SOLUTIONS. 



For the work at 25, 35, and 45, solutions were made up at 30, while for the 

 higher-temperature work the solutions were made up at 50. In all cases the mother- 

 solution was made by direct weighing of the carefully dried, anhydrous salt, and 

 from this the N/50 and N/100 solutions were made by dilution. These solutions 

 then served as the mother-solutions for the N/200 and N/400, from which, in turn, 

 the N/800 and N/1600 solutions were made. The highest dilution was made by 

 diluting the N/400 solution four times. 



Measurements were not made at dilutions greater than 1,600, on account of the 

 extremely high resistance and consequent difficulty in making the readings. In 

 pure glycerol measurements were made at intervals of 5 from 25 to 75, while in 

 the mixed solvents they were made only at 25, 35, and 45. 



SOLVENTS. 



Glycerol. The glycerol used was Kahlbaum's best double-distilled product, and 

 had a mean specific conductivity of about 0.9 X10" 7 at 25. Schmidt had showed 



"Amer.Chem. Journ.. 45, 295 (1911). mid., 41, 148 (1909). 



153 



