De ON THE CONDUCTIVITY, SPECIFIC GRAVITY AND 
The Wheatstone’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 1000 parts, each part being capable of sub- 
division by the eye into tenths. It was calibrated before and 
after the observations, by *Struuhal 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 eylindri- 
cal vessel, of diameter 3 cm., and depth 14cm. The electrodes 
were of stout platinum foil, firmly joimed 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 ina solution of platinum chloride and lead acetate. 
This solution was prepared from ?Lummer 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. 
1Wied Ann., 10, 326, 1880. 
2 Wied. Ann., 60, 315, 1897. 
