52 ON THE CONDUCTIVITY, SPECIFIC GRAVITY AND 



TheWheatstone's bridge consisted of four resistance coils, which 

 were certified by Queen & Co., of Philadelphia, to be correct to 

 one-fiftieth of one per cent, and a platinoid bridge wire wound 

 on a marble drum. This wire had a resistance of about 0.9 ohm, 

 and was divided into ]000 parts, each part being capable of sub- 

 division by the eye into tenths. It was calibrated before and 

 after the observations, by ^trouhal and Barus's method, ten 

 german-silver wires of equal length, with ends firmly soldered 

 into stout copper wire being used. Corrections were plotted 

 against the length, and a smooth curve drawn through the 

 points, and thus intermediate readings could be corrected. The 

 greatest correction found was 1.2 divisions. The small induction 

 coil used had a very rapid vibrator, and was kept in an adjoining 

 room, that its noise might not interfere with the clearness of the 

 sound minimum in the telephone. The telephone recommended 

 by Ostwald, and made by Ericsson of Stockholm, was used. 



With these appliances the minimum point could be deter- 

 mined to 0.3 of a division, corresponding to an error of 0.12 per 

 cent in the determination of the resistance at the centre of the 

 bridge, and 0.16 per cent at the point farthest from the centre 

 used in the experiments. 



Electrolytic Cell. 



The cell in which the solutions were placed for the determina- 

 tion of the resistance was of the Arrhenius form, a deep cylindri- 

 cal vessel, of diameter 3 cm., and depth 14 cm. The electrodes 

 were of stout platinum foil, firmly joined by heavy platinum 

 wire to the glass tubes. These electrodes after being well-cleaned 

 with alcohol and a strong solution of sodium hydroxide, were 

 platinized in a solution of platinum chloride and lead acetate. 

 This solution was prepared from 2 Lumrner and Kurlbaum's 

 recipe. When the electrodes had received a good coating of 

 platinum black, they were removed and well washed in hot water. 



Stout copper wires, well insulated, connected this cell with 

 the Wheatstone bridge. They had a resistance of .023 ohm. 



1 Wied Ann., 10, 326, 1880. 



2 Wied. Ann., 60, 315, 1897. 



