132 ON THE CALCULATION OF THE CONDUCTIVITY 
Experimental Methods. 
The hydrochloric acid was obtained from Eimer & Amend, 
and the sulphuric from Merck & Co. Both were guaranteed 
chemically pure. The redistilled water used in the preparation 
of the solutions was obtained by the method described in 
a former ‘paper, and it had a conductivity ranging from 
0.95 x 10~° to 1.01x10~° expressed in ?Kohlrausch’s new unit 
(Ghimig, cm.) 
The amount of hydrochloric or sulphuric acid in a solution 
was determined volumetrically by means of aqueous solutions of 
potassium hydroxide, the strength of these being determined 
daily by titration with known quantities of dry oxalic acid. 
Phenol-phthalein was the indicator used. The potassium 
hydroxide solutions were kept in bottles with stoppers, each 
containing a soda lime tube. The pipettes, burettes and flasks 
were calibrated and used as described in the paper referred to 
above. ‘The specific gravity at 18°C. was determined for many 
of the simple solutions with a pyknometer of the Ostwald- 
Sprengel form. The comparison of the values thus obtained 
with the values as given by Kohlrausch, acted as a check upon 
the concentration as determined above. 
Kohlrausch’s method with the alternating current and tele- 
phone was employed in the measurement of the conductivity. 
The bath used to obtain a constancy of temperature, for a 
time sufficient to make the determination of the resistance in, 
contained tap water kept continually stirred by a mechanical 
stirrer driven by one of Henrici’s small hot air motors. This 
motor worked without noise and on this account was found 
more serviceable than the hydraulic motor formerly employed. 
The thermometer used could be read to a hundredth of a degree, 
and had been tested at the Physikalisch-Technische Reichsanstalt, 
Berlin. 
The resistance of the solutions was measured in a U-shaped 
cell having electrodes of stout platinum foil connected by thick 
1Trans. N.S. Inst. Sci., 10, 49, 1898-9. 
2? Kohlrausch u. Holborn: Leitvermégen der Elektrolyte, 1898, p. 1. 
