AQUEOUS SOLUTIONS. MCKAY. 327 



inches. The electrodes were of stout platinum and supported 

 by platinum wires passing through the ebonite covers of the 

 cell. The diameter of the electrodes was 1J inches. The second 

 cell was a cylindrical vessel of diameter 1 J inches. The elec- 

 trodes, whose diameter was nearly as great, were also of 

 platinum. The platinum wires leading from them were fused 

 into glass tubes, in the interior of which they made connection 

 through mercury with the outside wires. The glass tubes were 

 moveable through holes in the cover of the cell so that the 

 distance between the electrodes could be adjusted. For any 

 given adjustment the tubes were held in place with sealing- 

 wax. The solutions, whose conductivity could be measured in 

 this cell, ranged from the most dilute to, in the case of sodium 

 chloride, about .02 gramme-equivalent per litre. The range of 

 of NaCl solutions which could be measured in the first cell 

 varied from 0.1 to 5 gramme-equivalent per litre. The electrodes 

 of both cells had been platinized in a solution containing 1 

 grm. of platinum tetrachloride and .008 grm. of lead acetate to 

 30 grm. of water. 



Measurements were made near the temperature 18C, almost 

 always within 0.3 degree of that temperature. The thermometer 

 could be read to .01 degree, and was corrected by compari- 

 son with a standard thermometer tested at the Physikalisch- 

 Technische Reichsanstalt, Berlin. The thermometer was kept in 

 a separate tube in the bath ; and it was found, on several occa- 

 sions, by placing another chermometer in the cell itself, that the 

 temperature of the liquid in the cell could be read off from the 

 thermometer in the tube in almost all cases to less than 0.1 

 degree. Where the measurements were not made at exactly 18, 

 correction was made by means of the temperature coefficients 

 given in Fitzpatrick's Table in the British Association Reports.* 



The bridge wire was calibrated by Strouhal and Barus' 

 method. The resistances for this purpose were made of German 

 silver wires, whose ends were soldered to short pieces of thick 



* Nottingham, 1893. 



