Conductivities of Some Unusual Salts. 147 



EXPERIMENTAL. 



APPARATUS. 



Bridge and Rheostat. All readings were made on an improved circular 

 slide- wire bridge constructed by the Leeds and Northrop Co., of Phila- 

 delphia. From a bridge of this type, readings can be made to a fraction 

 of a millimeter. The resistance-box had been recently standardized. 

 The plugs of this piece of apparatus were kept clean by frequently 

 rubbing them with a piece of soft chamois-skin moistened with alcohol. 



Cells. The cells used were of the same type described and sketched 

 in previous articles 1 on this subject. Since all cells used had been in 

 service for several years, no trouble was experienced from the leaching 

 out of soluble constituents from the glass. On account of the rather 

 wide range of conductivities shown by the salts studied, it was impos- 

 sible, in every instance, to use the same cell for the same dilution. 



Constant Temperature Baths. With the exception of the zero bath, 

 constant temperature was maintained by the application of a principle 

 developed here by Morse. 2 This is best described in his own words : 



"If all the water or air in a bath is made to pass rapidly (1) over a con- 

 tinuously cooled surface which is capable of reducing the temperature slightly 

 below that which it is desired to maintain, then (2) over a heated surface which 

 is more efficient than the cooled one, but under the control of a thermostat, 

 and (3) again over the cooled surface, etc., it should be practicable to maintain 

 in the bath any temperature for which the thermostat is set, and the con- 

 stancy of the temperature should depend only on the sensitiveness of the 

 thermostat and the rate of flow of the water or air. The principle is a general 

 one and provides for the maintenance of any temperature between zero and 

 the boiling-point of water." 



The particular type of bath and thermostat used was described fully 

 by Davis and Putnam in Publication No. 210 of the Carnegie Institu- 

 tion of Washington. In making a zero bath of the type described by 

 Jones and Jacobson, 3 it was found necessary to reduce the ice to a fine 

 state of division with an ice-shaver before a temperature of could 

 be obtained. 



Containing Vessels. All bottles and measuring flasks were of Jena 

 glass. After recalibrating the flasks by the weight method, the flasks 

 and the bottles were allowed to stand partly filled with a solution of 

 chromic acid for several weeks. During this time they were frequently 

 shaken to insure thorough cleansing. 



SOLUTIONS. 



Water. The water used in the preparation of the solutions was 

 purified by the method of Jones and MacKay 4 as modified by Schmidt. 6 

 In no case was the specific conductivity greater than 1.7X10" 6 . 



'Carnegie Inst. Wash. Pub. No. 170, 6 (1912). *Ibid., 19, 90 (1897). 



*Ibid., 198, (1914). *Ibid., 17, 83 (1895). 



3 Amer. Chem. Journ., 40, 361 (1908). 



