[ARCHIBALD] CONDUCTIVITY OF AQUEOUS SOLUTIONS 73 



platinvmi chloride and 0-008 of lead acetate to 30 of water. They wore 

 then connected with the terminals of two Eunsen cells, arranged in series; 

 the direction of the current being frequently changed. When the elec- 

 trodes had become covered with a velvety coating of platinum black they 

 were removed from the solution and thoi'oughly- washed with boiling 

 Avater to remove all traces of the chloroi)latinic acid. The platinizing 

 can be done more quickly and better with above solution than Avith the^ 

 chloroplatinic acid alone. 



Reduction Factor. 



To tind the factor which would reduce the observed conductivities to- 

 the standard emplo3'ed by Kohlrausch, the values of the conductivity 

 for a series of solutions of each salt, which were measured for the pur- 

 poses of calculation, were plotted against the concentrations (gramme- 

 equivalents per litre), and conductivities corresponding to the concentra- 

 tions examined by Kohlrausch, taken otf these curves and compared with 

 the values given by him. The ratio of these values was found to be prac- 

 tically constant for each salt through as wide a range of dilution as it was- 

 necessary for me to measure. 



Temperature. 



All conductivity measurements were made at 18° C. To make sure- 

 of this temperature, the cell containing the solution to be measured was. 

 placed in a water- bath, whose temperature was regulated by a thermostat 

 of the form recommended by Ostwald in his Physico-Cheraical Measure- 

 ments, p. 59, fig. 42. The regulating liquid, which was Avater, was 

 inclosed in a brass tube about 35 cms. long and 4 cms. in diameter, bent 

 so as to form three sides of a square. Two vanes fixed horizontally, near 

 the bottom of the bath, to a vertical axis, Avhich Avas turned by a small 

 hydraulic motor, kept the Avater of the bath Avell stirred. The ther- 

 mometer used Avas graduated to fiftieths of a degree ; and could easily 

 be read to hundredths. Its readings Avere compared Avith those of another 

 Avhose errors had recently been determined at the Physikalisch-Tech- 

 nische Reichsanstalt, Berlin. With this apparatus the temperature of the- 

 bath could be kept constant to Avithin a fiftieth of a degree for half an. 

 hour at a time. A A^ariation of one-fiftieth of a degree might cause an 

 error of 005 per cent in the determination of the resistance. 



That one might be sure that the temperature of the solution to be^ 

 measured had come to be that of the bath, two or moi-e determinations of 

 the resistance Avere always made at intervals of about five minutes, and 

 that reading taken Avhich Avas found to be the same for successive inter- 

 vals. 



