148 Conductivities and Viscosities in Pure and in Mixed Solvents. 



Salts. Kahlbaum's or Merck's best products were selected in all cases. 

 These were recrystallized from conductivity water before being used. 



Standardization. On account of the nature of the substances studied, 

 it was necessary to standardize most of the solutions by analytical 

 methods. These methods will be taken up briefly in connection with 

 the discussion of the individual salts. Standardization by analytical 

 means is open to the objection that solutions must stand for some time 

 before the conductivity measurements are made. This vitiates results 

 in the case of salts which are hydrolyzed or undergo slight decom- 

 position in solution. In the first instance alkali resulting from hydroly- 

 sis will attack the glass container, as was shown by the etching of a 

 Jena glass bottle in which a N/8 solution of trisodiumphosphate had 

 been standing for several weeks. By standardizing as rapidly as is con- 

 sistent with accuracy, and by keeping the solutions in a cool, dark place, 

 their deleterious effects are minimized. From the solution which had 

 been analyzed, the others were made by diluting with conductivity 

 water. Care was taken that no volume less than 35 c.c. should be 

 involved in these measurements. 



CELL CONSTANTS. 



The cell constants were frequently determined throughout this work 

 in the usual way, by means of a solution of pure potassium chloride. 

 For the cells with electrodes some distance apart, a N/50 solution was 

 used. The value found by Kohlrausch, 129.7 (Siemens units) at 25 

 was taken for the molecular conductivity of this solution. For the cells 

 having their electrodes closer together, a N/500 solution was employed. 

 The molecular conductivity of this had been determined in a cell the 

 constant of which had been found by the use of the N/50 solution. 



PRECAUTIONS. 



Before proceeding to the experimental data and methods of calcu- 

 lating them, it may be well to call attention to a few precautions which, 

 if taken, may assist those engaged in work requiring apparatus and 

 methods somewhat similar to those used in this investigation. 



(a) Jacobson 1 has already called attention to a method for the preven- 

 tion of the collection of air-bubbles on the electrodes at 25 and above. 

 He recommends heating the cell and contents a few degrees higher 

 than the temperature at which the conductivity is to be measured, and 

 then cooling them down to the desired temperature. In the light of 

 Shaeffer's 2 work, it is seen that in the case of certain salts, notably 

 chromium compounds, such treatment brings about a change in con- 

 ductivity which persists for months. Shaeffer's observation was veri- 

 fied in the course of the present investigation. It was noticed that the 

 conductivity of a solution of ammonium chromate was somewhat 



1 Amer. Chem. Journ., 40, 366 (1913). *Ibid., 49, 240 (1908). 



